DWR初次尝试

这几天听同事说DWR很好，比ajax好用多了，也很简单方便，就试试。我的开发环境是MyEclipse4.1+JDK1.4.2+TOMCAT5.0.2x。仿照DWR官方网站上的例子做了几个，感觉很好。不过我试着通过客户端传个参数到服务器就出现问题了（以前的都没有带参数），老报错Invalid reply from server。

web.xml

< servlet >
     < servlet-name > dwr-invoker </ servlet-name >
     < servlet-class > uk.ltd.getahead.dwr.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 >

dwr.xml

<? xml version="1.0" encoding="UTF-8" ?>
<! DOCTYPE dwr PUBLIC "-//GetAhead Limited//DTD Direct Web Remoting 1.0//EN" "http://www.getahead.ltd.uk/dwr/dwr10.dtd" >  
< dwr >  
< allow >  
< create  creator ="new"  javascript ="JDate" >  
< param  name ="class"  value ="com.huaying.caochen.TestDate" />  
</ create >  
</ allow >  
</ dwr >  

java类

package  com.huaying.caochen;

public   class  TestDate  ... {
    public String getHello(String str)
    ...{
        return str;
    }
}

index.jsp

 

< html >  
< head >  
< title > DWR - Test Home </ title >  
< script  type ='text/javascript'  src ='dwr/interface/JDate.js' ></ script >  
< script  type ='text/javascript'  src ='dwr/engine.js' ></ script >  
< script  type ='text/javascript'  src ='dwr/util.js' ></ script >
< script  type ='text/javascript'  language ="javascript" > ...  
function checkStr()...{ 
JDate.getHello(loadStr,DWRUtil.getValue("str"));
}
function loadStr(data)
...{
    DWRUtil.setValue("reply",data);
}
</ script >  
</ head >  
< body >
< form  action ="index.jsp"  method ="post" >
str: < input  type ="text"  name ="str"   />< br >
< input  type ="button"  onclick ="checkStr()"  value ="submit" />
</ form >
< span  id ="reply" ></ span >< br >
</ body >  
</ html >  

每次都报Invalid reply from server这个错误，不带参数的是好的，但是看官网上的例子是可以带参数的，估计就是开发环境的问题了。

我先把TOMCAT5.5装上，运行之后在控制台有错误消息提示，而这在以前那个版本是没有的，把这个错误消息baidu一下，根据http://www.pocketshark.com/blog/page/tempo?entry=javatwo_2006_ajax_client_server最后那个高人的指点有必要升级jdk的版本。

jdk1.5安装并且配置好之后重新启动tomcat，没有问题，不过执行http://localhost:8080/myapp/dwr/总是报下面的错误：

 

javax.servlet.ServletException: Servlet.init() for servlet dwr-invoker threw exception 
   org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java: 118 ) 
   org.apache.coyote.tomcat5.CoyoteAdapter.service(CoyoteAdapter.java: 160 ) 
   org.apache.coyote.http11.Http11Processor.process(Http11Processor.java: 799 ) 
   org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java: 705 ) 
   org.apache.tomcat.util.net.TcpWorkerThread.runIt(PoolTcpEndpoint.java: 577 ) 
   org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java: 683 ) 
   java.lang.Thread.run(Thread.java: 595 ) 

再baidu一下，找到http://jivesoftware.com/jive/thread.jspa?threadID=15861&tstart=15，说是Tomcat和JDK1.5中的 xml-parser 冲突，于是就把TOMCAT/common/endorsed/xml-apis.jar删掉，重启tomcat。

在DWR启动的时候还有错误：

 

java.lang.IllegalArgumentException: DefaultContainer can't find a classes
    at org.directwebremoting.impl.DefaultContainer.getBean(DefaultContainer.java: 216 )
    at org.directwebremoting.annotations.AnnotationsConfigurator.configure(AnnotationsConfigurator.java: 50 )
    at org.directwebremoting.servlet.DwrServlet.init(DwrServlet.java: 121 )
    at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java: 1105 )
    at org.apache.catalina.core.StandardWrapper.allocate(StandardWrapper.java: 757 )
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java: 130 )
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java: 178 )
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java: 126 )
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java: 105 )
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java: 107 )
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java: 148 )
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java: 869 )
    at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java: 664 )
    at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java: 527 )
    at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java: 80 )
    at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java: 684 )
    at java.lang.Thread.run(Thread.java: 595 )

再baidu查到http://www.javafan.cn/archives/2006/09/125.html，原因是因为启动时会检查JDK5的annotations，还没用到annotations注释，解决办法，就是初始化时加上java.lang.Object，如下：

 

< servlet >  
         < servlet - name > dwr - invoker </ servlet - name >  
         < display - name > DWR Servlet </ display - name >  
         < servlet - class > org.directwebremoting.servlet.DwrServlet </ servlet - class >  
         < init - param >  
             < param - name > debug </ param - name >  
             < param - value > false </ param - value >  
         </ init - param >  
          < init - param >  
            < param - name > classes </ param - name >  
            < param - value > java.lang.Object </ param - value >  
         </ init - param >  
         < load - on - startup > 1 </ load - on - startup >  
</ servlet >  
< servlet - mapping >  
         < servlet - name > dwr - invoker </ servlet - name >  
         < url - pattern >/ dwr /**/ /*</url-pattern> 
</servlet-mapping>

 好了，大功告成，主要原因是我的开发工具版本过低，不过总结一下自己的教训，给初学者一个参考吧！