如何读取JSch命令输出？

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];
}

试图从阅读器中读取内容已挂起。我该如何解决？我该如何寻找正在发生的事情？

Answer 1

在等待命令完成的同时，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，则该命令将挂起，等待缓冲区被消耗，这将永远不会发生。这样您就陷入僵局。

以下示例在监视命令状态的同时连续读取stdout和stderr。它基于官方的JSch
exec.java示例
（仅添加了stderr的阅读）。

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();

如果在while (!channel.isClosed()) {}之后添加channel.connect();，您会看到ishell
for循环中有足够大的空间（在我的环境中，10000就足够了），循环永远不会结束。