如何将 ProcessBuilder 的输出重定向到字符串？

Question

我正在使用以下代码启动流程构建器。我想知道如何将其输出重定向到String。

ProcessBuilder pb = new ProcessBuilder(
    System.getProperty("user.dir") + "/src/generate_list.sh", filename);
Process p = pb.start();

我尝试使用ByteArrayOutputStream，但它似乎不起作用。

Answer 1

从InputStream 读取。您可以将输出附加到 StringBuilder:

BufferedReader reader = 
                new BufferedReader(new InputStreamReader(process.getInputStream()));
StringBuilder builder = new StringBuilder();
String line = null;
while ( (line = reader.readLine()) != null) {
   builder.append(line);
   builder.append(System.getProperty("line.separator"));
}
String result = builder.toString();

Answer 2

你可以这样做：

private static BufferedReader getOutput(Process p) {
    return new BufferedReader(new InputStreamReader(p.getInputStream()));
}

private static BufferedReader getError(Process p) {
    return new BufferedReader(new InputStreamReader(p.getErrorStream()));
}
...
Process p = Runtime.getRuntime().exec(commande);
BufferedReader output = getOutput(p);
BufferedReader error = getError(p);
String ligne = "";

while ((ligne = output.readLine()) != null) {
    System.out.println(ligne);
}

while ((ligne = error.readLine()) != null) {
 System.out.println(ligne);
}

Answer 3

只需将.inheritIO(); 添加到流程构建器行。

IE：

ProcessBuilder pb = new ProcessBuilder(script.sh).inheritIO();

Answer 4

对于 Java 7 和 8，这应该可以工作：

private String getInputAsString(InputStream is)
{
   try(java.util.Scanner s = new java.util.Scanner(is)) 
   { 
       return s.useDelimiter("\\A").hasNext() ? s.next() : ""; 
   }
}

然后在您的代码中执行以下操作：

String stdOut = getInputAsString(p.getInputStream());
String stdErr = getInputAsString(p.getErrorStream());

我无耻地从 How to redirect Process Builder's output to a string? 那里偷了它

Answer 5

在 java 8 中有一个不错的 lines() 流，您可以将其与 String.join 和 System.lineSeparator() 结合使用：

    try (BufferedReader outReader = new BufferedReader(new InputStreamReader(p.getInputStream()))
    {
        return String.join(System.lineSeparator(), outReader.lines().collect(toList()));
        \\ OR using jOOλ if you like reduced verbosity
        return Seq.seq(outReader.lines()).toString(System.lineSeparator())
    }

Answer 6

使用 Apache Commons IOUtils 可以在一行中完成：

ProcessBuilder pb = new ProcessBuilder("pwd");
String output = IOUtils.toString(pb.start().getInputStream(), StandardCharsets.UTF_8);

Answer 7

在尝试处理不同的情况后（同时处理stderr和stdout并且不阻塞任何这些，超时后终止进程，正确转义斜杠，引号，特殊字符，空格......）我放弃了，发现Apache Commons Exec https://commons.apache.org/proper/commons-exec/tutorial.html 似乎在所有这些事情上都做得很好。

我建议所有需要在 java 中调用外部进程的人使用 Apache Commons Exec 库，而不是重新发明它。

Answer 8

Java 8 示例：

public static String runCommandForOutput(List<String> params) {
    ProcessBuilder pb = new ProcessBuilder(params);
    Process p;
    String result = "";
    try {
        p = pb.start();
        final BufferedReader reader = new BufferedReader(new InputStreamReader(p.getInputStream()));

        StringJoiner sj = new StringJoiner(System.getProperty("line.separator"));
        reader.lines().iterator().forEachRemaining(sj::add);
        result = sj.toString();

        p.waitFor();
        p.destroy();
    } catch (Exception e) {
        e.printStackTrace();
    }
    return result;
}

用法：

List<String> params = Arrays.asList("/bin/sh", "-c", "cat /proc/cpuinfo");
String result = runCommandForOutput(params);

我使用这个确切的代码，它适用于单行或多行结果。您也可以添加错误流处理程序。

Answer 9

解决方案

• 此代码是您问题的一般解决方案的运行示例：

如何将 Process Builder 的输出重定向到字符串？

• 在尝试了多种解决方案来运行各种命令并捕获其输出之后，Greg T 获得了荣誉，Greg T 的回答包含了特定解决方案的精髓。我希望一般示例对在捕获输出的同时结合多个需求的人有用。
• 要获得您的特定解决方案，您可以取消注释ProcessBuilder pb = new ProcessBuilder(System.getProperty("user.dir")+"/src/generate_list.sh", filename);，取消注释该行并注释掉：ProcessBuilder processBuilder = new ProcessBuilder(commands);。

功能

• 这是一个执行命令echo 1 并将输出作为字符串返回的工作示例。
• 我还添加了设置工作路径和环境变量，这对于您的特定示例不是必需的，因此您可以将其删除。

使用与验证

• 您可以将此代码复制粘贴为一个类，将其编译为 jar 并运行它。
• 已在 WSL Ubuntu 16.04 中验证。
• 设置工作目录通过设置binaryCommand[0]="touch";和binaryCommand[1]="1";进行验证，重新编译运行.jar文件。

限制

• 如果管道已满（由于输出“太大”），代码将挂起。

代码

import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.Map;
import java.util.StringJoiner;

public class GenerateOutput {

    /**
     * This code can execute a command and print the output accompanying that command.
     * compile this project into a .jar and run it with for example:
     * java -jar readOutputOfCommand.jar
     * 
     * @param args
     * @throws Exception 
     */
    public static void main(String[] args) throws Exception {
        boolean answerYes = false; // no yes answer to any command prompts is needed.

