并发王者课 - 青铜 6：借花献佛 - 如何格式化 Java 内存工具 JOL 输出

import org.openjdk.jol.info.ClassLayout;
import java.nio.ByteOrder;import java.util.ArrayList;import java.util.Collections;import java.util.List;import java.util.regex.Matcher;import java.util.regex.Pattern;
public class PrintObjectHeader {    /**     * Get binary data     *     * @param o     * @return     */    public static String getObjectHeader(Object o) {        ByteOrder order = ByteOrder.nativeOrder();//Byte order        String table = ClassLayout.parseInstance(o).toPrintable();        Pattern p = Pattern.compile("(0|1){8}");        Matcher matcher = p.matcher(table);        List<String> header = new ArrayList<String>();        while (matcher.find()) {            header.add(matcher.group());        }        //Little-endian machines, need to traverse in reverse        StringBuilder sb = new StringBuilder();        if (order.equals(ByteOrder.LITTLE_ENDIAN)) {            Collections.reverse(header);        }        for (String s : header) {            sb.append(s).append(" ");        }        return sb.toString().trim();    }
    /**     * Parsing object header function for 64bit jvm     * In 64bit jvm, the object header has two parts: Mark Word and Class Pointer, Mark Word takes 8 bytes, Class Pointer takes 4 bytes     *     * @param s Binary string of object header (each 8 bits, separated by a space)     */    public static void parseObjectHeader(String s) {        String[] tmp = s.split(" ");        System.out.print("Class Pointer: ");        for (int i = 0; i < 4; ++i) {            System.out.print(tmp[i] + " ");        }        System.out.println("\nMark Word:");        if (tmp[11].charAt(5) == '0' && tmp[11].substring(6).equals("01")) {//0 01 lock-free state, regardless of GC mark            //notice: Mark word structure without lock: unused(25bit) + hashcode(31bit) + unused(1bit) + age(4bit) + biased_lock_flag(1bit) + lock_type(2bit)            // The reason why hashcode only needs 31bit is: hashcode can only be greater than or equal to 0, eliminating the negative range, so you can use 31bit to store            System.out.print("\thashcode (31bit): ");            System.out.print(tmp[7].substring(1) + " ");            for (int i = 8; i < 11; ++i) System.out.print(tmp[i] + " ");            System.out.println();        } else if (tmp[11].charAt(5) == '1' && tmp[11].substring(6).equals("01")) {//1 01, which is the case of biased lock            //notice: The object is in a biased lock, its structure is: ThreadID(54bit) + epoch(2bit) + unused(1bit) + age(4bit) + biased_lock_flag(1bit) + lock_type(2bit)            // ThreadID here is the thread ID holding the biased lock, epoch: a timestamp of the biased lock, used for optimization of the biased lock            System.out.print("\tThreadID(54bit): ");            for (int i = 4; i < 10; ++i) System.out.print(tmp[i] + " ");            System.out.println(tmp[10].substring(0, 6));            System.out.println("\tepoch: " + tmp[10].substring(6));        } else {//In the case of lightweight locks or heavyweight locks, regardless of the GC mark            //notice: JavaThread*(62bit,include zero padding) + lock_type(2bit)            // At this point, JavaThread* points to the monitor of the lock record/heavyweight lock in the stack            System.out.print("\tjavaThread*(62bit,include zero padding): ");            for (int i = 4; i < 11; ++i) System.out.print(tmp[i] + " ");            System.out.println(tmp[11].substring(0, 6));            System.out.println("\tLockFlag (2bit): " + tmp[11].substring(6));            System.out.println();            return;        }        System.out.println("\tage (4bit): " + tmp[11].substring(1, 5));        System.out.println("\tbiasedLockFlag (1bit): " + tmp[11].charAt(5));        System.out.println("\tLockFlag (2bit): " + tmp[11].substring(6));
        System.out.println();    }
    public static void printObjectHeader(Object o) {        if (o == null) {            System.out.println("null object.");            return;        }        parseObjectHeader(getObjectHeader(o));    }}