Java-based mature server push frameworks include DWR.
DWR is an open-source solution using the Apache license protocol. It contains the server-side Java library, a DWR
Servlet and JavaScript library. Although DWR is not the only available Ajax-RPC toolkit on the Java platform, it is the most mature and provides many useful functions. From the simplest point of view, DWR is an engine that can expose methods of server-side Java objects to JavaScript code. Using DWR can effectively eliminate all Ajax request-response loops from application code. This means that the client Code no longer needs to directly process the XMLHTTPRequest object or server response. You no longer need to compile Object serialization code or use a third-party tool to convert an object into XML. You do not even need to write servlet code to adjust Ajax requests to call Java domain objects.
DWR has added the push function since 2.0, that is, it can send data from the web-server to the browser during asynchronous transmission.
A simple DWR push Program
Step 1 import jar packages related to DWR to the Project
Step 2 configure the Web. xml file
<? XML version = "1.0" encoding = "UTF-8"?> <Web-app version = "2.5" xmlns = "http://java.sun.com/xml/ns/javaee" xmlns: xsi = "http://www.w3.org/2001/XMLSchema-instance" xsi: schemalocation = "http://java.sun.com/xml/ns/javaeehttp://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"> <servlet-Name> DWR-invoker </servlet-Name> <servlet-class> Org. directwebremoting. servlet. dwrservlet </servlet-class> <! -- Set whether DWR push technology is allowed --> <init-param> <param-Name> activereverseajaxenabled </param-Name> <param-value> true </param-value> </init-param> <param-Name> maxwaitafterwrite </param-Name> <param-value>-1 </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> </Web-app>
Step 3: Compile the com. Im. Service. sendpushservice class
Public class sendpushservice {// send the message public void send (string MSG) {system. out. println ("=========== the send method is called ========="); scriptbuffer = new scriptbuffer (); // construct the JS script webcontext = webcontextfactory. get (); scriptsession myscsession = webcontext. getscriptsession (); scriptbuffer. appendscript ("dwrtest ("); scriptbuffer. appenddata (MSG); scriptbuffer. appendscript (")"); util = new util (myscsession); util. addscript (scriptbuffer); // push messages to the client }}
Step 4 define the externally exposed interface in the dwr. xml file
<allow><create creator="new" javascript="SendPushService"><param name="class" value="com.im.service.SendPushService"/></create></allow>
Step 5: compile a JSP file.
<% @ Page Language = "Java" Import = "Java. util. *" pageencoding = "UTF-8" %> <! Doctype HTML public "-// W3C // dtd xhtml 1.0 transitional // en" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <HTML xmlns = "http://www.w3.org/1999/xhtml">
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