Java Enterprise Best Practices

Understand How SAX Handles Entity Resolution

Another basic building block of the SAX API is the process of entity resolution. This process is handled through the org.xml.sax.EntityResolver interface. Like the aforementioned InputSource, the EntityResolver interface is often overlooked and ignored by SAX developers. However, through the use of a solid EntityResolver implementation, XML parsing speed can be dramatically enhanced.

At its simplest, an EntityResolver tells a SAX parser implementation how to look up resources specified in an XML document (such as entity references). For example, take a look at the following XML document fragment:

<entityContainer>
  <entity>&reference;</entity>
</entityContainer>

This document fragment illustrates an entity reference named reference. When a parser runs across this entity reference, it begins the process of resolving that entity. The parser will first consult the document’s DTD or XML schema for a definition, like this:

<!ENTITY reference 
    PUBLIC " -//O'Reilly//TEXT Best Practices Reference//EN"
    "reference.xml"
>

From this, it gains both the public ID (-//O'Reilly//TEXT Best Practices Reference//EN) and system ID (reference.xml) of the entity reference. At this point, the parser checks to see if an implementation of the EntityResolver interface has been registered with the setEntityResolver( ) method on an XMLReader instance. If one has been registered, the parser invokes the resolveEntity( ) method with the public and system IDs extracted ...