Java Naming And Directory Interface

From JavaProgramming

• 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 <jdk path, i.e. c:\jdk1.3>\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());
        },
      },
   },
  },