Java 5.0 Multithreading feature - Callable and Future

One of the very important feature of Java 5.0 is Callable Interface and Future.
The problem with Runnable interface or Thread class in multithreading was you can return any value from the thread.
But this drawback was removed in Java 5.0 with Callable Interface and Future.
In the code below, Callable<Interger> in CallableExample, the thread will return 'Integer' and this Integer value can be retrieved using Future object as shown in CallableExampleTest.

1. Callable Implementation:
----->

import java.util.concurrent.Callable;

/**
*
* @author vinitpatwa
*/
public class CallableExample implements Callable<Integer> {

private String word;

public CallableExample(String word) {

this.word = word;
}

public Integer call() {

return getWord().length();

}

public String getWord() {
return word;
}
}

<-----

2. Testing the Callable implementation
----->
import java.util.LinkedList;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

/**
*
* @author vinitpatwa
*/
public class CallableExampleTest {

public static void main(String args[]) throws Exception{

ExecutorService pool=Executors.newFixedThreadPool(1);
List<Future<Integer>> set=new LinkedList<Future<Integer>>();
String[] strArray={"Texas", "California", "Ohio"};
for(String word:strArray){

Callable cal=new CallableExample(word);
Future<Integer> future=pool.submit(cal);
set.add(future);

}

for(Future<Integer> future:set){
System.out.println("Length of word is : "+future.get());
}
}
}

<-----

Design Patterns Tutorial

1. Singleton Pattern
-------------------------------------
A Singleton is a class that can be instantiated only one time in a JVM per class loader. Repeated calls always returns the same instance. Ensures that a class has only one instance, and provide a global point of access. It can be an issue if singleton class gets loaded by multiple class loader or JVMs

An example of Singleton Pattern

public class OnlyOne{

private static OnlyOne one=new OnlyOne();

//private constructory
//This class can not be instantiated from outside and prevent subclassing
private OnlyOne(){}

public static OnlyOne getInstance(){
retrun one;
}

}


2. Factory Pattern
-------------------------------------
A factory method pattern is creational pattern. The creational patterns abstract the object instantiation process by hiding how the objects are created and make the system independent of the object creational process.
Factory pattern returns one of the several product subclasses. You should use a factory pattern, if you have a super class and number of subclasses, and based on some data provided, you have to return the object of one of the subclasses, But the calling code is unaware of the actual implementation.
Factory pattern reduces the coupling or the dependencies between calling code and the called object.

The abstract factory pattern is one level of abstraction higher than factory method pattern, which means it returns the factory classes.

3. FlyWeight Design Pattern:
-------------------------------------
When we create string objects String s1="A"; String s2="A".
It will check if it is already in the string pool, if it is there, then it will get it from there. Flyweight are like Shared objects and reusing them will have considerable performance gain


4. Decorater Design Pattern:
-------------------------------------
Decorator pattern attaches responsibilities to objects at runtime.
Java.io classes uses Decorator design pattern to construct different combination of behavior at runtime based on some basic classes.

File file=new File("C:/temp");
FileInputStream f=new FileInputStream(file);
BufferredInputStream output=new BufferredInputStream(f);

Decorator design pattern add or restrict functionality of decorator object before or after forwarding the request.
At runtime 'output' which is decorator objects forward the method calls to it's decorated object 'f'

5. Observer Pattern (publisher - subscriber design pattern)
-------------------------------------
(one publisher - one / multiple subscriber)
Intent of this design pattern is to define one to many dependency so that when one object(i.e. Publisher changes it's state, all it's dependents(i.e. all it's subscribers) are notified and updated successfully.

6. Reactor Design pattern
-------------------------------------
Unlike Observer pattern, Reactor design pattern handles multiple even sources (multiple publisher - one / multiple subscriber)
NIO(New I/O API) uses this, which demultiplexes events(separating single stream into multiple stream) and dispatches them to registered object handlers.

Using SQLite with SQLiteJDBC driver.

1. SQLite is serverless. With SQLiteJDBC driver, we can write programs to access SQLite using JAVA.
This tutorial will have step by step description about how to do it.

2. We will use Netbeans, but it will work in the same manner with eclipse too.

3. Download SQLiteJDBC driver jar, 'sqlitejdbc-v056.jar' from website: http://www.zentus.com/sqlitejdbc/

4. Create a java project named 'SQLite' in Netbeans.(You can give any name

5. Create a class called 'Test' in that project.

6. Add 'sqlitejdbc-v056.jar' in the class path of 'SQLite' project in Netbeans.

7. Paste following code in Test class


--->
import java.sql.*;

public class Test {

public static void main(String[] args) throws Exception {
Class.forName("org.sqlite.JDBC");
Connection conn =
DriverManager.getConnection("jdbc:sqlite:Vinit");
Statement stat = conn.createStatement();
stat.executeUpdate("drop table if exists school;");
stat.executeUpdate("create table school (name, state);");
PreparedStatement prep = conn.prepareStatement(
"insert into school values (?, ?);");

prep.setString(1, "UTD");
prep.setString(2, "texas");
prep.addBatch();
prep.setString(1, "USC");
prep.setString(2, "california");
prep.addBatch();
prep.setString(1, "MIT");
prep.setString(2, "massachusetts");
prep.addBatch();

conn.setAutoCommit(false);
prep.executeBatch();
conn.setAutoCommit(true);

