New SocketExceptions in JDK1.1 - JDK 5 Documentation v1.4.1, Java 2 SDK 英文文档

New SocketExceptions in JDK1.1

Previously, all network errors in java raised a SocketException, which didn't provide enough information to decipher what went wrong. Was the connection refused by the remote machine (no one listening on that port)? Or was the host unreachable (connect attempt timed out)? JDK 1.1 adds three new classes that provide a finer granularity of reported errors:

• java.net.BindException

  The local port is in use, or the requested bind address couldn't be assigned locally.

   	public class BindException extends SocketException {
  	...
  	}
  

• java.net.ConnectException

  This exception is raised when a connection is refused at the remote host (i.e., no process is listening on that port).

   	public class ConnectException extends SocketException {
  	...
  	}
  

• java.net.NoRouteToHostException

  The connect attempt timed out, or the remote host is otherwise unreachable.

   	public class NoRouteToHostException extends SocketException {
  	...
  	}
  

Simple Usage Examples:

• On the Client Side:

  import java.net.*;
  	...
  	Socket s = null;
  	try {
  	   s = new Socket("foo.org", 80);
  	} catch (UnknownHostException e) {
  	   // check spelling of hostname
  	} catch (ConnectException e) {
  	   // connection refused - is server down? Try another port.
  	} catch (NoRouteToHostException e) {
  	   // The connect attempt timed out.  Try connecting through a proxy
  	} catch (IOException e) {
  	   // another error occurred
  	}
  

• On the Server Side:

  import java.net.*;
   	...
  	ServerSocket ss = null;
  	try {
  	    /* try to bind to local address 129.144.175.156 */
  	    InetAddress in = InetAddress.getByName("129.144.175.156");
  	    int port = 8000;
  	    int backlog = 5;
  	    ss = new ServerSocket(port, backlog, in);
  	} catch (BindException e) {	   	
  	    // port 8000 in use, or can't bind to 129.144.175.156 as a local address
  	} catch (SocketException e) {
  	    // another error occurred
  	}
  

  ---

  David Brown