GenerateMoreNotPerfectBytecode.java

/*
 * Copyright 2016 the original author or authors.
 *
 * 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.glowroot.agent.weaving;

import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Type;

import org.glowroot.agent.weaving.ClassLoaders.LazyDefinedClass;

import static org.objectweb.asm.Opcodes.ACC_PUBLIC;
import static org.objectweb.asm.Opcodes.ACC_SUPER;
import static org.objectweb.asm.Opcodes.ALOAD;
import static org.objectweb.asm.Opcodes.ATHROW;
import static org.objectweb.asm.Opcodes.DUP;
import static org.objectweb.asm.Opcodes.INVOKESPECIAL;
import static org.objectweb.asm.Opcodes.RETURN;
import static org.objectweb.asm.Opcodes.V1_6;

public class GenerateMoreNotPerfectBytecode {

    static LazyDefinedClass generateMoreNotPerfectBytecode(boolean variant) throws Exception {

        ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_MAXS);
        MethodVisitor mv;

        cw.visit(V1_6, ACC_PUBLIC + ACC_SUPER, "MoreNotPerfectBytecode", null, "java/lang/Object",
                new String[] {Test.class.getName().replace('.', '/')});

        {
            mv = cw.visitMethod(ACC_PUBLIC, "<init>", "()V", null, null);
            mv.visitCode();
            mv.visitVarInsn(ALOAD, 0);
            mv.visitMethodInsn(INVOKESPECIAL, "java/lang/Object", "<init>", "()V", false);
            mv.visitInsn(RETURN);
            mv.visitMaxs(0, 0);
            mv.visitEnd();
        }
        {
            mv = cw.visitMethod(ACC_PUBLIC, "execute", "()V", null, null);
            mv.visitCode();
            mv.visitInsn(RETURN);
            if (variant) {
                mv.visitInsn(DUP);
            } else {
                mv.visitInsn(ATHROW);
            }
            mv.visitMaxs(0, 0);
            mv.visitEnd();
        }
        cw.visitEnd();

        return ImmutableLazyDefinedClass.builder()
                .type(Type.getObjectType("MoreNotPerfectBytecode"))
                .bytes(cw.toByteArray())
                .build();
    }

    public interface Test {
        void execute();
    }
}