dwr属于ajax的一个框架 所以说实现原理和ajax一样
dwr使用步骤：
1.导入dwr所用的jar包文件 dwr.jar和commons-logging.jar
2.在web.xml文件中配置dwr默认的信息 （即默认的servlet）
<servlet>
<servlet-name>dwr-invoker</servlet-name>
<servlet-class>org.directwebremoting.servlet.DwrServlet</servlet-class>
<init-param>
<param-name>debug</param-name>
<param-value>true</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>dwr-invoker</servlet-name>
<url-pattern>/dwr/*</url-pattern>
</servlet-mapping>
3.在web.xml文件的同一目录下面创建dwr.xml文件 并且在dwr.xml文件配置在javascript中需要调用的普通的java类（不是servlet）
4.检查一下dwr配置是否成功 检查方式：打开服务器 然后在浏览器中输入http://localhost/mydwr/dwr
5.在需要使用dwr的页面 导入三个js文件 然后就可以在该页面的javascript代码中直接通过名字调用到java类中的方法
dwr.xml文件中
普通（非单例模式的类）的配置
<create creator="new" javascript="dwrStudy">
<param name="class" value="com.pk.mydwr.test.DwrStudy" />
</create>
单例模式的类的配置
a).首先要导入单例模式需要的一些jar包
b).然后配置方式如下
<create creator="script" javascript="chinaCitySingletonDao">
<param name="language" value="beanshell"/>
<param name="script">
import com.puckasoft.dao.ChinaCitySingletonDao;
return ChinaCitySingletonDao.getInstance();
</param>
</create>
例子：已局部刷新邮箱是否注册为例
dwr.xml
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE dwr PUBLIC "-//GetAhead Limited//DTD Direct Web Remoting 2.0//EN" "http://www.getahead.ltd.uk/dwr/dwr20.dtd">
<dwr>
<allow>
<!-- DwrStudy dwrStudy = new DwrStudy();dwrStudy是用在javascript中的
即在javascript中使用dwrStudy就相当于调用了DwrStudy类的实例
-->
<!--非单例配置 <create creator="new" javascript="userDao">
<param name="class" value="com.pk.mydwr.dao.UserDao" />
</create>--> <create creator="script" javascript="userDao"> <param name="language" value="beanshell"/> <param name="script"> import com.pk.mydwr.dao.UserDao; return UserDao.getInstance(); </param></create><convert match="com.pk.mydwr.po.User" converter="bean"></convert></allow></dwr>
firstdwr.jsp
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>My JSP 'firstajax.jsp' starting page</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
<style type="text/css">
input {
width: 220px;
height: 34px;
font-size: 22px;
}
</style>
<script type='text/javascript' src='/mydwr/dwr/interface/userDao.js'></script>
<script type='text/javascript' src='/mydwr/dwr/engine.js'></script>
<script type='text/javascript' src='/mydwr/dwr/util.js'></script>
<script type="text/javascript">
function checkEmail(obj){
userDao.isOnly(obj,function(data){
var message = "<img src='images/right.jpg'>";
if(!data){
message = "<img src='images/wrong.jpg'><b style='color:red'>该邮箱已经被占用<b>";
}
document.getElementById("emailError").innerHTML = message;
});
}
</script>
</head>
<body>
<jsp:include page="top.jsp"></jsp:include>
<form action="" method="post">
<table align="center">
<tr>
<td>
邮箱:
</td>
<td>
<input type="text" name="email" id="email" onblur="checkEmail(this.value)"/>
<span id="emailError"></span>
</td>
</tr>
<tr>
<td>
昵称:
</td>
<td>
<input type="text" name="nickname" id="nickname"/>
<span id="nicknameError"></span>
</td>
</tr>
<tr>
<td>
</td>
<td>
<input type="submit" value="注册新用户"/>
</td>
</tr>
</table>
</form>
</body>
</html>
UserDao.java
public class UserDao {
private UserDao(){
}
private static UserDao dao = null;
public static UserDao getInstance(){
if(dao == null){
dao = new UserDao();
}
return dao;
}
public boolean isOnly(String email){
boolean flag = true;
Connection conn = null;
PreparedStatement ps = null;
ResultSet rs = null;
String sql = "select id from user where email=?";
try {
conn = DBConn.getConn();
ps = conn.prepareStatement(sql);
ps.setString(1,email);
rs = ps.executeQuery();
while (rs.next()) {
flag = false;
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
DBConn.closeAll(conn,ps,rs);
}
return flag;
}
}
（编辑：李大同）
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