Network Read/Write

1. Network Read/Write

2. 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 FileReaderfrdr = new FileReader(“filename.txt”); BufferedReaderrdr = new BufferedReader( frdr ); String line = rdr.readLine(); rdr.close(); Example 2 BufferedReaderrdr = new BufferedReader( new InputStreamReader( System.in ));

3. Review Output Streams • FileWriter • Create a FileWriter, write to it and close it. • You must write line separator characters FileWriterfw = new FileWriter(“filename.txt”); fw.write(“abcdef\n”); fw.close(); • PrintWriter • print() and println() will take of line separator characters. PrintWriterpw = 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

4. 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 PrintWriterfrom 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.

5. 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 BufferedReaderinstance InputStreamis = s.getInputStream(); InputStreamReaderisrdr = new InputStreamReader(is); BufferedReaderrdr = 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()); }

6. Get Current Weather Socket s = new Socket("weather.yahooapis.com", 80); OutputStreamos = s.getOutputStream(); OutputStreamWriterout = new OutputStreamWriter(os); out.write("GET /forecastrss?w=2453280 HTTP/1.1\r\n"+ "Host: weather.yahooapis.com\r\n"+ "\r\n"); out.flush(); InputStreamis = s.getInputStream(); InputStreamReaderisrdr = new InputStreamReader(is); BufferedReaderrdr = new BufferedReader(isrdr); String line = rdr.readLine(); while (line!=null){ .. Do something .. line = rdr.readLine(); } s.close();