Question

我正在尝试为ProcessBuilder对象添加一个环境变量，但是当我在ProcessBuilder中调用该新变量时，我收到一个错误。这就是我构建过程的方法

public class OTU
{
    public static void main(String[] args) throws Exception
    {
        ProcessBuilder pb = new ProcessBuilder();
        Map<String, String> env = pb.environment();
        //set environment variable u
        env.put("u", "util/");

        pb.command("echo $u");
        Process p = pb.start();
        String output = loadStream(p.getInputStream());
        String error  = loadStream(p.getErrorStream());
        int rc = p.waitFor();
        System.out.println("Process ended with rc=" + rc);
        System.out.println("\nStandard Output:\n");
        System.out.println(output);
        System.out.println("\nStandard Error:\n");
        System.out.println(error);
    }

    private static String loadStream(InputStream s) throws Exception
    {
        BufferedReader br = new BufferedReader(new InputStreamReader(s));
        StringBuilder sb = new StringBuilder();
        String line;
        while((line=br.readLine()) != null)
            sb.append(line).append("\n");
        return sb.toString();
    }
}

我收到错误

Exception in thread "main" java.io.IOException: Cannot run program "$u": java.io.IOException: error=2, No such file or directory
    at java.lang.ProcessBuilder.start(ProcessBuilder.java:475)
    at ca.utoronto.siseq_1_2.OTU.main(OTU.java:22)
Caused by: java.io.IOException: java.io.IOException: error=2, No such file or directory
    at java.lang.UNIXProcess.<init>(UNIXProcess.java:164)
    at java.lang.ProcessImpl.start(ProcessImpl.java:81)
    at java.lang.ProcessBuilder.start(ProcessBuilder.java:468)
    ... 1 more

如果我只为此Process设置变量，我不明白为什么我会收到错误。请帮我如何设置env变量，以便我可以在ProcessBuilder中使用它。

Answer 1

Alfredo O的例子为您提供了正确的想法。您需要告诉ProcessBuilder用于执行命令的程序。在这种情况下bash with the "-c" switch，它告诉bash解释接下来的内容（即“echo $ u”）作为命令。

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Map;

public class OTU {
    public static void main(String[] args) throws Exception {
        ProcessBuilder pb = new ProcessBuilder("/bin/bash", "-c", "echo $u");
        Map<String, String> env = pb.environment();
        // set environment variable u
        env.put("u", "util/");

        Process p = pb.start();
        String output = loadStream(p.getInputStream());
        String error = loadStream(p.getErrorStream());
        int rc = p.waitFor();
        System.out.println("Process ended with rc=" + rc);
        System.out.println("\nStandard Output:\n");
        System.out.println(output);
        System.out.println("\nStandard Error:\n");
        System.out.println(error);
    }

    private static String loadStream(InputStream s) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(s));
        StringBuilder sb = new StringBuilder();
        String line;
        while ((line = br.readLine()) != null)
            sb.append(line).append("\n");
        return sb.toString();
    }
}

这会产生以下输出：

Process ended with rc=0

Standard Output:

util/


Standard Error:

Answer 2

这适用于Windows：

@Test
public void testProcessBuilder() throws IOException {
    ProcessBuilder processBuilder = new ProcessBuilder("cmd.exe", "/C", "echo Hello %name%");
    Map<String, String> environment = processBuilder.environment();
    environment.put("name", "Alfredo Osorio");
    Process p = processBuilder.start();
    String line;
    BufferedReader r = new BufferedReader(new InputStreamReader(p.getInputStream()));
    while ((line = r.readLine()) != null) {
        System.out.println(line);
    }
    r.close();
}

<强>输出：

Hello Alfredo Osorio

正如您在Windows中看到的，您使用％environmentVariable％而不是$ environementVariable

java中的ProcessBuilder环境变量

2 个答案: