190

Performance Considerations

Internet

Intranet

Entity 

Resolution

 Schema 

 Cache

Repository

Entity 

Resolution

Web Service 

Order 

Web Service 

Front End

Processing 

Nonvalidated 

Client

Valid 

Center

XML

XML

Legend

Validate always plus caching in memory

Validate optionally plus caching in memory

Figure 4.15

An Architecture for Caching External Entities

There are two complementary ways to reduce the cost of referencing external

entities: 

1.

Caching using a proxy cache

 You can improve the efficiency of locating 

references to external entities that are on a remote repository by setting up a 

proxy that caches retrieved, external entities. However, references to external 

entities must be URLs whose protocols the proxy can handle. (See Figure 4.15, 

which should be viewed in the context of Figure 4.14.)

2.

Caching using a custom entity resolver

 SAX parsers allow XML applica 

tions to handle external entities in a customized way. Such applications have

to register their own implementation of the 

org.xml.sax.EntityResolver

 in 

terface with the parser using the 

setEntityResolver

 method. The applications

are then able to intercept external entities (including schemas) before they are

parsed. Similarly, JAXP defines the 

javax.xml.transform.URIResolver

 inter