Chapter 4: The Java Platform

4.12. Processes

Earlier in the chapter, we saw how easy it is to create and manipulate multiple threads of execution running within the same Java interpreter. Java also has a java.lang.Process class that represents a program running externally to the interpreter. A Java program can communicate with an external process using streams in the same way that it might communicate with a server running on some other computer on the network. Using a Process is always platform-dependent and is rarely portable, but it is sometimes a useful thing to do:

// Maximize portability by looking up the name of the command to execute
// in a configuration file. 
java.util.Properties config;  
String cmd = config.getProperty("sysloadcmd");
if (cmd != null) {
  // Execute the command; Process p represents the running command
  Process p = Runtime.getRuntime().exec(cmd);         // Start the command
  InputStream pin = p.getInputStream();               // Read bytes from it
  InputStreamReader cin = new InputStreamReader(pin); // Convert them to chars
  BufferedReader in = new BufferedReader(cin);        // Read lines of chars
  String load = in.readLine();                        // Get the command output
  in.close();                                         // Close the stream
}

4.11. Networking		4.13. Security

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