A Comprehensive Guide to IBM WebSphere Host Publisher Version 3.5

Chapter 18. XML Legacy Gateway 571

18.3.1 Sample servlet

The sample servlet renders host data windows in an HTML format and posts

these windows to a Web browser. This sample is a subset of the servlet which

Host Publisher uses to perform that same function as part of the Host Publisher

XML Legacy Gateway feature. As such, the sample has been simplified to

provide the Java programmer with the essentials for creating an application that

can interface to host application windows using an XML interface. The source

code is provided in the SDK and is documented throughout with comments so

that the programmer can understand the necessary steps involved in writing

similar servlets. This sample displays every host application window to the user.

A more typical application may seek to drive several application windows

automatically, and only display to the user a few pieces of data from the host

application windows. The user may then input data into the HTML form; the

application can then drive more host windows with this input, and so on.

The general flow of the servlet processing is as follows:

1. The user first accesses the servlet, causing the xmlLegacyGWSample servlet

to be instantiated and the doGet method to be invoked.

2. The servlet receives the host connection parameters via the parameters

passed with the URL.

3. The servlet sets up a hashtable to store these values, along with other initial

values. This hashtable is stored in a vector, which is then stored in a static

hashtable. The key value for the vector in the static hashtable is the Web

session ID. This allows for multiple instances of the servlet, for the same Web

session ID, to be easily manipulated.

4. The doGet method will also initialize an IBM Host On-Demand (HOD)

properties object, to be used for establishing a connection to the host.

5. An xmlLegacyProcessSample object is then instantiated and the first access

method of this object is called.

6. The xmlLegacyProcessSample object then uses the stored parameters to

establish a connection with the host. This is done by instantiating a Host

Publisher HostConnection JavaBean, and calling the acquireHostConnection

method. This function will return an HOD Session JavaBean.

7. The xmlLegacyProcessSample object will then instantiate a Host Publisher

xmlAppData JavaBean, and wire this bean to events generated by the HOD

Session bean.

8. The xmlLegacyProcessSample will then wire itself to events generated by the

xmlAppData bean. In this way the xmlLegacyProcessSample bean can

communicate with the xmlAppData bean using XML data formats, and the

572 IBM WebSphere Host Publisher Version 3.5

xmlAppData bean communicates with the host using the HOD Session bean.

This path yields the desired XML data interface to a host application.

A block diagram of the relationship of these components is illustrated in

Figure 18-2

Figure 18-2 XML Legacy Gateway architecture

When the xmlAppData bean signals that it has received data from the host, the

xmlLegacyProcessSample object retrieves this data in XML format. It then

combines this data with a stylesheet (an XSL file) using a stylesheet processor

that is included in IBM's WebSphere product. This process produces HTML

output. The HTML output contains JavaScript calls. The JavaScript file is called

lxgwfunctions.js, and is included in this sample.

The user then is presented with the host window, and is able to fill in the input

data fields and select an action to take on the windows (for example, Enter, PF1

function key, PF3, and so on) by clicking one of the buttons presented on the

HTML page.