Netty Socket Server.

Netty seems a good socket server for fast and non-blocking calls. According to my knowledge the netty supports for non-blocking I/O and asynchronous calls. Still the socket call can be happen through simple Java Socket Program. But java socket not handling the socket fail and other exceptions. We may  need to implement fail handling in java. 

This is high salable to handle thousands of call. So when you have a requirement to handle huge set of call then netty will be a right choice. 

This create each thread for each call, therefore the cost of the netty on servers may high. because It use memory resources as much as possible based on number of threads.

java.lang.OutOfMemoryError: PermGen space in Stanbol

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:2.3.1:compile (default-compile) on project org.apache.stanbol.commons.solr.web: Compilation failure
[ERROR] Failure executing javac, but could not parse the error:
[ERROR]
[ERROR]
[ERROR] The system is out of resources.
[ERROR] Consult the following stack trace for details.
[ERROR] java.lang.OutOfMemoryError: PermGen space
[ERROR] at java.lang.ClassLoader.defineClass1(Native Method)
[ERROR] at java.lang.ClassLoader.defineClass(ClassLoader.java:800)
[ERROR] at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
[ERROR] at java.net.URLClassLoader.defineClass(URLClassLoader.java:449)
[ERROR] at java.net.URLClassLoader.access$100(URLClassLoader.java:71)
[ERROR] at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
[ERROR] at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
[ERROR] at java.security.AccessController.doPrivileged(Native Method)
[ERROR] at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
[ERROR] at org.codehaus.plexus.compiler.javac.IsolatedClassLoader.loadClass(IsolatedClassLoader.java:56)
[ERROR] at com.sun.tools.javac.main.Main.compile(Main.java:424)
[ERROR] at com.sun.tools.javac.main.Main.compile(Main.java:353)
[ERROR] at com.sun.tools.javac.main.Main.compile(Main.java:342)
[ERROR] at com.sun.tools.javac.main.Main.compile(Main.java:333)
[ERROR] at com.sun.tools.javac.Main.compile(Main.java:94)
[ERROR] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
[ERROR] at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
[ERROR] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
[ERROR] at java.lang.reflect.Method.invoke(Method.java:606)
[ERROR] at org.codehaus.plexus.compiler.javac.JavacCompiler.compileInProcess(JavacCompiler.java:549)
[ERROR] at org.codehaus.plexus.compiler.javac.JavacCompiler.compile(JavacCompiler.java:156)
[ERROR] at org.apache.maven.plugin.AbstractCompilerMojo.execute(AbstractCompilerMojo.java:605)
[ERROR] at org.apache.maven.plugin.CompilerMojo.execute(CompilerMojo.java:128)
[ERROR] at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:101)
[ERROR] at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:209)
[ERROR] at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:153)
[ERROR] at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:145)
[ERROR] at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:84)
[ERROR] at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:59)
[ERROR] at org.apache.maven.lifecycle.internal.LifecycleStarter.singleThreadedBuild(LifecycleStarter.java:183)
[ERROR] at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:161)
[ERROR] at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:320)

The solution is,

This error is happening because the JVM parameters for the BigDataLite NoSQL has been not set properly. So you need to add the JVM memory paremeters in ~/.bashrc file. follow the steps,

sudo nano ~/.bashrc

Add the below line in to this file,

export JAVA_OPTS="-Xms128m -Xmx2048m -XX:PermSize=256m -XX:MaxPermSize=2048m"

Finally refresh the ~/.bashrc with the below command,

source ~/.bashrc

Now execute it again.

Best Eclipse plugin

http://www.eclipse.org/Xtext/index.html for any script or build language. This eclispe plugin helps lot.

Why use getters and setters?

• Encapsulation of behavior associated with getting or setting the property - this allows additional functionality (like validation) to be added more easily later.
• Hiding the internal representation of the property while exposing a property using an alternative representation.
• Insulating your public interface from change - allowing the public interface to remain constant while the implementation changes without affecting existing consumers.
• Controlling the lifetime and memory management (disposal) semantics of the property - particularly important in non-managed memory environments (like C++ or Objective-C).
• Providing a debugging interception point for when a property changes at runtime - debugging when and where a property changed to a particular value can be quite difficult without this in some languages.
• Improved interoperability with libraries that are designed to operate against property getter/setters - Mocking, Serialization, and WPF come to mind.
• Allowing inheritors to change the semantics of how the property behaves and is exposed by overriding the getter/setter methods.
• Allowing the getter/setter to be passed around as lambda expressions rather than values.
• Getters and setters can allow different access levels - for example the get may be public, but the set could be protected.

