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java能够经过

java.nio.ByteBuffer.allocateDirect(capacity)

直接运用

non java heap

（java堆外)的内存 。

一.运用意图：

1。拓荒数据缓冲区

2。能够打破jvm内存约束，操作更多的物理内存(不一样的jvm完成不一样,sun jvm会被约束，但能添加jvm能够操作的一倍内存,而

jrockit

基本上能够将物理内存悉数耗光)

二.运用难题:

经过

ByteBuffer.allocateDirect()

运用的内存不能够经过jvm关联内存东西:VisualVM等检查heap的内存占用,所以内存走漏也较难查找。

三. 测验如下:

Java代码

1. public class ByteBufferTest {
3. public static void main(String[] args) throws InterruptedException {
4. System.out.println(SystemRuntimeInfo.getMemoryInfo());
5. List list = new ArrayList();
6. for(int i = 0; i < 100; i++) {
7. list.add(ByteBuffer.allocateDirect(Integer.MAX_VALUE / 100));
8. System.out.println(i + ” ” + SystemRuntimeInfo.getMemoryInfo()); // 个人写的内存占用东西类
9. }
10. System.out.println(“start sleep,list.size()
    
    
    唐山票
    
    
    
    ​
    
    :”+list.size());
11. Thread.sleep(100000);
12. System.out.println(list.size());
14. // java.nio.ByteBuffer.allocate(capacity) 运用 java heap(java堆)分配内存: 能够直接经过东西检查出内存占用
15. // java.nio.ByteBuffer.allocateDirect(capacity) 运用non java heap(非java堆)经过操作系统直接分配内存: 会招致检查不出java heap的内存占用，招致走漏看不出来
17. }
19. }

打印成果:

Java代码

1. ———————-
2. totalHeapMemory:15MB  freeHeapMemory:14MB  maxHeapMemory:247MB totalPhysicalMemorySize:2047MB freePhysicalMemorySize:1285MB usedPhysicalMemory:762MB
3. 0 totalHeapMemory:15MB  freeHeapMemory:14MB  maxHeapMemory:247MB totalPhysicalMemorySize:2047MB freePhysicalMemorySize:1264MB usedPhysicalMemory:783MB
4. 1 totalHeapMemory:15MB  freeHeapMemory:14MB  maxHeapMemory:247MB totalPhysicalMemorySize:2047MB freePhysicalMemorySize:1244MB usedPhysicalMemory:803MB
5. 2 totalHeapMemory:15MB  freeHeapMemory:14MB  maxHeapMemory:247MB totalPhysicalMemorySize:2047MB freePhysicalMemorySize:1223MB usedPhysicalMemory:824MB
6. 3 totalHeapMemory:15MB  freeHeapMemory:14MB  maxHeapMemory:247MB totalPhysicalMemorySize:2047MB freePhysicalMemorySize:1203MB usedPhysicalMemory:844MB
7. 4 totalHeapMemory:15MB  freeHeapMemory:14MB  maxHeapMemory:247MB totalPhysicalMemorySize:2047MB freePhysicalMemorySize:1182MB usedPhysicalMemory:865MB
8. 5 totalHeapMemory:15MB  freeHeapMemory:14MB  maxHeapMemory:247MB totalPhysicalMemorySize:2047MB freePhysicalMemorySize:1162MB usedPhysicalMemory:885MB
9. 6 totalHeapMemory:15MB  freeHeapMemory:14MB  maxHeapMemory:247MB totalPhysicalMemorySize:2047MB freePhysicalMemorySize:1141MB usedPhysicalMemory:906MB
10. 7 totalHeapMemory:15MB  freeHeapMemory:14MB  maxHeapMemory:247MB totalPhysicalMemorySize:2047MB freePhysicalMemorySize:1121MB usedPhysicalMemory:926MB
11. 8 totalHeapMemory:15MB  freeHeapMemory:14MB  maxHeapMemory:247MB totalPhysicalMemorySize:2047MB freePhysicalMemorySize:1100MB usedPhysicalMemory:947MB
12. 9 totalHeapMemory:15MB  freeHeapMemory:14MB  maxHeapMemory:247MB totalPhysicalMemorySize:2047MB freePhysicalMemorySize:1079MB usedPhysicalMemory:968MB

VisualVM内存检查:

Heap内存分配

实践java进程内存占用:

经过VisualVM能够发现，java heap底子没有运用，但java进程的物理内存现已运用400MB+

四.测验定论:

​

1. 运用ByteBuffer.allocateDirect()分配出去的内存无法经过Heap检查

2. ByteBuffer.allocateDirect()分配的内容能够被GC收回,但走漏的话较难查找