java - 如何使用 ProcessBuilder 将值从 Python 脚本返回到 Java？

Question

我正在尝试使用 ProcessBuilder 将 python 脚本的返回值返回到 Java 中。我期待 Java 中的值“这就是我正在寻找的”。谁能指出以下逻辑有什么问题？

我正在使用 python3 并希望使用 java 标准库完成此操作。

测试.py代码

import sys

def main33():
    return "This is what I am looking for"


if __name__ == '__main__':
    globals()[sys.argv[1]]()

Java代码

String filePath = "D:\\test\\test.py";

ProcessBuilder pb = new ProcessBuilder().inheritIO().command("python", "-u", filePath, "main33");

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

BufferedReader in = new BufferedReader(new InputStreamReader(p.getInputStream()));
String line = "";

line = in.readLine();
while ((line = in.readLine()) != null){
    line = line + line;
}

System.out.println("Process exit value:"+exitCode);
System.out.println("value is : "+line);
in.close();

输出

Process exit value:0
value is : null

Answer 1

当您从另一个进程生成一个进程时，它们只能(主要是)通过它们的输入和输出流进行通信。因此你不能期望 python 中 main33() 的返回值到达 Java，它只会在 Python 运行时环境中结束它的生命。如果您需要将某些内容发送回 Java 进程，您需要将其写入 print()。

修改了你的 python 和 java 代码片段。

import sys
def main33():
    print("This is what I am looking for")

if __name__ == '__main__':
    globals()[sys.argv[1]]()
    #should be 0 for successful exit
    #however just to demostrate that this value will reach Java in exit code
    sys.exit(220)

public static void main(String[] args) throws Exception {       
        String filePath = "D:\\test\\test.py";      
        ProcessBuilder pb = new ProcessBuilder()
            .command("python", "-u", filePath, "main33");        
        Process p = pb.start(); 
        BufferedReader in = new BufferedReader(
            new InputStreamReader(p.getInputStream()));
        StringBuilder buffer = new StringBuilder();     
        String line = null;
        while ((line = in.readLine()) != null){           
            buffer.append(line);
        }
        int exitCode = p.waitFor();
        System.out.println("Value is: "+buffer.toString());                
        System.out.println("Process exit value:"+exitCode);        
        in.close();
    }