準(zhǔn)備一個(gè)測(cè)試類

package demo;

import java.util.HashMap;
import java.util.Map;

/**
 * @author shawn
 */
public class TestDump {
    /**
     * 聲明緩存對(duì)象
     */
    private static final Map<String, Object> TEST_MAP = new HashMap<>();

    public static void main(String[] args) {
        try {
            Thread.sleep(10000);

            //循環(huán)添加對(duì)象到緩存
            for (int i = 0; i < 4000000; i++) {
                Person t = new Person();
                TEST_MAP.put("key" + i, t);
            }
            Thread.sleep(Integer.MAX_VALUE);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

class Person {
    public String name = "shawn";
    public String address = "深圳";
}

執(zhí)行jmap命令

jmap -dump:format=b,file=demo.dump 15820

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使用jvisualvm進(jìn)行分析

文件->裝入 dump文件

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可以看到person類占用內(nèi)存

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person類被hashmap裝入了
點(diǎn)擊查看實(shí)例

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點(diǎn)擊大小排序

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可以看到引用的類的類型，就可以定位到相應(yīng)代碼位置分析

jstack pid命令

>jstack 20868
2021-03-11 15:58:56
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.201-b09 mixed mode):

"Service Thread" #13 daemon prio=9 os_prio=0 tid=0x000000001e7aa800 nid=0x5e64 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C1 CompilerThread3" #12 daemon prio=9 os_prio=2 tid=0x000000001e753000 nid=0x4ec0 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread2" #11 daemon prio=9 os_prio=2 tid=0x000000001e750000 nid=0x5810 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread1" #10 daemon prio=9 os_prio=2 tid=0x000000001e749000 nid=0x5d54 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread0" #9 daemon prio=9 os_prio=2 tid=0x000000001e746000 nid=0x34a0 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"JDWP Command Reader" #8 daemon prio=10 os_prio=0 tid=0x000000001e6c6000 nid=0x21c0 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"JDWP Event Helper Thread" #7 daemon prio=10 os_prio=0 tid=0x000000001e6c2800 nid=0x1328 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"JDWP Transport Listener: dt_socket" #6 daemon prio=10 os_prio=0 tid=0x000000001e6b7800 nid=0x423c runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Attach Listener" #5 daemon prio=5 os_prio=2 tid=0x000000001e658000 nid=0x4e04 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Signal Dispatcher" #4 daemon prio=9 os_prio=2 tid=0x000000001e657000 nid=0x55d8 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Finalizer" #3 daemon prio=8 os_prio=1 tid=0x000000001c85e000 nid=0x5b9c in Object.wait() [0x000000001ec1f000]
   java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x00000006c979bc60> (a java.lang.ref.ReferenceQueue$Lock)
        at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:144)
        - locked <0x00000006c979bc60> (a java.lang.ref.ReferenceQueue$Lock)
        at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:165)
        at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:216)

"Reference Handler" #2 daemon prio=10 os_prio=2 tid=0x000000001e640800 nid=0x2d28 in Object.wait() [0x000000001eb1f000]
   java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x00000006c979bca0> (a java.lang.ref.Reference$Lock)
        at java.lang.Object.wait(Object.java:502)
        at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
        - locked <0x00000006c979bca0> (a java.lang.ref.Reference$Lock)
        at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)

"main" #1 prio=5 os_prio=0 tid=0x0000000002e43800 nid=0x51f8 waiting on condition [0x0000000002c6f000]
   java.lang.Thread.State: TIMED_WAITING (sleeping)
        at java.lang.Thread.sleep(Native Method)
        at demo.TestDump.main(TestDump.java:24)

"VM Thread" os_prio=2 tid=0x000000001c859800 nid=0x1ba4 runnable

"GC task thread#0 (ParallelGC)" os_prio=0 tid=0x0000000002e59000 nid=0x5118 runnable

"GC task thread#1 (ParallelGC)" os_prio=0 tid=0x0000000002e5a800 nid=0xa54 runnable

"GC task thread#2 (ParallelGC)" os_prio=0 tid=0x0000000002e5c000 nid=0x5ca4 runnable

"GC task thread#3 (ParallelGC)" os_prio=0 tid=0x0000000002e5d800 nid=0x4200 runnable

"GC task thread#4 (ParallelGC)" os_prio=0 tid=0x0000000002e61000 nid=0x3a50 runnable

"GC task thread#5 (ParallelGC)" os_prio=0 tid=0x0000000002e62000 nid=0x4f90 runnable

"GC task thread#6 (ParallelGC)" os_prio=0 tid=0x0000000002e65000 nid=0x4850 runnable

"GC task thread#7 (ParallelGC)" os_prio=0 tid=0x0000000002e66800 nid=0x5ae8 runnable

"VM Periodic Task Thread" os_prio=2 tid=0x000000001e7ae800 nid=0x5124 waiting on condition

JNI global references: 1476

重點(diǎn)關(guān)注線程狀態(tài)

runnable：運(yùn)行中狀態(tài)，在虛擬機(jī)內(nèi)部執(zhí)行，可能已經(jīng)獲取到了鎖，可以觀察是否有l(wèi)ocked字樣。
blocked：被阻塞并等待鎖的釋放。
wating：處于等待狀態(tài)，等待特定的操作被喚醒，一般停留在park(), wait(), sleep(),join() 等語(yǔ)句里。
time_wating：有時(shí)限的等待另一個(gè)線程的特定操作。
terminated：線程已經(jīng)退出。

"main" #1 prio=5 os_prio=0 tid=0x0000000002e43800 nid=0x51f8 waiting on condition [0x0000000002c6f000]
   java.lang.Thread.State: TIMED_WAITING (sleeping)
        at java.lang.Thread.sleep(Native Method)
        at demo.TestDump.main(TestDump.java:24)

名稱為‘main’的線程當(dāng)前處于等待狀態(tài)，休眠時(shí)間結(jié)束后將自動(dòng)喚醒