Javassist Classpool.get() does not find class when using fully qualified name

Question

I am attempting to get a simple Javassist example going. Consider the following code. Assume variable classPath points to a correct class folder that contains the required .class file.

When running, the first invocation of classPool.get() succeeds and the second fails. The spec of method ClassPool.get() requires a fully-qualified class name. Why is that?

package com.domain.jcp;

import javassist.ClassPool;
import javassist.CtClass;
import javassist.NotFoundException;

public class Jcp  {
    public static void main(String[] args) throws NotFoundException {
        ClassPool classPool = ClassPool.getDefault();
        String classPath = "[CORRECT PATH TRUNK]\\target\\test-classes\\com\\domain\\jcp";
        classPool.insertClassPath(classPath);
        CtClass clazz1 = classPool.get("JcpTest");
        CtClass clazz2 = classPool.get("com.domain.jcp.JcpTest");
    }
}

The folder layout is a standard layout for a Maven project.

Answer 1

You simply need to use the correct classpath. This is wrong, because you are pointing into a package subdirectory rather than straight to the root:

String classPath = "[CORRECT PATH TRUNK]\\target\\test-classes\\com\\domain\\jcp";

This is correct:

String classPath = "[CORRECT PATH TRUNK]\\target\\test-classes";

Then you need to use the fully qualified package name, i.e. of these

CtClass clazz1 = classPool.get("JcpTest");
CtClass clazz2 = classPool.get("com.domain.jcp.JcpTest");

only the latter is correct, while the former is not.

---

Update: Here is what happens if you misunderstand what a Java classpath is:

import javassist.ClassPool;
import javassist.CtClass;
import javassist.NotFoundException;

public class JavassistGetClass {
  private static final String BASE_PATH = "...";

  public static void main(String[] args) throws NotFoundException {
    ClassPool classPool = ClassPool.getDefault();

    // How to correctly use a classpath in Javassist
    String classPath = BASE_PATH + "\\target\\classes";
    classPool.insertClassPath(classPath);
    CtClass ctClass = classPool.get("de.scrum_master.stackoverflow.q70786275.Application");
    System.out.println("Correct package name: " + ctClass.getPackageName());

    // How NOT to use a classpath in Javassist (or anywhere else)
    String classPathIncorrect = BASE_PATH + "\\target\\classes\\de\\scrum_master\\stackoverflow\\q70786275";
    classPool.insertClassPath(classPathIncorrect);
    CtClass ctClassIncorrect = classPool.get("Application");
    System.out.println("Incorrect package name: " + ctClassIncorrect.getPackageName());
  }
}

Console log:

Correct package name: de.scrum_master.stackoverflow.q70786275
Incorrect package name: null