Integration of DWR using DWRSpringServlet

DWR is a Easy Ajax for Java. To know more click here.

In this article we will see sample codes for integration of DWR with DWRSpringServlet

Step 1 - Create a web project in eclipse.

Step 2 - Add below Spring libraries

• Spring Core libraries
• Spring Web libraries
• Spring AOP libraries

Step 3 - Add dwr.jar

Download appropriate version of dwr.jar and add it in your application classpath. For example DWR 3 requires Spring version 2.5 or greater.

Step 4 - Create dependent files

web.xml

The DwrSpringServlet can be used if you are not using Spring MVC. This servlet gains access to the Spring context configured in your web.xml. You can create your own context file, in our case it is dwrcontext.xml.

dwrcontext.xml

DWRService.java

index.jsp

Step 5 - Deploy the project in tomcat (or any other web server) and check the output

Integration of DWR using Spring MVC

DWR is a Easy Ajax for Java. To know more click here.

In this article we will see sample codes for integration of DWR with spring MVC

Step 1 - Create a web project in eclipse.

Step 2 - Add below Spring libraries

• Spring Core libraries
• Spring Web libraries
• Spring AOP libraries

Step 3 - Add dwr.jar
Download appropriate version of dwr.jar and add it in your application classpath. For example DWR 3 requires Spring version 2.5 or greater.

Step 4 - Create dependent files

web.xml
Create spring DispatcherServlet and map URL pattern as shown below

javaxp-servlet.xml
If you are using Spring MVC you must declare dwr controller and url mapping i.e. SimpleUrlHandlerMapping as shown below

DWRService.java

index.jsp

Step 5 - Deploy the project in tomcat (or any other web server) and check the output

Spring bean syntax

1. Import resources

Below is the syntax to import resources from various files. It is helpful when you want to bifurcated beans and database configuration in separate files and merger everything into single servlet. Here you can provide absolute or relative path of the source file.

<beans>
<import resource="file1.xml" />
<import resource="../file2.xml" />
</beans>

2. Spring MVC Dispatcher Servlet, syntax to load XMLs using init param

You can use it in web.xml file to XMLs using init param. You can load various XMLs like  beans and database configuration etc.

<web-app>
    <servlet>
        <servlet-name>test</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>            
            <param-name>contextConfigLocation</param-name>
            <param-value>
                /WEB-INF/test/*.xml
            </param-value>        
        </init-param>        
        <load-on-startup>1</load-on-startup>
    </servlet>

    <servlet-mapping>
        <servlet-name>test</servlet-name>
        <url-pattern>/test/*.do</url-pattern>
    </servlet-mapping>
</web-app>

3. Url Handler Mapping syntax

Below is the example for Mapping URLs with respective beans, this is useful when you want to keep all URLs mapping together at one place.

<beans>

    <bean id="handlerMapping" class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
        <property name="mappings">
        <props>
            <prop key="/sfc.do">simpleFormController</prop>
            <prop key="/mac.do">multiActionController</prop>
        </props>
        </property>
    </bean>


    <bean id="simpleFormController" class="com.javaxp.FormController" autowire="byName">
        <property name="commandName" value="formBean"></property>
        <property name="commandClass" value="com.javaxp.FormBean"></property>
        <property name="formView" value="form"></property>
        <property name="successView" value="submit"></property>        
    </bean>

    <bean id="multiActionController" class="org.springframework.web.servlet.mvc.multiaction.ParameterMethodNameResolver">
<property name="paramName" value="action" />
<property name="defaultMethodName" value="defaultPage" />
    </bean>

</beans>

SAXException - Failed to resolve: arg0=-//GetAhead Limited//DTD Direct Web Remoting *.0//EN

In my previous article I have shown you a simple hello world DWR example however while trying to implement it in an application I faced below exception.


