在调用Runtime.exec时捕获stdout

Question

在客户端计算机上遇到网络问题时,我希望能够运行一些命令行并将结果通过电子邮件发送给自己.

我发现Runtime.exec允许我执行任意命令,但在String中收集结果更有趣.

我意识到我可以将输出重定向到一个文件,然后从文件中读取,但我的蜘蛛侠意识告诉我有一种更优雅的方式.

建议？

Answer 1

您需要在此过程中捕获std out和std err.然后,您可以将std写入文件/邮件或类似文件.

有关更多信息,请参阅此文章,特别注意StreamGobbler在单独的线程中捕获stdout/err 的机制.这对于防止阻塞至关重要,如果您没有正确执行,则会导致大量错误!

Answer 2

使用ProcessBuilder.在调用start()之后,您将获得一个Process对象,您可以从中获取stderr和stdout流.

更新:ProcessBuilder为您提供更多控制; 您不必使用它,但从长远来看,我发现它更容易.特别是将stderr重定向到stdout的能力,这意味着你只需要吸收一个流.

Answer 3

使用Plexus Utils,Maven使用它来执行所有外部进程.

Commandline commandLine = new Commandline();
commandLine.setExecutable(executable.getAbsolutePath());

Collection<String> args = getArguments();

for (String arg : args) {
    Arg _arg = commandLine.createArg();
    _arg.setValue(arg);
}

WriterStreamConsumer systemOut = new WriterStreamConsumer(console);
WriterStreamConsumer systemErr = new WriterStreamConsumer(console);

returnCode = CommandLineUtils.executeCommandLine(commandLine, systemOut, systemErr, 10);
if (returnCode != 0) {
    // bad
} else {
    // good
}

Answer 4

这是我多年来一直使用的助手类。一小班。它有 JavaWorld Streamgobbler 类来修复 JVM 资源泄漏。不知道对于 JVM6 和 JVM7 是否仍然有效，但不会造成伤害。助手可以读取输出缓冲区以供以后使用。

import java.io.*;

/**
 * Execute external process and optionally read output buffer.
 */
public class ShellExec {
    private int exitCode;
    private boolean readOutput, readError;
    private StreamGobbler errorGobbler, outputGobbler;

    public ShellExec() { 
        this(false, false);
    }

    public ShellExec(boolean readOutput, boolean readError) {
        this.readOutput = readOutput;
        this.readError = readError;
    }

    /**
     * Execute a command.
     * @param command   command ("c:/some/folder/script.bat" or "some/folder/script.sh")
     * @param workdir   working directory or NULL to use command folder
     * @param wait  wait for process to end
     * @param args  0..n command line arguments
     * @return  process exit code
     */
    public int execute(String command, String workdir, boolean wait, String...args) throws IOException {
        String[] cmdArr;
        if (args != null && args.length > 0) {
            cmdArr = new String[1+args.length];
            cmdArr[0] = command;
            System.arraycopy(args, 0, cmdArr, 1, args.length);
        } else {
            cmdArr = new String[] { command };
        }

        ProcessBuilder pb =  new ProcessBuilder(cmdArr);
        File workingDir = (workdir==null ? new File(command).getParentFile() : new File(workdir) );
        pb.directory(workingDir);

        Process process = pb.start();

        // Consume streams, older jvm's had a memory leak if streams were not read,
        // some other jvm+OS combinations may block unless streams are consumed.
        errorGobbler  = new StreamGobbler(process.getErrorStream(), readError);
        outputGobbler = new StreamGobbler(process.getInputStream(), readOutput);
        errorGobbler.start();
        outputGobbler.start();

        exitCode = 0;
        if (wait) {
            try { 
                process.waitFor();
                exitCode = process.exitValue();                 
            } catch (InterruptedException ex) { }
        }
        return exitCode;
    }   

    public int getExitCode() {
        return exitCode;
    }

    public boolean isOutputCompleted() {
        return (outputGobbler != null ? outputGobbler.isCompleted() : false);
    }

    public boolean isErrorCompleted() {
        return (errorGobbler != null ? errorGobbler.isCompleted() : false);
    }

    public String getOutput() {
        return (outputGobbler != null ? outputGobbler.getOutput() : null);        
    }

    public String getError() {
        return (errorGobbler != null ? errorGobbler.getOutput() : null);        
    }

//********************************************
//********************************************    

    /**
     * StreamGobbler reads inputstream to "gobble" it.
     * This is used by Executor class when running 
     * a commandline applications. Gobblers must read/purge
     * INSTR and ERRSTR process streams.
     * http://www.javaworld.com/javaworld/jw-12-2000/jw-1229-traps.html?page=4
     */
    private class StreamGobbler extends Thread {
        private InputStream is;
        private StringBuilder output;
        private volatile boolean completed; // mark volatile to guarantee a thread safety

        public StreamGobbler(InputStream is, boolean readStream) {
            this.is = is;
            this.output = (readStream ? new StringBuilder(256) : null);
        }

        public void run() {
            completed = false;
            try {
                String NL = System.getProperty("line.separator", "\r\n");

                InputStreamReader isr = new InputStreamReader(is);
                BufferedReader br = new BufferedReader(isr);
                String line;
                while ( (line = br.readLine()) != null) {
                    if (output != null)
                        output.append(line + NL); 
                }
            } catch (IOException ex) {
                // ex.printStackTrace();
            }
            completed = true;
        }

        /**
         * Get inputstream buffer or null if stream
         * was not consumed.
         * @return
         */
        public String getOutput() {
            return (output != null ? output.toString() : null);
        }

        /**
         * Is input stream completed.
         * @return
         */
        public boolean isCompleted() {
            return completed;
        }

    }

}

以下是从 .vbs 脚本读取输出的示例，但 Linux sh 脚本的工作类似。

   ShellExec exec = new ShellExec(true, false);
   exec.execute("cscript.exe", null, true,
      "//Nologo",
      "//B",            // batch mode, no prompts
      "//T:320",        // timeout seconds
      "c:/my/script/test1.vbs",  // unix path delim works for script.exe
      "script arg 1",
      "script arg 2",
   );
   System.out.println(exec.getOutput());

Answer 5

对于没有产生太多输出的进程,我认为这个使用Apache IOUtils的简单解决方案就足够了:

Process p = Runtime.getRuntime().exec("script");
p.waitFor();
String output = IOUtils.toString(p.getInputStream());
String errorOutput = IOUtils.toString(p.getErrorStream());

警告:但是,如果您的进程生成大量输出,则此方法可能会导致问题,如Process类JavaDoc中所述:

创建的子进程没有自己的终端或控制台.它的所有标准io(即stdin,stdout,stderr)操作将通过三个流(getOutputStream(),getInputStream(),getErrorStream())重定向到父进程.父进程使用这些流向子进程提供输入并从子进程获取输出.由于某些本机平台仅为标准输入和输出流提供有限的缓冲区大小,因此无法及时写入输入流或读取子进程的输出流可能导致子进程阻塞甚至死锁.