Programming notes

OWASP Top Ten Web-sites Security leaks

2012-02-28T15:46:00.001+02:00

Source:
Link

C3P0 ConnectionPool: How To configure

2012-02-21T21:51:00.000+02:00

C3P0 - is a connection pool, connection pool is a cache of database connections maintained, so that the connections can be reused when future requests to the database are required.

The main question is how to cofigure it, because default values are not perfect. First of all I found oficial doc with description of the values. Next I found this one C3P0 ConnectionPool Configuration Rules of Thumb. After some perfomance testing of my application, I can confirm that cofiguring like in this article, can greatly increase your performance, in my case it was abouth twisly.

References:

Download C3P0

YUI: Compressing JavaScript and CSS files with Ant

2011-12-22T10:48:00.006+02:00

The YUI Compressor is JavaScript and CSS minifier designed to be 100% safe and yield a higher compression ratio than most other tools.

First of all you should download latest version of yuicompressor
If you want to run it in eclipse with ant,you need ant-task
You should edit your ant build.xml file, and add this lines of code:

<project name="test">
<property name="web.dir" value="WebContent"/>
    <property name="input.dir" value="${web.dir}/js"/>
    <property name="output.dir" value="${web.dir}/jscompressed"/>
    
    <target name="clean_compressed_js" description="Clean output directories">
            <delete>
                <fileset dir="${output.dir}">
                    <include name="*.js"/>
                </fileset>
            </delete>
        </target>
     
    <taskdef name="yuicompress" classname="net.noha.tools.ant.yuicompressor.tasks.YuiCompressorTask">
        <classpath>
            <pathelement path="${web.dir}/WEB-INF/lib/yuicompressor-2.4.7.jar" />
            <pathelement path="${web.dir}/WEB-INF/lib/yui-compressor-ant-task-0.5.jar" />
            <pathelement path="${web.dir}/WEB-INF/lib/rhino-1.6R7.jar" />

        </classpath>
    </taskdef>   
    

    <target name="compress_javascript" depends="clean_compressed_js">
        <echo>Compressing files</echo>
        <yuicompress munge="yes"  preserveallsemicolons="yes" toDir="${output.dir}" fromDir="${input.dir}" csssuffix=".css" jssuffix=".js" >
                <include name="*.js"/>
        </yuicompress>
    </target>
</project>

PS: Next step of optimisation should be creating gzip archive with compressed files, if your server support it

References:
http://developer.yahoo.com/yui/compressor/
http://webo.in/articles/habrahabr/112-minify-combine-javascript-troubles/
Also tools for testing your web-site speed:
http://loads.in/
http://tools.pingdom.com/
http://gtmetrix.com/
https://developers.google.com/pagespeed/

Tsung: Web Application Performance and Stress Testing

2011-11-12T11:54:00.009+02:00

The purpose of Tsung is to simulate users in order to test the scalability and performance of IP based client/server applications. You can use it to do load and stress testing of your servers.You can test with Tsung HTTP, WebDAV, SOAP, PostgreSQL, MySQL, LDAP and XMPP/Jabber.

Installation
To install tsung you need Linux distributive, I am using debian.

apt-get install erlang
apt-get install gnuplot-nox libtemplate-perl libhtml-template-perl libhtml-template-expr-perl
Download latest distributive - http://tsung.erlang-projects.org/dist/tsung-1.4.1.tar.gz
tar -zxvf tsung-1.4.1 .tar.gz
cd tsung-1.4.1
./configure && make && make install
also you should create .tsung folder in root and tsung.xml inside it (ypu can see tsung.xml examples in tsung folder)

Thats all after typing tsung command in console, you should see tsung help information.

Configuration tsung.xml
1. Server configuration

<servers>
   <server host="example.com" port="80" type="tcp"></server>
</servers>

2.Client configuration
Very important to specify maxusers

<clients>
     <client host="localhost" use_controller_vm="true" maxusers="7000"/>
</clients>

3.Define the load that we want our server to be exposed to
Tsung simulates the user arrivals in the application. The example below describes 2 different phases.The first will last 5 minutes and every second will come 10 new users, at all 5 minute x 10 users = 3000 users. Next phase will last 10 minutes and every second will come 25 new users , 10 minutes x 25 users = 15 000 users.

<load>
<arrivalphase phase="1" duration="5" unit="minute">
<users arrivalrate="10" unit="second"/>
</arrivalphase>
<arrivalphase phase="2" duration="10" unit="minute">
<users arrivalrate="25" unit="second"/>
</arrivalphase>
</load>

4. Recording script
To test smth, you should provide sequence of actions, what tsung should to do. This configuration you should put in tag <sessions> ..</sessions> tsung.xml. I will test web-site and easiest way it's to use tsung proxy to record actions. To achieve that we must first tell our browser to pass through a proxy listening to port 8090 (Firefox preferences - Advanced - Network - Settings) and ip of the your server.

To start recording use tsung-recorder start
To stop recording use tsung-recorder stop

We will end up with an xml representing the newly recorded session located in ~/.tsung/tsung_recorderyyyymmdd-HH:MM.xml. Just copy-paste this session into the main tsung xml file:

<sessions>
<session name='login_settings' probability='25' type='ts_http'>
<request> <http ... /> </request>
<thinktime random="true" value="4"/>
<transaction name="Login">
<request> ... </request>
...
</transaction>
<request> ... </request>
...
</session>
<session name='login_add_people' probability='75' type='ts_http'>
...
</session>
...
</sessions>

Running
To run Tsung tsung start and to stop tsung stop. Tsung is logging data in the ~/.tsung/log/yyyymmdd-HH:MM folder. To view status tsung status. Wery important to set ulimit value greater than default, type in console ulimit -n 100000. One time i have situation when tsung process not terminated, but tsung stop command didn't worked, in this case you could use ps ax | grep tsung to see all processes and kill -9 <process pid>

Generating HTML report
In order to use these info, we launch the tsung_stats.pl script which will produce a nice html report.
cd .tsung/log/yyyymmdd-HH:MM
and copy tsung_stats.pl file here or specify absolute path type perl tsung_stats.pl . This script will create in this folder reports.

Here is my example, of Simultaneous Users:

And more reports examples here

References:
The Tsung manual
Tsung home page
This article in Russian

JavaEE: Spring MVC blog

2011-09-27T22:58:00.001+03:00

Recently I found a good blog about Spring MVC - http://krams915.blogspot.com/p/tutorials.html

JavaEE: A beginner's guide to Enterprise Java Beans (EJB)

2011-09-22T15:09:00.007+03:00

EJB - is a managed, server-side component architecture for modular construction of enterprise applications. Simply EJB provide instrument to write business layer(logic) of your application.

There are three most used types of java beans:
1)Session Beans
2)Mesage-drivien Beans
3)Entities

1)Session Beans
There are three types of session beans: Stateful, Stateless and Singleton (till EJB 3.1). For Stateless and Stateful beans need to provide interfaces: remote and local. Remote beans are accessed via a network call and local beans are accessed within the same JVM.

