Wednesday, March 21, 2012

How to install springsource tool suite on linux

Download the STS self-extracting shell script (*.sh) that matches your OS and machine architecture from the following Url:

Please make sure to download and install STS versions that match your JDK installation.

Once downloaded, launch the installation by running the following command in a terminal session:
$ sh

Follow the on-screen instructions to finish the installation. See “Running the STS Installer”.

Tuesday, March 20, 2012

How to find MYSQl Port No and Version ?

mysql> show variables like 'port';
| Variable_name | Value |
| port          | 3306  |
1 row in set (0.02 sec)

mysql> show variables like 'version';
| Variable_name | Value             |
| version       | 5.0.45-community-nt |
1 row in set (0.00 sec) 

Monday, March 12, 2012

Java JVM Shutdown Hook - tutorial

JVM shutdown hooks provide a clean and simple mechanism for registering application-specific behavior that performs the required cleanup work when a JVM terminates.

It is a Java feature that let you have a piece of Java code run whenever the JVM terminates under one of the following conditions:

  - The program exits normally, such as when the last non-daemon thread exits or when the                         Runtime.exit() method is invoked.

  -  The virtual machine is terminated in response to a user interrupt, such as typing CTRL-C, or a                      system-wide event, such as user logoff or system shutdown (for example, the JVM receives               one of  the interrupt signals SIGHUP (Unix Only), SIGINT, or SIGTERM).

A shutdown hook is a Java class that extends java.lang.Thread and is get registered with the Runtime.addShutdownHook()method. Your application may install multiple shutdown hooks. On JVM termination, each shutdown hook will be started and will run concurrently, so the normal rules of thread synchronization apply. You can write shutdown hooks to do anything that a normal thread would do; the JVM will treat them like any other.

Generally we write a shutdown hook to do any last-minute tidying, such as flushing memory buffers, closing files, or displaying an exit message. The JVM will always wait until all shutdown hooks have completed before continuing with the rest of the shutdown sequence, so it is important that your shutdown hooks do actually complete.

The following example shows how to write and install a Java shutdown hook.

 * Implementation of JVM shutdown hook
 * @author abdul
public class ShutDownHook {
    public static void main(String args[]) {
        ShutDownHook hook = new ShutDownHook();
        System.out.println( "Running Main Application..." );
        // Java code to register shutdown hook:
        // You can unregister the shutdon hook too.

    Thread shutdown =new Thread() {
        public void run() {
            //Do your cleaning stuff here eg closing connection,Saving some logs etc
            System.out.println("Inside Add Shutdown Hook");

    private void attachShutDownHook() {
        System.out.println("Shut Down Hook Attached.");

    public void removeShutdownHook(){


There is also a method named removeShutdownHook, which also takes the reference to the Thread object as a parameter. This method allows you to remove a Thread from the list of threads to be started by the VM before it closes (Runtime.getRuntime().removeShutdownHook(shutdown); for the above shutdown hook example).

FAQ On JVM Shutdown Hook API

Thursday, March 8, 2012

Java HashMap Example

The HashMap class uses a hash table to implement the Map interface. This allows the execution time of basic operations, such as get() and put(), to remain constant even for large sets.

The following constructors are defined:  
HashMap( )
HashMap(Map m)
HashMap(int capacity)
HashMap(int capacity, float fillRatio)


Hash map does not guarantee the order of its elements. Therefore, the order in which elements are added to a hash map is not necessarily the order in which they are read.

Here is the code:
import java.util.HashMap;
import java.util.Map;

 * This Java HashMap example describes the basic operations performed on the HashMap
 * @author abdul
public class HashMapExample {
    public static void main(String args[]){
        // constructs a new empty HashMap with default initial capacity       
        Map<Integer,String> hashMap = new HashMap<Integer,String>();
        // adding value into HashMap
        hashMap.put(new Integer(1),"DELL");
        hashMap.put(new Integer(2),"SONY");
        hashMap.put(new Integer(3),"LENOVO");
        hashMap.put(new Integer(4),"SAMSUNG");
        hashMap.put(new Integer(5),"HP");
        //To get the size of HashMap       
        System.out.println("HashMap Size: " + hashMap.size());
        // To Find particular value from the HashMap:
            System.out.println("HashMap contains HP");
            System.out.println("HashMap does not contain HP");
        //To find particular key in HashMap
        if( hashMap.containsKey(new Integer(2)) ){
            System.out.println("HashMap contains key");
            System.out.println("HashMap does not contain key");
        Use get method of HashMap to get value mapped to particular key.       
        Signature of the get method is,       
        Object get(Object key)       
        String value = hashMap.get(new Integer(5));       
        System.out.println("Value : " + value);

        //To get the key value pair of hashMap
        for (Map.Entry<Integer, String> entry1 : hashMap.entrySet()) {
            Integer key = entry1.getKey();
            String data = entry1.getValue();
            System.out.println("key value : " + key + "\t" + data );

        // To remove something from the hashmap      
        System.out.println( hashMap.remove(new Integer(4)) + " removed from the hashMap");
        //Display value of HashMap
        System.out.println("HashMap : " + hashMap );

HashMap Size: 5
HashMap contains HP
HashMap contains key
Value : HP
key value : 1    DELL
key value : 2    SONY
key value : 3    LENOVO
key value : 4    SAMSUNG
key value : 5    HP
SAMSUNG removed from the hashMap
HashMap : {1=DELL, 2=SONY, 3=LENOVO, 5=HP}

How to get free disk space of a drive in java ?

JDK 1.6 provides few new methods  getTotalSpace(),getFreeSpace(), bundled with These methods provides essential information regarding disk space.

getFreeSpace() method-   Returns the number of unallocated bytes in the partition named by this abstract path name.
getTotalSpace() method - Returns the size of the partition named by this abstract pathname.

Here is the code: 


 * Program that returns the number of unallocated bytes , total space in the partition.
 * @author abdul
public class DiskDetail {
    public static void main(String[] args) {
        File file = new File("C:");
        long totalSpace = file.getTotalSpace(); // total disk space in bytes.
        long freeSpace = file.getFreeSpace(); // unallocated / free disk space
        long  diskUsage = (totalSpace - freeSpace);
        System.out.println("Total size : " + totalSpace + " bytes");
        System.out.println("Space free : " + freeSpace + " bytes");
        System.out.println("Used Space : " + diskUsage + "bytes");

Total size : 107373129728 bytes
Space free : 44510306304 bytes
Used Space : 62862823424bytes



Friday, February 24, 2012

JAXB - II (jaxb.index file and ObjectFactory)

I was getting a Exception like, javax.xml.bind.JAXBException: "doesnt contain ObjectFactory.class or jaxb.index" while trying to create a JAXBContext using JAXBContext.newInstance(String contextPath).

It took me a while to figure out what went wrong. So now that I've got things working correctly, I thought I'd post this example and solution to hopefully save you some time.

When we create a marshaller, we first need to create a JAXBContext via its newInstance() factory method. You can create a context for a specific JAXB class  or you can create a context for a list of packages.

There are two ways to resolve this issue : 
  - By creating ObjectFactory
  - By adding jaxb.index file

jaxb.index :

The jaxb.index file is a text file contains a listing of the classes on the containing package that have JAXB annotations.
Note : The name of the clases is their simple name not their classified name.

Rather than creating a ObjectFactory, I guess adding a jaxb.index file is much easy part. Just you need to add class names to the file and place the file in the package (directory) where your JAXB annotated classes reside.
Its just the class name, not the fully qualified name (the package name is determined by the directory you placed the file in) or the.class name.

     JAXBContext context = JAXBContext.newInstance(className.getClass().getPackage().getName());

If the package following package does not have jaxb.index file, this change will cause the test to throw the JAXBException. Add the file and everything works great.

Thursday, February 23, 2012

Java Architecture for XML Binding (JAXB)

 - Java Architecture for XML Binding (JAXB) is a Java standard that defines how Java objects are converted to/from XML (specified using a standard set of mappings).

 - It defines a programmer API for reading and writing Java objects to / from XML documents and a service provider which / from from XML documents allows the selection of the JAXB implementation

 - It makes reading  and writing of XML via Java very easy.

 - It allows Java developers to access and process XML data without having to know XML or XML processing

 - It is used heavily by JAX-WS


 - It provides ways to generate XML content from a Java representation , to generate a Java representation from XML file , to generate XML schema from Java Objects

 - The JAXBContext class provides the client's entry point to the JAXB API. It provides an abstraction for managing the XML/Java binding information necessary to implement the JAXB binding framework operations: unmarshal, marshal and validate.

- A client application obtains new instances of this class via the newInstance(contextPath) method.            
          JAXBContext jc = JAXBContext.newInstance( "customer.class" );
The contextPath contains a list of Java package names that contain schema derived interfaces

Marshalling :

The Marshaller class provides the client application the ability to convert a Java content tree back into XML data. 

Here is a simple example that unmarshals an XML document and then marshals it back out:

          JAXBContext jc = JAXBContext.newInstance( "Customer.class" );
          Unmarshaller u = jc.createUnmarshaller(); 
          Customer customer = (Customer)u.unmarshal( new File( "test.xml" ) );
          Marshaller m = jc.createMarshaller(); m.marshal( customer, System.out );


The Unmarshaller class provides the client application the ability to convert XML data into a tree of Java content objects. 

For example: 
       JAXBContext jc = JAXBContext.newInstance( "customer.class" ); 
       Unmarshaller u = jc.createUnmarshaller();
       Customer customer = (Customer)u.unmarshal( new File( "test.xml" ) ); // ok                                                                                                            
                                                                                          to be continued...



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