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());
          }
        }
     }
    }