Stateless - do not maintain states ex. charging credit card ; checking credit history

@Local
public interface StoreManagerLocal extends StoreManager {
    public List<Customer> findAllCustomers();
}

@Remote
public interface StoreManagerRemote extends StoreManager {
    public List<Customer> findAllCustomers();
}

@Stateless
@RemoteBinding(jndiBinding="AppStoreEJB/remote")
@LocalBinding(jndiBinding="AppStoreEJB/local")
public class StoreManagerBean implements StoreManagerLocal,StoreManagerRemote 
{
    @PersistenceContext(unitName="MyStore")
    private EntityManager em;
    
    @Override
    public List<Customer> findAllCustomers() {
        Query query = em.createQuery("FROM Customer");
        List<Customer> customerList = query.getResultList();
        return customerList;
    }

}

How to call:

public class Tester extends HttpServlet {
 private static final long serialVersionUID = 1L;
 
 @EJB(mappedName = "AppStoreEJB/local")  
 private StoreManager storeManager;

 //....
}

Stateful - saves bean state between client invocations ex. shopping cart on online shops.

@Stateful
public class ShoppingCart implements ShoppingCartLocal,ShoppingCartRemote
{
   //...
}

Singleton - is a session bean with a guarantee that there is at most one instance in the application ex. loading common values for several objects till EJB 3.1

@Startup
@Singleton
public class StatusBean {
  private String status;

  @PostConstruct
  void init {
    status = "Ready";
  }
  //...
}

2)Mesage-drivien Bean
-are business objects whose execution is triggered by messages instead of by method calls.( are stateless,server-side, transaction-aware components, for processing asynchronous JMS messages.)

@MessageDriven(activationConfig = {
        @ActivationConfigProperty(propertyName = "destinationType", propertyValue = "javax.jms.Queue"),
        @ActivationConfigProperty(propertyName = "destination", propertyValue = "queue/exampleQueue") })
public class MessageConsumer implements MessageListener {

    @Resource(mappedName = "java:/MySqlDS")
    private DataSource datasource;

    @Override
    public void onMessage(Message msg) {
        if (msg instanceof TextMessage) {
                TextMessage tmsg = (TextMessage) msg;
               logger.info("MESSAGE BEAN: Message received: " + tmsg.getText());
    }
}

How to call:

    public static void main(String[] args) throws Exception {
        String destinationName = "queue/exampleQueue";

        Context ic = null;
        ConnectionFactory cf = null;
        Connection connection =  null;

        // need try, catch and close context
        ic = getInitialContext();  

        cf = (ConnectionFactory)ic.lookup("/ConnectionFactory");  
        Queue queue = (Queue)ic.lookup(destinationName);

        connection = cf.createConnection();
        Session session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);  
        MessageProducer sender = session.createProducer(queue);

        TextMessage message = session.createTextMessage("Frank");   
        sender.send(message); 
        ic.close();
    }

3)Entities
- represents persistent data maintained in a database.In EJB 3.0, Entity Beans were replaced by the Java Persistence API.

@Entity
@Table(name="customer")
public class Customer implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    @Column(name="ID")
    private int id;

    @Column(name="COUNTRY")
    private String country;

//...
}

More details abouth Entities relationships in the next post.

References:
The Java EE 6 Tutorial - Enterprise Beans
Francesco Marchioni - JBoss AS 5 Development

Android: Image viewer

2011-09-17T10:54:00.005+03:00

View images loaded from Internet(using xml parsing) features: Delete, Reload, Save to SD card, Find, Delete All. Like list and menu I am using my classes extended from ArrayAdapter.

Later will upload on github or google code, now only .zip

More screens:

Android: Android Packaging Problem

2011-09-16T21:51:00.000+03:00

Strange error: "Conversion to Dalvik format failed with error 1 MyApplication Unknown Android Packaging Problem "

Solution: Menu->Project->Clean.

Моя дипломная работа: разработка RIA при помощи Flex

2011-09-10T21:26:00.002+03:00

Посмотреть работу

Посмотреть программу Flex Image Editor

Does Java Use Pass-By-Value Semantics?

2011-08-16T20:46:00.002+03:00

Java is actually pass-by-value for all variables running within a single
VM. Pass-by-value means pass-by-variable-value. And that means, pass-by-copy-ofthe-
variable!

It makes no difference if you're passing primitive or reference variables, you are
always passing a copy of the bits in the variable. So for a primitive variable, you're
passing a copy of the bits representing the value. For example, if you pass an int
variable with the value of 3, you're passing a copy of the bits representing 3. The
called method then gets its own copy of the value, to do with it what it likes.

And if you're passing an object reference variable, you're passing a copy of the
bits representing the reference to an object. The called method then gets its own
copy of the reference variable, to do with it what it likes. But because two identical reference variables refer to the exact same object, if the called method modifies the object (by invoking setter methods, for example), the caller will see that the object the caller's original variable refers to has also been changed. In the next section, we'll look at how the picture changes when we're talking about primitives.

The bottom line on pass-by-value: the called method can't change the caller's
variable, although for object reference variables, the called method can change the
object the variable referred to. What's the difference between changing the variable
and changing the object? For object references, it means the called method can't
reassign the caller's original reference variable and make it refer to a different object,or null. For example, in the following code fragment,

void bar() {
Foo f = new Foo();
doStuff(f);
}
void doStuff(Foo g) {
g.setName("Boo");
g = new Foo();
}

reassigning g does not reassign f! At the end of the bar() method, two Foo objects
have been created, one referenced by the local variable f and one referenced by
the local (argument) variable g. Because the doStuff() method has a copy of the
reference variable, it has a way to get to the original Foo object, for instance to call the setName() method. But, the doStuff() method does not have a way to get to
the f reference variable. So doStuff() can change values within the object f refers
to, but doStuff() can't change the actual contents (bit pattern) of f. In other
words, doStuff() can change the state of the object that f refers to, but it can't
make f refer to a different object!

References:
From SCJP6 book
Also

JavaEE: Building web project using Ant

2011-07-06T12:08:00.003+03:00

Ant is a great tool for building your projects. In this example I'll create simple jar (of course you can create war and ear archives in this case you should use <war ...> and <ear ...> tags) and deploy it on Jboss .

Usually in web projects we have many libraries and need to include them (in my case i use jboss jar)

<?xml version="1.0"?>

<project name="testProject" default="deploy">    
    <property name="app.name" value="testProject"/>
    <property name="jar.name" value="${app.name}.jar" />
    <property name="build.dir" value="build"/>
    <property name="classes.dir" location="${build.dir}/classes" />
    <property name="jar.location" location="${build.dir}/jar" />
    <property name="compiler.src.encoding" value="UTF-8" />
    <property name="jboss_home" location="C:/serverTest/jboss-5.0.0.GA" />
    <property name="deploy.dir" location="C:/serverTest/jboss-5.0.0.GA/server/default/deploy" />
    
    <target name="create-dirs"> 
        <echo message="CREATING DIRS" /> 
        <mkdir dir="${classes.dir}" />
        <mkdir dir="${jar.location}" />
    </target>
    
    <target name="clean">
        <echo message="CLEANING PROJECT" /> 
        <delete dir="${build.dir}" />
        <delete dir="${jar.location}" />
    </target>
    
    <target name="compile" description="Compiling classes" depends="clean,create-dirs">
        <echo message="COMPILING CLASSES" /> 
        <javac srcdir="ejbModule" destdir="${classes.dir}" 
                optimize="true" encoding="${compiler.src.encoding}" 
                classpath="${jboss_home}/common/lib/jboss-javaee.jar">                
        </javac>
    </target>
    
    <target name="build-jar" description="Create jar" depends="compile">
        <echo message="CREATING JAR" /> 
        <jar jarfile="${jar.location}/${jar.name}" index="true" update="false" duplicate="fail">
            <fileset dir="${classes.dir}" />
        </jar>
    </target>
        
    <target name="deploy" depends="build-jar">
        <echo message="DEPLOYING APPLICATION" /> 
        <delete dir="${deploy.dir}/${jar.name}" />
        <copy todir="${deploy.dir}" file="${jar.location}/${jar.name}" overwrite="true" />
    </target>
</project>

Android: Tic Tac Toe game on google code

2011-05-14T16:36:00.005+03:00

Decided to upload my old project - Android Tic Tac Toe Game. This project was created for educational scope.

Here is a link

https://andoid-tictactoe.googlecode.com/

Auto Generate Database(ER) Diagram MySql

2011-05-03T15:46:00.001+03:00

To create ER diagram from db schema you can use SchemaSpy.

Here are few steps:
1. Download SchemaSpy

2. Install flowing:
- Java
- JDBC MySQL Connector
- Graphviz (and dot program, which is part of GraphViz)

3.Execute command in console

C:\test>java -jar schemaSpy_5.0.0.jar -t mysql -o folderWhereCreate -host dbHost -db dbName -u dbUser -p dbPassword -dp mysql-connector-java-3.1.13-bin.jar

ps: You can download all in one archive

References:
Automate the generation of your developer and user documentation

Java: Loading data from file into Oracle database

2011-04-27T17:17:00.006+03:00

It's possible to do using Sql Loader.SQL*Loader is a bulk loader utility used for moving data from external files into the Oracle database.

Here are the steps you should implement:

1) Intall oracle db, full or express

2) Create files

*.txt file with data (may be any extension) and *.ctl file, it's using for specify mapping with data in file and database fields

example test.txt :

Bob     12 1999
George  9  1977

example test.ctl:

-- loading data
OPTIONS (ERRORS=999999)
LOAD
infile *
INTO TABLE PEOPLES
    REPLACE
  {
  persone_name POSITION(1:8) CHAR ,     
 persone_month POSITION(8:9) CHAR,
 persone_year POSITION(12:14) CHAR,
   }

In place of Replace you can use also APPEND - if data doesn't already exist,INSERT - it requires the table to be empty

3) Execute in the console

String command = "sqlldr userid=" + "oracleuser/oraclepassword" + " control=" + "test.ctl"+ " data=" + "test.txt";
Process process = Runtime.getRuntime().exec(command);
int exitVal = process.waitFor();

exitVal may be:
0 - successful
1 - failed
2 - warn
3 - fatal

References:
Oracle - SQL*Loader Control File Reference
Some examples

JavaEE: Using @EJB annotation

2011-04-22T16:05:00.003+03:00

Shows use of @EJB in a Stateless to have another Stateless bean injected into it.Using Jboss 5 + Seam framework

Bean:

@Stateless
@Name(DataStoreImpl.COMPONENT_NAME)
@Scope(ScopeType.STATELESS)
public class DataStoreImpl implements DataStoreLocal{
        public static final String COMPONENT_NAME = "dataStoreImpl";

 @EJB
 protected Test test;

 public String getData() {
  // using test
 }
}

Local business interface:

@Local
public interface DataStoreLocal {
 
 public String getData();
 
}

Call:

DataStoreLocal data = (DataStoreLocal) Component.getInstance(
     DataStoreImpl.COMPONENT_NAME, true);

Flex / AS3: The best way to encode JPEG

2011-03-06T15:35:00.013+02:00

Recently in my diploma I need to encode jpeg file on client, after some research I found library created using Alchemy project( from C/C++ language).It allows you to encode jpeg both synchronous and asynchronous with maximum speed(unlike standard encode() method).

After downloading library and including it in your project, you should do:

1. Init library
This nethod should start with application running s:application applicationcomplete="initAlchemy()"

private var init1:CLibInit;
      private var lib : Object; 
    
      private function initAlchemy():void
      {
        init1 = new CLibInit();
        lib = init1.init();
      }

2.Prepare your image

private var bd:BitmapData ; //your image here
  public var byteArr:ByteArray = bd.getPixels( bd.rect );

3.1 Encode your image synchronous

var ba:ByteArray = bd.getPixels( bd.rect );
   ba.position = 0;
   byteArr = new ByteArray();

  //result will be in byteArr
  lib.encode(ba, byteArr, bd.width, bd.height, 100);
  fileRef.save(byteArr,"NewFileName1.jpg");

encode( src:BimapData, image_data:ByteArrat, imageWidth:uint, imageHeight:uint, quality:int );

Parameters:

src:BitmapData - bitmapData to be encoded. cannot be null !
image_data:ByteArray - buffer where jpeg image will be written to. cannot be null !
imageWidth:int - 'src' image width
imageHeight:int - 'src' image height
quality:int - jpeg quality (1-100)

3.2 Or encode your image asynchronous

lib.encodeAsync( finish, bd, ba,bd.width, bd.height, 100, tuning:int );

encodeAsync( callback:Function, src:BimapData, image_data:ByteArrat, imageWidth:uint, imageHeight:uint, quality:int, tuning:int );

Parameters:

callback:Function - callback function to be called when compression is finished. function is invoked with out parameter, image_data byteArray (the same passed as a image_data parameter
src:BitmapData - see synchronous method
image_data:ByteArray - see synchronous method
imageWidth:int - see synchronous method
imageHeight:int - see synchronous method
quality:int - see synchronous method
tuning:int - this is most important parameter, it defines 'how often' method is going to interrupted and control flow returned to other parts of application. it should be interpreted, rather as a 'number of scanlines to be compressed in a single timeslice'

References:
Flex Tutorial - An Asynchronous JPEG Encoder
Alchemy - asynchronous jpeg encoding #2
Alchemy - asynchronous jpeg encoding
First I tried bytearray.org

Approximate string matching algorithm (fuzzy search)

2011-02-10T00:29:00.015+02:00

This is a great algorithm to find similarity coefficient of the two words.
Author is Viterbi or Bellman.I didn't find anything about it in the Internet.

For example exists dictionary: mother, uncle, cat, dog. And you typed smth like
"maaather", as the result will be "maaather" -> mother.
This algorithm possible to use in spell checking,sound recognition etc.

