hotfix/source/openejb-core/src/main/java/org/apache/openejb/core/cmp/cmp2/PostCreateGenerator.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.openejb.core.cmp.cmp2;

import org.apache.xbean.asm.ClassWriter;
import org.apache.xbean.asm.Type;
import org.apache.xbean.asm.MethodVisitor;
import org.apache.xbean.asm.Opcodes;

import java.lang.reflect.Method;
import java.lang.reflect.Modifier;

/**
 * Generate concrete implementations of EjbPostCreatexxx
 * methods for a bean class.  This is implemented in a separate  
 * class because it is used by both the CMP1 and CMP2 generators. 
 * @version $Rev: 1153797 $ $Date: 2011-08-04 02:09:44 -0700 (Thu, 04 Aug 2011) $
 */
public class PostCreateGenerator {
    private final Class beanClass;
    private final ClassWriter cw;

    /**
     * Constructor for a PostCreateGenerator.
     * 
     * @param beanClass The source EJB implementation class (the user
     *                  provided class).
     * @param cw        The ClassWriter instance used for constructing the
     *                  instantiation class.  This has already gone through
     *                  other generation steps, we're implementing additional
     *                  stages of the process.
     */
    public PostCreateGenerator(Class beanClass, ClassWriter cw) {
        this.beanClass = beanClass;
        this.cw = cw;
    }

    
    /**
     * Generate the ejbPostCreatexxxx methods.  Inorder to 
     * be considered for generation, there must A) be a 
     * corresponding ejbCreatexxxx method and B) the 
     * target method must either not exist or exist but be
     * abstract.
     */
    public void generate() {
        // ok, scan the class for the ejbCreate methods and check to see if 
        // we need to provide an ejbPostCreate implementation. 
        for (Method ejbCreate : beanClass.getMethods()) {
            if (!ejbCreate.getName().startsWith("ejbCreate")) 
            {
                continue;
            }

            StringBuilder ejbPostCreateName = new StringBuilder(ejbCreate.getName());
            ejbPostCreateName.replace(0, "ejbC".length(), "ejbPostC");

            // if there is a concrete method here, we just skip this. 
            if (hasMethod(beanClass, ejbPostCreateName.toString(), ejbCreate.getParameterTypes())) {
                continue;
            }
            // we need to generate this method 
            createEjbPostCreate(ejbPostCreateName.toString(), ejbCreate);
        }
    }

    /**
     * Test whether a class provides a concrete implementation 
     * of a class with the given name and parameter types. 
     * 
     * @param beanClass The source implementation class.
     * @param name      The required method name.
     * @param args      The list of argument types.
     * 
     * @return true if the method exists and is NOT abstract.  Returns 
     *         false if the method is not found or IS abstract.
     */
    private boolean hasMethod(Class beanClass, String name, Class... args) {
        try {
            Method method = beanClass.getMethod(name, args);
            return !Modifier.isAbstract(method.getModifiers());
        } catch (NoSuchMethodException e) {
            return false;
        }
    }

    /**
     * Generate an ejbPostCreatexxxx method corresponding 
     * to an ejbCreatexxxx method definition.  These provided 
     * methods are just empty stubs. 
     * 
     * @param ejbPostCreateName
     *                  The name we're creating under.
     * @param ejbCreate The matching ejbCreate method.  The post create method
     *                  will match this one in terms of method signature.
     */
    public void createEjbPostCreate(String ejbPostCreateName, Method ejbCreate) {
        String methodDescriptor = Type.getMethodDescriptor(Type.VOID_TYPE, Type.getArgumentTypes(ejbCreate));
        MethodVisitor mv = cw.visitMethod(Opcodes.ACC_PUBLIC, ejbPostCreateName, methodDescriptor, null, null);
        mv.visitCode();
        mv.visitInsn(Opcodes.RETURN);
        mv.visitMaxs(0, ejbCreate.getParameterTypes().length + 1);
        mv.visitEnd();
    }
}