举例讲解Java中synchronized关键字的用法

public synchronized void method(){   //…. } public void method() {   synchronized (this){     //…..   } }

Class Main {   public synchronized static void method1(){     //….   }   public void method2(){     synchronized(Main.class) //    } }

package com.asiainfolinkage.ems.web.controller.base;  import java.math.BigInteger; import java.util.Date; import java.util.HashMap; import java.util.Map; import java.util.Random;  import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpSession;  /**  * 附带token的控制器  * @version 1.0 Copyright 2013年7月29日 下午3:38:30  */ public abstract class TokenBaseController extends BaseController {    private static Map<String, String> springmvc_token = new HashMap<String, String>();    /** 生成一个唯一值的token */   public String generateGUID(HttpSession session) {     String token = "";     Date date = new Date();     synchronized (springmvc_token) {       try {         Object obj = session.getAttribute(Constants.SPRING_MVC_TOKENNAME);         if (obj != null)           springmvc_token = (Map<String, String>) session.getAttribute(Constants.SPRING_MVC_TOKENNAME);         token = new BigInteger(165, new Random()).toString(36).toUpperCase();         springmvc_token.put(Constants.DEFAULT_TOKEN_NAME + "." + token, token);         session.setAttribute(Constants.SPRING_MVC_TOKENNAME, springmvc_token);         Constants.TOKEN_VALUE = token;       } catch (IllegalStateException e) {         _log.error("generateGUID() mothod find bug,by token session...");       }     }     return token;   }    /** 验证表单token值和session中的token值是否一致 */   public boolean validToken(HttpServletRequest request) {     String inputToken = getInputToken(request);      if (inputToken == null) {       _log.warn("token is not valid!inputToken is NULL");       return false;     }     HttpSession session = request.getSession();     Map<String, String> tokenMap = (Map<String, String>) session.getAttribute(Constants.SPRING_MVC_TOKENNAME);     if (tokenMap == null || tokenMap.size() < 1) {       _log.warn("token is not valid!sessionToken is NULL");       return false;     }     String sessionToken = tokenMap.get(Constants.DEFAULT_TOKEN_NAME + "." + inputToken);     if (!inputToken.equals(sessionToken)) {       _log.warn("token is not valid!inputToken='" + inputToken + "',sessionToken = '" + sessionToken + "'");       return false;     }     tokenMap.remove(Constants.DEFAULT_TOKEN_NAME + "." + inputToken);     session.setAttribute(Constants.SPRING_MVC_TOKENNAME, tokenMap);      return true;   }    /** 获取表单中token值 */   private String getInputToken(HttpServletRequest request) {     Map params = request.getParameterMap();     if (!params.containsKey(Constants.DEFAULT_TOKEN_NAME)) {       _log.warn("Could not find token name in params.");       return null;     }     String[] tokens = (String[]) (String[]) params.get(Constants.DEFAULT_TOKEN_NAME);     if ((tokens == null) || (tokens.length < 1)) {       _log.warn("Got a null or empty token name.");       return null;     }     return tokens[0];   } }