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					Sockets and URLs

   A socket is a low-level software device for connecting
    two computers together
       Sockets can also be used to connect two programs running on
        the same computer
   There are two kinds of sockets:
       A Socket is a client socket, and initiates the communication
       A ServerSocket waits for a request; it then
            May perform the requested action
            May return a result to the requester

    Socket constructors

   Socket(InetAddress address, int port)
       Creates a stream socket and connects it to the specified
        port number at the specified IP address
   ServerSocket(int port)
       Creates a server socket on the specified port, with a
        default queue length of 50
   The actual work, for both kinds of sockets, is done
    by an instance of the SocketImpl class

        Some Socket methods
   getInputStream()
       Returns an input stream for this socket
   getOutputStream()
       Returns an output stream for this socket
   close()
       Closes this socket

        Some ServerSocket methods
   accept()
       Listens for a connection to be made to this socket and
        accepts it
       Returns a Socket as its result

   For input, use the getInputStream() and
    getOutputStream() methods on the returned

   close()
       Closes this socket

        Socket fields
   protected InetAddress address
       The IP address of the remote end of this socket
   protected FileDescriptor fd
       The file descriptor object for this socket
   protected int localport
       The local port number to which this socket is connected
   protected int port
            The port number on the remote host to which this socket is connected

   A URL is a Uniform Resource Locator, typically a Web
   Some constructors:
       URL(String spec)
            Creates a URL object from the information in the String
       URL(String protocol, String host, int port, String file)
            Creates a URL object from the specified protocol, host, port number,
             and file
       URL(String protocol, String host, String file)
            Same as above, but uses the default port for this protocol

        Some URL methods
   openStream()
       Opens a connection to this URL and returns an InputStream
        for reading from that connection
   openConnection()
       Returns a URLConnection object that represents a
        connection to the remote object referred to by the URL
   getProtocol(), getHost(), getPort(), getFile(),

        Using a URLConnection
   The steps in using a URLConnection are:
       Use openConnection() to create the URLConnection object
       Set the parameters as desired:
            setAllowUserInteraction, setDoInput, setDoOutput,
             setIfModifiedSince, setUseCaches, setRequestProperty
       Use the connect method to make the actual connection
       Use the remote object

        Some URLConnection methods
   getHeaderField(int n)
       Returns the value for the nth header field
   getHeaderField(String name)
       Returns the value of the named header field
   getHeaderFieldKey(int n)
       Returns the key for the nth header field
   getInputStream()
       Returns an input stream that reads from this open connection
   getOutputStream()
       Returns an output stream that writes to this connection

The End


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