Algorithm description will be later

Here is the source code:

/**
 *
 * This class is for finding coefficient of similarity of the two words
 * using Viterbi(Bellman) algorithm
 * @author Sergey
 */
public class Analyzer {
  
    private double init[][];
    private double result[][];
    private int n;
    private int m;
 
    private void calculateASCIIDifference(String str1, String str2) {
     try{
        n = str1.length();
        m = str2.length();
        init = new double[n][m];
        for (int i = n - 1,i2 = 0; i >= 0; i--, i2++) {
            for (int j = 0; j < m; j++) {
                 init[i2][j] = Math.abs((int) str1.charAt(i) - (int) str2.charAt(j));
            }
        }
     } catch(Exception e){
         System.out.println("calculateASCIIDifference exception: "+e.toString());
        }
    }
 
    public double[][] getASCIIDifference() {
        return init;
    }
 
    public void setASCIIDifference(double[][] a,int n, int m) {
        this.n = n;
        this.m = m;
        this.init = a;
    }
 
    // Calculate matrix by values from calculateASCIIDifference()
    public double calculateSimilarity(String str1, String str2) {
     
     calculateASCIIDifference(str1,str2);    
     try{
         result = new double[n][m];
         double res, val1, val2, val3;
  
         //initialize first element
         result[n - 1][0] = init[n - 1][0];
         
         //initialize first column
         for (int i = n - 2; i >= 0; i--) {
             result[i][0] = result[i + 1][0] + init[i][0];
         }  
         //initialize first row(from down)
         for (int j = 1; j < m; j++) {
             result[n - 1][j] = result[n - 1][j - 1] + init[n - 1][j];
         }  
         //initialize others
         for (int i = n - 2; i >= 0; i--) {
             for (int j = 1; j < m; j++) {
                 val1 = result[i][j - 1] + init[i][j];
                 val2 = result[i + 1][j] + init[i][j];
                 val3 = result[i + 1][j - 1] + (init[i][j] * 2);
  
                 //minimum of the 3 val's
                 res = val1 < val2 ? val1 : val2;
                 res = res < val3 ? res : val3;
  
                 result[i][j] = res;
             }
         }
         return getSimilarityValue();
     }
     catch(Exception e){
      System.out.println("calculateSimilarity exception: "+e.toString());
     }
     return -1;
    }
    //getting result of Similarity
    public double getSimilarityValue() {
     //need to devide if m != n
      if(m != n)
         return result[0][m - 1] / (m + n);
      else
      return result[0][m - 1];
    }
 
    //getting result array
    public double[][] getSimilarityArray() {
        return result;
    }
    
    //to test   
    public static void main(String[] args) {  
     double result1,result2;    
     Analyzer an = new Analyzer();
     result1 = an.calculateSimilarity("mather","mother");   
     result2 = an.calculateSimilarity("father","mother"); 
     //result1 will be less than result2 => result1 is more similar
     System.out.println(result1 + " " + result2);
    }
}

References:
Something common Similarity Metrics

Java: Collections basics

2011-01-28T21:57:00.005+02:00

In this article i'll describe basics of java collections

ArrayList
An ArrayList is better than Array to use when you have no knowledge in advance about elements number. ArrayList are slower than Arrays. So, if you need efficiency try to use Arrays if possible.Also it is not synchronized. The add operation runs O(n) time.Permits null elements

Vector
Very similar to the ArrayList class. Slover than ArrayList .Also it is synchronized.

LinkedList
LinkedList is much more flexible and lets you insert, add and remove elements from both sides of your collection - it can be used as queue and even double-ended queue.Manipulation with data is fast but showing or getting some element only after enumeration all.

HashMap
A hash table or hash map is a data structure that uses a hash function to map identifying values, known as keys(Key -- Value) HashMap is not synchronized.HashMap allows one null key and any number of null values.

TreeMap
is the sorted version of the HashMap, offers the ability to traverse the contents of the Map in a determined order.

HashTable
Is very similar to the HashMap. It's synchronized.Hashtable does not allow null keys or values.

HashSet
Set is a collection of distinct objects.It stores its elements in a hash table.Order -undefined.Performance - better than LinkedHashSet

LinkedHashSet
is implemented as a hash table with a linked list running through it.Order - insertion.Performance - has fast adding to the start of the list, and fast deletion from the interior via iteration

TreeSet
It stores its elements in a red-black tree.Order - ascending.Performance - Slow

References:
TreeSet vs HashSet vs LinkedHashSet
Array vs ArrayList vs LinkedList vs Vector
Java Collections

Java: Using SQLite

2011-01-28T21:13:00.003+02:00

SQLite - is embedded relational database management system.In other words you can use it without server.

First of all you should download SQLite JDBC driver and add it in your project.Next some code manipulations.Here is an example:

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.Statement;

public class main {
private static Connection con;

public void run() throws Exception {

//sq lite driver
Class.forName("org.sqlite.JDBC");
//database path, if it's new data base it will be created in project folder
con = DriverManager.getConnection("jdbc:sqlite:mydb.db");
Statement stat = con.createStatement();

stat.executeUpdate("drop table if exists weights");

//creating table
stat.executeUpdate("create table weights(id integer,"
+ "firstName varchar(30)," + "age INT," + "sex varchar(15),"
+ "weight INT," + "height INT,"
+ "idealweight INT, primary key (id));");

PreparedStatement prep = con
.prepareStatement("insert into weights values(?,?,?,?,?,?,?);");
prep.setString(2, "vasea");
prep.setString(3, "21");
prep.setString(4, "male");
prep.setString(5, "77");
prep.setString(6, "185");
prep.setString(7, "76");
prep.execute();

//getting data
ResultSet res = stat.executeQuery("select * from weights");
while (res.next()) {
System.out.println(res.getString("id") + " " + res.getString("age")
+ " " + res.getString("firstName") + " "
+ res.getString("sex") + " " + res.getString("weight")
+ " " + res.getString("height") + " "
+ res.getString("idealweight"));
}

}

/**
* @param args
*/
public static void main(String[] args) {
  try {
    new main().run();
  } catch (Exception e) {
  // TODO Auto-generated catch block
     e.printStackTrace();
    }
}

}

Java: Drawing charts it's easy

2011-01-16T16:47:00.003+02:00

Recently I need to draw a chart, and after short search I found great library JFreeChart. It provides drawing and saving charts to the png file.

Here is the code sample:

import javax.swing.JFrame;
import org.jfree.chart.ChartFactory;
import org.jfree.chart.ChartPanel;
import org.jfree.chart.JFreeChart;
import org.jfree.chart.plot.PlotOrientation;
import org.jfree.data.xy.XYDataset;
import org.jfree.data.xy.XYSeries;
import org.jfree.data.xy.XYSeriesCollection;
 
public class MyChart {
  public static void main(String[] args) {
    XYSeries series = new XYSeries("cos(a)");
 
    //calculating points
    for(float i = -10; i < 10; i+=0.1){
      series.add(i, Math.cos(i));
    }
 
    XYDataset xyDataset = new XYSeriesCollection(series);

    //creating chart
    JFreeChart chart = ChartFactory
        .createXYLineChart("y = cos(x)", "x", "y",
                           xyDataset, 
                           PlotOrientation.VERTICAL,
                           true, true, true);
    JFrame frame = 
        new JFrame("Chart");

    //adding chart to the frame
    frame.getContentPane()
        .add(new ChartPanel(chart));
    frame.setSize(400,300);
    frame.show();
  }
}

References:
JFreeChart tutorial

Java:Code coverage for Eclipse

2010-12-25T19:30:00.004+02:00

Code coverage describes the degree to which the source code of a program has been tested.

When you test method you can find coverage using EclEmma plug-in for eclipse.It's simply add new view.

Java: JDBC basics

2010-12-25T18:59:00.007+02:00

JDBC is an API for the Java programming language that defines how a client may access a database. It provides methods for querying and updating data in a database.

How it works?
1.First you should specify sql driver
Class.forName("com.mysql.jdbc.Driver");

2.Next url to your sql server
Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/dbName", "userName", "userPassword");

3.And finally execute query using Statement or PreparedStatement

Example

import java.sql.Connection;
import java.sql.Date;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;

class jdbcTest {
 public static void main(String args[]) {
  try {
   //connecting
   Class.forName("com.mysql.jdbc.Driver");
   String url = "jdbc:mysql://localhost:3306/dbName";
   Connection con = DriverManager.getConnection(url, "root", "");
   List groups = new ArrayList();
   
   //using Statement to select
   Statement stmt = null;
   ResultSet rs = null;
   try {
    stmt = con.createStatement();
    rs = stmt
      .executeQuery("SELECT group_id, groupName FROM groups");
    while (rs.next()) {     
       Group gr = new Group(); 
       gr.setGroupId(rs.getInt(1));
       gr.setNameGroup(rs.getString(2));      
       groups.add(gr);      
    }
    
    
   //using prepared Statement to insert 
    PreparedStatement stmt2 = null;
          try {
              stmt = con.prepareStatement(
                      "INSERT INTO groups " +
                      "(group_id, groupName) " +
                      "VALUES (?, ?)");
              stmt2.setInt(1, group.getId());
              stmt2.setString(2, group.getName());          
              stmt2.execute();
   } finally {
    if (rs != null) {
     rs.close();
    }
    if (stmt != null) {
     stmt.close();
    }
   }
  } catch (Exception e) {
   e.printStackTrace();
  } 
 }
}

Java: Parameterized unit tests with JUnit

2010-12-21T16:35:00.005+02:00

JUnit is a unit testing framework for the Java programming language.In this article I will explain how to create test with predefined values.This feature works in JUnit 4.

Structure of a parameterized test class

To mark a test class as a parameterized test, you must first annotate it with @RunWith(Parameterized.class). The class must then provide at least three entities:

A static method that generates and returns test data,
A constructor that stores the test data
A test

The method that generates test data must be annotated with @Parameters, and it must return a Collection of Arrays.

How it's work
Values from static method goes in our constructor and instantiate class over and over.(Number of parameters in constructor should correspond to the number of parameters in each array)

Example
I this example test will check does 1 + 4 =5 and other, all data it will take from array.

//tested class
public class Counter {
 private double x;
 private double y;
 
 public Counter(double x, double y){
  this.x = x;
  this.y = y;
 }
        public double addXandY(){
  return x + y;
 }
}

import java.util.Arrays;
import java.util.Collection;
import org.junit.Test;
import org.junit.runners.Parameterized;
import org.junit.runners.Parameterized.Parameters;
import org.junit.runner.RunWith;
import static org.junit.Assert.*;

@RunWith(Parameterized.class)
public class ParameterizedTestExample {

 private double number;
 private double number2;
 private double result;
 private Counter coun;

        //constructor takes parameters from array 
 public ParameterizedTestExample(double number, double number2,
   double result1) {
  this.number = number;
  this.number2 = number2;
  this.result = result1;
  coun = new Counter(number, number2);
 }

  //array with parameters
  @Parameters
  public static Collection<Object[]> data() {
      Object[][] data = new Object[][] { { 1, 4, 5 }, { 2, 7, 9 },
           { 3, 7, 10 }, { 4, 9, 13 } };
 return Arrays.asList(data);
 }
   //running our test     
   @Test
   public void testCounter() {
 assertEquals("Result add x y", result, coun.addXandY(), 0);
   }
}

Android : Working with XML on Android

2010-12-15T16:57:00.000+02:00

Recently I found great article from ibm with source code examples, here it is

JavaEE : Hibernate tutorial

2010-12-12T17:36:00.022+02:00

Hibernate is an object-relational mapping (ORM) library for the Java language, providing a framework for mapping an object-oriented domain model to a traditional relational database.

Why it's need?
For example you want insert something in your database.

In sql:

PreparedStatement prep = con

.prepareStatement("insert into weights values(?,?,?,?,?,?,?);");

prep.setString(2, "vasea");

prep.setString(3, "21");

prep.setString(4, "male");

prep.setString(5, "77");

prep.setString(6, "185");

prep.setString(7, "76");

prep.execute();

In hibernate:

Factory.getInstance().getEmployeDAO().addEmployee(new Human("vasea",21,77,185,76));

Hibernate gives you possibility to manage database abstractly, also it's useful when you want to change some logic.

Hibernate Setup
To use Hibernate with Eclipse you should download Hibernate libraries (hibernate-annotations-3.4.0.GA + hibernate-distribution-3.3.2.GA-dist) and export them to the project. (Download from official site or finished my library jars)
You may create your library, that contains required files:

click in Eclipse Window > Preferences > Java > Build Path > User Libraries and click New.
enter name, and click Add jars..
after library creation, you should include it click Project > Properties > Java Build Path > Add library > User library

SQL Setup
You should create database, any what do you want. I use db-derby . You should configure hibernate, for working with your database. For this you need database-url, password and user name. You can create database from Eclipse in Data Source Explorer.

Database diagramm:

hiberante.cfg.xml
This file using to describe configuration of your database. When you work with annotations use <mapping class="entity.Human"/> otherwise use <mapping resource="entity/Human.hbm.xml"/>.Next i will use approach with annotations.

hiberante.cfg.xml sample:

<?xml version='1.0' encoding='utf-8'?>

<!DOCTYPE hibernate-configuration PUBLIC

"-//Hibernate/Hibernate Configuration DTD 3.0//EN"

"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">



  <hibernate-configuration>

   <session-factory>

    <!-- Database connection settings -->

    <property name="connection.driver_class">org.apache.derby.jdbc.ClientDriver</property>

    <property name="connection.url">jdbc:derby://localhost:1527/HibernateDb;create=true</property>

    <property name="connection.username">user</property>

    <property name="connection.password">password</property>



    <!-- JDBC connection pool (use the built-in) -->

    <property name="connection.pool_size">2</property>



    <!-- SQL dialect -->

    <property name="dialect">org.hibernate.dialect.DerbyDialect</property>



    <property name="current_session_context_class">thread</property>



    <!-- Disable the second-level cache  -->

    <property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property>



    <!-- Echo all executed SQL to stdout -->

    <property name="show_sql">true</property>



    <mapping class="entity.Employer"/>

    <mapping class="entity.Human"/>

   </session-factory

</hibernate-configuration>

HibernateUtil class:
Hibernate use this class for getting data from hiberante.cfg.xml and configure hibernate

public class HibernateUtil {

   private static final SessionFactory sessionFactory;

     static {

       try {  

         sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();

       } catch (Throwable ex) {

         System.err.println("Initial SessionFactory creation failed." + ex);

         throw new ExceptionInInitializerError(ex);

       }

     }



     public static SessionFactory getSessionFactory() {

       return sessionFactory;

     }

 }

Entities
You should create simple pojo classes thats will store structure of our tables(id, name, sex and etc.)
Also you should specify how tables are related.

