Network Read/Write

Review of Streams and Files java.io package InputStream and OutputStream classes for binary bytes Reader and Writer classes for characters Reading files: FileReader class – FileReader reads 1 char at a time; use BufferedReader – readLine() returns null at end of file Example 1 FileReader frdr = new FileReader(“filename.txt”); BufferedReader rdr = new BufferedReader( frdr ); String line = rdr.readLine(); rdr.close(); Example 2 BufferedReader rdr = new BufferedReader( new InputStreamReader( System.in ));

Review Output Streams FileWriter – Create a FileWriter, write to it and close it. – You must write line separator characters FileWriter fw = new FileWriter(“filename.txt”); fw.write(“abc def\n”); fw.close(); PrintWriter – print() and println() will take of line separator characters. PrintWriter pw = new PrintWriter( new FileWriter(“filename.txt”)); pw.print( “abc “); pw.println( “def”); pw.close(); Exceptions: IOException – File methods must be in a try/catch block for IOException

Sockets Data stream between client and server – Have to deal with security firewalls Client – Create a Socket Arguments: host address or name, listener port number – Create PrintWriter from the socket – Create BufferedReader from the socket – Close socket when done. Server – Create ServerSocket (port number ) – Wait for incoming connection from client – Accept connection A new port number is assigned to connection. – Create BufferedReader, PrintWriter using Socket Reading and writing is typically done on separate thread so that the main thread that is listening for incoming connections is not blocked. – Close socket when done.

Get Official Time from Time Server try { // Step1. Create a Socket object instance Socket s = new Socket("utcnist.colorado.edu", 13); // Step 2. Create a BufferedReader instance InputStream is = s.getInputStream(); InputStreamReader isrdr = new InputStreamReader(is); BufferedReader rdr = new BufferedReader(isrdr); // Step 3. Repeat readLine() method until null value String line = rdr.readLine(); while (line!=null){ System.out.println(line); line = rdr.readLine(); }; // Step 4. Close the socket connection. s.close(); } catch (Exception e){ System.out.println(e.getMessage()); }

Get Current Weather Socket s = new Socket("weather.yahooapis.com", 80); OutputStream os = s.getOutputStream(); OutputStreamWriter out = new OutputStreamWriter(os); out.write("GET /forecastrss?w= HTTP/1.1\r\n"+ "Host: weather.yahooapis.com\r\n"+ "\r\n"); out.flush(); InputStream is = s.getInputStream(); InputStreamReader isrdr = new InputStreamReader(is); BufferedReader rdr = new BufferedReader(isrdr); String line = rdr.readLine(); while (line!=null){.. Do something.. line = rdr.readLine(); } s.close();