C:UsersAdministrator>jmap -help
Usage:
    jmap [option] <pid>
        (to connect to running process)
    jmap [option] <executable <core>
        (to connect to a core file)
    jmap [option] [server_id@]<remote server IP or hostname>
        (to connect to remote debug server)
 
where <option> is one of:
    <none>               to print same info as Solaris pmap
    -heap                to print java heap summary
    -histo[:live]        to print histogram of java object heap; if the "live"
                         suboption is specified, only count live objects
    -clstats             to print class loader statistics
    -finalizerinfo       to print information on objects awaiting finalization
    -dump:<dump-options> to dump java heap in hprof binary format
                         dump-options:
                           live         dump only live objects; if not specified,
                                        all objects in the heap are dumped.
                           format=b     binary format
                           file=<file>  dump heap to <file>
                         Example: jmap -dump:live,format=b,file=heap.bin <pid>
    -F                   force. Use with -dump:<dump-options> <pid> or -histo
                         to force a heap dump or histogram when <pid> does not
                         respond. The "live" suboption is not supported
                         in this mode.
    -h | -help           to print this help message
    -J<flag>             to pass <flag> directly to the runtime system

[root@wkp ~]# jmap -heap 3177
Attaching to process ID 3177, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 24.80-b11
 
using thread-local object allocation.
Parallel GC with 2 thread(s)
 
Heap Configuration:
   MinHeapFreeRatio = 0
   MaxHeapFreeRatio = 100
   MaxHeapSize      = 2099249152 (2002.0MB)
   NewSize          = 1310720 (1.25MB)
   MaxNewSize       = 17592186044415 MB
   OldSize          = 5439488 (5.1875MB)
   NewRatio         = 2
   SurvivorRatio    = 8
   PermSize         = 21757952 (20.75MB)
   MaxPermSize      = 85983232 (82.0MB)
   G1HeapRegionSize = 0 (0.0MB)
 
Heap Usage:
PS Young Generation
Eden Space:
   capacity = 371720192 (354.5MB)
   used     = 330326552 (315.0239486694336MB)
   free     = 41393640 (39.476051330566406MB)
   88.86430145823232% used
From Space:
   capacity = 5242880 (5.0MB)
   used     = 5073520 (4.8384857177734375MB)
   free     = 169360 (0.1615142822265625MB)
   96.76971435546875% used
To Space:
   capacity = 47710208 (45.5MB)
   used     = 0 (0.0MB)
   free     = 47710208 (45.5MB)
   0.0% used
PS Old Generation
   capacity = 159383552 (152.0MB)
   used     = 113434496 (108.1795654296875MB)
   free     = 45949056 (43.8204345703125MB)
   71.17076673005757% used
PS Perm Generation
   capacity = 42991616 (41.0MB)
   used     = 42852648 (40.867469787597656MB)
   free     = 138968 (0.13253021240234375MB)
   99.67675557950648% used
 
19120 interned Strings occupying 2253456 bytes.

[root@wkp ~]# jmap -heap 8543
Attaching to process ID 8543, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.171-b11
 
using thread-local object allocation.
Parallel GC with 4 thread(s)
 
Heap Configuration:
   MinHeapFreeRatio         = 0
   MaxHeapFreeRatio         = 100
   MaxHeapSize              = 2051014656 (1956.0MB)
   NewSize                  = 42991616 (41.0MB)
   MaxNewSize               = 683671552 (652.0MB)
   OldSize                  = 87031808 (83.0MB)
   NewRatio                 = 2
   SurvivorRatio            = 8
   MetaspaceSize            = 21807104 (20.796875MB)
   CompressedClassSpaceSize = 1073741824 (1024.0MB)
   MaxMetaspaceSize         = 17592186044415 MB
   G1HeapRegionSize         = 0 (0.0MB)
 
Heap Usage:
PS Young Generation
Eden Space:
   capacity = 28311552 (27.0MB)
   used     = 13137328 (12.528732299804688MB)
   free     = 15174224 (14.471267700195312MB)
   46.402712221498845% used
From Space:
   capacity = 524288 (0.5MB)
   used     = 98304 (0.09375MB)
   free     = 425984 (0.40625MB)
   18.75% used
To Space:
   capacity = 524288 (0.5MB)
   used     = 0 (0.0MB)
   free     = 524288 (0.5MB)
   0.0% used
PS Old Generation
   capacity = 76021760 (72.5MB)
   used     = 27335480 (26.06914520263672MB)
   free     = 48686280 (46.43085479736328MB)
   35.957441658809266% used
 
24117 interned Strings occupying 2830304 bytes.

[root@wkp ~]# jmap -dump:live,format=b,file=/usr/local/heap.hprof 12632
Dumping heap to /usr/local/heap.hprof ...
Heap dump file created

@RestController
public class MemoryController {
	
	private List<User> userList = new ArrayList<User>();
 
	/**
	 *-Xmx32M -Xms32M -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=./
	 */
	@GetMapping("/heap")
	public String heap() {
		int i=0;
		 while(true){
			 userList.add(new User(i++, UUID.randomUUID().toString()));
		 }
	}
}

public class User {
	private int id;
	private String name;
	
	public User(int id, String name) {
		super();
		this.id = id;
		this.name = name;
	}
	//省略set,get方法
}

transient Object[] elementData; // non-private to simplify nested class access
/**
  * Constructs an empty list with an initial capacity of ten.
 */
public ArrayList() {
    this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
}