A Comprehensive Guide to IBM WebSphere Host Publisher Version 3.5

Chapter 18. XML Legacy Gateway 581

18.6 XML Legacy Gateway JavaBean interface

The XML Legacy Gateway provides two components that communicate with a

host application:

򐂰 The xmlLegacyGateway servlet

򐂰 The xmlAppData JavaBean

Note: In addition, the HostConnection class is provided by Host Publisher.

18.6.1 The xmlLegacyGateway servlet

The xmlLegacyGateway servlet transforms XML data into HTML format. This

servlet enables viewing of a host window in a Web browser. A user can interact

with the host window in the browser by typing in the fields in the window or by

using the function keys, which are displayed as buttons in the browser. Because

the servlet interacts with the host application, most of the data processing takes

place at the server. This enables browser access to host applications from a thin

client.

The servlet uses Extensible Stylesheet Language (XSL) processing to transform

XML data to HTML format. This is a powerful example of how to transform the

host window into XML data and, through the use of a stylesheet, present it to the

end user in a different format. By replacing or modifying this servlet, the supplied

stylesheet, or both, and by using an XSL processor such as the one included in

WebSphere Application Server, the application programmer can easily render

host data onto a variety of devices using a single servlet with multiple style

sheets. The source code for the servlet is included with the Host Publisher

product.

Refer to Figure 18-2 on page 572 to see how the xmlLegacyGateway servlet

relates to the other components of the XML Legacy Gateway.

The xmlLegacyGateway servlet:

1. Is instantiated with form parameters that describe the desired host session.

These parameters describe the Telnet name of the host, the terminal format

(3270 or 5250) of the session, and so on.

2. Initiates a host session using Host Publisher and IBM Host On-Demand Java

objects and properties.

3. Instantiates the xmlAppData JavaBean and makes the JavaBean a listener for

Host On-Demand events.

4. Retrieves, after a programmed delay, the current state of the host window as

XML data from the xmlAppData JavaBean.

582 IBM WebSphere Host Publisher Version 3.5

5. Formats the XML data as HTML output using an XSL stylesheet and an XSL

processor. This output is returned to the browser.

The HTML output returned to the browser shows how the window displays on a

traditional terminal. The user can input data directly onto the HTML host window.

The user can move the cursor to the input fields using the mouse or the Tab key.

The traditional terminal function keys are presented to the user as buttons in the

browser window. The user can select the buttons by using the mouse or using

the Tab key and pressing the Enter key on the keyboard.

Two additional buttons are presented on the user's browser page: Refresh and

Disconnect. The Refresh button updates the browser's host window to the

current state of the host session, ignoring possible input. The Disconnect button

terminates the current host session. Disconnection enables an efficient use of

Host Publisher resources. The user should disconnect the host session when

interaction with the host application is no longer needed.

While the servlet is a useful application, it is an example of how to interact with

Host Publisher to encapsulate host data in XML format. The servlet could be

changed to interact with the host application using XML processing techniques,

in an automated fashion, presenting the user with a specific subset of information

obtained from the host.

The data can also be rendered in different formats by using a different XSL

stylesheet when processing the data. The servlet can be changed to render the

data in a format that matches the output preference of the user or the user's

access device. The servlet can do this at run time by specifying the XSL

stylesheet used for this particular instance of the servlet.

To facilitate the writing of Host Publisher XML Legacy Gateway servlets, the

source code for the xmlLegacyGateway servlet is included with Host Publisher.

HTML documentation is also included. The source code and all documentation

can be accessed starting with the following file:

install_dir\SDK\XLGW\Introduction.html

where install_dir is the directory in which Host Publisher is installed.

In summary, the xmlLegacyGateway servlet provides a detailed sample of how to

interface with host applications using the xmlAppData Bean. It implements basic

TN3270 and TN5250 HTML-to-Host Emulation by using about 90% of the XML

gateway application interface.

Note: The sample XML Legacy Gateway Administration is located in the

<HostPub>\SDK\XLGW\Servlet\xmlLegacyGatewayServletSample.