Java version 1.6.0_13
Java HotSpot(TM) Client VM
11.3-b02
Sun Microsystems Inc.
Direct access using member field:
47 125 47 46 46
average time = 66 ms.
Reference access to member field:
109 109 110 94 109
average time = 106 ms.
Reflection access to member field:
13094 12984 13063 13062 13094
average time = 13051 ms.
Java version 1.6.0_13
Java HotSpot(TM) Client VM
11.3-b02
Sun Microsystems Inc.
Direct call using member field:
47 31 109 109 31
average time = 70 ms.
Direct call using passed value:
16 16 16 31 15
average time = 20 ms.
Call to object using member field:
46 47 47 47 32
average time = 43 ms.
Call to object using passed value:
15 16 31 16 16
average time = 20 ms.
Reflection call using member field:
812 782 844 844 844
average time = 829 ms.
Reflection call using passed value:
938 953 954 1031 953
average time = 973 ms.
Java version 1.6.0_13
Java HotSpot(TM) Client VM
11.3-b02
Sun Microsystems Inc.
Direct Object creation:
62 47 78 32 93
average time = 63 ms.
Reflection Object creation:
125 94 94 109 187
average time = 121 ms.
Direct byte[8] creation:
125 187 94 172 94
average time = 137 ms.
Reflection byte[8] creation:
266 171 187 188 219
average time = 191 ms.
Direct byte[64] creation:
250 172 156 125 203
average time = 164 ms.
Reflection byte[64] creation:
281 219 203 203 219
average time = 211 ms.
]]>
wtp(web tools platform )目在eclipseq_上进行扩展，是一个开发j2ee web应用E序的工具集。wtp包含以下工具Q?/p>
* 一个源码编辑器www.ssbbww.com用来~辑html, javascript, css, jsp, sql, xml, dtd, xsd, 和wsdl?/p>
* 一个图形编辑器用来~辑xsd与wsdl?/p>
* j2ee目构徏器和一个j2ee向导工具?/p>
* 一个web服务创徏向导和管理器Q和ws-i 试工具?/p>
* 一个数据库讉KQ查询工L?/p>
wtp׃个子目构成:wst(web标准工具? 与jst(j2ee标准工具?8ttt8 wtp是什么意?是什么东西_什么叫-什么是wtp
wtp支付愿意原则Q用于分析社会成员ؓ目所产出的效益愿意支付的价倹{?/p>
2.安装及工E创建发布：eclipse for java ee 里已l安装wtp,so不用׃动手Qeclipse l典版安装wtp?
工程的创建及发布
见【传送门】：http://www.vogella.de/articles/EclipseWTP/article.html
3.wtp{疑见【传送门?a >http://wiki.eclipse.org/WTP_Tomcat_FAQ
4.接着创徏一个xfire webservice
http://blog.csdn.net/alex197963/archive/2009/07/20/4363328.aspx
]]>
4.eclipse->window->General->Editors->file associations 右侧 [file types] ->add 输入 *.class ->ok
选中新加?.class,下面的[associated editors] 选中[jadclipse class file viewer] -> default ->ok
重启 eclipse;打开一个class文gQ即可查看反~译代码Q欧?img src ="http://www.aygfsteel.com/Todd/aggbug/346074.html" width = "1" height = "1" />
]]>
]]>
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
/**
* 用于的 Browser 不缓存页面的qo?br />
*/
public class ForceNoCacheFilter implements Filter {
public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws IOException, ServletException
{
((HttpServletResponse) response).setHeader("Cache-Control","no-cache");
((HttpServletResponse) response).setHeader("Pragma","no-cache");
((HttpServletResponse) response).setDateHeader ("Expires", -1);
filterChain.doFilter(request, response);
}
public void destroy()
{
}
public void init(FilterConfig filterConfig) throws ServletException
{
}
}
二、检用h否登陆的qo?/p>
import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.util.List;
