通过PlayFramework获取Javassist类

Question

I'm trying to obtain CtClass reference to my model class. I started with simpliest version ClassPool.getDefault().get(className); and it worked fine. But only on my machine. It doesn't work on server.

Anyway i think that the version shouldn't work because Playframework stores classes in tmp/classses. So by now i finished with this version:

ClassPool pool = new ClassPool();
pool.appendClassPath(Play.applicationPath + "/tmp/classes");
CtClass cls = pool.get(className);

But i am not sure about this version. Will it work always? Are there better options?

I also tried using ClassClassPath and LoaderClassPath but without any success.

Answer 1

Usually you should not touch javassist class unless you are writing plugin and need to enhance the application code. in which case, you will have a MyPluginEnhancer extends play.classloading.enhancers.Enhancer , then you can get the javassist class instance by calling makeClass(ApplicationClass appClass) method.

For a workable example, please refer to https://github.com/greenlaw110/play-morphia/blob/master/src/play/modules/morphia/MorphiaEnhancer.java .

PS: About play.classloading.enhancers.Enhancer.makeClass method implementation

/**
 * Construct a javassist CtClass from an application class.
 */
public CtClass makeClass(ApplicationClass applicationClass) throws IOException {
    return classPool.makeClass(new ByteArrayInputStream(applicationClass.enhancedByteCode));
}

Where classPool comes from the following code:

public Enhancer() {
    this.classPool = newClassPool();
}

public static ClassPool newClassPool() {
    ClassPool classPool = new ClassPool();
    classPool.appendSystemPath();
    classPool.appendClassPath(new LoaderClassPath(Enhancer.class.getClassLoader()));
    classPool.appendClassPath(new ApplicationClassesClasspath());
    return classPool;
}