读取 java exec 的输出

Question

你好，我有一些关于java的问题。 这是我的代码：

public static void main(String[] args) throws Exception {
    Process pr = Runtime.getRuntime().exec("java -version");

    BufferedReader in = new BufferedReader(new InputStreamReader(pr.getInputStream()));
    String line;
    while ((line = in.readLine()) != null) {
        System.out.println(line);
    }
    pr.waitFor();
    System.out.println("ok!");

    in.close();
    System.exit(0);
}

在该代码中，我试图获取 java 版本命令，执行正常，但我无法读取输出，它只是返回 null。为什么？

Answer 1

使用 getErrorStream()。

BufferedReader in = new BufferedReader(new InputStreamReader(pr.getErrorStream()));

编辑：

您可以使用 ProcessBuilder （并阅读文档）

ProcessBuilder   ps=new ProcessBuilder("java.exe","-version");

//From the DOC:  Initially, this property is false, meaning that the 
//standard output and error output of a subprocess are sent to two 
//separate streams
ps.redirectErrorStream(true);

Process pr = ps.start();  

BufferedReader in = new BufferedReader(new InputStreamReader(pr.getInputStream()));
String line;
while ((line = in.readLine()) != null) {
    System.out.println(line);
}
pr.waitFor();
System.out.println("ok!");

in.close();
System.exit(0);

Answer 2

请注意，我们正在将流程输出逐行读取到 StringBuilder。由于 try-with-resources 声明我们不需要手动关闭流。 ProcessBuilder class 让我们向其构造函数提交程序名称和参数数量。

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class ProcessOutputExample
{
    public static void main(String[] arguments) throws IOException,
            InterruptedException
    {
        System.out.println(getProcessOutput());
    }

    public static String getProcessOutput() throws IOException, InterruptedException
    {
        ProcessBuilder processBuilder = new ProcessBuilder("java",
                "-version");

        processBuilder.redirectErrorStream(true);

        Process process = processBuilder.start();
        StringBuilder processOutput = new StringBuilder();

        try (BufferedReader processOutputReader = new BufferedReader(
                new InputStreamReader(process.getInputStream()));)
        {
            String readLine;

            while ((readLine = processOutputReader.readLine()) != null)
            {
                processOutput.append(readLine + System.lineSeparator());
            }

            process.waitFor();
        }

        return processOutput.toString().trim();
    }
}

印刷：

java version "1.8.0_45"
Java(TM) SE Runtime Environment (build 1.8.0_45-b15)
Java HotSpot(TM) 64-Bit Server VM (build 25.45-b02, mixed mode)

Answer 3

您已经拥有进程-对象（名称公关）。您可以获得输入、输出和错误流。在您的情况下，您需要 pr。 getInputStream()。从其中读取，它连接到过程的输出。

Answer 4

试试这个

public static final Pair<Integer,Integer> javaVersion(File file) throws IOException {
    final ProcessBuilder pb = new ProcessBuilder("java", "-version");
    pb.directory(new File(file.getCanonicalPath() + File.separator  + "bin"));
    pb.redirectErrorStream(true);

    // Call the test target
    final Process process = pb.start();
    final InputStream in = process.getInputStream();
    final InputStream err = process.getErrorStream();

    BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(in,"UTF-8"));
    String s = bufferedReader.readLine();
    int start = s.indexOf('\"');
    int end = s.lastIndexOf('\"');
    String substring = s.substring(start + 1, end);
    String[] split = substring.split("\\.");

    return new Pair<>(Integer.parseInt(split[0]),Integer.parseInt(split[1]));
}

Answer 5

我也遇到了这个问题，因为我没有正确设置 $JAVA_HOME 。 （我忘记了目录/主页）。
在我编辑 $JAVA_HOME，更新 Gradle JVM，并删除 .idea 目录以使用 gradle 重新构建后，效果很好。