How to execute Python script from Java?

Question

I can execute Linux commands like ls or pwd from Java without problems but couldn\'t get a Python script executed.

This is my code:

Answer 1

First, open terminal and type "which python3". You will get the complete path of python3. For example "/usr/local/bin/python3"

String[] cmd = {"/usr/local/bin/python3", "arg1", "arg2"};
Process p = Runtime.getRuntime().exec(cmd);
p.waitFor();

String line = "", output = "";
StringBuilder sb = new StringBuilder();

BufferedReader br = new BufferedReader(new InputStreamReader(p.getInputStream()));
while ((line = br.readLine())!= null) {sb = sb.append(line).append("\n"); }

output = sb.toString();
System.out.println(output);

Answer 2

@Alper's answer should work. Better yet, though, don't use a shell script and redirection at all. You can write the password directly to the process' stdin using the (confusingly named) Process.getOutputStream().

Process p = Runtime.exec(
    new String[]{"python", "script.py", packet.toString()});

BufferedWriter writer = new BufferedWriter(
    new OutputStreamWriter(p.getOutputStream()));

writer.write("password");
writer.newLine();
writer.close();

Answer 3

You would do worse than to try embedding jython and executing your script. A simple example should help:

ScriptEngine engine = new ScriptEngineManager().getEngineByName("python");

// Using the eval() method on the engine causes a direct
// interpretataion and execution of the code string passed into it
engine.eval("import sys");
engine.eval("print sys");

If you need further help, leave a comment. This does not create an additional process.

Answer 4

You cannot use the PIPE inside the Runtime.getRuntime().exec() as you do in your example. PIPE is part of the shell.

You could do either

• Put your command to a shell script and execute that shell script with .exec() or

• You can do something similar to the following

  String[] cmd = {
          "/bin/bash",
          "-c",
          "echo password | python script.py '" + packet.toString() + "'"
      };
  Runtime.getRuntime().exec(cmd);