<转>JSCH 如何实现在远程机器上执行linux命令

原链：http://blog.csdn.net/hongbinchen/article/details/6567395

jsch 是纯java实现ssh功能，
下面是如何实现在远程机器上执行linux命令
摘自hadoop开源包的源码:



/**

* Licensed to the Apache Software Foundation (ASF) under one

* or more contributor license agreements.  See the NOTICE file

* distributed with this work for additional information

* regarding copyright ownership.  The ASF licenses this file

* to you under the Apache License, Version 2.0 (the

* "License"); you may not use this file except in compliance

* with the License.  You may obtain a copy of the License at

*

*     http://www.apache.org/licenses/LICENSE-2.0

*

* Unless required by applicable law or agreed to in writing, software

* distributed under the License is distributed on an "AS IS" BASIS,

* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

* See the License for the specific language governing permissions and

* limitations under the License.

*/



package org.apache.hadoop.util;



import com.jcraft.jsch.*;

import org.apache.commons.logging.LogFactory;

import org.apache.commons.logging.Log;



import java.io.BufferedReader;

import java.io.IOException;

import java.io.InputStreamReader;

import java.util.Properties;



/**

* Remote Execution of commands  on a remote machine.

*/



public class SSHRemoteExecution implements RemoteExecution {



  static final Log LOG = LogFactory.getLog(SSHRemoteExecution.class);

  static final int SSH_PORT = 22;

  static final String DEFAULT_IDENTITY="id_dsa";

  static final String DEFAULT_KNOWNHOSTS="known_hosts";

  static final String FS = System.getProperty("file.separator");

  static final String LS = System.getProperty("line.separator");

  private int exitCode;

  private StringBuffer output;

  private String commandString;



  final StringBuffer errorMessage = new StringBuffer();

  public SSHRemoteExecution() throws Exception {

  }



  protected String getHomeDir() {

    String currentUser=System.getProperty("user.name");

    String userHome=System.getProperty("user.home");



    return userHome.substring(0, userHome.indexOf(currentUser)-1);

  }



  /**

   * Execute command at remote host under given user

   * @param remoteHostName remote host name

   * @param user is the name of the user to be login under;

   *   current user will be used if this is set to <code>null</code>

   * @param command to be executed remotely

   * @param identityFile is the name of alternative identity file; default

   *   is ~user/.ssh/id_dsa

   * @param portNumber remote SSH daemon port number, default is 22

   * @throws Exception in case of errors

   */

  public void executeCommand (String remoteHostName, String user,

          String  command, String identityFile, int portNumber) throws Exception {

    commandString = command;

    String sessionUser = System.getProperty("user.name");

    String userHome=System.getProperty("user.home");

    if (user != null) {

      sessionUser = user;

      userHome = getHomeDir() + FS + user;

    }

    String dotSSHDir = userHome + FS + ".ssh";

    String sessionIdentity = dotSSHDir + FS + DEFAULT_IDENTITY;

    if (identityFile != null) {

      sessionIdentity = identityFile;

    }



    JSch jsch = new JSch();



    Session session = jsch.getSession(sessionUser, remoteHostName, portNumber);

    jsch.setKnownHosts(dotSSHDir + FS + DEFAULT_KNOWNHOSTS);

    jsch.addIdentity(sessionIdentity);



    Properties config = new Properties();

    config.put("StrictHostKeyChecking", "no");

    session.setConfig(config);



    session.connect(30000);   // making a connection with timeout.



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

    ((ChannelExec)channel).setCommand(command);

    channel.setInputStream(null);



    final BufferedReader errReader =

            new BufferedReader(

              new InputStreamReader(((ChannelExec)channel).getErrStream()));

    BufferedReader inReader =

            new BufferedReader(new InputStreamReader(channel.getInputStream()));



    channel.connect();

    Thread errorThread = new Thread() {

      @Override

      public void run() {

        try {

          String line = errReader.readLine();

          while((line != null) && !isInterrupted()) {

            errorMessage.append(line);

            errorMessage.append(LS);

            line = errReader.readLine();

          }

        } catch(IOException ioe) {

          LOG.warn("Error reading the error stream", ioe);

        }

      }

    };



    try {

      errorThread.start();

    } catch (IllegalStateException e) {

      LOG.debug(e);

    }

    try {

      parseExecResult(inReader);

      String line = inReader.readLine();

      while (line != null) {

        line = inReader.readLine();

      }



      if(channel.isClosed()) {

        exitCode = channel.getExitStatus();

        LOG.debug("exit-status: " + exitCode);

      }

      try {

        // make sure that the error thread exits

        errorThread.join();

      } catch (InterruptedException ie) {

        LOG.warn("Interrupted while reading the error stream", ie);

      }

    } catch (Exception ie) {

      throw new IOException(ie.toString());

    }

    finally {

      try {

        inReader.close();

      } catch (IOException ioe) {

        LOG.warn("Error while closing the input stream", ioe);

      }

      try {

        errReader.close();

      } catch (IOException ioe) {

        LOG.warn("Error while closing the error stream", ioe);

      }

      channel.disconnect();

      session.disconnect();

    }

  }



  /**

   * Execute command at remote host under given username

   * Default identity is ~/.ssh/id_dsa key will be used

   * Default known_hosts file is ~/.ssh/known_hosts will be used

   * @param remoteHostName remote host name

   * @param user is the name of the user to be login under;

   *   if equals to <code>null</code> then current user name will be used

   * @param command to be executed remotely

   */

  @Override

  public void executeCommand (String remoteHostName, String user,

          String  command) throws Exception {

    executeCommand(remoteHostName, user, command, null, SSH_PORT);

  }



  @Override

  public int getExitCode() {

    return exitCode;

  }



  protected void parseExecResult(BufferedReader lines) throws IOException {

    output = new StringBuffer();

    char[] buf = new char[512];

    int nRead;

    while ( (nRead = lines.read(buf, 0, buf.length)) > 0 ) {

      output.append(buf, 0, nRead);

    }

  }



  /** Get the output of the ssh command.*/

  @Override

  public String getOutput() {

    return (output == null) ? "" : output.toString();

  }



  /** Get the String representation of ssh command */

  @Override

  public String getCommandString() {

    return commandString;

  }

}