java运行时环境无结果

Question

我正在尝试在我的java代码中调用python。然而，我发现如果我在python代码中导入numpy，这就是我的java代码。

Process pcs = Runtime.getRuntime().exec(cmd);
String result = null;
    

BufferedInputStream in = new BufferedInputStream(pcs.getInputStream());
BufferedReader br = new BufferedReader(new InputStreamReader(in));        
System.out.println("\nExecuting python script file now.");
String lineStr = null;
    while ((lineStr = br.readLine()) != null) {
    result = lineStr;
}
br.close();
in.close();
System.out.println("done!");
System.out.println(result);

这是我的python代码：

import sys 
import os
import numpy as np

a = sys.argv[1]
b = sys.argv[2]
print("hello world!")
print("%s * %s = %s"%(a,b,int(a)*int(b)))

如果不包含"import numpy as np“，结果: 10 * 11 = 110

如果包含"import numpy as np“，则结果为空

有什么直观的解释吗？

Answer 1

import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.InputStreamReader;
public class Hello{
  public static void main(String[] args)throws java.io.IOException{
    Process pcs=Runtime.getRuntime().exec("python test.py 8 5");// in linux or unix use python3 or python
    String result=null;
    BufferedInputStream in = new BufferedInputStream(pcs.getInputStream());
    BufferedReader br = new BufferedReader(new InputStreamReader(in));        
    System.out.println("\nExecuting python script file now.");
    String lineStr = null;
    while ((lineStr = br.readLine()) != null) {
      result = lineStr;
    }
    br.close();
    in.close();
    System.out.println("done!");
    System.out.println(result);
  }
 }

java代码

编译：

javac Hello.java

运行：

java Hello

#test.py
import sys 
import os
import numpy as np
a = sys.argv[1]
b = sys.argv[2]
print("hello world!")
print("%s * %s = %s"%(a,b,int(a)*int(b)))

Answer 2

您的应用程序中是否有正确的PYTHONPATH设置？当你的代码中有import numpy as np的时候，你可能会收到一个空的stdout值和一个STDERR格式的ModuleNotFoundError。您可以通过提取STDERR来确认-或者使用以下代码进行检查：

Launch.exe(cmd);

其中，Launch.java是：

public class Launch
{
    /** Launch using FILE redirects */
    public static int exec(String[] cmd) throws InterruptedException, IOException
    {
        System.out.println("exec "+Arrays.toString(cmd));

        Path tmpdir = Path.of(System.getProperty("java.io.tmpdir"));
        ProcessBuilder pb = new ProcessBuilder(cmd);

        Path out = tmpdir.resolve(cmd[0]+"-stdout.log");
        Path err = tmpdir.resolve(cmd[0]+"-stderr.log");
        pb.redirectError(out.toFile());
        pb.redirectOutput(err.toFile());

        Process p = pb.start();
        int rc = p.waitFor();

        System.out.println("Exit "+rc +' '+(rc == 0 ? "OK":"**** ERROR ****")
                          +" STDOUT \""+Files.readString(out)+'"'
                          +" STDERR \""+Files.readString(err)+'"');
        System.out.println();
        return rc;
    }
}

使用numpy的修复方法应该是在调用start()之前访问ProcessBuilder pb.environment()并设置子进程的PYTHONPATH