Entities sample:

@Entity

@Table(name="EMPLOYEE")

public class Employee {

 @Id

 @GeneratedValue(strategy=GenerationType.IDENTITY)

 @Column(name="employee_id")

 private int employeeId;

 

 @Column(name="salary")

 private double salary;

 

 @OneToOne(cascade = CascadeType.ALL,fetch=FetchType.LAZY)

 @PrimaryKeyJoinColumn

 private Human humData;

 

 public int getEmployeeId() {

  return employeeId;

 }

 public void setEmployeeId(int employeeId) {

  this.employeeId = employeeId;

 }

 public int getSalary() {

  return salary;

 }

 public void setSalary(int salary) {

  this.salary = salary;

 }

 public int getHumData() {

  return humData;

 }

 public void setHumData(int humData) {

  this.humData = humData;

 } 

}



@Entity

@Table(name="HUMAN")

public class Human {

 @Id

 @GeneratedValue(strategy=GenerationType.IDENTITY)

 @Column(name="human_id")

 private int humId;

 

 @Column(name="hum_name")

 private String name; 

 

 public int getHumId() {

  return humId;

 }

 public void setHumId(int humId) {

  this.humId = humId;

 }

 public String getName() {

  return name;

 }

 public void setName(String name) {

  this.name = name;

 }

}

DAO:
It's just simple interface with methods to interact with your table. Here is description. You should create interface for every table, but if all methods are the same you can use this way.

DAO sample:

public interface HumanDAO {

 void addHuman(Human human) throws SQLException;

 void updateHuman(Human hum) throws SQLException;

 public Collection getAllHumans() throws SQLException;

 public Human getHumanById(int id) throws SQLException;

 public void deleteHuman(Human hum) throws SQLException;

}

DAOImpl:

public class HumanDAOImpl implements HumanDAO {



 @Override

 public Human getHumanById(int id) throws SQLException {

  Session session = null;

  Human human = null;

  try {

   session = HibernateUtil.getSessionFactory().openSession();

   human = (Human) session.load(Human.class, id);

   Hibernate.initialize(human);

  } catch (Exception e) {

   System.out.print("Error in getting by id");

  } finally {

   if (session != null && session.isOpen()) {

    session.close();

   }

  }

  return human;

 }



 @Override

 public void addHuman(Human human) throws SQLException {

   Session session = null;

      try {

        session = HibernateUtil.getSessionFactory().openSession();

        session.beginTransaction();

        session.save(human);

        session.flush();

        session.getTransaction().commit();

      } catch (Exception e) {

       System.out.println("Error in inserting: " + e.toString());

      } finally {

        if (session != null && session.isOpen()) {



          session.close();

        }

      }  

  

 }

  //etc.))

}

Factory:
This class need to return your dao. Also you can read here

public class Factory {

 

  private static EmployeeDAO employeeDAO = null;

  private static HumanDAO humanDAO = null;

  

  public static synchronized Factory getInstance(){

      if (instance == null){

        instance = new Factory();

      }

      return instance;

    }



  public EmployeeDAO getEmployee(){

   if (employeeDAO == null){

    employeeDAO = new EmployeeDAOImpl();

      }

      return employeeDAO;

  }

  public HumanDAO getHumanDAO(){

   if (humanDAO == null){

    humanDAO = new HumanDAOImpl();

      }

      return humanDAO;

  }

Main method:
Finally we running our project, for this we should create our tables(with hibernate or manually).Next we adding data to our tables. We call Factory thats return required entity and use our methods.

public class Main {

 public  static void createTables(){

  AnnotationConfiguration config = new AnnotationConfiguration();

  config.addAnnotatedClass(Human.class);

  config.addAnnotatedClass(Employee.class);

  config.configure("hibernate.cfg.xml");  

  new SchemaExport(config).create(true,true);

 }

        public static void main(String[] args) {

        //creating tables

          createTables();

          Human hum = new Human();

          hum.setName("Vasea");

          Employee emp = new Employee();

          emp.setSalary(1000);

          emp.setHumData(hum);

         //adding data 

   try {

         Factory.getInstance().getEmployeDAO().addEmployee(emp);  

  } catch (SQLException e) {

   e.printStackTrace();

  }

       }

}

References
Very useful are Official docs abouth annotations .
Video lesson on YouTube about hibernate here.
Hibernate basics (Russian lang) here

Ps: This is not optimal solution, everything becomes really easy when you use Application server(Jboss, Glasfish and etc.) with some framework

PHP: Working with XML

2010-12-03T15:54:00.020+02:00

In this article I'll implement base functions to interact with XML like: loading, showing, saving, adding, deleting, editing.

My XML document sample:

<?xml version="1.0" encoding="UTF-8"?>
<catalog>
<spectacle>
<image>images/8780_185540_img2.jpg</image>
<date>16.09.10</date>
<time>19:00</time>
<title>Hamlet</title>
<author>W.Shakespeare</author>
<genre> tragedy</genre>
</spectacle>
</catalog>

HTML action :
<form method="post" action="begin.php" name="adminForm" >

Exists 3 methods in PHP 5 which allow us to interact with XML: DOM, Simple XML and XPath.

The simplest way is to use Simple XML :). But it have and disadvantages when you need more methods to interact with XML, in this cases you may use DOM.

When you want to get an element use:

$catalog->spectacle[0]; //return sprectacle

When you want to get an attribute use:

$image['att_name'];

When you want to get data use:

echo ($xml->catalog->spectacle[0]->title);

So here is my source code:

$spectacles = Array();
/*add to xml specified spectacle node*/
function addToXml()
{
  $xml = simplexml_load_file("catalog.xml"); //This line will load the XML file. 

  $sxe = new SimpleXMLElement($xml->asXML());  
  //The following lines will add a new child 
  $spectacle = $sxe->addChild("spectacle"); 
  $spectacle->addChild("image", $_POST["image"]); 
  $spectacle->addChild("date", $_POST["date"]); 
  $spectacle->addChild("time", $_POST["time"]); 
  $spectacle->addChild("title", $_POST["title"]); 
  $spectacle->addChild("author", $_POST["author"]); 
  $spectacle->addChild("genre", $_POST["genre"]);  
  
  //use for format output
  $dom = new DOMDocument('1.0');
  $dom->preserveWhiteSpace = false;
     $dom->formatOutput = true;
  $dom->loadXML($sxe->asXML());
     $dom->saveXML();
  $dom->save("catalog.xml");
}
/*loading xml to global array*/
function loadXML()
{ 
   global $spectacles;

    $xml = simplexml_load_file("catalog.xml");
 
 foreach($xml->spectacle as $spectacle)
    {
     array_push($spectacles, $spectacle);
  
    }
}
/*showing xml in table view*/
function showXML()
{
   //print_r($spectacles);
   global $spectacles;
   echo "<table border='1'><tr>";
   echo "<td>Image</td>";
   echo "<td>Date</td>";
   echo "<td>Time</td>";
   echo "<td>Title</td>";
   echo "<td>Author</td>";
   echo "<td>Genre</td>";
   echo "</tr>\n";
    
 foreach ($spectacles as $spectacle) 
 { 
      echo "<tr>";   
      echo "<td>".$spectacle->image."</td>"; 
      echo "<td>".$spectacle->date."</td>"; 
      echo "<td>".$spectacle->time."</td>"; 
      echo "<td>".$spectacle->title."</td>"; 
      echo "<td>".$spectacle->author."</td>"; 
      echo "<td>".$spectacle->genre."</td>"; 
      echo "</tr>\n";
 }
 echo "</table";
}

