java实现内存调试与诊断的示例代码

// ==============================
// 文件：MemoryAgent.java
// 包名：com.debugger.memory
// 功能：Java Agent 入口，注册字节码增强
// ==============================
package com.debugger.memory;
 
import java.lang.instrument.Instrumentation;
 
public class MemoryAgent {
    public static void premain(String agentArgs, Instrumentation inst) {
        System.out.println("[MemoryDebugger] Agent start with args: " + agentArgs);
        // 注册字节码转换器
        inst.addTransformer(new MemoryClassFileTransformer());
        // 初始化 GC 监听
        MemoryDebugger.initGCListener();
        // 初始化数据缓冲区和快照 MBean
        MemoryDebugger.initDataCollector();
    }
}
 
// ==============================
// 文件：MemoryClassFileTransformer.java
// 包名：com.debugger.memory
// 功能：对类字节码进行增强，拦截对象分配
// ==============================
package com.debugger.memory;
 
import java.lang.instrument.ClassFileTransformer;
import java.security.ProtectionDomain;
import org.objectweb.asm.*;
 
public class MemoryClassFileTransformer implements ClassFileTransformer {
    @Override
    public byte[] transform(
        ClassLoader loader, String className, Class<?> classBeingRedefined,
        ProtectionDomain pd, byte[] classfileBuffer) {
        // 仅增强业务包下的类，排除 JVM、第三方库
        if (className == null || !className.startsWith("com/myapp")) {
            return classfileBuffer;
        }
        ClassReader cr = new ClassReader(classfileBuffer);
        ClassWriter cw = new ClassWriter(cr, ClassWriter.COMPUTE_MAXS);
        ClassVisitor cv = new ClassVisitor(Opcodes.ASM9, cw) {
            @Override
            public MethodVisitor visitMethod(
                int access, String name, String desc, String signature, String[] exceptions) {
                MethodVisitor mv = super.visitMethod(access, name, desc, signature, exceptions);
                return new MemoryMethodVisitor(Opcodes.ASM9, mv);
            }
        };
        cr.accept(cv, 0);
        return cw.toByteArray();
    }
}
 
// ==============================
// 文件：MemoryMethodVisitor.java
// 包名：com.debugger.memory
// 功能：拦截 NEW 指令，插入监控调用
// ==============================
package com.debugger.memory;
 
import org.objectweb.asm.*;
 
public class MemoryMethodVisitor extends MethodVisitor {
    public MemoryMethodVisitor(int api, MethodVisitor mv) {
        super(api, mv);
    }
 
    @Override
    public void visitTypeInsn(int opcode, String type) {
        // 对 NEW 操作插桩
        if (opcode == Opcodes.NEW) {
            mv.visitInsn(Opcodes.DUP);
            mv.visitTypeInsn(Opcodes.NEW, type);
            mv.visitInsn(Opcodes.DUP);
            // 调用监控方法
            mv.visitMethodInsn(
                Opcodes.INVOKESTATIC,
                "com/debugger/memory/MemoryDebugger",
                "onObjectAllocate",
                "(Ljava/lang/Object;)V",
                false
            );
        } else {
            super.visitTypeInsn(opcode, type);
        }
    }
}
 
// ==============================
// 文件：MemoryDebugger.java
// 包名：com.debugger.memory
// 功能：核心监控逻辑，包括分配记录与 GC 回调
// ==============================
package com.debugger.memory;
 
import java.lang.management.*;
import java.util.*;
import javax.management.*;
import com.sun.management.GarbageCollectionNotificationInfo;
import java.util.concurrent.*;
 
public class MemoryDebugger {
    // 环形缓冲区存储分配记录
    private static final int BUFFER_SIZE = 1 << 20;
    private static final RingBuffer<Record> buffer = new RingBuffer<>(BUFFER_SIZE);
 
    public static void initGCListener() {
        // 注册 GC 通知监听
        for (GarbageCollectorMXBean gcBean : ManagementFactory.getGarbageCollectorMXBeans()) {
            if (gcBean instanceof NotificationEmitter) {
                NotificationEmitter emitter = (NotificationEmitter) gcBean;
                emitter.addNotificationListener((notif, handback) -> {
                    // 处理 GC 开始/结束事件
                    MemoryDebugger.onGCEvent(notif);
                }, null, null);
            }
        }
    }
 
    public static void initDataCollector() {
        // 注册 JMX MBean，用于触发快照
        try {
            MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();
            ObjectName name = new ObjectName("com.debugger.memory:type=DataCollector");
            mbs.registerMBean(new DataCollector(), name);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
 
    public static void onObjectAllocate(Object obj) {
        // 采样：仅记录指定包或大对象
        String className = obj.getClass().getName();
        long size = getObjectSize(obj);
        Record r = new Record(
            Thread.currentThread().getName(),
            className,
            System.nanoTime(),
            size,
            getStackTrace(5)
        );
        buffer.put(r);
    }
 
    private static long getObjectSize(Object obj) {
        // 通过 Instrumentation 获取对象大小（需在 Agent 中传入）
        return InstrumentationHolder.getInstrumentation().getObjectSize(obj);
    }
 
    private static String[] getStackTrace(int depth) {
        StackTraceElement[] st = Thread.currentThread().getStackTrace();
        String[] arr = new String[Math.min(depth, st.length - 2)];
        for (int i = 2; i < arr.length + 2; i++) {
            arr[i - 2] = st[i].toString();
        }
        return arr;
    }
 
    public static void onGCEvent(javax.management.Notification notif) {
        // GC 事件解析
        CompositeData cd = (CompositeData) notif.getUserData();
        GarbageCollectionNotificationInfo info = GarbageCollectionNotificationInfo.from(cd);
        // 解析 GC 信息并输出报告或关联分配记录
        GCRecord rec = new GCRecord(info.getGcAction(), info.getGcName(),
            info.getGcInfo().getId(), info.getGcInfo().getDuration(),
            info.getGcInfo().getMemoryUsageBeforeGc(),
            info.getGcInfo().getMemoryUsageAfterGc(),
            System.nanoTime());
        buffer.put(rec);
    }
 
    // 省略其他辅助类与方法，如 Record、GCRecord、RingBuffer、DataCollector MBean
}
 
// ==============================
// 文件：DataCollector.java
// 包名：com.debugger.memory
// 功能：JMX MBean，用于触发内存快照
// ==============================
package com.debugger.memory;
 
public class DataCollector implements DataCollectorMBean {
    @Override
    public void takeSnapshot() {
        MemoryReport.generateReport();  // 导出 JSON/HTML 报告
    }
}
 
// ==============================
// 文件：MemoryReport.java
// 包名：com.debugger.memory
// 功能：生成内存调试报告
// ==============================
package com.debugger.memory;
 
import java.io.*;
import java.util.*;
import freemarker.template.*;
 
public class MemoryReport {
    public static void generateReport() {
        List<Record> records = RingBuffer.drainAll();
        // 用 FreeMarker 渲染模板，生成 HTML 报告
        // 模板包含 TopN 分配类、存活时间分布直方图、GC 关联分析
        // 省略具体实现
    }
}