JDK14/Java14源码在线阅读

/*
 * Copyright (c) 2013, 2018, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package jdk.jfr.internal.instrument;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.List;

import jdk.internal.org.objectweb.asm.ClassReader;
import jdk.internal.org.objectweb.asm.ClassVisitor;
import jdk.internal.org.objectweb.asm.ClassWriter;
import jdk.internal.org.objectweb.asm.Opcodes;
import jdk.internal.org.objectweb.asm.tree.ClassNode;
import jdk.jfr.internal.SecuritySupport;
import jdk.jfr.internal.Utils;

/**
 * This class will perform byte code instrumentation given an "instrumentor" class.
 *
 * @see JITracer
 *
 * @author Staffan Larsen
 */
@Deprecated
final class JIClassInstrumentation {
    private final Class<?> instrumentor;
    private final String targetName;
    private final String instrumentorName;
    private final byte[] newBytes;
    private final ClassReader targetClassReader;
    private final ClassReader instrClassReader;

    /**
     * Creates an instance and performs the instrumentation.
     *
     * @param instrumentor instrumentor class
     * @param target target class
     * @param old_target_bytes bytes in target
     *
     * @throws ClassNotFoundException
     * @throws IOException
     */
    JIClassInstrumentation(Class<?> instrumentor, Class<?> target, byte[] old_target_bytes) throws ClassNotFoundException, IOException {
        instrumentorName = instrumentor.getName();
        this.targetName = target.getName();
        this.instrumentor = instrumentor;
        this.targetClassReader = new ClassReader(old_target_bytes);
        this.instrClassReader = new ClassReader(getOriginalClassBytes(instrumentor));
        this.newBytes = makeBytecode();
        Utils.writeGeneratedASM(target.getName(), newBytes);
    }

    private static byte[] getOriginalClassBytes(Class<?> clazz) throws IOException {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        String name = "/" + clazz.getName().replace(".", "/") + ".class";
        InputStream is = SecuritySupport.getResourceAsStream(name);
        int bytesRead;
        byte[] buffer = new byte[16384];
        while ((bytesRead = is.read(buffer, 0, buffer.length)) != -1) {
            baos.write(buffer, 0, bytesRead);
        }
        baos.flush();
        is.close();
        return baos.toByteArray();
    }

    private byte[] makeBytecode() throws IOException, ClassNotFoundException {

        // Find the methods to instrument and inline

        final List<Method> instrumentationMethods = new ArrayList<>();
        for (final Method m : instrumentor.getDeclaredMethods()) {
            JIInstrumentationMethod im = m.getAnnotation(JIInstrumentationMethod.class);
            if (im != null) {
                instrumentationMethods.add(m);
            }
        }

        // We begin by inlining the target's methods into the instrumentor

        ClassNode temporary = new ClassNode();
        ClassVisitor inliner = new JIInliner(
                Opcodes.ASM7,
                temporary,
                targetName,
                instrumentorName,
                targetClassReader,
                instrumentationMethods);
        instrClassReader.accept(inliner, ClassReader.EXPAND_FRAMES);

        // Now we have the target's methods inlined into the instrumentation code (in 'temporary').
        // We now need to replace the target's method with the code in the
        // instrumentation method.

        ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_FRAMES);

/**代码未完, 请加载全部代码(NowJava.com).**/