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<td><h1>JiBX: Performance with JiBX</h1>
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<strong>JiBX Basics</strong>
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<strong>Usage API</strong>
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<strong>Subprojects</strong>
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<a href="jibxtools/index.html">Generator Tools</a>
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<a href="jibxsoap/index.html">JibxSoap</a>
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<a href="siteamatic/index.html">SiteAMatic</a>
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<a href="xsd2jibx/index.html">Xsd2Jibx</a>
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<div class="h3">
<h3><a name="performance">Performance</a></h3>
<p>JiBX is designed for runtime performance. There are three main
aspects of this: Efficient unmarshalling, direct access to data, and
lean runtime. The first aspect is probably the most difficult to
explain. To understand how this applies in JiBX you have to know the
difference between the common event-driven approach to parsing XML (as
implemented by SAX/SAX2 parsers) and the newer pull parser apprach (as
with XMLPull). Event-driven parsers deliver document components
(elements and character data content) to your code one at a time, using
callbacks. You call the parser from your code, defining a "handler" to
process these callbacks. The parser runs through the entire document
with a call to your handler for each component, and then returns. It's
up to your handler code to organize the information contained in the
document components.</p>
<p>The problem with this approach is that it requires your
handler code to track where the parser is at in the document and
interpret the components appropriately. At the most basic level, the
start tag for an element containing a text value is reported first by
the parser, followed by one or more chunks of text, followed finally by
the end tag. Your handler generally needs to accumulate the text until
the end tag is reported, then do something with the text. The
"something" it does may be effected by other items, such as the
attributes of the start tag, so that's more information that needs to be
held. The net result is that handler code for event-driven parsers
tends to involve a lot of <code>String</code> matching on element names
in chained "if"<span style="font-weight: bold;"></span> statements (or
the equivalent using a <code>Hashtable</code> lookup). This is both messy to
write and maintain, and inefficient.</p>
<p>Pull parsing turns the parse event reporting around. Instead
of the parser calling methods in your handler to report document
components, you call the parser to get each component in turn - the
parser becomes essentially an iterator for moving through the components
of a document. When you write code using this approach the state
information is actually inherent in the code. To take the case of an
element containing text, you can write your code with the knowledge
that the element you're processing has text content, and just process it
directly - effectively one call to get the start tag, one call to get
the content, and a third to get the end tag. Even better, you can write
a method that handles <span style="font-style: italic;">any</span>
element containing a text value - just call the method with the expected
element name, and it returns the text content or an error. Since most
XML documents use fixed ordering of child elements, processing the
children of a particular element becomes as simple as just making once
call after another to this method.</p>
<p>JiBX uses a pull parser for unmarshalling so that it can take advantage
of this code structure advantage. Because the code for pull parsing can
be much simpler than that for event-driven parsing, JiBX is able to use
byte code enhancement to add both marshalling and unmarshalling code to
your class definitions. Using byte code enhancement in turn lets JiBX
make use of the other two performance aspects.</p>
<p>"Direct access to data" just means that JiBX accesses data from your
objects in whatever way is most natural. Normally this is by loading and
storing field values directly in the marshalling and unmarshalling code
added to your classes by byte code enhancement. It can also be by using
JavaBean-style get/set methods, if that's a better solution for your
code. Because JiBX uses byte code enhancement there's no need to make
the fields or get/set methods public, unlike most other data binding
frameworks. There's also no runtime cost for accessing the data, unlike
the frameworks that use reflection to move data in and out of objects.</p>
<p>The final performance aspect of JiBX is that the runtime is lean and
mean - configuration information is normally processed at application assembly
time (after compiling classes), and is embedded directly in the code
added by byte code enhancment. Other frameworks that read configuration
files at runtime (most do not) suffer a performance disadvantage both
from the actual processing time and from the added code needed to
support this. This can make for a very slow start on execution, as
classes are loaded and compiled to native code by the JVM. JiBX's
approach of handling all the configuration prior to running the
application minimizes startup overhead, both directly and through
avoiding unnecessary runtime code. JiBX's use of a pull parser also
helps keep the runtime small and efficient, as does its limited
validation support - JiBX automatically checks many aspects of a
document based on your mapping when unmarshalling, but does not support
in-memory validation.</p>
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<td> © 2003-2005, Dennis M. Sosnoski (<a href="http://www.sosnoski.com">Sosnoski Software Solutions, Inc.</a>).
Licensed to the JiBX Project for free distribution and use. </td>
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