/*delete node with specified date & title*/
function deleteNodeXML()
{
   global $spectacles;
   $spectacle_final = Array();

   foreach($spectacles as $spectacle)
   {
  if($spectacle->date != $_POST['date'] && $spectacle->title != $_POST['title'])
  {
   array_push($spectacle_final, $spectacle);
  }
 }
 saveDom($spectacle_final); //saving our array to xml
}

/*edit node with specified date & title*/
function editXml()
{
   global $spectacles;
   $spectacle_final = Array();

   foreach($spectacles as $spectacle)
   {
  if($spectacle->date == $_POST['date'] && $spectacle->title == $_POST['title'])
  {
      $spectacle->image = $_POST['imageNew'];
            $spectacle->date = $_POST['dateNew'];
   $spectacle->time = $_POST['timeNew'];
   $spectacle->title = $_POST['titleNew'];
   $spectacle->author = $_POST['authorNew'];
   $spectacle->genre = $_POST['genreNew'];
   
   array_push($spectacle_final, $spectacle);
  }
  else 
  {
   array_push($spectacle_final, $spectacle);
  }
 }
 saveDom($spectacle_final); //saving our array to xml
}

/*saving array to xml*/
function saveDom($spectacle_final)
{
    $doc = new DOMDocument('1.0','UTF-8');
 $doc->encoding='UTF-8';
 
 // we want a nice output
 $doc->formatOutput = true;

 $root = $doc->createElement('catalog');
 $root = $doc->appendChild($root);

 foreach($spectacle_final as $spectacle)
 { 
  $spect = $doc->createElement('spectacle');
  $spect = $root->appendChild($spect);

  $imag = $doc->createElement('image');
  $imag = $spect->appendChild($imag);  
  $text = $doc->createTextNode($spectacle->image);
  $text = $imag->appendChild($text);
  
  $dat = $doc->createElement('date');
  $dat = $spect->appendChild($dat);  
  $text = $doc->createTextNode($spectacle->date);
  $text = $dat->appendChild($text);
  
  $tim = $doc->createElement('time');
  $tim = $spect->appendChild($tim);  
  $text = $doc->createTextNode($spectacle->time);
  $text = $tim->appendChild($text);
  
  $tit = $doc->createElement('title');
  $tit = $spect->appendChild($tit);  
  $text = $doc->createTextNode($spectacle->title);
  $text = $tit->appendChild($text);
  
  $aut = $doc->createElement('author');
  $aut = $spect->appendChild($aut);  
  $text = $doc->createTextNode($spectacle->author);
  $text = $aut->appendChild($text);
  
  $gen = $doc->createElement('genre');
  $gen = $spect->appendChild($gen);  
  $text = $doc->createTextNode($spectacle->genre);
  $text = $gen->appendChild($text);
 }

   $doc->saveXML() . "\n"; 
   $doc->save("catalog.xml");
}

References:

Using XML: A PHP Developer's Primer
Official php documentation

С++: Cube Root mistake

2010-11-18T22:05:00.005+02:00

You may say that it is trivial task, but it have some difficulties

First i tried like this:

int root(double num)
{
  double calc = pow(num, 1. / 3.);
  return (int)calc;
}

It's succesefylly working for 8 and 27 but with 64 will be inaccuracy in calculation. Inaccuracy appears because pow(64, 1. / 3.) return 3.99999999 and after rounding to int result will be 3
I solved problem this way:

int root(double num)
{
  double calc = pow(num, 1. / 3.);
  double calc2 = ceil(calc); //rounding
  return (int)calc2;
}

PHP: DOMDocument and encoding

2010-11-18T18:17:00.008+02:00

If you want to save document with not typical encoding, for example utf-8 (russian letters)

If you do like this:

$doc = new DOMDocument('1.0','UTF-8');

It will be wrong, because php does't know what encoding will be.For normal working you should use:

$doc->encoding='UTF-8';

ps: Next will be some articles about working with xml in php

Photoshop Keyboard shortcuts

2010-11-18T18:10:00.002+02:00

Recently I found cool list with photoshop shortcuts

Android: Menu button click event

2010-10-31T10:25:00.001+02:00

If you want to do smth after hardware MENU button clicks, not default menu creation but something slightly different.The easiest way is to capture the onKeyDown event for the menu button click

 @Override
 public boolean onKeyDown(int keycode, KeyEvent event ) {
  if(keycode == KeyEvent.KEYCODE_MENU){
   AlertDialog.Builder dialogBuilder 
   = new AlertDialog.Builder(this)
   .setMessage("Test")
   .setTitle("Menu dialog");
   dialogBuilder.create().show();
  }
  return super.onKeyDown(keycode,event);  
 }

Android: Center position of the button (fill_parent, wrap_content)

2010-10-17T11:44:00.011+03:00

<Button android:id="@+id/btClick" android:gravity="center_vertical|center_horizontal"
android:layout_gravity="center_vertical|center_horizontal|center" 
android:layout_height="wrap_content" 
android:layout_width="100px" 
android:text=""/>

android:layout_width="fill_parent" - object have width like parent
android:layout_height="wrap_content" - parent height wants to be just big enough to enclose its content

Andoid: Change progress in progress dialog from the different thread

2010-10-07T11:34:00.006+03:00

We should use Handler that allows you to send message to the thread

  private int increment;
  private ProgressDialog m_ProgressDialog; 
  public void onCreate(Bundle savedInstanceState) {

    Runnable viewImages = new Runnable(){
    @Override
      public void run() {
        getImages();
      }
    };
  
    m_ProgressDialog = new ProgressDialog(this);
    m_ProgressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
    m_ProgressDialog.setMessage("Loading...");
    m_ProgressDialog.show();

   Thread thread =  new Thread(null, viewImages, "MagentoBackground");
   thread.start();
}

  //obtain message from thred
  Handler progressHandler = new Handler() {
      public void handleMessage(Message msg) {
           m_ProgressDialog.incrementProgressBy(increment);
      }
  };

  private void getImages(){
    try{
    //do smth, load image for example, in may be cycle
    increment = 100/ images.size();
    progressHandler.sendMessage(progressHandler.obtainMessage());  //send message
    Thread.sleep(2000);
    } catch (Exception e) {
         Log.e("BACKGROUND_PROC", e.getMessage());
    }
  }

Android: Context menu in ListView after clicking

2010-10-05T20:52:00.004+03:00

The easiest way) to create context menu

1)Firs of all you should create ListView maybe with some adapter, so main class should extends ListActivity
2) To register our menu, use:

registerForContextMenu(getListView());

3) Then override

final int CONTEXT_MENU_DELETE_ITEM =1;
 final int CONTEXT_MENU_UPDATE =2;
 @Override
 public void onCreateContextMenu(ContextMenu menu, View v,ContextMenu.ContextMenuInfo menuInfo) {
          
  menu.add(Menu.NONE, CONTEXT_MENU_DELETE_ITEM, Menu.NONE, "Delete");
  menu.add(Menu.NONE, CONTEXT_MENU_UPDATE, Menu.NONE, "update");
 }