        // to execute a command with spaces in it in terminal, put them in an array of Strings.
        String[] binaryCommand = new String[2];

        // write a command that gives a binary output:
        binaryCommand[0] = "echo";
        binaryCommand[1] = "1";

        // pass the commands to a method that executes them
        System.out.println("The output of the echo command = "+executeCommands(binaryCommand,answerYes));
    }

    /**
     * This executes the commands in terminal. 
     * Additionally it sets an environment variable (not necessary for your particular solution)
     * Additionally it sets a working path (not necessary for your particular solution)
     * @param commandData
     * @param ansYes
     * @throws Exception 
     */
    public static String executeCommands(String[] commands,Boolean ansYes) throws Exception {
        String capturedCommandOutput = null;
        System.out.println("Incoming commandData = "+Arrays.deepToString(commands));
        File workingDirectory = new File("/mnt/c/testfolder b/");

        // create a ProcessBuilder to execute the commands in
        ProcessBuilder processBuilder = new ProcessBuilder(commands);
        //ProcessBuilder processBuilder = new ProcessBuilder(System.getProperty("user.dir")+"/src/generate_list.sh", "a");

        // this is not necessary but can be used to set an environment variable for the command
        processBuilder = setEnvironmentVariable(processBuilder); 

        // this is not necessary but can be used to set the working directory for the command
        processBuilder.directory(workingDirectory);

        // execute the actual commands
        try {

             Process process = processBuilder.start();

             // capture the output stream of the command
             BufferedReader reader = new BufferedReader(new InputStreamReader(process.getInputStream()));
            StringJoiner sj = new StringJoiner(System.getProperty("line.separator"));
            reader.lines().iterator().forEachRemaining(sj::add);
            capturedCommandOutput = sj.toString();
            System.out.println("The output of this command ="+ capturedCommandOutput);

             // here you connect the output of your command to any new input, e.g. if you get prompted for `yes`
             new Thread(new SyncPipe(process.getErrorStream(), System.err)).start();
             new Thread(new SyncPipe(process.getInputStream(), System.out)).start();
            PrintWriter stdin = new PrintWriter(process.getOutputStream());

            //This is not necessary but can be used to answer yes to being prompted
            if (ansYes) {
                System.out.println("WITH YES!");
            stdin.println("yes");
            }

            // write any other commands you want here

            stdin.close();

            // this lets you know whether the command execution led to an error(!=0), or not (=0).
            int returnCode = process.waitFor();
            System.out.println("Return code = " + returnCode);
        } catch (IOException e1) {
            e1.printStackTrace();
        }
        return capturedCommandOutput;
    }


    /**
     * source: https://stackoverflow.com/questions/7369664/using-export-in-java
     * @param processBuilder
     * @param varName
     * @param varContent
     * @return
     */
    private static ProcessBuilder setEnvironmentVariable(ProcessBuilder processBuilder){
        String varName = "variableName";
        String varContent = "/mnt/c/testfolder a/";

        Map<String, String> env = processBuilder.environment();
         System.out.println("Setting environment variable "+varName+"="+varContent);
         env.put(varName, varContent);

         processBuilder.environment().put(varName, varContent);

         return processBuilder;
    }
}


class SyncPipe implements Runnable
{   
    /**
     * This class pipes the output of your command to any new input you generated
     * with stdin. For example, suppose you run cp /mnt/c/a.txt /mnt/b/
     * but for some reason you are prompted: "do you really want to copy there yes/no?
     * then you can answer yes since your input is piped to the output of your
     * original command. (At least that is my practical interpretation might be wrong.)
     * @param istrm
     * @param ostrm
     */
    public SyncPipe(InputStream istrm, OutputStream ostrm) {
        istrm_ = istrm;
        ostrm_ = ostrm;
    }
    public void run() {

      try
      {
          final byte[] buffer = new byte[1024];
          for (int length = 0; (length = istrm_.read(buffer)) != -1; )
          {
              ostrm_.write(buffer, 0, length);                
              }
          }
          catch (Exception e)
          {
              e.printStackTrace();
          }
      }
      private final OutputStream ostrm_;
      private final InputStream istrm_;
}

Answer 10

从 Java 9 开始，我们终于有了一个内衬：

ProcessBuilder pb = new ProcessBuilder("pwd");
Process process = pb.start();

String result = new String(process.getInputStream().readAllBytes());

Answer 11

Java 8 的另一种解决方案：

BufferedReader stdOut = new BufferedReader(new InputStreamReader(process.getInputStream()));
String stdOutStr = stdOut.lines()
                   .collect(Collectors.joining(System.lineSeparator()));