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

public class ByteBufferTest {

public static void main(String[] args) throws InterruptedException {

System.out.println(SystemRuntimeInfo.getMemoryInfo());

List list = new ArrayList();

for(int i = 0; i

list.add(ByteBuffer.allocateDirect(Integer.MAX_VALUE / 100));

System.out.println(i + " " + SystemRuntimeInfo.getMemoryInfo()); // 个人写的内存占用东西类

}

System.out.println("start sleep,list.size() 唐山票​:"+list.size());

Thread.sleep(100000);

System.out.println(list.size());

// 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

// 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

}

}

打印成果:

Java代码

----------------------

totalHeapMemory:15MB  freeHeapMemory:14MB  maxHeapMemory:247MB totalPhysicalMemorySize:2047MB freePhysicalMemorySize:1285MB usedPhysicalMemory:762MB

0 totalHeapMemory:15MB  freeHeapMemory:14MB  maxHeapMemory:247MB totalPhysicalMemorySize:2047MB freePhysicalMemorySize:1264MB usedPhysicalMemory:783MB

1 totalHeapMemory:15MB  freeHeapMemory:14MB  maxHeapMemory:247MB totalPhysicalMemorySize:2047MB freePhysicalMemorySize:1244MB usedPhysicalMemory:803MB

2 totalHeapMemory:15MB  freeHeapMemory:14MB  maxHeapMemory:247MB totalPhysicalMemorySize:2047MB freePhysicalMemorySize:1223MB usedPhysicalMemory:824MB

3 totalHeapMemory:15MB  freeHeapMemory:14MB  maxHeapMemory:247MB totalPhysicalMemorySize:2047MB freePhysicalMemorySize:1203MB usedPhysicalMemory:844MB

4 totalHeapMemory:15MB  freeHeapMemory:14MB  maxHeapMemory:247MB totalPhysicalMemorySize:2047MB freePhysicalMemorySize:1182MB usedPhysicalMemory:865MB

5 totalHeapMemory:15MB  freeHeapMemory:14MB  maxHeapMemory:247MB totalPhysicalMemorySize:2047MB freePhysicalMemorySize:1162MB usedPhysicalMemory:885MB

6 totalHeapMemory:15MB  freeHeapMemory:14MB  maxHeapMemory:247MB totalPhysicalMemorySize:2047MB freePhysicalMemorySize:1141MB usedPhysicalMemory:906MB

7 totalHeapMemory:15MB  freeHeapMemory:14MB  maxHeapMemory:247MB totalPhysicalMemorySize:2047MB freePhysicalMemorySize:1121MB usedPhysicalMemory:926MB

8 totalHeapMemory:15MB  freeHeapMemory:14MB  maxHeapMemory:247MB totalPhysicalMemorySize:2047MB freePhysicalMemorySize:1100MB usedPhysicalMemory:947MB

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