Java JSP如何取得HashMap的大小_框架

Java里面没有提供像C,C++那样的Sizeof()方法，所以不可以直接取得内存资源大小

但是有提供RuntimegetRuntime ()totalMemory ()和RuntimegetRuntime ()freeMemory ()这样的方法

所以内存使用大小 = totalMemory () - freeMemory();

但是又不能直接传送Hashmap对象去计算必须在创建Haspmap之前gc一次，然后得到大小，创建HaspMap之后再gc一次，得到内存大小，然后相减

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是的，这种方法统计的内存大小是Java使用的内存但是Java垃圾回收机制，所以不能精确到KB那就是我们在计算得时候必须GC得原因

还有一个办法就是上面这么兄弟说得，用序列化把HaspMap序列化（其实就是写入到一个临时文件）然后这个临时文件得大小，就是内存占用得大小这个可以精确到KB，但是效率上，值得考究

MapActionjava

Java代码

package comzxdemoaction;

import javautilArrayList;

import javautilHashMap;

import javautilList;

import javautilMap;

import comopensymphonyxwork2ActionSupport;

import comzxdemomodelProduct;

import comzxdemomodelStudent;

public class MapAction extends ActionSupport

{

private Map<String,String> map;

private Map<String,Student> studentMap;

private Map<String,String[]> arrayMap;

private Map<String,List<Student>> listMap;

public String testMap()

{

map=new HashMap<String,String>();

mapput("1", "one");

mapput("2", "two");

studentMap=new HashMap<String,Student>();

studentMapput("student1",new Student(new Long(1),"20034140201","张三1","男",25));

studentMapput("student2",new Student(new Long(2),"20034140202","张三2","女",26));

studentMapput("student3",new Student(new Long(3),"20034140202","张三3","男",27));

arrayMap=new HashMap<String,String[]>();

arrayMapput("arr1", new String[]{"1","2003401","leejie","male","20"});

arrayMapput("arr2", new String[]{"2","2003402","huanglie","male","25"});

arrayMapput("arr3", new String[]{"3","2003403","lixiaoning","male","21"});

listMap=new HashMap<String,List<Student>>();

List<Student> list1=new ArrayList<Student>();

list1add(new Student(new Long(1),"20034140201","张三1","男",25));

list1add(new Student(new Long(2),"20034140202","张三2","男",25));

list1add(new Student(new Long(3),"20034140203","张三3","男",25));

listMapput("class1", list1);

List<Student> list2=new ArrayList<Student>();

list2add(new Student(new Long(1),"20034140301","李四1","男",20));

list2add(new Student(new Long(2),"20034140302","李四2","男",21));

list2add(new Student(new Long(3),"20034140303","李四3","男",22));

list2add(new Student(new Long(4),"20034140304","李四4","男",23));

listMapput("class2", list2);

return SUCCESS;

}

public Map<String, String> getMap() {

return map;

}

public void setMap(Map<String, String> map) {

thismap = map;

}

public Map<String, Student> getStudentMap() {

return studentMap;

}

public void setStudentMap(Map<String, Student> studentMap) {

thisstudentMap = studentMap;

}

public Map<String, String[]> getArrayMap() {

return arrayMap;

}

public void setArrayMap(Map<String, String[]> arrayMap) {

thisarrayMap = arrayMap;

}

public Map<String, List<Student>> getListMap() {

return listMap;

}

public void setListMap(Map<String, List<Student>> listMap) {

thislistMap = listMap;

}

2testMapjsp

Java代码

<%@ page contentType="text/html;charset=UTF-8" %>

<%@ taglib prefix="s" uri="/struts-tags" %>

<html>

<head>

<title>struts2中的map遍历总结</title>

</head>

<body>

<b>1map中的value为String字符串</b><br>

<s:iterator value="map" id="column">

<s:property value="#column"/><br>

key: <s:property value="key"/><br>

value:<s:property value="value"/><br>

<br>

</s:iterator>

<b>2map中的value为Student对象</b>

<tr>

<td>key=value</td>

</tr>

<s:iterator value="studentMap" id="column">

<tr>

</tr>

</s:iterator>

</table>

<p>

<b>3map中的value为String数组</b>

<tr>

<td>key=value</td>

</tr>

<s:iterator value="arrayMap" id="column">

<tr>

</tr>

</s:iterator>

</table>

<p>

<b>4map中的value为list集合</b>

<tr>

<td>class</td>

</tr>

<s:iterator value="listMap" id="column">

<s:set name="total" value="#columnvaluesize"/>

<s:iterator value="#columnvalue" status="s">

<tr>

<s:if test="#sfirst"><td rowspan="${total}"><s:property value="#columnkey"/></td></s:if>

</tr>

</s:iterator>

</table>

</body>

</html>

<s:iterator begin="1" end="stepflag-1" step="1" status="st">

<textarea name="reason" id="reason" cols="75" rows="3" readonly="readonly">${dataMap['reason'+stindex+1]}</textarea>

index是从0开始取值的

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Java JSP如何取得HashMap的大小

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