我使用Runtime exec()方法在
Java中创建子进程.但是,由于子进程是一个交互式程序,我需要在需要时为它提供输入.另外,我需要显示子进程的输出.我怎样才能以最简单的方式做到这一点?
我使用StreamGobbler使用process.getInputStream()显示程序输出.但是,我不知道如何识别程序何时等待输入以及何时使用proc.getOutputStream提供输入.我怎样才能做到这一点?
解决方法
您需要复制子进程的流和系统流(System.in,System.out和System.err)之间的输入和输出.这与
my recent quesion有关.到目前为止,我找到的最佳解决方案是:
- import java.io.FileInputStream;
- import java.io.FilterInputStream;
- import java.io.IOException;
- import java.io.InputStream;
- import java.io.OutputStream;
- import java.lang.reflect.Field;
- import java.nio.ByteBuffer;
- import java.nio.channels.AsynchronousCloseException;
- import java.nio.channels.FileChannel;
- class StreamCopier implements Runnable {
- private InputStream in;
- private OutputStream out;
- public StreamCopier(InputStream in,OutputStream out) {
- this.in = in;
- this.out = out;
- }
- public void run() {
- try {
- int n;
- byte[] buffer = new byte[4096];
- while ((n = in.read(buffer)) != -1) {
- out.write(buffer,n);
- out.flush();
- }
- }
- catch (IOException e) {
- System.out.println(e);
- }
- }
- }
- class InputCopier implements Runnable {
- private FileChannel in;
- private OutputStream out;
- public InputCopier(FileChannel in,OutputStream out) {
- this.in = in;
- this.out = out;
- }
- public void run() {
- try {
- int n;
- ByteBuffer buffer = ByteBuffer.allocate(4096);
- while ((n = in.read(buffer)) != -1) {
- out.write(buffer.array(),n);
- out.flush();
- }
- out.close();
- }
- catch (AsynchronousCloseException e) {}
- catch (IOException e) {
- System.out.println(e);
- }
- }
- }
- public class Test {
- private static FileChannel getChannel(InputStream in)
- throws NoSuchFieldException,IllegalAccessException {
- Field f = FilterInputStream.class.getDeclaredField("in");
- f.setAccessible(true);
- while (in instanceof FilterInputStream)
- in = (InputStream)f.get((FilterInputStream)in);
- return ((FileInputStream)in).getChannel();
- }
- public static void main(String[] args)
- throws IOException,InterruptedException,NoSuchFieldException,IllegalAccessException {
- Process process = Runtime.getRuntime().exec("sh -i +m");
- Thread outThread = new Thread(new StreamCopier(
- process.getInputStream(),System.out));
- outThread.start();
- Thread errThread = new Thread(new StreamCopier(
- process.getErrorStream(),System.err));
- errThread.start();
- Thread inThread = new Thread(new InputCopier(
- getChannel(System.in),process.getOutputStream()));
- inThread.start();
- process.waitFor();
- System.in.close();
- outThread.join();
- errThread.join();
- inThread.join();
- }
- }
这里棘手的部分是从System.in中提取一个通道.如果没有这个,你将无法在子进程终止时中断读取输入的线程.
这种方法有一个严重的缺点:关闭System.in之后,你再也无法读取它了.我目前使用的解决方法是使用单个输入重定向线程用于所有子进程.