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Java Sockets Programming

Java Sockets Programming. The package java.net provides support for sockets programming (and more). Typically you import everything defined in this package with: import java.net.*;. Classes. InetAddress Socket ServerSocket DatagramSocket DatagramPacket. InetAddress class.

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Java Sockets Programming

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  1. Java Sockets Programming • The package java.net provides support for sockets programming (and more). • Typically you import everything defined in this package with: import java.net.*; Netprog: Java Sockets

  2. Classes InetAddress Socket ServerSocket DatagramSocket DatagramPacket Netprog: Java Sockets

  3. InetAddress class • static methods you can use to create new InetAddress objects. • getByName(String host) • getLocalHost() InetAddress x = InetAddress.getByName( “monte.cs.rpi.edu”); Netprog: Java Sockets

  4. Sample Code: Lookup.java • Uses InetAddress class to lookup hostnames found on command line. > java Lookup monte www.yahoo.com monte:128.213.8.110 www.yahoo.com:64.58.76.176 Netprog: Java Sockets

  5. try { InetAddress a = InetAddress.getByName(hostname); System.out.println(hostname + ":" + a.getHostAddress()); } catch (UnknownHostException e) { System.out.println("No address found for " + hostname); } Netprog: Java Sockets

  6. Socket class • Corresponds to active TCP sockets only! • client sockets • socket returned by accept(); • Passive sockets are supported by a different class: ServerSocket • UDP sockets are supported by DatagramSocket Netprog: Java Sockets

  7. Socket Constructors • Constructor creates a TCP connection to a named TCP server. • There are a number of constructors: Socket(InetAddress server, int port); Socket(InetAddress server, int port, InetAddress local, int localport); Socket(String hostname, int port); Netprog: Java Sockets

  8. Socket Methods void close(); InetAddress getInetAddress();getpeername InetAddress getLocalAddress(); getsockname InputStream getInputStream(); OutputStream getOutputStream(); • Lots more (setting/getting socket options, partial close, etc.) Netprog: Java Sockets

  9. Socket I/O • Socket I/O is based on the Java I/O support (in the package java.io). • InputStream and OutputStream are abstract classes • common operations defined for all kinds of InputStreams, OutputStreams… Netprog: Java Sockets

  10. InputStream Basics // reads some number of bytes and // puts in buffer array b int read(byte[] b); // reads up to len bytes int read(byte[] b, int off, int len); Both methods can throw IOException. Both return –1 on EOF. Netprog: Java Sockets

  11. OutputStream Basics // writes b.length bytes void write(byte[] b); // writes len bytes starting // at offset off void write(byte[] b, int off, int len); Both methods can throw IOException. Netprog: Java Sockets

  12. ServerSocket Class(TCP Passive Socket) • Constructors: ServerSocket(int port); ServerSocket(int port, int backlog); ServerSocket(int port, int backlog, InetAddress bindAddr); Netprog: Java Sockets

  13. ServerSocket Methods Socket accept(); void close(); InetAddress getInetAddress(); int getLocalPort(); throw IOException, SecurityException Netprog: Java Sockets

  14. Sample Echo Server TCPEchoServer.java Simple TCP Echo server. Based on code from: TCP/IP Sockets in Java Netprog: Java Sockets

  15. UDP Sockets • DatagramSocket class • DatagramPacket class needed to specify the payload (incoming or outgoing). Netprog: Java Sockets

  16. DatagramSocket Constructors DatagramSocket(); DatagramSocket(int port); DatagramSocket(int port, InetAddress a); All can throw SocketException or SecurityException. Netprog: Java Sockets

  17. Datagram Methods void connect(InetAddress, int port); void close(); void receive(DatagramPacket p); void send(DatagramPacket p); Lots more! Netprog: Java Sockets

  18. DatagramPacket • Contain the payload (a byte array). • Can also be used to specify the destination address (when not using connected mode UDP). Netprog: Java Sockets

  19. DatagramPacket Constructors For receiving: DatagramPacket( byte[] buf, int len); For sending: DatagramPacket( byte[] buf, int len InetAddress a, int port); Netprog: Java Sockets

  20. DatagramPacket methods byte[] getData(); void setData(byte[] buf); void setAddress(InetAddress a); void setPort(int port); InetAddress getAddress(); int getPort(); destination address could be either address (depends on context) Netprog: Java Sockets

  21. Sample UDP code UDPEchoServer.java Simple UDP Echo server. Test using nc as the client (netcat): > nc –u hostname port Netprog: Java Sockets

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