import java.util.ArrayList;
import java.util.StringTokenizer;
import java.io.IOException;
/**
* 用于用h否登陆的qo器，如果未登录，则重定向到指的登录页?lt;p>
* 配置参数<p>
* checkSessionKey 需查的?Session 中保存的关键?lt;br/>
* redirectURL 如果用户未登录，则重定向到指定的面QURL不包?ContextPath<br/>
* notCheckURLList 不做查的URL列表Q以分号分开Qƈ?URL 中不包括 ContextPath<br/>
*/
public class CheckLoginFilter
implements Filter
{
protected FilterConfig filterConfig = null;
private String redirectURL = null;
private List notCheckURLList = new ArrayList();
private String sessionKey = null;
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException
{
HttpServletRequest request = (HttpServletRequest) servletRequest;
HttpServletResponse response = (HttpServletResponse) servletResponse;
HttpSession session = request.getSession();
if(sessionKey == null)
{
filterChain.doFilter(request, response);
return;
}
if((!checkRequestURIIntNotFilterList(request)) && session.getAttribute(sessionKey) == null)
{
response.sendRedirect(request.getContextPath() + redirectURL);
return;
}
filterChain.doFilter(servletRequest, servletResponse);
}
public void destroy()
{
notCheckURLList.clear();
}
private boolean checkRequestURIIntNotFilterList(HttpServletRequest request)
{
String uri = request.getServletPath() + (request.getPathInfo() == null ? "" : request.getPathInfo());
return notCheckURLList.contains(uri);
}
public void init(FilterConfig filterConfig) throws ServletException
{
this.filterConfig = filterConfig;
redirectURL = filterConfig.getInitParameter("redirectURL");
sessionKey = filterConfig.getInitParameter("checkSessionKey");
String notCheckURLListStr = filterConfig.getInitParameter("notCheckURLList");
if(notCheckURLListStr != null)
{
StringTokenizer st = new StringTokenizer(notCheckURLListStr, ";");
notCheckURLList.clear();
while(st.hasMoreTokens())
{
notCheckURLList.add(st.nextToken());
}
}
}
}
三、字W编码的qo?/p>
import javax.servlet.*;
import java.io.IOException;
/**
* 用于讄 HTTP h字符~码的过滤器Q通过qo器参数encoding指明使用何种字符~码,用于处理Html Formh参数的中文问?br />
*/
public class CharacterEncodingFilter
implements Filter
{
protected FilterConfig filterConfig = null;
protected String encoding = "";
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException
{
if(encoding != null)
servletRequest.setCharacterEncoding(encoding);
filterChain.doFilter(servletRequest, servletResponse);
}
public void destroy()
{
filterConfig = null;
encoding = null;
}
public void init(FilterConfig filterConfig) throws ServletException
{
this.filterConfig = filterConfig;
this.encoding = filterConfig.getInitParameter("encoding");
}
}
四、资源保护过滤器
