使用AJAX完成用户名是否存在异步校验

function checkUsername(){     // 获得文件框值:     var username = document.getElementById("username").value;     // 1.创建异步交互对象     var xhr = createXmlHttp();     // 2.设置监听     xhr.onreadystatechange = function(){       if(xhr.readyState == 4){         if(xhr.status == 200){           document.getElementById("span1").innerHTML = xhr.responseText;         }       }     }     // 3.打开连接     xhr.open("GET","${pageContext.request.contextPath}/user_findByName.action?time="+new Date().getTime()+"&username="+username,true);     // 4.发送     xhr.send(null);   }   function createXmlHttp(){       var xmlHttp;       try{ // Firefox, Opera 8.0+, Safari         xmlHttp=new XMLHttpRequest();       }       catch (e){         try{// Internet Explorer            xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");          }         catch (e){          try{            xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");          }          catch (e){}          }       }       return xmlHttp;      } 

public String findByName() throws IOException {     // 调用Service进行查询:     User existUser = userService.findByUsername(user.getUsername());     // 获得response对象,项页面输出:     HttpServletResponse response = ServletActionContext.getResponse();     response.setContentType("text/html;charset=UTF-8");     // 判断     if (existUser != null) {       // 查询到该用户:用户名已经存在       response.getWriter().println("<font color='red'>用户名已经存在</font>");     } else {       // 没查询到该用户:用户名可以使用       response.getWriter().println("<font color='green'>用户名可以使用</font>");     }     return NONE;   } 

private UserDao userDao;   public void setUserDao(UserDao userDao) {     this.userDao = userDao;   }   // 按用户名查询用户的方法:   public User findByUsername(String username){     return userDao.findByUsername(username);   } 

public User findByUsername(String username){     String hql = "from User where username = ?";     List<User> list = this.getHibernateTemplate().find(hql, username);     if(list != null && list.size() > 0){       return list.get(0);     }     return null;   } 

<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans"   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"   xmlns:context="http://www.springframework.org/schema/context"   xmlns:aop="http://www.springframework.org/schema/aop"   xmlns:tx="http://www.springframework.org/schema/tx"   xsi:schemaLocation="http://www.springframework.org/schema/beans    http://www.springframework.org/schema/beans/spring-beans.xsd   http://www.springframework.org/schema/context   http://www.springframework.org/schema/context/spring-context.xsd   http://www.springframework.org/schema/aop   http://www.springframework.org/schema/aop/spring-aop.xsd   http://www.springframework.org/schema/tx    http://www.springframework.org/schema/tx/spring-tx.xsd">   <!-- 配置连接池: -->   <!-- 引入外部属性文件 -->   <context:property-placeholder location="classpath:jdbc.properties"/>   <!-- 配置C3P0连接池: -->   <bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">     <property name="driverClass" value="${jdbc.driver}"/>     <property name="jdbcUrl" value="${jdbc.url}"/>     <property name="user" value="${jdbc.user}"/>     <property name="password" value="${jdbc.password}"/>   </bean>   <!-- Hibernate的相关信息 -->   <bean id="sessionFactory" class="org.springframework.orm.hibernate3.LocalSessionFactoryBean">     <!-- 注入连接池 -->     <property name="dataSource" ref="dataSource"/>     <!-- 配置Hibernate的其他的属性 -->     <property name="hibernateProperties">       <props>         <prop key="hibernate.dialect">org.hibernate.dialect.MySQLDialect</prop>         <prop key="hibernate.show_sql">true</prop>         <prop key="hibernate.format_sql">true</prop>         <prop key="hibernate.connection.autocommit">false</prop>         <prop key="hibernate.hbm2ddl.auto">update</prop>       </props>     </property>     <!-- 配置Hibernate的映射文件 -->     <property name="mappingResources">       <list>         <value>cn/itcast/shop/user/vo/User.hbm.xml</value>       </list>     </property>   </bean>   <!-- 事务管理: -->   <!-- 事务管理器 -->   <bean id="transactionManager" class="org.springframework.orm.hibernate3.HibernateTransactionManager">     <property name="sessionFactory" ref="sessionFactory"/>   </bean>   <!-- 开启注解事务 -->   <tx:annotation-driven transaction-manager="transactionManager"/>   <!-- Action的配置 ===========================-->   <!-- 首页访问的Action -->   <bean id="indexAction" class="cn.itcast.shop.index.action.IndexAction" scope="prototype">   </bean>   <!-- 配置验证码Action -->   <bean id="checkImgAction" class="cn.itcast.shop.user.action.CheckImgAction" scope="prototype">   </bean>   <!-- 用户模块的Action -->   <bean id="userAction" class="cn.itcast.shop.user.action.UserAction" scope="prototype">     <!-- 注入Service -->     <property name="userService" ref="userService"/>   </bean>   <!-- Service的配置 ===========================-->   <bean id="userService" class="cn.itcast.shop.user.service.UserService">     <property name="userDao" ref="userDao"/>   </bean>   <!-- Dao的配置 ===========================-->   <bean id="userDao" class="cn.itcast.shop.user.dao.UserDao">     <property name="sessionFactory" ref="sessionFactory"/>   </bean> </beans> [html] view plain copy 在CODE上查看代码片派生到我的代码片<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE struts PUBLIC   "-//Apache Software Foundation//DTD Struts Configuration 2.3//EN"   "http://struts.apache.org/dtds/struts-2.3.dtd"> <struts>   <constant name="struts.devMode" value="false" />   <constant name="struts.enable.DynamicMethodInvocation" value="true"/>   <package name="shop" extends="struts-default" namespace="/">     <global-results>       <result name="msg">/WEB-INF/jsp/msg.jsp</result>     </global-results>     <!-- 配置首页访问的Action -->     <action name="index" class="indexAction">       <result name="index">/WEB-INF/jsp/index.jsp</result>     </action>     <!-- 配置用户模块的Action -->     <action name="user_*" class="userAction" method="{1}">       <result name="registPage">/WEB-INF/jsp/regist.jsp</result>       <result name="input">/WEB-INF/jsp/regist.jsp</result>       <result name="loginPage">/WEB-INF/jsp/login.jsp</result>       <result name="login">/WEB-INF/jsp/login.jsp</result>       <result name="loginSuccess" type="redirectAction">index</result>       <result name="quit" type="redirectAction">index</result>       <result name="checkcodeFail">/WEB-INF/jsp/regist.jsp</result>     </action>     <!-- 验证码Action -->     <action name="checkImg" class="checkImgAction"></action>   </package> </struts>