For example, if foo was public, I could easily set it to null and then someone else could try to call a method on the object. But it's not there anymore! With a setFoo method, I could ensure that foo was never set to null.

Accessors and mutators also allow for encapsulation - if you aren't supposed to see the value once its set (perhaps it's set in the constructor and then used by methods, but never supposed to be changed), it will never been seen by anyone. But if you can allow other classes to see or change it, you can provide the proper accessor and/or mutator.

How to generate UML Diagrams from Java code in Eclipse

UML diagrams compliment inline documentation ( javadoc ) and allow to better explore / understand a design. Moreover, you can print and bring them to table to discuss a design.

In this post, we will install and use the ObjectAid plugin for Eclipse to produce jUnit lib class diagrams. Then, we will be able to generate UML diagrams by simply dragging and dropping classes into the editor. We can further manipulate the diagram by selecting which references, operations or attributes to display.

Open Eclipse and go to Help > Install New Software
Click on add to add a new repository
Enter name ObjectAid UML Explorer
Enter Location http://www.objectaid.net/update

Difference between Process and Thread

Process

• An executing instance of a program is called a process.
• Some operating systems use the term ‘task‘ to refer to a program that is being executed.
• A process is always stored in the main memory also termed as the primary memory or random access memory.
• Therefore, a process is termed as an active entity. It disappears if the machine is rebooted.
• Several process may be associated with a same program.
• On a multiprocessor system, multiple processes can be executed in parallel.
• On a uni-processor system, though true parallelism is not achieved, a process scheduling algorithm is applied and the processor is scheduled to execute each process one at a time yielding an illusion of concurrency.
• Example: Executing multiple instances of the ‘Calculator’ program. Each of the instances are termed as a process.

Thread

• A thread is a subset of the process.
• It is termed as a ‘lightweight process’, since it is similar to a real process but executes within the context of a process and shares the same resources allotted to the process by the kernel (See kquest.co.cc/2010/03/operating-system for more info on the term ‘kernel’).
• Usually, a process has only one thread of control – one set of machine instructions executing at a time.
• A process may also be made up of multiple threads of execution that execute instructions concurrently.
• Multiple threads of control can exploit the true parallelism possible on multiprocessor systems.
• On a uni-processor system, a thread scheduling algorithm is applied and the processor is scheduled to run each thread one at a time.
• All the threads running within a process share the same address space, file descriptor, stack and other process related attributes.
• Since the threads of a process share the same memory, synchronizing the access to the shared data withing the process gains unprecedented importance.

What is Java thread

A thread is a thread of execution in a program. The Java Virtual Machine allows an application to have multiple threads of execution running concurrently.

Every thread has a priority. Threads with higher priority are executed in preference to threads with lower priority. Each thread may or may not also be marked as a daemon. When code running in some thread creates a new Thread object, the new thread has its priority initially set equal to the priority of the creating thread, and is a daemon thread if and only if the creating thread is a daemon.

Difference between “implements Runnable” and “extends Thread” in java

In java language, as we all know that there are two ways to create threads. One using Runnable interface and another by extending Thread class.

There has been a good amount of debate on which is better way. Well, I also tried to find out and below is my learning:

1) Implementing Runnable is the preferred way to do it. Here, you’re not really specializing or modifying the thread’s behavior. You’re just giving the thread something to run. That means composition is the better way to go.

2) Java only supports single inheritance, so you can only extend one class.

3) Instantiating an interface gives a cleaner separation between your code and the implementation of threads.

4) Implementing Runnable makes your class more flexible. If you extend thread then the action you’re doing is always going to be in a thread. However, if you extend Runnable it doesn’t have to be. You can run it in a thread, or pass it to some kind of executor service, or just pass it around as a task within a single threaded application.

5) By extending Thread, each of your threads has a unique object associated with it, whereas implementing Runnable, many threads can share the same runnable instance.

6) If you are working on JDK 4 or lesser, then there is bug :

Crop Image Using Java

 import java.awt.image.BufferedImage;  
 import java.io.File;  
 import java.io.IOException;  
 import javax.imageio.ImageIO;  
 public class test {  
      public static void main(String[] args) throws IOException {  
           test t = new test();  
           t.getCropImage();  
      }  
      public void getCropImage() throws IOException {  
           int widthOfNewImage = 100;  
           int heightOfNewImage = 100;  
           int offsetFromLeft = 10;  
           int offsetFromTop = 100;  
           String path = "input.gif";  
           String newPath = "newImage.png";  
           String imageFormat = "png";  
           BufferedImage image = ImageIO.read(new File(path));  
           int height = image.getHeight();  
           int width = image.getWidth();  
           System.out.println("Height : " + height + "\nWidth : " + width);  
           BufferedImage out = image.getSubimage(offsetFromLeft, offsetFromTop,  
                     widthOfNewImage, heightOfNewImage);  
           ImageIO.write(out, imageFormat, new File(newPath));  
      }  
 }  

How to change eclipse background Theme

Installation

If you are on Eclipse 3.6 (Helios), the easiest way to install the plugin is from the Eclipse Marketplace. Go to Help→Eclipse Marketplace..., then search for Eclipse Color Theme and install it.

