Among today’s fashionable buzzwords in web development is Ajax. Fortunately, when you’re using the BEA WebLogic Portal framework, it’s easy to add a bit of this hot new technology to your application. For a project I did this year, we used the JSON-RPC-Java Ajax implementation. To use JSONRPC(JavaScript Object Notation remote procedure call protocol), you drop the downloaded jsonrpc.jar in your application’s APP-INF/lib directory. This library contains a servlet that will catch and process your Ajax actions. You’ll have to configure the servlet in the web.xml (see the detailed instructions). Then it’s up to you to do some JavaScript coding.

It works like this: first, reference a JSONRPCBridge object which you can use to connect to Java objects:

<jsp:useBean id="JSONRPCBridge" scope="session"
    class="com.metaparadigm.jsonrpc.JSONRPCBridge" />

Next, you declare what Java object you want to make available in JavaScript. The Java object can be a POJO that you instantiate right there in your JSP:

<% JSONRPCBridge.registerObject("myObject",
    new com.package.myobjects.MyObject()); %>

Alternatively, in order to be able to communicate with your pageflow, you could have the pageflow instantiate an object, pass whatever data you need, and make that object available to the JSP through a getter method on the pageflow. Then on the JSP, do a getData to put the object on the pageContext where JSONRPC can pick it up:

<netui-data:getData resultId="myObject"
    value="{pageFlow.myObject}" />
<% JSONRPCBridge.registerObject("myObject",
    pageContext.getAttribute("myObject")); %>

After this comes the JavaScript part. Start by defining a jsonrpc JavaScript variable that knows where to find the servlet. As if by magic, this JavaScript variable will know about the Java objects you’ve declared earlier. You can now call, in JavaScript, any public methods on the Java object:

<script language="javascript">
    jsonrpc = new JSONRpcClient("/MyWebAppName/JSON-RPC");
    function getInterestingDataFromJava() {
        return jsonrpc.myObject.getInterestingData();
    }
</script>

You might wonder, why not make the pageflow itself available to JSONRPC? Technically this would be possible, but remember: all of the public methods will be available in JavaScript. Do you really want this? I think it might well be a security issue, so I always use a facade object to control what I make available.

A JSP tag for readonly access

If all you want is to access a Java bean’s properties in JavaScript, you could use the JSONSerializer which is included in the JSON API. This class contains a utility method, serialize(), that will write out the JavaScript code to create and initialize a hash array containing the property names and values of the Java object you pass it. Furthermore, you could write a custom JSP tag that does this for you, which you could use like this:

<script language="javascript">
    function getFullName() {
        return <jsonrpc value="{actionForm.firstname}" />
                + ' '
                + <jsonrpc value="{actionForm.lastname}" />;
    }
</script>

This only works for reading the properties, though; for write access you’ll have to call a setter on the object.