ResultSet rs = stat.executeQuery("select * from school;");
while (rs.next()) {
System.out.print("Name of School = " + rs.getString("name") + " ");
System.out.println("state = " + rs.getString("state"));
}
rs.close();
conn.close();
}
}


--->

8. Run the project as java application.

9. It will create database file by name 'Vinit' in the Netbeans 'SQLite' project folder.

10. Here is in above code, we are creating sqlite database 'Vinit'.

I hope it will be helpful.

source:
http://www.zentus.com/sqlitejdbc/
http://www.sqlite.org/download.html

How to run command on Karaf command prompt from other java program

I wanted to uninstall 'clock_3.0' bundle which is running in karaf. So I can do it by typing 'features:uninstall clock_3.0' command on karaf command prompt.
But Now I wanted to run this command from some other Java program.

We can do this by running following command:

Process ls_proc1;
ls_proc1 = Runtime.getRuntime().exec("cmd.exe /C java -jar C:\\apache-felix-karaf-1.2.0\\lib\\karaf-client.jar features:uninstall clock_3.0");

where apache-felix-karaf-1.2.0 is installed at C: on my computer.

We can even display the output of this command:

try {
BufferedReader br = new BufferedReader(new InputStreamReader(ls_in));
while ((ls_str1 = br.readLine()) != null) {
System.out.println(ls_str1);
}
} catch (IOException e1) {
e1.printStackTrace();
}

How to display HTML tags, code in blogs

When you try displaying HTML tags in blogs, it as disappear when you try publishing it.

So if you want to display something like

<html>
Hello World
</html>

When you will try publishing the post, it will only show,

Hello World

All the HTML tags won't be displayed.

If you want to do that, there is an easy way around.

Just Replace

And you can display all your HTML tags in your blog.

Maven build lifecycle

I came across this really good article which talks about Maven build life cycle.

A Build Lifecycle is Made Up of Phases

Each of these build lifecycles is defined by a different list of build phases, wherein a build phase represents a stage in the lifecycle.

For example, the default lifecycle has the following build phases (for a complete list of the build phases, refer to the Lifecycle Reference):

• validate - validate the project is correct and all necessary information is available
• compile - compile the source code of the project
• test - test the compiled source code using a suitable unit testing framework. These tests should not require the code be packaged or deployed
• package - take the compiled code and package it in its distributable format, such as a JAR.
• integration-test - process and deploy the package if necessary into an environment where integration tests can be run
• verify - run any checks to verify the package is valid and meets quality criteria
• install - install the package into the local repository, for use as a dependency in other projects locally
• deploy - done in an integration or release environment, copies the final package to the remote repository for sharing with other developers and projects.

These build phases (plus the other build phases not shown here) are executed sequentially to complete the default lifecycle. Given the build phases above, this means that when the default lifecycle is used, Maven will first validate the project, then will try to compile the sources, run those against the tests, package the binaries (e.g. jar), run integration tests against that package, verify the package, install the verifed package to the local repository, then deploy the installed package in a specified environment.

To do all those, you only need to call the last build phase to be executed, in this case, deploy:

mvn deploy

That is because if you call a build phase, it will execute not only that build phase, but also every build phase prior to the called build phase.

source:http://stackoverflow.com/questions/1544619/if-i-run-mvn-deploy-does-it-build-new-artifacts-or-it-just-deploy-the-already-exi

How can we turn on the display of folders/directories in web browser which present under tomcat ROOT directory.

I downloaded apache tomcat server and added a folder repository in 'apache-tomcat-6.0.26\webapps\ROOT' directory which contains many subfolders/subdirectories and html pages, jars inside those folders/directories.
I can go index page in 'apache-tomcat-6.0.26\webapps\ROOT' folder by typing the URL as 'http://localhost:8080'

But now if I want to download any jar present in some subfolder of repository directory, I can do it by typing the relative path of the jar file and adding the URL.

Suppose x.jar is present in the directory 'repository\xx\yy\x.jar', then I can download it by accessing following URL : 'http://localhost:8080/repository/xx/yy/x.jar'

But I type something like 'http://localhost:8080/repository/xx/yy' it will give me error page.

If you want to turn on the display of directories/folders in the web browser in case the default file like index.html is not present, then it should display the list of files and directories present under that directory mentioned in the URL.

