问题描述
我正在尝试制作一个运行 Python 程序的成熟 Java 程序。 python程序如下:
print('Enter two numbers')
a = int(input())
b = int(input())
c = a + b
print(c)
如果我执行这段代码,终端看起来像这样:
Enter two numbers
5
3
8
现在,当从 Java 执行此代码时,我想要相同的输出。这是我的 Java 代码:
import java.io.*;
class RunPython {
public static void main(String[] args) throws IOException {
String program = "print('Enter two numbers')\na = int(input())\nb = int(input())\nc = a + b\nprint(a)\nprint(b)\nprint(c)";
FileWriter fileWriter = new FileWriter("testjava.py");
BufferedWriter bufferedWriter = new BufferedWriter(fileWriter);
bufferedWriter.write(program);
bufferedWriter.close();
Process process = Runtime.getRuntime().exec("python testjava.py");
InputStreamReader inputStreamReader = new InputStreamReader(process.getInputStream());
BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
OutputStreamWriter outputStreamWriter = new OutputStreamWriter(process.getoutputStream());
InputStreamReader read = new InputStreamReader(system.in);
BufferedReader in = new BufferedReader(read);
String output;
while (process.isAlive()) {
while (!bufferedReader.ready());
System.out.println(bufferedReader.ready());
while (!(output = bufferedReader.readLine()).isEmpty()) {
System.out.println(output);
}
bufferedReader.close();
if (process.isAlive()) {
outputStreamWriter.write(in.readLine());
}
}
}
}
但是在运行这个程序时,只显示了第一行,并采用了第一个输入。之后,程序没有响应。 我犯了什么错误?解决办法是什么?
解决方法
处理输入和输出到另一个进程有点乱,你可以阅读 关于如何做到这一点的好答案here
因此,将这些答案应用到您的代码中可能是这样的:
import java.io.*;
import java.util.Scanner;
class RunPython {
public static void main(String[] args) throws IOException {
// String program = "print('Enter two numbers')\na = int(input())\nprint(a)\nb = int(input())\nprint(b)\nc = a + b\nprint(c)";
// If you are using Java 15 or newer you can write code blocks
String program = """
print('Enter first number')
a = int(input())
print(a)
print('Enter second number')
b = int(input())
print(b)
c = a + b
print(c)
""";
FileWriter fileWriter = new FileWriter("testjava.py");
BufferedWriter bufferedWriter = new BufferedWriter(fileWriter);
bufferedWriter.write(program);
bufferedWriter.close();
Process process =
new ProcessBuilder("python","testjava.py")
.redirectErrorStream(true)
.start();
Scanner scan = new Scanner(System.in);
BufferedReader pythonOutput = new BufferedReader(new InputStreamReader(process.getInputStream()));
BufferedWriter pythonInput = new BufferedWriter(new OutputStreamWriter(process.getOutputStream()));
Thread thread = new Thread(() -> {
String input;
while (process.isAlive() && (input = scan.nextLine()) != null) {
try {
pythonInput.write(input);
pythonInput.newLine();
pythonInput.flush();
} catch (IOException e) {
System.out.println(e.getLocalizedMessage());
process.destroy();
System.out.println("Python program terminated.");
}
}
});
thread.start();
String output;
while (process.isAlive() && (output = pythonOutput.readLine()) != null) {
System.out.println(output);
}
pythonOutput.close();
pythonInput.close();
}
}
注意pythonInput是Java中的BufferedWriter,反之亦然 pythonOutput 是一个 BufferedReader。
,使用Process
:
Process p = new ProcessBuilder(
"python","myScript.py","firstargument Custom input to a Python program from a Java program"
).start();
您可以在运行时添加任意数量的参数。
使用 Jython(更简单的选项):
//Java code implementing Jython and calling your python_script.py
import org.python.util.PythonInterpreter;
import org.python.core.*;
public class ImportExample {
public static void main(String [] args) throws PyException
{
PythonInterpreter pi = new PythonInterpreter();
pi.execfile("path_to_script\\main.py");
pi.exec("Any custom input from this java program in python to be run");
}
}
其中嵌入了 Jython 并且可以阅读有关 here 的信息。
注意:如果您想使用已安装的任何软件包,您可能需要使用 python.path
初始化您的解释器。您可以通过在已经给出的代码上方添加以下代码来实现:
Properties properties = System.getProperties();
properties.put("python.path",".\\src\\test\\resources"); // example of path to custom modules (you change this to where the custom modules you would want to import are)
PythonInterpreter.initialize(System.getProperties(),properties,new String[0]);
如果您需要反过来,您也可以返回值,这可以在 Jython documentation