10 XDK JavaBeans

Database Connectivity

Database Connectivity is included with the XDK JavaBeans. The beans can now connect directly to a JDBC-enabled database to retrieve and store XML and XSL files.

XDK JavaBeans Overview

XDK JavaBeans comprises the following beans:

Use for Asynchronous Parsing in the Background

The DOMBuilder bean encapsulates the XML Parser for Java with a bean interface. It extends its functionality to permit asynchronous parsing. By registering a listener, a Java application can parse documents and return control return to the caller.

Asynchronous parsing in a background thread can be used interactively in visual applications. For example, when parsing a large file with the normal parser, the user interface freezes until the parsing has completed. This can be avoided with the DOMBuilder bean. After calling the DOMBuilder bean parse method, the application can immediately regain control and display "Parsing, please wait". If a "Cancel" button is included you can also cancel the operation. The application can continue when domBuilderOver() method is called by DOMBuilder bean when background parsing task has completed.

When parsing a large number of files, DOMBuilder JavaBean can save time. Response times that are up to 40% faster have been recorded when compared to parsing the files one by one.

DOMBuilder JavaBean Usage

Figure 10-1 illustrates DOMBuilder JavaBean usage.

1. The XML document to be parsed is input as a file, string buffer, or URL.

2. This inputs the method DOMBuilder.addDOMBuilderListener(DOMBuilderListener) and adds DOMBuilderListener.

3. The DOMBuilder.parser() method parses the XML document.

4. Optionally, the parsed result undergoes further processing.

5. DOMBuilderListener API is called using DOMBuilderOver() method. This is called when it receives an asynchronous call from an application. This interface must be implemented to receive notifications about events during asynchronous parsing. The class implementing this interface must be added to the DOMBuilder using addDOMBuilderListener method.

   Available DOMBuilderListener methods are:

   • domBuilderError(DOMBuilderEvent). This method is called when parse errors occur.

   • domBuilderOver(DOMBuilderEvent). This method is called when the parse completes.

   • domBuilderStarted(DOMBuilderEvent). This method is called when parsing begins.

6. DOMBuilder.getDocument() fetches the resulting DOM document and outputs the DOM document.

Figure 10-1 DOMBuilder JavaBean Usage

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XSLTransformer JavaBean: Regenerating HTML Only When Data Changes

This scenario illustrates one way of applying XSLTransformer JavaBean.

1. Create a SQL query. Store the selected XML data in a CLOB table.

2. Using the XSLTransfomer JavaBean, create an XSL stylesheet and interactively apply this to the XML data until you are satisfied with the data presentation. The output can be HTML produced by the XSL transformation.

3. Now that you have the desired SQL (data selection) and XSL (data presentation), create a trigger on the table or view used by your SQL query. The trigger can execute a stored procedure. The stored procedure, do the following:

   • Run the query

   • Apply the stylesheet

   • Store the resulting HTML in a CLOB table

4. This process can repeat whenever the source data table is updated.

   The HTML stored in the CLOB table always mirrors the last data stored in the tables being queried. A JSP (JavaServer Page) can display the HTML.

   In this scenario, multiple end users do not produce multiple data queries that contribute to increased use of the database. The HTML is regenerated only when the underlying data changes.

How to Use XSLTransformer JavaBean

Figure 10-2 illustrates XSLTransformer bean usage.

Figure 10-2 XSLTransformer JavaBean Usage

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1. An XSL stylesheet and XML document are input to the XSLTransformer using the XSLTransfomer.addXSLTransformerListener (XSLTransformerListener)method. This adds a listener.

2. The XSLTransfomer.processXSL() method initiates the XSL transformation in the background.

3. Optionally, other work can be assigned to the XSLTransformer bean.

4. When the transformation is complete, an asynchronous call is made and the XSLTransformerListener.xslTransformerOver() method is called. This interface must be implemented to receive notifications about events during the asynchronous transformation. The class implementing this interface must be added to the XSLTransformer event queue using the method addXSLTransformerListener.

5. The XSLTransformer.getResult() method returns the XML document fragment for the resulting document.

6. It ouputs the XML document fragment.

DBAcess JavaBean Usage

Figure 10-3 illustrates the DBAccess bean usage. It shows how DBAccess bean maintains, and manipulates XML documents stored in CLOBs.

Figure 10-3 DBAccess JavaBean Usage Diagram

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Installing the JavaBean Examples

The JavaBeans require, as a minimum, JDK 1.2.2.

Here are the steps you take to generate the sample executables:

1. Download and install the following components used by the XDK JavaBeans:

   • Oracle JDBC Driver for thin client (file classes12.zip)

   • Oracle XML SQL Utility (xsu12.jar)

   • JAR file containing the XMLType definitions (file xdb.jar)

   After installing these components, include the files in your CLASSPATH.

2. Change JDKPATH in Makefile to point to your JDK path. If you do not have an ORACLE_HOME set, then set it to the root directory of your XDK JavaBeans installation.

3. Generate .class files. Run the sample programs using the following commands, which use labels in the file Makefile:

   gmake sample3
   gmake sample5
   gmake sample6
   gmake sample7
   gmake sample10
   
   

XMLDiffSample.java

Sample6 is a demo for XMLDiff JavaBean. It invokes a GUI which allows you to choose the input data files from the File menu using 'Compare XML Files' item. The XSLT generated can be applied on input XML file1 using Transform menu. The resulting XML file (which is the same as input file2) can be saved using 'Save' As item under File menu. By default, the two XML files XMLDiffData1.txt and XMLDiffData2.txt are compared and the output XSLT is stored as XMLDiffSample.xsl.

If the input XML files have a DTD which accesses a URL outside the firewall, then modify XMLDiffSample.java to include the proxy server settings before the setFiles() call:

/* Set proxy to access dtd through firewall */
    Properties p = System.getProperties();
    p.put("proxyHost", "www.proxyservername.com");
    p.put("proxyPort", "80");
    p.put("proxySet", "true");

You also have to import java.util.*;

XSDValidatorSample.java

Sample10 is a demonstration for the XSDValidator JavaBean. It takes as default the data file purchaseorder.xml and the purchaseorder.xsd schema file. The output displays the validation errors.