Runtime.getRuntime（）。exec（“ C：\ cygwin \ bin \ bash.exe”）没有要读取的输入

我正在尝试执行一个新流程，并从Java中的输入流中读取内容。我已经成功使用Runtime.getRuntime（）。exec（String）来启动和接收来自多个进程的输入。但是，当我尝试在其他某些进程上使用exec时，输入流的read方法将阻塞，并且似乎没有输入。是什么原因导致其中某些过程的输入流为空？具体来说，我想知道为什么bash.exe没有输出任何内容。

我已经编写了一个JUnit测试用例来演示此问题：

import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import junit.framework.TESTCase;

public class TestExec extends TESTCase {

    public void testExec() throws IOException {
        List<InputPrinter> threads = new ArrayList<InputPrinter>();

        // Create a process for each of the commands and make sure that
        // it outputs at least one line to its input stream.
        threads.add(testExec("cmd"));
        threads.add(testExec("java"));
        threads.add(testExec("C:/cygwin/bin/vim-nox.exe"));

        // these bottom two fail,even though execuTing these
        // commands in cmd.exe results in immediate output
        threads.add(testExec("javac"));
        threads.add(testExec("C:/cygwin/bin/bash.exe"));

        // Give the threads a second to execute
        try {
            Thread.sleep(1000);
        } catch (InterruptedException E) {
            e.printStackTrace();
            fail();
        }

        // Test that each command had input to read
        for(InputPrinter ip : threads) {
            assertTrue(ip.command + " has not read any input",ip.hasRead);
        }
    }

    // Starts a process for the given command and returns an
    // InputPrinter that can be used to check if the process
    // has had an input to read.
    public InputPrinter testExec(String command) throws IOException {
        Process proc = Runtime.getRuntime().exec(command);
        InputStream in = proc.geTinputStream();

        InputPrinter ip = new InputPrinter(in,command);
        new Thread(ip).start();

        return ip;
    }

    // Simple Runnable to read from an InputStream. hasRead will be
    // true if at least one input has been read from the stream
    private class InputPrinter implements Runnable {
        InputStream in;
        String command;
        Boolean hasRead;

        public InputPrinter(InputStream in,String command) {
            this.in = in;
            this.command = command;
            this.hasRead = false;
        }

        // Loop indefinitely while prinTing any received input
        public void run() {
            try {
                final byte[] b = new byte[1024];
                while (true) {
                    int n = in.read(b);
                    if (n > 0) {
                        System.out.print(new String(Arrays.copyOf(b,n)));
                        hasRead = true;
                    }
                }
            } catch (IOException E) {
                e.printStackTrace();
                fail();
            }
        }
    }

}

编辑：

据我所知，如果程序未使用stdout或stderr，则Windows命令提示符下不会显示任何内容。启动bash进程时，我期望看到的是“ bash-3.2
$”，这与打开命令提示符并运行“ bash.exe”时看到的相同：

@H_821_7@microsoft Windows [Version 6.1.7600]
Copyright (C) 2009 Microsoft Corporation.  All rights reserved.

C:\cygwin\bin>bash.exe
bash-3.2$