JavassistVerifyError.java

package com.stackoverflow;

import javassist.*;

public class JavassistVerifyError {

    public interface Domain {
        Integer getIdentifier();
        Object getColumnByIndex(int i);
    }

    public static void main(final String[] args) throws NotFoundException, CannotCompileException, InstantiationException, IllegalAccessException {

        final ClassPool pool = ClassPool.getDefault();
        final CtClass cc = pool.makeClass("Person");
        cc.addInterface(resolveCtClass(Domain.class));

        final CtField idField = new CtField(resolveCtClass(Integer.class), "id", cc);
        final CtMethod idGetter = CtNewMethod.getter("getId", idField);
        final CtMethod idSetter = CtNewMethod.setter("setId", idField);
        cc.addField(idField);
        cc.addMethod(idGetter);
        cc.addMethod(idSetter);

        final CtField firstNameField = new CtField(resolveCtClass(String.class), "firstName", cc);
        final CtMethod firstNameGetter = CtNewMethod.getter("getFirstName", firstNameField);
        final CtMethod firstNameSetter = CtNewMethod.setter("setFirstName", firstNameField);
        cc.addField(firstNameField);
        cc.addMethod(firstNameSetter);
        cc.addMethod(firstNameGetter);

        final CtMethod getIdentifier = CtNewMethod.make("public Integer getIdentifier () { return id; }", cc);
        cc.addMethod(getIdentifier);


        final CtMethod getColumnByIndex = CtNewMethod.make(
                "public Object getColumnByIndex(int i) {"
                        +   "switch (i) {"
                        +       "case 0:"
                        +           "return id;"
                        +       "case 1:"
                        +           "return firstName;"
                        +       "default: "
                        +           "throw new IllegalArgumentException(\"Tried getting column index i, but this column index does not exist\");"
                        +   "}"
                        + "}"
                , cc);

        cc.addMethod(getColumnByIndex);
        final Class<?> dynamicClass = cc.toClass();

        final Domain domainImpl = (Domain) dynamicClass.newInstance();
        System.out.println(domainImpl.getIdentifier());
        System.out.println(domainImpl.getColumnByIndex(0));
    }

    private static CtClass resolveCtClass(final Class<?> clazz) throws NotFoundException {
        final ClassPool pool = ClassPool.getDefault();
        return pool.get(clazz.getName());
    }
}