package catalog.view.util; import javax.servlet.Filter; import javax.servlet.FilterConfig; import javax.servlet.ServletRequest; import javax.servlet.ServletResponse; import javax.servlet.FilterChain; import javax.servlet.ServletException; import javax.servlet.http.HttpServletRequest; import java.io.IOException; import java.util.Iterator; import java.util.Set; import java.util.HashSet; // import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; /** * This Filter class handle the security of the application. ** It should be configured inside the web.xml. * * @author Derek Y. Shen */ public class SecurityFilter implements Filter { //the login page uri private static final String LOGIN_PAGE_URI = "login.jsf"; //the logger object private Log logger = LogFactory.getLog(this.getClass()); //a set of restricted resources private Set restrictedResources; /** * Initializes the Filter. */ public void init(FilterConfig filterConfig) throws ServletException { this.restrictedResources = new HashSet(); this.restrictedResources.add("/createProduct.jsf"); this.restrictedResources.add("/editProduct.jsf"); this.restrictedResources.add("/productList.jsf"); } /** * Standard doFilter object. */ public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException { this.logger.debug("doFilter"); String contextPath = ((HttpServletRequest)req).getContextPath(); String requestUri = ((HttpServletRequest)req).getRequestURI(); this.logger.debug("contextPath = " + contextPath); this.logger.debug("requestUri = " + requestUri); if (this.contains(requestUri, contextPath) && !this.authorize((HttpServletRequest)req)) { this.logger.debug("authorization failed"); ((HttpServletRequest)req).getRequestDispatcher(LOGIN_PAGE_URI).forward(req, res); } else { this.logger.debug("authorization succeeded"); chain.doFilter(req, res); } } public void destroy() {} private boolean contains(String value, String contextPath) { Iterator ite = this.restrictedResources.iterator(); while (ite.hasNext()) { String restrictedResource = (String)ite.next(); if ((contextPath + restrictedResource).equalsIgnoreCase(value)) { return true; } } return false; } private boolean authorize(HttpServletRequest req) { //处理用户d /* UserBean user = (UserBean)req.getSession().getAttribute(BeanNames.USER_BEAN); if (user != null && user.getLoggedIn()) { //user logged in return true; } else { return false; }*/ } }
]]>
我也懒得写了Q直接引用了我觉得写的挺好的两篇文章Q?br />
什么是Big Endian和Little EndianQ?/a>
来源Qhttp://blog.ednchina.com/qinyonglyz/194674/message.aspx
1Q故事的h
“endian”q个词出自《格列佛游记》。小人国的内战就源于吃鸡蛋时是究竟从大头(Big-Endian)敲开q是从小?Little-Endian)敲开Q由此曾发生q六ơ叛乱，其中一个皇帝送了命，另一个丢了王位?/p>
我们一般将endian译?#8220;字节?#8221;Q将big endian和little endianUC“大尾”?#8220;尾”?/p>
2Q什么是Big Endian和Little EndianQ?/strong>
在设计计机pȝ的时候，有两U处理内存中数据的方法。一U叫为little-endianQ存攑֜内存中最低位的数值是来自数据的最双部分Q也是数据的最低位部分Q。比如一?6q制数字0x12345678Q在内存存放的方式如下：
|
?/p> |
0111Q?000 |
0101Q?110 |
0011Q?100 |
0001Q?010 |
|
地址 |
100 |
101 |
102 |
103 |
另一U称为big-endianQ正好相反，存放在内存中最低位的数值是来自数据的最左边辚w分（也就是数据的最高ؓ部分Q。比如一?6q制数字0x12345678Q在内存存放的方式如下：
|
?/p> |
0001Q?010 |
0011Q?100 |
0101Q?110 |
0111Q?000 |
|
地址 |
100 |
101 |
102 |
103 |
比如某些文g需要在不同q_处理Q或者通过Socket通信。这斚w我们可以借助ntohl(), ntohs(), htonl(), and htons()函数q行格式转换?/p>
3Q如何判断系l是Big Endianq是Little EndianQ?/strong>
