• A Common Situation:
  • An application must communicate through a proxy
• The Layers/Protocol:
  • At the application layer HTTP requests might need to be sent through an HTTP proxy
  • At the transport layer TCP segments (or UDP segments) may need to be sent through a SOCKS proxy

• The Abstract SocketAddress Class:
  • Encapsulates a socket address with no protocol
• The Proxy Class:
  • Encapsulates a proxy setting/protocol and a socket address
• The Abstract URLConnection Class:
  • Encapsulates an abstract communications link with a URL

• Actual Proxies:
  • Proxy.Type.HTTP
  • Proxy.Type.SOCKS
• No Proxy:
  • Proxy.Type.DIRECT

• Getting Started:
  • Construct a concrete specialization of a SocketAddress
  • Construct a Proxy
• Using the Proxy:
  • Construct a concrete speciaization of a URLConnection or a Socket
  • Use the URLConnection or Socket to connect() through the Proxy

An HTTP Example

  // Getting Started
  SocketAddress address = new InetSocketAddress(proxyname, proxyport);
  Proxy         proxy   = new Proxy(Proxy.Type.HTTP, address);

  // Using the Proxy
  URL           url     = new URL(resource);
  URLConnection conn    = url.openConnection(proxy);

  // Use the URLConnection

  

A TCP Example

  // Getting Started
  SocketAddress address = new InetSocketAddress(hostname, port);
  Proxy         proxy   = new Proxy(Proxy.Type.SOCKS, address);

  // Using the Proxy
  Socket        socket  = new Socket(proxy);
  SocketAddress server  = new InetSocketAddress(servername, serverport);

  socket.connect(server);

  // Use the Socket

  

• Possible Uses:
  • Load balancing across proxies
  • Different proxies for different hosts
• The Approach:
  • Install a ProxySelector (by calling its static setDefault() method) that has a select() method that is called by the protocol handler to determine which proxy to use