4)Now we should handle click events of our context menu

@Override
 public boolean onContextItemSelected(MenuItem item) {

      AdapterView.AdapterContextMenuInfo info= (AdapterView.AdapterContextMenuInfo) item.getMenuInfo();
      Long id = getListAdapter().getItemId(info.position);/*what item was selected is ListView*/

      switch (item.getItemId()) {
              case CONTEXT_MENU_DELETE_ITEM:
                    //do smth
                   return(true);
             case CONTEXT_MENU_UPDATE:
                   //do smth else)
                   return(true);    
      }
  return(super.onOptionsItemSelected(item));
}

Ps: I found one disadvantage of this method, you can't use icons in this context menu

Android: Native icons how to use

2010-10-04T23:23:00.001+03:00

In your android phone are many beautiful icons.Here is the list:http://developer.android.com/reference/android/R.drawable.html and here is images http://androiddrawableexplorer.appspot.com/

To use:

in recourses android:icon="@android:drawable/<name of your element>"

in java code android.R.drawable.<name of your element>

Android: Unparsed aapt error

2010-10-04T23:06:00.001+03:00

This error appears when you change smth in xml and it changes in recourses not correctly( may be it's bug)
Solution: go in Eclipse to Project>clean it will load last successful build, Good Luck!)

Android: Menu button click event & Options Menu

2010-10-02T13:24:00.006+03:00

1)First of all we should create our menu.xml(create new folder menu in res):

<menu xmlns:android="http://schemas.android.com/apk/res/android">
<item android:id="@+id/search"
android:title="search"
android:icon="@drawable/icon" />
<item android:id="@+id/deleteall"
android:title="delete all"
android:icon="@drawable/icon" />
</menu>

2) To handle event we need override:

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.menu, menu);
        return true;
    }

3)And for determine what button is pressed:

 @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.deleteall:Log.v("ttt", "You pressed the icon!");
                  break;
            case R.id.search:Log.v("ttt", "You pressed the text!");
                  break;
        }
        return true;
    }

Android:The easiest way to load image from URL

2010-09-30T18:54:00.021+03:00

The easiest way to download image from URL is to use method Drawable.createFromStream:

main.xml:

<linearlayout android:id="@+id/LinearLayout01" 
android:layout_height="fill_parent" 
android:layout_width="fill_parent" 
xmlns:android="http://schemas.android.com/apk/res/android">
<imageview android:id="@+id/ImageView1" 
android:layout_height="wrap_content" 
android:layout_width="wrap_content">
</imageview></linearlayout>

Java file:

import java.io.InputStream;
import java.net.URL;
import android.app.Activity;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.widget.ImageView;

public class ImageFromUrlExample extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        ImageView imgView =(ImageView)findViewById(R.id.ImageView1);
        Drawable drawable = LoadImageFromWeb("http://www.example.com/android.png");
        imgView.setImageDrawable(drawable);

    }

   private Drawable LoadImageFromWeb(String url)
   {
  try
  {
   InputStream is = (InputStream) new URL(url).getContent();
   Drawable d = Drawable.createFromStream(is, "src name");
   return d;
  }catch (Exception e) {
   System.out.println("Exc="+e);
   return null;
  }
 }
}

Android: Download progress

2010-09-30T12:06:00.017+03:00

How to create progress of file downloading

The main idea is that we need to download our file by parts , in our case part = 1 kb

public class DownloadImageTask extends AsyncTask<String, Integer, Drawable> {

  private Drawable d; 
     private HttpURLConnection conn;
     private InputStream stream; //to read 
     private ByteArrayOutputStream out; //to write
     
     private double fileSize;
     private double downloaded; // number of bytes downloaded
     private int status = DOWNLOADING; //status of current process
     
     private ProgressDialog progressDialog;     

     private static final int MAX_BUFFER_SIZE = 1024; //1kb
     public static final int DOWNLOADING = 0;
     public static final int COMPLETE = 1;
     
     public  DownloadImageTask(){
      d = null;
      conn = null;
      fileSize = 0;
      downloaded = 0;
      status = DOWNLOADING;
     }
   public boolean isOnline() {
   try {
    ConnectivityManager cm = (ConnectivityManager) 
             getSystemService(Context.CONNECTIVITY_SERVICE);
    return cm.getActiveNetworkInfo().isConnectedOrConnecting();
   } catch (Exception e) {
    return false;
   }
  }
   @Override
  protected Drawable doInBackground(String... url) {

   try {
    if (isOnline() == true) {

     Log.v("Test", "Starting loading image by URL: ");
     conn = (HttpURLConnection) new URL(url[0]).openConnection();
     fileSize = conn.getContentLength();
     out = new ByteArrayOutputStream((int) fileSize);
     conn.connect();

     stream = conn.getInputStream();
     // loop with step 1kb
     while (status == DOWNLOADING) {
      byte buffer[];

      if (fileSize - downloaded > MAX_BUFFER_SIZE) {
       buffer = new byte[MAX_BUFFER_SIZE];
      } else {
       buffer = new byte[(int) (fileSize - downloaded)];
      }
      int read = stream.read(buffer);

      if (read == -1) {
       publishProgress(100);
       break;
      }
      // writing to buffer
      out.write(buffer, 0, read);
      downloaded += read;
      // update progress bar
      publishProgress((int) ((downloaded / fileSize) * 100));
     }// end of while

     if (status == DOWNLOADING) {
      status = COMPLETE;
     }
     d = Drawable.createFromStream(
       (InputStream) new ByteArrayInputStream(out
         .toByteArray()), "filename");
     return d;

    }// end of if isOnline
    else {
     return null;
    }
   } catch (Exception e) {
    System.out.println("Exception: " + e);
    return null;
   }// end of catch
  }// end of class DownloadImageTask()
   
  @Override
  protected void onProgressUpdate(Integer... changed) {
   progressDialog.setProgress(changed[0]);
     }
  
  @Override
  protected void onPreExecute() {
   progressDialog = new ProgressDialog(ImageViewer.this);
   progressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
   progressDialog.setMessage("Loading...");
   progressDialog.setCancelable(false);
   progressDialog.show();
  }
  
  @Override
  protected void onPostExecute(Drawable result) {
   if(result != null){
   progressDialog.dismiss();
   setImage(d);
   }
   else {
    progressDialog.dismiss();
    AlertDialog alertDialog;
    alertDialog = new AlertDialog.Builder(ImageViewer.this).create();
    alertDialog.setTitle(R.string.infoLabel);
    alertDialog.setMessage(getString(R.string.loadErrorLabel));
    alertDialog.setButton(getString(R.string.closeLabel),
      new DialogInterface.OnClickListener() {
       public void onClick(DialogInterface dlg, int sum) {
        // do nothing, close
       }
      });
    alertDialog.show();
   }
  }
 }//end of class DownloadImageTask()

Android: Beginning

2010-09-29T12:00:00.004+03:00

Here are a few steps to begin develop for Android:

Install JDK
Install Eclipse IDE
Install Android SDK
Instal Eclipse Android plugin

References:
How to do all steps more detailed here (Russian lang)