java - 为什么在调用 Session::execCommand() 后会引发 IOException？

Question

我正在尝试使用 SSH 协议(protocol)在远程计算机上运行服务。我使用 Ganymed SSH-2 for Java 库(版本 262)，执行单个命令时效果很好，但在单个 session 期间尝试执行多个命令时我遇到了一些困难。

您能帮我找出引发 IOException 的原因以及如何修复它吗？

请在下面的摘录中找到代码:

private static void executeShellCommands(Connection connection, List<String> commandList) throws Exception {
    Session session = connection.openSession();
    InputStream stdout = new StreamGobbler(session.getStdout());
    session.requestDumbPTY();
    session.startShell();
    for(String command : commandList) {
        // The next line throws java.io.IOException
        session.execCommand(command); 
        try (BufferedReader br = new BufferedReader(new InputStreamReader(stdout))) {
            String line = br.readLine() + "\n";
            StringBuilder shellOutput = new StringBuilder();
            while (line != null) {
                shellOutput.append(line);
                line = br.readLine() + "\n";
            }
        }
    }
    session.close();
}

堆栈跟踪是:

java.io.IOException: A remote execution has already started.

at ch.ethz.ssh2.Session.execCommand(Session.java:282)
at ch.ethz.ssh2.Session.execCommand(Session.java:260)
at com.myproject.test.ssh.util.SshOperations.executeShellCommands(SshOperations.java:124)
at com.myproject.test.ssh.util.SshOperations.runBatchProcessingService(SshOperations.java:147)
at com.myproject.test.ssh.step.definitions.DocumentBatchProcessingStepDefs.testFileIsCopiedToBpsViaSSH(DocumentBatchProcessingStepDefs.java:97)
at ✽.Given test file is copied to BPS via SSH (myrepo/src/test/resources/cucumber/Regression.feature:21)

提前谢谢您。

Answer 1

ch.ethz.ssh2.Session的Javadoc中提到了

A Session is a remote execution of a program. "Program" means in this context either a shell, an application or a system command [.... ] Only one single program can be started on a session. However, multiple sessions can be active simultaneously.

我认为您应该使用多个 session ，例如如下所示:

private static void executeShellCommands(Connection connection, List<String> commandList) throws Exception {
    for(String command : commandList) {
        Session session = connection.openSession();
        InputStream stdout = new StreamGobbler(session.getStdout());
        session.requestDumbPTY();
        session.startShell();
        session.execCommand(command); 
        try (BufferedReader br = new BufferedReader(new InputStreamReader(stdout))) {
            String line = br.readLine() + "\n";
            StringBuilder shellOutput = new StringBuilder();
            while (line != null) {
                shellOutput.append(line);
                line = br.readLine() + "\n";
            }
        }
        session.close();
    }
}