For enabling this, you have to set 'listings' parameter in the default servlet to true. You have to edit the web.xml flie present at location: 'apache-tomcat-6.0.26\conf' directory.

Set it as shown below:

<init-param>
<param-name>listings</param-name>
<param-value>true</param-value>
</init-param>


Once you do this, You can see web browser will display the directory structure, the list of files and sub-directories present the directory mentioned in URL

Linear Search Java Example

Below is linear Searching Algorithm implemented in Java.



import java.util.Scanner;

//##################################################
// Linear Search
//##################################################
//Program has list of integers saved in an array and
//program will take inputs from user and search that
//if that input is present in Array of Integers.

public class linearSearch {

public static void main(String args[]) {

int[] listOfIntegers = { 1, 34, 53, 23, 77, 98, 101, 20, 45, 66, 84 };
int inputTobeSearch;

Scanner sn = new Scanner(System.in);
inputTobeSearch = sn.nextInt();
int token = -1;

for (int i = 0; i < listOfIntegers.length; i++) {

if (listOfIntegers[i] == inputTobeSearch) {
token = i;
}
}

if (token != (-1)) {
System.out
.println("Input integer " + inputTobeSearch
+ " is present at " + (token + 1)
+ "th place in the Array");
} else
System.out.println("Input integer " + inputTobeSearch
+ " is not present in the Array");

}

}

Execute a command from Java Program on Windows Mac or *nix System

I was working on some project and I wanted to write a code which will execute command from Java Program and it should run irrespective of Operating system.

So wrote a code and thought it will be nice to share, or may be it will be good for me, if I want to look at it after a while :)

The code below will run command from Java file even if it is Windows or Mac OS or Unix





//Package name is of the package
package finalgui;

import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.IOException;
import java.io.InputStreamReader;

/**
*
* @author Vinit Patwa
*/
public class RunCommand {

private static String ls_str;

public static void main(String args[]) {

try {
Process ls_proc;

//we want to run command "mvn clean install"
//It is expected that "mvn" is in your PATH
String mvnClean = "mvn clean install";

//We are storing the OS on system in String OS
String OS = System.getProperty("os.name");
System.out.println("OS is: " + OS);


if (OS.contains("Windows")) {
ls_proc = Runtime.getRuntime().exec("cmd.exe /C mvn clean install");
} else {
ls_proc = Runtime.getRuntime().exec(mvnClean);
}


//We can also display the output of the command Here
DataInputStream ls_in = new DataInputStream(
ls_proc.getInputStream());
try {
BufferedReader br = new BufferedReader(new InputStreamReader(ls_in));
while ((ls_str = br.readLine()) != null) {
System.out.println(ls_str);
}
} catch (IOException e1) {
System.exit(0);
}
} catch (Exception e) {
System.out.println(e.toString());
e.printStackTrace();

}
}
}

1. Tutorials on Socket:

C/C++

JAVA

2. Tutorials on Threads

Pthreads

JAVA

Source: http://vinitpatwa.wordpress.com/2009/09/01/socket-programming-and-multithreading-resources/

JBPM new web based BPMN editor

The jBPM Modeller is an advanced web based BPMN editor aimed at non technical business users. No software needs to be installed on the user's machine, a plain web browser is enough to get the job done. Business analysts can easiliy produce complex process models with the tool, which then later can be imported by developers in their Eclipse environment without any conversion needed.

The jBPM Modeller is based on the fantasic web based modeling tool by Signavio. In less than a minute, every stakeholder involved can view, edit and collaborate on process models through their own brower. source: www.jboss.org

java.io.IOException: CreateProcess: ... error=193

When I tried running an executable from from Java Jar file, while executing following code -

Runtime.getRuntime().exec("C:\\maven\\apache-maven-2.2.1\\bin\\mvn pax:provision");

I got following Exception -

java.io.IOException: Cannot run program "C:\maven\apache-maven-2.2.1\bin\mvn": CreateProcess error=193, %1 is not a valid Win32 application

To resolve this problem, the command should be invoked as:

Runtime.getRuntime().exec("cmd.exe /C C:\\maven\\apache-maven-2.2.1\\bin\\mvn pax:provision");

And it worked.

(Running executable from Java Jar file)

Install Maven Pax Plugin

MAVEN PAX PLUGIN:

The Pax Plugin is a "Swiss Army(tm) knife" for OSGi that provides goals to create, build, manage and deploy many types of OSGi bundles. While the easiest way to install and use this plugin is by using the Pax-Construct scripts, its goals can also be used directly on the Maven command line, or inside other Maven POMs.

Steps for installing Maven Pax Construct Plugin:

1. Get the pax zip and unzip it to temp (or any other directory you prefer):

http://repo1.maven.org/maven2/org/ops4j/pax/construct/scripts/1.4/scripts-1.4.zip

2. Open up the command prompt and enter the command:

set PATH=C:\temp\pax-construct-1.4\bin;%PATH%