Java Naming And Directory Interface

A naming service binds objects to meaningful names
Many different namings services exists
JNDI is a Java interface to any underlying naming service
A directory service allows attributes to be defined for objects
Each attribute has an identifier and a value
Many different directory services exists
JNDI is a Java interface to directory services


        /* UseService.java */

        import javax.naming.*;

        import java.io.File;

        import java.util.Hashtable;

/**

Demonstrates the use of a JNDI service (Java Naming and Directory Interface)
Before using this program you must download a File System Server from
Sun at http://java.sun.com/products/jndi/serviceproviders.html
The donwloaded zip file should contain two jar files:
fscontext.jar and providerutil.jar
These files can be placed in \jre\lib\ext
thereby making the jar files available to the JVM without
needing to adjust the classpath


        class UseService {

        public static void main(String[] args) {

        // Set up the environment for creating the initial context

        Hashtable env = new Hashtable();

        // Set up context for JNDI file system service

        env.put(Context.INITIAL_CONTEXT_FACTORY,

        "com.sun.jndi.fscontext.RefFSContextFactory");

        // This will allow you to inspect the folder c:\java

        env.put(Context.PROVIDER_URL,

        "file:/java");

        // ctx must be initialised, when calling Context.close() in the finally block

        Context ctx = null;

        try {

        // Create the initial context

        // May generate NamingException

        ctx = new InitialContext(env);

        // Call lookup() on this object, to lookup a file relative to the

        // /java folder.

        // Cast return type from lookup() into a File type

        // May generate NamingException

        File file = (File)ctx.lookup("JNDI/UseService.java");

        // For example, you can specify "JNDI/UseService.java" to

        // find out information about your current file (!).

        System.out.println("Length: " + file.length());

        System.out.println("Can read: " + file.canRead());

        // Output:

        // Length: xxxx

        // Can read: true

        }

        // Remember to catch any NamingExceptions and

        // display any error information on the console.

        catch (NamingException ex) {

        System.out.println(ex.getMessage());

        }

        finally {

        try {

        // Allways close server connections in a finally block.

        // If close() is called in the try block it might not be called

        // when an exception occurs on a previous line.

        // Not closing the connection will leave dangling resources on the server

        // May generate NamingException

        ctx.close();

        }

        catch (NamingException ex) {

        System.out.println(ex.getMessage());

        }

        }

        }

        }