SEVERE: DwrServlet.init() failed
org.xml.sax.SAXException: Failed to resolve: arg0=-//GetAhead Limited//DTD Direct Web Remoting 3.0//EN arg1=http://directwebremoting.org/schema/dwr30.dtd
at org.directwebremoting.impl.DTDEntityResolver.resolveEntity(DTDEntityResolver.java:59)
at com.sun.org.apache.xerces.internal.util.EntityResolverWrapper.resolveEntity(EntityResolverWrapper.java:107)
at com.sun.org.apache.xerces.internal.impl.XMLEntityManager.resolveEntityAsPerStax(XMLEntityManager.java:1018)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$DTDDriver.dispatch(XMLDocumentScannerImpl.java:1190)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$DTDDriver.next(XMLDocumentScannerImpl.java:1089)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$PrologDriver.next(XMLDocumentScannerImpl.java:1002)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:648)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:510)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:807)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:737)
at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:107)
at com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(DOMParser.java:225)
at com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(DocumentBuilderImpl.java:283)
at javax.xml.parsers.DocumentBuilder.parse(DocumentBuilder.java:124)
at org.directwebremoting.impl.DwrXmlConfigurator.setInputStream(DwrXmlConfigurator.java:132)
at org.directwebremoting.impl.DwrXmlConfigurator.setServletResourceName(DwrXmlConfigurator.java:87)
at org.directwebremoting.impl.ContainerUtil.configureFromDefaultDwrXml(ContainerUtil.java:263)
at org.directwebremoting.impl.ContainerUtil.configureContainerFully(ContainerUtil.java:421)
at org.directwebremoting.servlet.DwrServlet.init(DwrServlet.java:79)
at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1139)
at org.apache.catalina.core.StandardWrapper.allocate(StandardWrapper.java:791)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:127)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:174)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:108)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:174)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:874)
at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:665)
at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:528)
at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:81)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:689)
at java.lang.Thread.run(Thread.java:619)
Jan 16, 2013 2:05:46 AM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Allocate exception for servlet dwr-invoker
org.xml.sax.SAXException: Failed to resolve: arg0=-//GetAhead Limited//DTD Direct Web Remoting 3.0//EN arg1=http://directwebremoting.org/schema/dwr30.dtd
at org.directwebremoting.impl.DTDEntityResolver.resolveEntity(DTDEntityResolver.java:59)
at com.sun.org.apache.xerces.internal.util.EntityResolverWrapper.resolveEntity(EntityResolverWrapper.java:107)
at com.sun.org.apache.xerces.internal.impl.XMLEntityManager.resolveEntityAsPerStax(XMLEntityManager.java:1018)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$DTDDriver.dispatch(XMLDocumentScannerImpl.java:1190)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$DTDDriver.next(XMLDocumentScannerImpl.java:1089)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$PrologDriver.next(XMLDocumentScannerImpl.java:1002)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:648)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:510)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:807)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:737)
at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:107)
at com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(DOMParser.java:225)
at com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(DocumentBuilderImpl.java:283)
at javax.xml.parsers.DocumentBuilder.parse(DocumentBuilder.java:124)
at org.directwebremoting.impl.DwrXmlConfigurator.setInputStream(DwrXmlConfigurator.java:132)
at org.directwebremoting.impl.DwrXmlConfigurator.setServletResourceName(DwrXmlConfigurator.java:87)
at org.directwebremoting.impl.ContainerUtil.configureFromDefaultDwrXml(ContainerUtil.java:263)
at org.directwebremoting.impl.ContainerUtil.configureContainerFully(ContainerUtil.java:421)
at org.directwebremoting.servlet.DwrServlet.init(DwrServlet.java:79)
at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1139)
at org.apache.catalina.core.StandardWrapper.allocate(StandardWrapper.java:791)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:127)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:174)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:108)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:174)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:874)
at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:665)
at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:528)
at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:81)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:689)
at java.lang.Thread.run(Thread.java:619)
Jan 16, 2013 2:09:33 AM org.apache.catalina.startup.HostConfig checkResources

JSTL: How to access fmt:message from Javascript

You might have seen How to use fmt:message and ResourceBundle from JSP and Java in my earlier post, click here.

Now we will see how to use fmt:message from Javascript. Its very simple to use JSTL's fmt tag in JavaScript to localize alert messages.

I found two ways in which you can access values from a property file in javascript. Please see the sample codes below.

Method 1.

