print java object header

ObjectHeaderUtil.java

import sun.misc.Unsafe;

import java.lang.reflect.Field;

public class ObjectHeaderUtil {
    private static Unsafe getUnsafe() throws Exception {
        Class<?> unsafeClass = Class.forName("sun.misc.Unsafe");
        Field field = unsafeClass.getDeclaredField("theUnsafe");
        field.setAccessible(true);
        return  (Unsafe) field.get(null);
    }
    private static void printLockHeader(Object obj) throws Exception {
        Unsafe us = getUnsafe();
        StringBuilder sb = new StringBuilder();
        int status = us.getByte(obj, 0L) & 0B11;
        // 0 轻量级 1 无锁或偏向 2 重量级 3 GC标记
        switch (status){
            case 0:
                // ptr_to_lock_record:62|lock:2
                long ptrToLockRecord =
                        (byteMod(us.getByte(obj, 0L))>>2) +
                                (byteMod(us.getByte(obj, 1L))<<6) +
                                (byteMod(us.getByte(obj, 2L))<<14) +
                                (byteMod(us.getByte(obj, 3L))<<22) +
                                (byteMod(us.getByte(obj, 4L))<<30) +
                                (byteMod(us.getByte(obj, 5L))<<38) +
                                (byteMod(us.getByte(obj, 6L))<<46) +
                                (byteMod(us.getByte(obj, 7L))<<54);
                sb.append("锁状态：轻量级锁，LockRecord地址：")
                        .append(Long.toHexString(ptrToLockRecord))
                ;
                break;
            case 1:
                boolean biased = (us.getByte(obj, 0L)&4) == 4;
                if(!biased){
                    // unused:25 | identity_hashcode:31 | unused:1 | age:4 | biased_lock:1 | lock:2
                    int hashCode = (int)(byteMod(us.getByte(obj, 1L))
                            + (byteMod(us.getByte(obj, 2L))<<8)
                            + (byteMod(us.getByte(obj, 3L))<<16)
                            + ((byteMod(us.getByte(obj, 4L))&Integer.MAX_VALUE) <<24))
                            ;
                    int age = (us.getByte(obj,0L)>>3)&0B1111;
                    sb.append("锁状态：无锁，hashCode：")
                            .append(hashCode)
                            .append(",age: ")
                            .append(age);
                }else{
                    //thread:54|epoch:2|unused:1| age:4 | biased_lock:1 | lock:2
                    long thread = (byteMod(us.getByte(obj, 1L))>>2) +
                            (byteMod(us.getByte(obj, 2L))<<6) +
                            (byteMod(us.getByte(obj, 3L))<<14) +
                            (byteMod(us.getByte(obj, 4L))<<22) +
                            (byteMod(us.getByte(obj, 5L))<<30) +
                            (byteMod(us.getByte(obj, 6L))<<38) +
                            (byteMod(us.getByte(obj, 7L))<<46);
                    ;
                    int epoch = us.getByte(obj, 1L) & 0B11;
                    int age = (us.getByte(obj,0L)>>3)&0B1111;
                    sb.append("锁状态：偏向锁，thread：")
                            .append(thread)
                            .append(",epoch: ")
                            .append(epoch)
                            .append(",age: ")
                            .append(age);
                }
                break;
            case 2:
                // ptr_to_heavyweight_monitor:62| lock:2
                long ptrToMonitor =
                        (byteMod(us.getByte(obj, 0L))>>2) +
                                (byteMod(us.getByte(obj, 1L))<<6) +
                                (byteMod(us.getByte(obj, 2L))<<14) +
                                (byteMod(us.getByte(obj, 3L))<<22) +
                                (byteMod(us.getByte(obj, 4L))<<30) +
                                (byteMod(us.getByte(obj, 5L))<<38) +
                                (byteMod(us.getByte(obj, 6L))<<46) +
                                (byteMod(us.getByte(obj, 7L))<<54);
                sb.append("锁状态：重量级锁，Monitor地址：")
                        .append(Long.toHexString(ptrToMonitor))
                ;
                break;
            case 3:
                sb.append("锁状态：GC标记");
                break;
            default:
                break;
        }
        if(obj instanceof Object[]){
            int arrLen = us.getInt(obj, 3L);
            sb.append("对象为数组类型，数组长度:")
                    .append(arrLen);
        }
        sb.append("\n").append("---------------").append("\n");
        System.out.println(sb.toString());
    }
    private static long byteMod(byte b){
        if(b>=0){
            return b;
        }
        return b + 256;
    }
}