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This jar bundles all the bits of Weld and CDI required for running in a Servlet container.
There is a newer version: 6.0.0.Beta4
/*
 * JBoss, Home of Professional Open Source
 * Copyright 2008, Red Hat, Inc., and individual contributors
 * by the @authors tag. See the copyright.txt in the distribution for a
 * full listing of individual contributors.
 *
 * Licensed 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.jboss.weld.util.bytecode;

import static org.jboss.classfilewriter.util.DescriptorUtils.methodDescriptor;

import java.util.List;

import org.jboss.classfilewriter.AccessFlag;
import org.jboss.classfilewriter.ClassFile;
import org.jboss.classfilewriter.ClassMethod;
import org.jboss.classfilewriter.DuplicateMemberException;
import org.jboss.classfilewriter.code.CodeAttribute;
import org.jboss.weld.bean.proxy.ProxyFactory;

/**
 * Utility class for working with constructors in the low level javassist API
 *
 * @author Stuart Douglas
 */
public class ConstructorUtils {

    private ConstructorUtils() {
    }

    /**
     * adds a constructor that calls super()
     */
    public static void addDefaultConstructor(ClassFile file, List initialValueBytecode, final boolean useUnsafeInstantiators) {
        addConstructor(BytecodeUtils.VOID_CLASS_DESCRIPTOR, new String[0], new String[0], file, initialValueBytecode, useUnsafeInstantiators);
    }

    /**
     * Adds a constructor that delegates to a super constructor with the same
     * descriptor. The bytecode in initialValueBytecode will be executed at the
     * start of the constructor and can be used to initialize fields to a default
     * value. As the object is not properly constructed at this point this
     * bytecode may not reference this (i.e. the variable at location 0)
     *
     * @param returnType           the constructor descriptor
     * @param exceptions           any exceptions that are thrown
     * @param file                 the classfile to add the constructor to
     * @param initialValueBytecode bytecode that can be used to set initial values
     */
    public static void addConstructor(String returnType, String[] params, String[] exceptions, ClassFile file, List initialValueBytecode, final boolean useUnsafeInstantiators) {
        try {

            final String initMethodName = "";
            final ClassMethod ctor = file.addMethod(AccessFlag.PUBLIC, initMethodName, returnType, params);
            ctor.addCheckedExceptions(exceptions);
            final CodeAttribute b = ctor.getCodeAttribute();
            for(final DeferredBytecode iv : initialValueBytecode) {
                iv.apply(b);
            }
            // we need to generate a constructor with a single invokespecial call
            // to the super constructor
            // to do this we need to push all the arguments on the stack first
            // local variables is the number of parameters +1 for this
            // if some of the parameters are wide this may go up.
            b.aload(0);
            b.loadMethodParameters();
            // now we have the parameters on the stack
            b.invokespecial(file.getSuperclass(), initMethodName, methodDescriptor(params, returnType));
            if(!useUnsafeInstantiators) {
                // now set constructed to true
                b.aload(0);
                b.iconst(1);
                b.putfield(file.getName(), ProxyFactory.CONSTRUCTED_FLAG_NAME, BytecodeUtils.BOOLEAN_CLASS_DESCRIPTOR);
            }
            b.returnInstruction();
        }  catch (DuplicateMemberException e) {
            throw new RuntimeException(e);
        }
    }
}