Sockets and URLs
26-Jul-16
Sockets
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A socket is a low-level software device for connecting
two computers together
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Sockets can also be used to connect two programs running on
the same computer
There are two kinds of sockets:
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A Socket is a client socket, and initiates the communication
A ServerSocket waits for a request; it then
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May perform the requested action
May return a result to the requester
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Socket constructors
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Socket(InetAddress address, int port)
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ServerSocket(int port)
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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 SocketImpl class
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Some Socket methods
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getInputStream()
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getOutputStream()
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Returns an input stream for this socket
Returns an output stream for this socket
close()
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Closes this socket
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Some ServerSocket methods
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accept()
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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
Socket
close()
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Closes this socket
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Socket fields
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protected InetAddress address
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protected FileDescriptor fd
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The file descriptor object for this socket
protected int localport
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The IP address of the remote end of this socket
The local port number to which this socket is connected
protected int port
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The port number on the remote host to which this socket is connected
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URLs
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A URL is a Uniform Resource Locator, typically a Web
address
Some constructors:
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URL(String spec)
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URL(String protocol, String host, int port, String file)
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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)
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Same as above, but uses the default port for this protocol
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Some URL methods
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openStream()
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openConnection()
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Opens a connection to this URL and returns an InputStream
for reading from that connection
Returns a URLConnection object that represents a
connection to the remote object referred to by the URL
getProtocol(), getHost(), getPort(), getFile(),
getQuery()
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Using a URLConnection
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The steps in using a URLConnection are:
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Use openConnection() to create the URLConnection object
Set the parameters as desired:
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setAllowUserInteraction, setDoInput, setDoOutput,
setIfModifiedSince, setUseCaches, setRequestProperty
Use the connect method to make the actual connection
Use the remote object
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Some URLConnection methods
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getHeaderField(int n)
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getHeaderField(String name)
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Returns the key for the nth header field
getInputStream()
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Returns the value of the named header field
getHeaderFieldKey(int n)
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Returns the value for the nth header field
Returns an input stream that reads from this open connection
getOutputStream()
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Returns an output stream that writes to this connection
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The End
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