jmap -heap

根据引用[1]中的jmap语法格式，jmap -heap命令可以用于打印Java进程的堆信息。具体来说，它将打印出Java堆的配置和使用情况，包括堆的总容量、已使用的容量、可用的容量等信息。以下是一个示例：

jmap -heap 12345

其中，12345是Java进程的PID。执行上述命令后，将会输出类似以下的信息：

Attaching to process ID 12345, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.191-b12

using thread-local object allocation.
Parallel GC with 4 thread(s)

Heap Configuration:
   MinHeapFreeRatio = 0
   MaxHeapFreeRatio = 100
   MaxHeapSize      = 2147483648 (2048.0MB)
   NewSize          = 1363144 (1.2999954223632812MB)
   MaxNewSize       = 17592186044415 MB
   OldSize          = 5452592 (5.1999969482421875MB)
   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 = 536870912 (512.0MB)
   used     = 0 (0.0MB)
   free     = 536870912 (512.0MB)
   0.0% used
From Space:
   capacity = 0 (0.0MB)
   used     = 0 (0.0MB)
   free     = 0 (0.0MB)
   0.0% used
To Space:
   capacity = 0 (0.0MB)
   used     = 0 (0.0MB)
   free     = 0 (0.0MB)
   0.0% used
PS Old Generation
   capacity = 1073741824 (1024.0MB)
   used     = 0 (0.0MB)
   free     = 1073741824 (1024.0MB)
   0.0% used

...

以上输出中包含了Java堆的配置和使用情况，以及Young Generation和Old Generation的使用情况等信息。