Sockets and URLs Sockets n A socket is

Sockets and URLs

Sockets n A socket is a low-level software device for connecting two computers together n n Sockets can also be used to connect two programs running on the same computer There are two kinds of sockets: n n A Socket is a client socket, and initiates the communication A Server. Socket waits for a request; it then n n May perform the requested action May return a result to the requester 2

Socket constructors n Socket(Inet. Address address, int port) n n Server. Socket(int port) n n Creates a stream socket and connects it to the specified port number at the specified IP address 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 Socket. Impl class 3

Some Socket methods n get. Input. Stream() n n get. Output. Stream() n n Returns an input stream for this socket Returns an output stream for this socket close() n Closes this socket 4

Some Server. Socket methods n accept() n n Listens for a connection to be made to this socket and accepts it Returns a Socket as its result For input, use the get. Input. Stream() and get. Output. Stream() methods on the returned Socket close() n Closes this socket 5

Socket fields n protected Inet. Address address n n protected File. Descriptor fd n n The file descriptor object for this socket protected int localport n n The IP address of the remote end of this socket The local port number to which this socket is connected protected int port n The port number on the remote host to which this socket is connected 6

URLs n n A URL is a Uniform Resource Locator, typically a Web address Some constructors: n URL(String spec) n n URL(String protocol, String host, int port, String file) n n Creates a URL object from the information in the String Creates a URL object from the specified protocol, host, port number, and file URL(String protocol, String host, String file) n Same as above, but uses the default port for this protocol 7

Some URL methods n open. Stream() n n open. Connection() n n Opens a connection to this URL and returns an Input. Stream for reading from that connection Returns a URLConnection object that represents a connection to the remote object referred to by the URL get. Protocol(), get. Host(), get. Port(), get. File(), get. Query() 8

Using a URLConnection n The steps in using a URLConnection are: n n Use open. Connection() to create the URLConnection object Set the parameters as desired: n n n set. Allow. User. Interaction, set. Do. Input, set. Do. Output, set. If. Modified. Since, set. Use. Caches, set. Request. Property Use the connect method to make the actual connection Use the remote object 9

Some URLConnection methods n get. Header. Field(int n) n n get. Header. Field(String name) n n Returns the key for the nth header field get. Input. Stream() n n Returns the value of the named header field get. Header. Field. Key(int n) n n Returns the value for the nth header field Returns an input stream that reads from this open connection get. Output. Stream() n Returns an output stream that writes to this connection 10

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