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DWR (Direct Web Remoting) Integration

This document describes the DWR integration in TreeBASE and its Spring 5 compatibility implementation.

Overview

DWR (Direct Web Remoting) is a Java library that enables AJAX functionality by allowing JavaScript in the browser to call Java methods on the server. Remote calls appear as local JavaScript function calls.

DWR Usage in TreeBASE

TreeBASE uses DWR for interactive features:

  1. Person Email Autocomplete - RemotePersonService.findCompleteEmailAddress()
  2. Software Name Autocomplete - RemoteSoftwareNameService.findCompleteSoftwareName()
  3. Journal Name Autocomplete - RemoteJournalNameService.findCompleteJournalName()
  4. Algorithm Suggestions - RemoteUniqueOtherAlgorithmService.findAllUniqueOtherAlgorithmDescriptions()
  5. File Upload Progress - RemoteAjaxProgressListener.getStatus()

Spring 5 Compatibility

The Challenge

DWR 3.0.2-RELEASE was released before Spring 5.0 (September 2017) and uses Spring APIs that changed in Spring 5.x. The main issue is how DWR's DwrSpringServlet retrieves the Spring WebApplicationContext.

The Solution

A Spring 5-compatible wrapper servlet was created: org.cipres.treebase.web.dwr.Spring5CompatibleDwrServlet

This servlet:

  • Extends org.directwebremoting.spring.DwrSpringServlet
  • Uses Spring 5-compatible methods to retrieve the WebApplicationContext
  • Ensures proper initialization order

Configuration

Maven Dependency

In treebase-web/pom.xml:

<dependency>
    <groupId>org.directwebremoting</groupId>
    <artifactId>dwr</artifactId>
    <version>3.0.2-RELEASE</version>
</dependency>

Servlet Configuration

In WEB-INF/web.xml:

<servlet>
    <servlet-name>dwr</servlet-name>
    <servlet-class>org.cipres.treebase.web.dwr.Spring5CompatibleDwrServlet</servlet-class>
    <init-param>
        <param-name>allowGetForSafariButMakeForgeryEasier</param-name>
        <param-value>true</param-value>
    </init-param>
    <init-param>
        <param-name>debug</param-name>
        <param-value>true</param-value>
    </init-param>
</servlet>

<servlet-mapping>
    <servlet-name>dwr</servlet-name>
    <url-pattern>/dwr/*</url-pattern>
</servlet-mapping>

Spring Bean Configuration

In WEB-INF/applicationContext.xml:

<beans xmlns:dwr="http://www.directwebremoting.org/schema/spring-dwr"
       xsi:schemaLocation="...
       http://www.directwebremoting.org/schema/spring-dwr
       http://www.directwebremoting.org/schema/spring-dwr-3.0.xsd">

    <bean id="remotePersonService" class="org.cipres.treebase.dao.admin.PersonDAO">
        <dwr:remote javascript="RemotePersonService">
            <dwr:include method="findCompleteEmailAddress" />
        </dwr:remote>
        <property name="sessionFactory"><ref bean="sessionFactory"></ref></property>
    </bean>
    
    <!-- Additional remote services configured similarly -->
</beans>

DWR Configuration

In WEB-INF/dwr.xml:

<!DOCTYPE dwr PUBLIC
    "-//GetAhead Limited//DTD Direct Web Remoting 3.0//EN"
    "http://getahead.org/dwr/dwr30.dtd">
<dwr>
    <allow>
        <!-- Additional DWR configurations can be added here -->
    </allow>
</dwr>

JavaScript Usage

In JSP templates:

// Include DWR JavaScript libraries
<script src="<c:url value='/dwr/interface/RemotePersonService.js'/>"></script>
<script src="<c:url value='/dwr/engine.js'/>"></script>
<script src="<c:url value='/dwr/util.js'/>"></script>

// Call remote methods
function updateList(autocompleter, token) {
    RemotePersonService.findCompleteEmailAddress(token, function(data) {
        autocompleter.setChoices(data)
    });
}

Testing DWR

To test if DWR is working:

  1. Start the application
  2. Navigate to: http://your-server/treebase-web/dwr/
  3. You should see the DWR index page listing all exposed methods
  4. Click on any service to test it interactively

Troubleshooting

No Spring WebApplicationContext Found

Cause: Spring context not initialized before DWR

Solution: Ensure StartupListener (extends ContextLoaderListener) is configured in web.xml and Spring context files load properly.

DWR JavaScript Errors

Causes:

  • URL pattern /dwr/* not correctly mapped
  • JavaScript includes in wrong order

Solutions:

  • Verify servlet mapping in web.xml
  • Check browser console for detailed errors
  • Enable DWR debug mode during development

Method Not Found Errors

Causes:

  • Method not public in DAO class
  • Missing or incorrect <dwr:include> configuration
  • Bean not properly injected

Solutions:

  • Verify method is public
  • Check <dwr:include method="methodName" /> configuration
  • Ensure bean has required dependencies (e.g., sessionFactory)

References