?usr/include/中（包括子目录）查找字符串BYTE_ORDER(或_BYTE_ORDER, __BYTE_ORDER)Q确定其倹{这个g般在endian.h或machine/endian.h文g中可以找?有时在feature.h中，不同?a onclick="javascript:tagshow(event, '%B2%D9%D7%F7%CF%B5%CD%B3');" href="javascript:;" target="_self">操作pȝ可能有所不同。一般来_Little EndianpȝBYTE_ORDER(或_BYTE_ORDER,__BYTE_ORDER)?234QBig Endianpȝ?321。大部分用户的操作系l（如windows, FreeBsd,LinuxQ是Little Endian的。少部分Q如MAC OS ,是Big Endian 的。本质上_Little Endianq是Big Endian与操作系l和芯片cd都有关系?/p>
======================================================================
ext3 文gpȝ在硬盘分Z的数据是按照 Intel ?Little-endian 格式存放的，如果是在 PC 以外的^C开?ext3 相关的程序，要特别注意这一炏V?/font>
谈到字节序的问题Q必然牵涉到两大 CPUz。那是Motorola的PowerPCpdCPU和Intel的x86pdCPU。PowerPCpd采用big endian方式存储数据Q而x86pd则采用little endian方式存储数据。那么究竟什么是big endianQ什么又是little endian呢？
其实big endian是指低地址存放最高有效字节（MSBQ，而little endian则是低地址存放最低有效字节（LSBQ?/font>
用文字说明可能比较抽象，下面用图像加以说明。比如数?x12345678在两U不同字节序CPU中的存储序如下所C：
Big Endian
低地址 高地址
----------------------------------------->
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 12 | 34 | 56 | 78 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Little Endian
低地址 高地址
----------------------------------------->
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 78 | 56 | 34 | 12 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
从上面两囑֏以看出，采用big endian方式存储数据是符合我们hcȝ思维习惯的。而little endianQ?@#$%^&*Q见鬼去?-_-|||
Z么要注意字节序的问题呢？你可能这么问。当Ӟ如果你写的程序只在单机环境下面运行，q且不和别h的程序打交道Q那么你完全可以忽略字节序的存在。但是，如果你的E序要跟别h的程序生交互呢Q在q里我想说说两种语言。C/C++语言~写的程序里数据存储序是跟~译q_所在的CPU相关的，?JAVA~写的程序则唯一采用big endian方式来存储数据。试惻I如果你用C/C++语言在x86q_下编写的E序跟别人的JAVAE序互通时会生什么结果？拿上面?0x12345678来说Q你的程序传递给别h的一个数据，指?x12345678的指针传l了JAVAE序Q由于JAVA采取big endian方式存储数据Q很自然的它会将你的数据译?x78563412。什么？竟然变成另外一个数字了Q是的，是q种后果。因此，在你的CE序传给JAVAE序之前有必要进行字节序的{?a onclick="javascript:tagshow(event, '%B9%A4%D7%F7');" href="javascript:;" target="_self">工作?br />
无独有偶Q所有网l协议也都是采用big endian的方式来传输数据的。所以有时我们也会把big endian方式UC为网l字节序。当两台采用不同字节序的L通信Ӟ在发送数据之前都必须l过字节序的转换成ؓ|络字节序后再进行传输?/font>
|络字节序与L字节?/a>
来源Qhttp://www.cnblogs.com/jacktu/archive/2008/11/24/1339789.html
不同的CPU有不同的字节序类?q些字节序是指整数在内存中保存的序 q个叫做L?br />
最常见的有两种
1Q?Little endianQ将低序字节存储在v始地址
2Q?Big endianQ将高序字节存储在v始地址
LE little-endian
最W合人的思维的字节序
地址低位存储值的低位
地址高位存储值的高位
怎么讲是最W合人的思维的字节序Q是因ؓ从h的第一观感来说
低位值小Q就应该攑֜内存地址的地方Q也卛_存地址低位
反之Q高位值就应该攑֜内存地址大的地方Q也卛_存地址高位
BE big-endian
最直观的字节序
地址低位存储值的高位
地址高位存储值的低位
Z么说直观Q不要考虑对应关系
只需要把内存地址从左到右按照׃到高的顺序写?br />
把值按照通常的高位到低位的顺序写?br />
两者对照，一个字节一个字节的填充q去
例子Q在内存中双?x01020304(DWORD)的存储方?br />
内存地址
4000 4001 4002 4003
LE 04 03 02 01
BE 01 02 03 04
例子Q如果我们将0x1234abcd写入C0x0000开始的内存中，则结果ؓ
big-endian little-endian
0x0000 0x12 0xcd
0x0001 0x23 0xab
0x0002 0xab 0x34
0x0003 0xcd 0x12
x86pdCPU都是little-endian的字节序.
|络字节序是TCP/IP中规定好的一U数据表C格式，它与具体的CPUcd、操作系l等无关Q从而可以保证数据在不同L之间传输时能够被正确解释。网l字节顺序采用big endian排序方式?br />
Zq行转换 bsd socket提供了{换的函数 有下面四?br />
htons 把unsigned shortcd从主机序转换到网l序
htonl 把unsigned longcd从主机序转换到网l序
ntohs 把unsigned shortcd从网l序转换C机序
ntohl 把unsigned longcd从网l序转换C机序
在用little endian的系l中 q些函数会把字节序进行{?br />
在用big endiancd的系l中 q些函数会定义成I宏
同样 在网l程序开发时 或是跨^台开发时 也应该注意保证只用一U字节序 不然两方的解释不一样就会生bug.
