我想从Java中启动一个进程，读取其输出并获取其返回代码。但在它执行时，我想能够取消它。我首先启动进程：
ProcessBuilder pb = new ProcessBuilder(args);
pb.redirectErrorStream(true);
Process proc = pb.start();
如果我调用proc.waitFor()，直到进程退出之前我就不能做任何事情。因此，我认为我需要像这样做:
while (true) {
see if process has exited
capture some output from the process
decide if I want to cancel it, and if so, cancel it
sleep for a while
}
这样做对吗？有人能给我一个在Java中实现这个的例子吗？
以下是我认为您想要做的示例：
ProcessBuilder pb = new ProcessBuilder(args);
pb.redirectErrorStream(true);
Process proc = pb.start();
InputStream is = proc.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String line;
int exit = -1;
while ((line = br.readLine()) != null) {
// Outputs your process execution
System.out.println(line);
try {
exit = proc.exitValue();
if (exit == 0) {
// Process finished
}
} catch (IllegalThreadStateException t) {
// The process has not yet finished.
// Should we stop it?
if (processMustStop())
// processMustStop can return true
// after time out, for example.
proc.destroy();
}
}
你可以改进它 :-) 我现在没有真正的环境来测试它，但是你可以在这里找到更多信息。
public class ProcessWatcher implements Runnable {
private Process p;
private volatile boolean finished = false;
public ProcessWatcher(Process p) {
this.p = p;
new Thread(this).start();
}
public boolean isFinished() {
return finished;
}
public void run() {
try {
p.waitFor();
} catch (Exception e) {}
finished = true;
}
}
Process p = Runtime.getRuntime().exec("whatever command");
ProcessWatcher pw = new ProcessWatcher(p);
InputStream output = p.getInputStream();
while(!pw.isFinished()) {
processOutput(output);
if(shouldCancel()) p.destroy();
Thread.sleep(500);
}
根据您想要销毁进程的条件，您可能希望在单独的线程中执行此操作。否则，您可能会在等待更多程序输出进行处理时被阻塞，从而无法真正选择销毁它。
编辑：麦克道尔在下面的评论中是100％正确的，因此我已将finished变量设为volatile。
/**
* Wait for the process to stop, logging its output in parallel.
* @param process The process to wait for
* @return Stdout produced by the process
* @throws InterruptedException If interrupted in between
*/
private String waitFor(final Process process) throws InterruptedException {
final BufferedReader reader = new BufferedReader(
new InputStreamReader(process.getInputStream())
);
final CountDownLatch done = new CountDownLatch(1);
final StringBuffer stdout = new StringBuffer();
new Thread(
new VerboseRunnable(
new Callable<Void>() {
@Override
public Void call() throws Exception {
while (true) {
final String line = reader.readLine();
if (line == null) {
break;
}
System.out.println(">> " + line);
stdout.append(line);
}
done.countDown();
return null;
}
},
false
)
).start();
try {
process.waitFor();
} finally {
done.await();
IOUtils.closeQuietly(reader);
}
return stdout.toString();
}
com.jcabi.log.VerboseProcess类来使用此实现。