IO流必知必会(10)——Java虚拟机读写其它进程的数据

Runtime对象的exec()方法可以运行平台上其它程序，该方法产生一个Process()对象代表子进程，Process类中就提供了进程通信的方法。

public class ReadFromTest {
    public static void main(String[] args) throws IOException {
        Process p = Runtime.getRuntime().exec("javac");
        try (BufferedReader br = new BufferedReader(new InputStreamReader(
                p.getErrorStream()))) {
            String buff = null;
            while ((buff = br.readLine()) != null) {
                System.out.println(buff);
            }
        }
    }
}

上述代码获取了javac进程的错误流，进行了打印。在下列代码中可以在Java程序中启动Java虚拟机运行另一个java程序，并向另一个程序中输入数据。

public class WriteToProcess {
    public static void main(String[] args) throws IOException {
        Process p = Runtime.getRuntime().exec("java ReadStandard");
        try (
        // 以p进程的输出流创建PrintStream，该输出流对本进程为输出流，对p进程则为输入流
        PrintStream ps = new PrintStream(p.getOutputStream())) {
            ps.println("normal string");
            ps.println(new WriteToProcess());
        }
    }
}

class ReadStandard {
    public static void main(String[] args) throws FileNotFoundException {
        try (Scanner scan = new Scanner(System.in);
                PrintStream ps = new PrintStream(
                        new FileOutputStream("out.txt"))) {
            scan.useDelimiter("\n");
            while (scan.hasNext()) {
                ps.println("KeyBoards input:" + scan.next());
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}