注：
1、网l与L字节转换函数:htons ntohs htonl ntohl (s 是short l是long h是host n是network)
2、不同的CPU上运行不同的操作pȝQ字节序也是不同的，参见下表?br />
处理?nbsp; 操作pȝ 字节排序
Alpha 全部 Little endian
HP-PA NT Little endian
HP-PA UNIX Big endian
Intelx86 全部 Little endian <-----x86pȝ是小端字节序pȝ
Motorola680x() 全部 Big endian
MIPS NT Little endian
MIPS UNIX Big endian
PowerPC NT Little endian
PowerPC 非NT Big endian <-----PPCpȝ是大端字节序pȝ
RS/6000 UNIX Big endian
SPARC UNIX Big endian
IXP1200 ARM核心 全部 Little endian
=============================================
字节序{换类Q?br />
/**
* 通信格式转换
*
* Java和一些windows~程语言如c、c++、delphi所写的|络E序q行通讯Ӟ需要进行相应的转换
* 高、低字节之间的{?br />
* windows的字节序Z字节开?br />
* linux,unix的字节序为高字节开?br />
* java则无论^台变化，都是高字节开?br />
*/
public class FormatTransfer {
/**
* int转ؓ低字节在前，高字节在后的byte数组
* @param n int
* @return byte[]
*/
public static byte[] toLH(int n) {
byte[] b = new byte[4];
b[0] = (byte) (n & 0xff);
b[1] = (byte) (n >> 8 & 0xff);
b[2] = (byte) (n >> 16 & 0xff);
b[3] = (byte) (n >> 24 & 0xff);
return b;
}
/**
* int转ؓ高字节在前，低字节在后的byte数组
* @param n int
* @return byte[]
*/
public static byte[] toHH(int n) {
byte[] b = new byte[4];
b[3] = (byte) (n & 0xff);
b[2] = (byte) (n >> 8 & 0xff);
b[1] = (byte) (n >> 16 & 0xff);
b[0] = (byte) (n >> 24 & 0xff);
return b;
}
/**
* short转ؓ低字节在前，高字节在后的byte数组
* @param n short
* @return byte[]
*/
public static byte[] toLH(short n) {
byte[] b = new byte[2];
b[0] = (byte) (n & 0xff);
b[1] = (byte) (n >> 8 & 0xff);
return b;
}
/**
* short转ؓ高字节在前，低字节在后的byte数组
* @param n short
* @return byte[]
*/
public static byte[] toHH(short n) {
byte[] b = new byte[2];
b[1] = (byte) (n & 0xff);
b[0] = (byte) (n >> 8 & 0xff);
return b;
}
/**
* 将int转ؓ高字节在前，低字节在后的byte数组
public static byte[] toHH(int number) {
int temp = number;
byte[] b = new byte[4];
for (int i = b.length - 1; i > -1; i--) {
b = new Integer(temp & 0xff).byteValue();
temp = temp >> 8;
}
return b;
}
public static byte[] IntToByteArray(int i) {
byte[] abyte0 = new byte[4];
abyte0[3] = (byte) (0xff & i);
abyte0[2] = (byte) ((0xff00 & i) >> 8);
abyte0[1] = (byte) ((0xff0000 & i) >> 16);
abyte0[0] = (byte) ((0xff000000 & i) >> 24);
return abyte0;
}
*/
/**
* float转ؓ低字节在前，高字节在后的byte数组
*/
public static byte[] toLH(float f) {
return toLH(Float.floatToRawIntBits(f));
}
/**
* float转ؓ高字节在前，低字节在后的byte数组
*/
public static byte[] toHH(float f) {
return toHH(Float.floatToRawIntBits(f));
}
/**
* String转ؓbyte数组
*/
public static byte[] stringToBytes(String s, int length) {
while (s.getBytes().length < length) {
s += " ";
}
return s.getBytes();
}
/**
* 字节数l{换ؓString
* @param b byte[]
* @return String
*/
public static String bytesToString(byte[] b) {
StringBuffer result = new StringBuffer("");
int length = b.length;
for (int i=0; i<length; i++) {
result.append((char)(b & 0xff));
}
return result.toString();
}
/**
* 字W串转换为byte数组
* @param s String
* @return byte[]
*/
public static byte[] stringToBytes(String s) {
return s.getBytes();
}
/**
* 高字节数组转换为int
* @param b byte[]
* @return int
*/
public static int hBytesToInt(byte[] b) {
int s = 0;
for (int i = 0; i < 3; i++) {
if (b >= 0) {