<%@ taglib uri="http://java.sun.com/jsp/jstl/fmt" prefix="fmt"%>
<script type="text/javascript">
<!--
var msg = {
prop1: "<fmt:message key="prop1" />",
prop2: "<fmt:message key="prop2" />"
};

function test() {  
 alert(msg.prop1);
alert(msg.prop2);
}

//-->
</script>

Method 2.

<%@ taglib uri="http://java.sun.com/jsp/jstl/fmt" prefix="fmt"%>
<script type="text/javascript">
<!--
<fmt:message key="prop1" var="prop1"/>    
var prop1 = "${prop1}";

function test() {  
 alert(prop1);
}

//-->
</script>

Javascript : On scroll fill data at the end of the page

Other day while browsing facebook, i saw when we scroll to the end of the home page it fills more data without refreshing the whole page. Again when u reach to the end of the page it fetches more data and this continues. I didn't bother to check its upper limit, may be at some point of time it will go out of memory of the browser.

So lets see how this functionality can be achieved. Below javascript variables can be used to detect when user have reached to the end of the body.

• document.body.scrollTop - scroll bar position
• document.body.scrollHeight - height of the scroll bar
• document.body.clientHeight - total height of the body

so if (scrollHeight - scrollTop) is equal to clientHeight you have reached to the end of the body. And obviously you can use various APIs like AJAX, DWR, Ext JS etc to load data without refreshing the whole page.

Below is the standalone tested HTML code, directly you can test this example no need to have any server. Please see the self explanatory html code.


<HTML>

<HEAD>
<TITLE>Scroll Example</TITLE>
<SCRIPT LANGUAGE="JavaScript">
<!--
divCount = 1;
function onScrollDiv()
{
if((document.body.scrollHeight - document.body.scrollTop) == document.body.clientHeight)
{
onLoadData();
}

return false;
}

function onLoadData()
{
previousCount = divCount;
divCount++;

//Get data using AJAX, DWR, Ext JS etc
htmlData = "<table width='50%' border='1'><tr><td height='200px' align='center'>"+new Date()+"</td></tr></table>";

document.getElementById("div"+previousCount).innerHTML = htmlData;

var newDiv = document.createElement("div");
newDiv.innerHTML = "<div id='div"+divCount+"'>Loading...</div>"
var previousDiv = document.getElementById("div"+previousCount);

insertAfter(newDiv,previousDiv.parentNode);
return false;
}

function insertAfter(new_node, existing_node) {

if (existing_node.nextSibling) {
existing_node.parentNode.insertBefore(new_node, existing_node.nextSibling);
} else {
existing_node.parentNode.appendChild(new_node);
}
}

//-->
</SCRIPT>
</HEAD>
<BODY onload="onLoadData();" onscroll="onScrollDiv();">
<center>
Simple Javascript example which fills data when you scroll at the end of the file same like Facebook
<br />
Resize the window so that scroll bar appears on the right hand side then you can test it.

<div>
<div id="div1"></div>
</div>

</center>
</BODY>
</HTML>

DWR Hello World example

DWR - Direct Web Remoting

DWR is a Java library that enables Java on the server and JavaScript in a browser to interact and call each other as simply as possible. In simple words DWR is Easy Ajax for Java. Unlike AJAX you don't have to write codes to get XHTML object or check for state change etc. To know more about DWR, click here.

DWR is supported by almost all browsers like Firefox,Internet Explorer,Opera and Safari. To know more, click here.

About the example

We will create a simple java class (i.e HelloWorld.java) with a method sayHello() which will accept a name and print Hello name. We can call this java fuction with JavaScript in a browser. Same as Ajax call without refreshing the whole page.

Below are the steps to run the example.

1. For running the below example you need to add below mentioned JAR file in lib folder of your web project.

• dwr.jar
• commons-logging-1.1.1.jar 

For downloading dwr.jar, click here. 
commons-logging-1.1.1.jar, click here.


2. Add the DWR servlet definition and mapping to your application's web.xml. This is just like defining a normal servlet.

<servlet>
  <display-name>DWR Servlet</display-name>
  <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>