DWR框架学习
我的理解：DWR框架是javaWeb中前后端直接交互的解决方案，用DWR框架，前端js能够直接调用后端服务，后端服务也可以直接调用前端js函数。
配置：
（1）需要Dwr.jar 包，pom配置如下：
<dependency> <groupId>org.directwebremoting</groupId> <artifactId>dwr</artifactId> <version>3.0.M1</version> </dependency>
（2）在Web.xml中配置servelet,如下：
<!-- DWR配置 --> <servlet> <servlet-name>dwr-invoker</servlet-name> <servlet-class> org.directwebremoting.servlet.DwrServlet </servlet-class> <init-param> <param-name> org.directwebremoting.extend.ServerLoadMonitor </param-name> <param-value> org.directwebremoting.impl.PollingServerLoadMonitor </param-value> </init-param> <!-- 默认轮询的周期是5秒中,也就是5000毫秒.如果想改变这个默认值需要下面的配置改为6秒 --> <init-param> <param-name>disconnectedTime</param-name> <param-value>5000</param-value> </init-param> <init-param> <description>使用服务器推技术(反转AJAX)</description> <param-name>activeReverseAjaxEnabled</param-name> <param-value>true</param-value> </init-param> <init-param> <param-name>crossDomainSessionSecurity</param-name> <param-value>false</param-value> </init-param> </servlet> <servlet-mapping> <servlet-name>dwr-invoker</servlet-name> <url-pattern>/dwr/*</url-pattern> </servlet-mapping>
（3）实现一个后端服务，就是一个普通的类
public class MessageServiceImpl { public void sendMassage() { ScriptBuffer sb = new ScriptBuffer(); sb.appendScript("alert(12345)"); scriptSession.addScript(sb); } }
scriptSession对应每个链接的会话，通过写入script脚本去前端执行。scriptSession可以通过如下方式获取：
WebContext context = WebContextFactory.get();
ScriptSession session = context.getScriptSession();
（4）在WEB-INF目录下创建dwr.xml文件
<dwr>
<allow>
<create creator="new" javascript="MessageServiceImpl" scope = "session"> <param name="class" value=".....MessageServiceImpl"></param> </create>
</allow>
</dwr>
(5)jsp中调用后端服务
<%@page contentType="text/html" pageEncoding="UTF-8"%> <!DOCTYPE html> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>JSP Page</title> <script src="<%=request.getContextPath()%>/dwr/engine.js"></script> <script src="<%=request.getContextPath()%>/dwr/interface/MessageServiceImpl.js"></script> <script> MessageServiceImpl.sendMessage(); </script> </head> <body> <h1>Hello World!</h1> </body> </html>
（6）接收后端推送
dwr.engine.setActiveReverseAjax(true);