If you are on Eclipse 3.5 (Galileo), go to Help→Install New Software..., press Add Site and enterEclipse Color Theme as the name and http://eclipse-color-theme.github.com/update as the URL. Then select the new entry from the select box labeled Work with, mark Eclipse Color Theme for installation and proceed.

Please note: If you are using a version of the plugin lower than 0.6, please uninstall and reinstall it following the instructions above. Update site and plugin ID have changed.

Usage

After the installation, go to Window→Preferences→General→Appereance→Color Theme to change the color theme.

If you have a feature request, create an issue or a pull request on GitHub.

Deployment of Apache Tomcat 7 in Amazon server

 Before Installation Check your java Jdk installed or not.  
 Step 1:  
 Download the Apache tomcat 7 from the bellow link,  
 Step2:  
 md5sum apache-tomcat-[#].tar.gz  
 Next, extract the package:  
 tar xvzf apache-tomcat-[#].tar.gz  
 And move the extracted folder into a dedicated directory:  
 sudo mv apache-tomcat-[#] /usr/local/apache  
 Step3: Set the path   
 vi ~/.bashrc  
 export CATALINA_HOME=/usr/local/apache  
 Log out and log back into bash to have your changes take effect.  
 Step4: Start tomcat  
 sudo /usr/local/apache/bin/startup.sh  
 Step 5 : Check  
 Go to web browser and type ,  
 http://localhost:8080  

Install Oracle java using terminal

sudo add-apt-repository ppa:webupd8team/java
sudo apt-get update
sudo apt-get install oracle-java7-installer

Deployment of Glassfish In amazon server

GlassFish is an open-source application server project started by Sun Microsystems for the Java EE platform and now sponsored by Oracle Corporation. The supported version is called Oracle GlassFish Server. GlassFish is free software, dual-licensed under two free software licences: the Common Development and Distribution License (CDDL) and the GNU General Public License (GPL) with the classpath exception.

GlassFish is the reference implementation of Java EE and as such supports Enterprise JavaBeans, JPA, JavaServer Faces, JMS, RMI, JavaServer Pages, servlets, etc. This allows developers to create enterprise applications that are portable and scalable, and that integrate with legacy technologies. Optional components can also be installed for additional services.

 Step 1:   
 Connect the Amazon server through terminal using DNS and the KEY.  
 To connect with amazon server:  
 ssh -i <key_path> <username>@<ip_adress_server>  
 First of all we need to check the java dependencies.  
 sudo apt-get update  
 sudo apt-get remove openjdk-6-jre-headless  
 sudo apt-get install sun-java6-jdk sun-java6-jre sun-java6-javadb  
 sudo apt-get autoremove  
 Step 2:  
 go to terminal in Ubuntu  
 go to your home directory in terminal   
 enter wget http://download.java.net/glassfish/4.0/release/glassfish-4.0.zip to download the glassfish in to your server.  
 Step 3:  
 Configure and change default port for Glassfish if tomcat already use port 8080.Because usually it use the port 4848.If you need as default please avoid thid Step 3.  
 vim glassfishv3/glassfish/domains/domain1/config/domain.xml  
 <network-listeners>  
 <network-listener port="8081" protocol="http-listener-1" transport="tcp" name="http-listener-1" thread-pool="http-thread-pool" />  
 <network-listener port="8181" protocol="http-listener-2" transport="tcp" name="http-listener-2" thread-pool="http-thread-pool" />  
 <network-listener port="4848" protocol="admin-listener" transport="tcp" name="admin-listener" thread-pool="http-thread-pool" />  
 </network-listeners>  
 Step 4:  
 Running by Glassfish  
 ./glassfishv3/glassfish/bin/asadmin start-domain --verbose  
 Step5:  
 Go to your-domain:8081 to see web page and your-domain:4848 for administrator pages  
 Glassfish Controls :  
 Create domain  
 Start and Stop Domain  
 Delete Domain  
 Enable secure Admin  

 Error may occur:  
 Solution:  
 http://charleech.wordpress.com/2012/03/23/glassfish-version-3-1-2-secure-admin-must-be-enabled-to-access-the-das-remotely/  
 http://coders-kitchen.com/tag/secure-admin-must-be-enabled-to-access-the-das-remotely/