Calling Python from Java through scripting engine (jython)?

问题

I'm trying to call Jython from a Java 6 application using javax.script:

import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;

public class jythonEx
{
    public static void main (String args[]) throws ScriptException
    {
        ScriptEngineManager mgr = new ScriptEngineManager();
        ScriptEngine pyEngine = mgr.getEngineByName("python");
        try {
            pyEngine.eval("print \"Python - Hello, world!\"");
        } catch (Exception ex) {
            ex.printStackTrace();
        }       
    }
}

This is causing a NullPointerException:

java.lang.NullPointerException
        at jythonEx.main(jythonEx.java:12)

Does anyone have any idea what I'm doing wrong here?

Edit:

Thanks for the responses! I added jython.jar to the classpath and it runs properly:

java -cp "./;jython.jar" jythonEx

回答1:

You have to register your engine first.

From: ScriptEngineManager.getEngineByName:

[...] first searches for a ScriptEngineFactory that has been registered as a handle [...] Returns null if no such factory was found

The user guide says to use it with JSR-223 you have to:

As of Jython 2.5.1 an implementation of JSR 223 is bundled in jython.jar. Simply add jython to your CLASSPATH and ask for the python script engine.

~~Did you do that already?~~

EDIT About your comment: I think you should open a new question, you'll get better answers.

回答2:

You'd probably have to register a ScriptEngineFactory for'python'

来源：https://stackoverflow.com/questions/2671768/calling-python-from-java-through-scripting-engine-jython

标签

java

python

jython

javax.script