如何使用ProcessBuilder將值從Python腳本返回到Java？

Question

我試圖使用ProcessBuilder從python腳本獲取返回值到Java。 我期待Java中的值“這就是我要找的東西”。 任何人都可以指出我在下面的邏輯中有什么問題嗎？

我正在使用python3並希望使用java標准庫完成此操作。

test.py代碼

import sys

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


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

Java代碼

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();

產量

Process exit value:0
value is : null

Answer 1

當您從另一個進程生成進程時，它們只能（通常更確切地說）通過其輸入和輸出流進行通信。 因此，您不能指望python中main33（）的返回值到達Java，它將僅在Python運行時環境中終止它的生命。 如果您需要將某些內容發送回Java進程，則需要將其寫入print（）。

修改了你的python和java代碼片段。

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();
    }

Answer 2

你過度使用變量line 。 它不能同時輸出的電流線和迄今所看到的所有行。 添加第二個變量以跟蹤累積的輸出。

String line;
StringBuilder output = new StringBuilder();

while ((line = in.readLine()) != null) {
    output.append(line);
          .append('\n');
}

System.out.println("value is : " + output);