Question

我有以下代码：

JSch jsch = new JSch();
jsch.setKnownHosts(dotSshDir + "/known_hosts");
jsch.addIdentity(dotSshDir + "/id_rsa");

Session session = jsch.getSession(userName, hostname, 22);
session.connect();

ChannelExec channel = (ChannelExec) session.openChannel("exec");
channel.setCommand(command);
channel.setInputStream(null);
channel.setErrStream(System.err);
Reader reader = new InputStreamReader(channel.getInputStream());

char[] buf = new char[1024];
int numRead;
while ((numRead = reader.read(buf)) != -1) {
    String readData = String.valueOf(buf, 0, numRead);
    result.append(readData);
    buf = new char[1024];
}

它试图从读者那里读取。我该如何解决？我如何去寻找正在发生的事情？

Answer 1

悬挂实际上是由于命令中的一些不平衡的引号。

对于后人，最终代码（在处理其他一些问题之后）是：

public String call(String hostname, String[] argv) throws SubprocessException {
    StringBuffer result = new StringBuffer();

    Session session = null;
    ChannelExec channel = null;

    try {
        // TODO: Emit friendly error if ~/.ssh doesn't exist.
        String dotSshDir = System.getProperty("user.home") + "/.ssh";
        String userName = System.getProperty("user.name");

        // TODO: Emit friendly error if ~/.ssh/known_hosts doesn't exist.
        jSch.setKnownHosts(dotSshDir + "/known_hosts");
        // TODO: Emit friendly error if ~/.ssh/id_rsa doesn't exist.
        jSch.addIdentity(dotSshDir + "/id_rsa");

        session = jSch.getSession(userName, hostname, 22);
        session.connect();

        channel = (ChannelExec) session.openChannel("exec");
        channel.setCommand(Joiner.on(" ").join(argv));
        channel.setInputStream(null);
        InputStream stdout = channel.getInputStream();
        InputStream stderr = channel.getErrStream();
        channel.connect();

        waitForChannelClosed(channel);

        if (channel.getExitStatus() != 0) {
            BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(stderr));
            readAll(bufferedReader, result);

            throw new Exception(result.toString());
        } else {
            BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(stdout));
            readAll(bufferedReader, result);
        }
    } catch (Exception e) {
        throw new SubprocessException(e);
    } finally {
        if (channel != null) {
            channel.disconnect();
        }

        if (session != null) {
            session.disconnect();
        }
    }

    return result.toString();
}

Answer 2

@NoelYap接受的答案是错误的。

在等待命令完成时，必须连续读取输出。否则，如果命令产生足够的输出以填充输出缓冲区，则命令将挂起，等待缓冲区被消耗，从未发生过。所以你陷入了僵局。

以下示例在监视命令状态的同时连续读取stdout和stderr。它基于official JSch exec.java example（只是增加了stderr的读数）。

ChannelExec channel = (ChannelExec)session.openChannel("exec");

channel.setCommand(
    "for((i=1;i<=10000;i+=2)); do echo \"Long output - $i\"; done ; " +
    "echo error output >&2");
InputStream commandOutput = channel.getExtInputStream();

StringBuilder outputBuffer = new StringBuilder();
StringBuilder errorBuffer = new StringBuilder();

InputStream in = channel.getInputStream();
InputStream err = channel.getExtInputStream();

channel.connect();

byte[] tmp = new byte[1024];
while (true) {
    while (in.available() > 0) {
        int i = in.read(tmp, 0, 1024);
        if (i < 0) break;
        outputBuffer.append(new String(tmp, 0, i));
    }
    while (err.available() > 0) {
        int i = err.read(tmp, 0, 1024);
        if (i < 0) break;
        errorBuffer.append(new String(tmp, 0, i));
    }
    if (channel.isClosed()) {
        if ((in.available() > 0) || (err.available() > 0)) continue; 
        System.out.println("exit-status: " + channel.getExitStatus());
        break;
    }
    try { 
      Thread.sleep(1000);
    } catch (Exception ee) {
    }
}

System.out.println("output: " + outputBuffer.toString());
System.out.println("error: " + errorBuffer.toString());

channel.disconnect();

如果您在while (!channel.isClosed()) {}之后添加channel.connect();，则会在shell i循环中看到足够大的for（在我的环境中10000就足够了），循环永远不会结束。

如何阅读JSch命令输出？

2 个答案: