Networking. Lecture 25 ish? COP 3252 Summer July 11, 2017

Transcription

1 Networking Lecture 25 ish? COP 3252 Summer 2017 July 11, 2017

2 Open-Read/Write-Close The Unix I/O system follows a paradigm usually referred to as Open-Read/Write-Close. Before a program/process can perform I/O operations, it has to acquire permission for the resource. Once the resource has been opened, read or write operations can be performed to it. Once the process is done with the resource, it Closes the resource to inform the OS that it is done with the resource. The resource should usually be a derivative of the Closeable interface. Such resources include Files and Input/Output Streams.

3 Sockets, Datagrams and Streams Client/server relationship client requests some information or action server performs the action and responds to the client A socket is one end-point of a two-way communication link between two programs running on the network. There are two communication protocols that one can use for socket programming: datagram communication and stream communication. The User Datagram Protocol (UDP) is a connectionless protocol. Client and Server send individual messages. Eg. The Transmission Control Protocol (TCP) is a connection oriented protocol. Client and Server communicate back and forth. Eg - Skype Call Both of these are 4th layer protocols and work just under the application.

4 URL s and Ports URL - Uniform Resource Locator java.net.url - a Java class for wrapping up a URL and working with it Can use a URL object to help create connections, retrieve the web page or file it points to, and query other info about it (many get methods) Ports are a way to separate the data arriving at the Network Interface based on application. The TCP and UDP protocols use ports to map incoming data to a particular process running on a computer.

5 Opening a web page with a URL object, from Java From inside an applet Retrieve a reference to the applet s context (usually the browser window) with the getappletcontext() method (class Applet) Call the showdocument method (which takes a URL as a parameter), from the AppletContext inferface From inside an application using javax.swing.jeditorpane JEditorPane is a swing component that supports plain text, HTML text, and RTF (rich text) already It also supports the processing of hyperlink events, using interface HyperLinkListener Call method SetPage (from JEditorPane) and pass in the URL object as the parameter

6 Building Server Sockets 1. Create a ServerSocket object: The port number identifies the application on the host computer. (web = port 80, for example) queue length = max number of clients that can connect to server ServerSocket serv = new ServerSocket(portNumber, queuelength); 2. Listen for a client connection. Call method accept(): Socket connection = serv.accept(); 3. Retrieve the OutputStream and InputStream objects associated with the socket: OutputStream os = connection.getoutputstream(); InputStream is = connection.getinputstream();

7 Building Server Sockets If we desire, we can wrap these up in other types of streams: ObjectInputStream objin = new ObjectInputStream(is); // etc Process data with the stream objects (like writing to and reading from files) close the connections by invoking the close() method on the streams and the Socket connection.close();

8 Client Sockets Create a socket to connect to the server: Socket connection = new Socket(serverAddress, port); Obtain the socket s InputStream and OutputStream references (like step 3 of server) Process data Close the socket

9 Datagram Sockets Datagram sockets are used for connectionless communication between programs class DatagramSocket used for creation of datagram sockets. Examples: DatagramSocket s1, s2; s1=new DatagramSocket(12345); //bind to port s2 = new DatagramSocket(); // bind to any available port on local host machine class DatagramPacket used to build packets of information to send over datagram sockets. Examples: DatagramPacket p1, p2; byte[] data1 = new byte[500]; p1 = new DatagramPacket(data1, data1.length);

10 Using Datagram Sockets String message = "Hello, World"; byte[] data2 = message.getbytes(); // convert string to byte array p2 = new DatagramPacket(data2, data2.length, InetAddress.getLocalHost(), 1234); Send a packet by calling the send method: s2.send(p2); Receive a datagram packet with the receive method: s1.receive(p1);