s = s + b;
} else {
s = s + 256 + b;
}
s = s * 256;
}
if (b[3] >= 0) {
s = s + b[3];
} else {
s = s + 256 + b[3];
}
return s;
}
/**
* 低字节数组转换为int
* @param b byte[]
* @return int
*/
public static int lBytesToInt(byte[] b) {
int s = 0;
for (int i = 0; i < 3; i++) {
if (b[3-i] >= 0) {
s = s + b[3-i];
} else {
s = s + 256 + b[3-i];
}
s = s * 256;
}
if (b[0] >= 0) {
s = s + b[0];
} else {
s = s + 256 + b[0];
}
return s;
}
/**
* 高字节数l到short的{?br />
* @param b byte[]
* @return short
*/
public static short hBytesToShort(byte[] b) {
int s = 0;
if (b[0] >= 0) {
s = s + b[0];
} else {
s = s + 256 + b[0];
}
s = s * 256;
if (b[1] >= 0) {
s = s + b[1];
} else {
s = s + 256 + b[1];
}
short result = (short)s;
return result;
}
/**
* 低字节数l到short的{?br />
* @param b byte[]
* @return short
*/
public static short lBytesToShort(byte[] b) {
int s = 0;
if (b[1] >= 0) {
s = s + b[1];
} else {
s = s + 256 + b[1];
}
s = s * 256;
if (b[0] >= 0) {
s = s + b[0];
} else {
s = s + 256 + b[0];
}
short result = (short)s;
return result;
}
/**
* 高字节数l{换ؓfloat
* @param b byte[]
* @return float
*/
public static float hBytesToFloat(byte[] b) {
int i = 0;
Float F = new Float(0.0);
i = ((((b[0]&0xff)<<8 | (b[1]&0xff))<<8) | (b[2]&0xff))<<8 | (b[3]&0xff);
return F.intBitsToFloat(i);
}
/**
* 低字节数l{换ؓfloat
* @param b byte[]
* @return float
*/
public static float lBytesToFloat(byte[] b) {
int i = 0;
Float F = new Float(0.0);
i = ((((b[3]&0xff)<<8 | (b[2]&0xff))<<8) | (b[1]&0xff))<<8 | (b[0]&0xff);
return F.intBitsToFloat(i);
}
/**
* byte数组中的元素倒序排列
*/
public static byte[] bytesReverseOrder(byte[] b) {
int length = b.length;
byte[] result = new byte[length];
for(int i=0; i<length; i++) {
result[length-i-1] = b;
}
return result;
}
/**
* 打印byte数组
*/
public static void printBytes(byte[] bb) {
int length = bb.length;
for (int i=0; i<length; i++) {
System.out.print(bb + " ");
}
System.out.println("");
}
public static void logBytes(byte[] bb) {
int length = bb.length;
String ut = "";
for (int i=0; i<length; i++) {
ut = out + bb + " ";
}
}
/**
* intcd的D{换ؓ字节序颠倒过来对应的int?br />
* @param i int
* @return int
*/
public static int reverseInt(int i) {
int result = FormatTransfer.hBytesToInt(FormatTransfer.toLH(i));
return result;
}
/**
* shortcd的D{换ؓ字节序颠倒过来对应的short?br />
* @param s short
* @return short
*/
public static short reverseShort(short s) {
short result = FormatTransfer.hBytesToShort(FormatTransfer.toLH(s));
return result;
}
/**
* floatcd的D{换ؓ字节序颠倒过来对应的float?br />
* @param f float
* @return float
*/
public static float reverseFloat(float f) {
float result = FormatTransfer.hBytesToFloat(FormatTransfer.toLH(f));
return result;
}
}
]]>
3、put、removeҎ要用锁Q但q不一定有锁争用，原因在于ConcurrentHashMap缓存的变量分到多个SegmentQ每个Segment上有一个锁Q只要多个线E访问的不是一个Segment没有锁争用Q就没有堵塞Q各U程用各自的锁，ConcurrentHashMap~省情况下生?6个SegmentQ也是允许16个线Eƈ发的更新而尽量没有锁争用Q?br /> 4、Iterator、Enumeration获得的对象，不一定是和其它更新线E同步，获得的对象可能是更新前的对象QConcurrentHashMap允许一Ҏ新、一辚w历，未遍历到的key一般能放映value更新Q?br /> 5、有些情况下q种不一致是允许的，如果需要最大的性能、吞吐量Q则正好使用ConcurrentHashMap?
目前只想到能用于~存无关紧要的信息，对于d 都须同步的操作，竟然q要加synchronizedQ悲剧的U程安全
]]>