代理模式Proxy

//Purpose.  Proxy design pattern
//1. Create a "wrapper" for a remote, or expensive, or sensitive target
//2. Encapsulate the complexity/overhead of the target in the wrapper
//3. The client deals with the wrapper
//4. The wrapper delegates to the target
//5. To support plug-compatibility of wrapper and target, create an interface


interface SocketInterface {                // 5. To support plug-compatibility 
String readLine();                      //    between the wrapper and the
void   writeLine( String str );         //    target, create an interface
void   dispose(); }

public class ProxyDemo {
public static void main( String[] args ) {
   SocketInterface socket = new SocketProxy( "127.0.0.1", 8189,
      args[0].equals("first") ? true : false );     // 3. The client deals
   String  str = null;                              //    with the wrapper
   boolean skip = true;
   while (true) {
      if (args[0].equals("second")  &&  skip) skip = ! skip;
      else {
         str = socket.readLine();
         System.out.println( "Receive - " + str );  // java ProxyDemo first
         if (str.equals("quit")) break;             // Receive - 123 456
      }                                             // Send ---- 234 567
      System.out.print( "Send ---- " );             // Receive - 345 678
      str = Read.aString();                         // 
      socket.writeLine( str );                      // java ProxyDemo second
      if (str.equals("quit")) break;                // Send ---- 123 456
   }                                                // Receive - 234 567
   socket.dispose();                                // Send ---- 345 678
}  }

class SocketProxy implements SocketInterface { // 1. Create a "wrapper" for a
private Socket         socket;              //    remote, or expensive, or
private BufferedReader in;                  //    sensitive target
private PrintWriter    out;

public SocketProxy( String host, int port, boolean wait ) {
   try {
      if (wait) {
         ServerSocket server = new ServerSocket( port );
         socket = server.accept();           // 2. Encapsulate the complexi-
      } else                                 //    ty/overhead of the target
         socket = new Socket( host, port );  //    in the wrapper
      in  = new BufferedReader( new InputStreamReader(
               socket.getInputStream()));
      out = new PrintWriter( socket.getOutputStream(), true );
   } catch( IOException e ) { e.printStackTrace(); }
}
public String readLine() {
   String str = null;
   try { str = in.readLine();
   } catch( IOException e ) { e.printStackTrace(); }
   return str;
}
public void writeLine( String str ) {
   out.println( str );             // 4. The wrapper delegates to the target
}
public void dispose() {
   try { socket.close();
   } catch( IOException e ) { e.printStackTrace(); }
}  }