如何从Java YoungGen和OldGen中获取？

Question

如何从Java获取以下YoungGen（Eden，Survivor0，Survivor1），OldGen区域的已分配和空闲内存的值？

我看到tomcat页面显示了这个信息，我如何从java代码中获取它？

关于maxMemory()，，，我知道，但并不完全清楚如何获取确切的totalMemory()内存freeMemory()区域的值，例如Tomcat。

Answer 1

您可以使用管理 API，尤其是MemoryMXBean.

例如

import java.lang.management.*;

class Memory {
    public static void main(String[] args) {
        MemoryMXBean m = ManagementFactory.getMemoryMXBean();
        for(MemoryType type: MemoryType.values()) {
            usage(type, type == MemoryType.HEAP?
                m.getHeapMemoryUsage(): m.getNonHeapMemoryUsage());
            System.out.println();
            for(MemoryPoolMXBean mp: ManagementFactory.getMemoryPoolMXBeans())
                if(mp.getType() == type) usage(mp.getName(), mp.getUsage());
            System.out.println();
        }
    }
  
    private static void usage(Object header, MemoryUsage mu) {
        long used = mu.getUsed(), max = mu.getMax();
        System.out.printf(
            max > 0? "%-30s %,d (%,d MiB) of %,d (%,d MiB)%n": "%-30s %,d (%,d MiB)%n",
            header, used, used >>> 20, max, max >>> 20);
    }
}

Ideone 上的演示

Heap memory                    2,820,696 (2 MiB) of 1,037,959,168 (989 MiB)

Tenured Gen                    0 (0 MiB) of 715,849,728 (682 MiB)
Eden Space                     4,231,056 (4 MiB) of 286,326,784 (273 MiB)
Survivor Space                 0 (0 MiB) of 35,782,656 (34 MiB)

Non-heap memory                2,833,312 (2 MiB) of 352,321,536 (336 MiB)

CodeHeap 'non-nmethods'        1,079,040 (1 MiB) of 5,828,608 (5 MiB)
Metaspace                      1,078,264 (1 MiB) of 67,108,864 (64 MiB)
CodeHeap 'profiled nmethods'   489,472 (0 MiB) of 122,912,768 (117 MiB)
Compressed Class Space         114,560 (0 MiB) of 33,554,432 (32 MiB)
CodeHeap 'non-profiled nmethods' 89,856 (0 MiB) of 122,916,864 (117 MiB)

有关如何获取有关垃圾收集及其结果的通知的示例，请参阅此答案。