XML stands for eXtensible Markup Language.
It is a markup language similar to HTML. XML is a markup language for structuring
data rather than formatting information. You use XML to create a document that
contains structured data that can be used or interpreted by other applications.
The format or structure is straightforward and can be used by any person or
program that can read text.
The Benefits of Using XML
One significant benefit of XML is that you can exchange data
between applications in a simple, nonproprietary format. Because the language
is extensible, you create tags that are specific to your business. For example,
your document may contain tags to structure information about books. Those tags
may include <title>, <author>, and <desc>. With these tags,
other applications can parse the document for specific information, ignore some
information, or even search for a specific title.
<?xml version='1.0'?>
<LIBRARY>
<BOOK>
<TITLE>Is This Your Child</TITLE>
<AUTHOR>Doris Rapp M.D.</AUTHOR>
<DESC>Discovering and treating unrecognized allergies
in children and adults.</DESC>
</BOOK>
</LIBRARY>
XML and Parsing
In order to programmatically access an XML document, you need
to parse it. There are several standards-based ways to do so with the
most common one being DOM (Document Object Model). DOM parsing is a W3C
standard and while available in the Oracle XML Parser, it is not an optimum
choice when working with large XML documents because it constructs an in-memory
document tree that can be more than 10 times the size of the original document.
There is an alternative to DOM called SAX (Simple API for
XML), which is an event-driven form of parsing and thus consumes very few resources
regardless of the document size. SAX parsing is also available in the
Oracle XML Parser. While SAX parsing does not support in-memory manipulation
of a document, it can effectively be used to do simple transformations that
do not require navigating backwards or significant structure change of the entire
document.
Obviously, preparing a document to be printed is a simple
transformation that is well suited for SAX parsing. Instead of requiring
you to create the necessary event handlers to implement printing, the Oracle
SAX Parser provide this new class built-in XMLSAXSerializer.
XML, Databases and the XDK
The ability to extract data with its meta-data providing the
context is a common XML function. Unfortunately, from a programmer’s
viewpoint, this data can many times consist of hundreds if not thousands of
rows that then need to be encapsulated into XML. The standard way to implement
this would be to use the DOM to construct this document, however because of
the need to construct it entirely in memory before it could be serialized, this
approach is not practical.
The Oracle XDK includes the XML SQL Utility, which simplifies
the extraction of the data already tagged in XML, and with its ability to generate
SAX events as its XML output along with the new XMLSAXSerializer class makes
this implementation easy and efficient.
Having installed Oracle Database 10g as part of the pre-requisites,
you will have installed the XDK. The main part of the XDK can be found
at <ORACLE_HOME>/xdk, the Java XDK library (xmlparserv2.jar) and the
Java XSU library (xsu12.jar) in <ORACLE_HOME>/lib. Oracle's JDBC
driver can also be found at <ORACLE_HOME>/jdbc/lib/classes12.jar.
In order to build an XML Application using JDeveloper , you
need to perform the following steps:
You need to create a workspace and project before you start
creating the application.
1.
Open JDeveloper.
2.
Click File > New . Select Workspace. Click OK.
3.
Change the Directory and Filename as easyxml.
Make sure Add a New Empty Project is checked . Click OK.
4.
Enter the project directory and file name as easyxml
and click OK.
5.
Once the Project is created you will see it in the System
Navigator.
Configure the project for XML
You need set the projects classpath to include the XML libraries.
Perform the following:
1.
Right click on the easyxml.jpr project and select Project
Settings.
2.
Select the Libraries entry in the settings navigator.
Here you can configure the CLASSPATH of your project. In the
Available Libraries you might already have entries for the Oracle XML
Parser V2 and the Oracle XML SQL Utility. Since you are
using an older version of JDeveloper these are not the 10g libraries and
you need to create some new librarys. Click the New button.
3.
Name the library 10gXML and press the Edit
button for the Class Path.
4.
Click Add Entry.
5.
In the Directory Name field enter/u01/app/oracle/product/10.1.0/db_1/lib
and press enter.
6.
Select xmlparserv2.jar
and xsu12.jar and
click Select.
7.
Click OK to add the jar files to the classpath.
8.
Click OK to create the library.
9.
You need to also create a library for JDBC. Click
the New button again.
10.
Name the library 10gJDBC and press the Edit
button for the Class Path.
11.
Click Add Entry.
12.
In the Directory Name field enter /u01/app/oracle/product/10.1.0/db_1/jdbc/lib
and press enter.
13.
Select classes12.jar
and nls_charset12.jar
and click Select.
You can not retrieve the database data as an XML Document
by performing the following:
1.
Download the example source file available here. Unzip it into the easyxml project directory
/home/oracle/jdevhome/mywork/easyxml/easyxml.
2.
In JDeveloper select the easyxml project in the
navigator and press the add file button in the System Navigator pane.
3.
Browse to the src/oracle/xml/sample
directory and add the XSUSAXPrint.java
file to the project.
4.
You can now look at the source code and see how the
database data is retrieved by SAX streaming. You need to make sure that
the following import statements are included:
You need to set up the JDBC connection to the database.
In this example, you will connect to the SH sample schema assuming
the password for SH is "SH".
6.
You need to create an instance of the SAXSerializer.
7.
To set up the XSU to send out SAX events you call the
OracleXMLQuery.getXMLSAX() interface and pass in the SAX content handler
as input. In this example, you pass in the SAXSerializer instance
"sample".
8.
You are now ready to run the easyxml project. Right
click on easyxml.jpr and select Run XSUSAXPrint.java.
8.
You should receive an exit code 0 in the log window.
In this lesson, you will use the SAXSerializer to print
out the query results to a file. However the SAXSerializer allows
you to print out the SAX output into any output stream supported in Java. To
print database data as an XML document, perform the following:
1.
You open a FileOutputStream and pass it to the
SAXSerializer.
2.
Right Click on the easyxml.jpr project and select Project
Settings. Select the Runner option. Browse
to the /home/oracle/jdevhome/mywork/easyxml/easyxml/src/oracle/xml/sample
directory and add the XSUSAXPrint.java
file as the run target. Then click
OK.
3.
Run the program by right clicking the project and select
Run easyxml.jpr
4.
Take a look at the Run Directory, you will see a large
XML document out.xml in the directory. Open the file in your browser to
review the contents.
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