SAX2

The EntityResolver Interface

As mentioned earlier, this interface is used when a parser needs to access and parse external entities in the DTD or document content. It is not used to access the document entity itself. Cases where an EntityResolver should be used include:

• When “more local” copies of entity data should be used. Such copies might be from a local filesystem or from a smart caching proxy. A normal web server may be unavailable or may only be accessible through a slow or congested network link; such remote access can cause application slowdowns and failures. This is generically called catalog or cache processing.

• When the entity’s systemId uses a URI scheme that is not understood by the underlying JVM. Built-in schemes usually include http://, file://, ftp://, and increasingly https://. Schemes not supported by the JVM include urn: and application-specific schemes. (You may need to put such URI schemes into publicID values, in order to prevent problems resolving relative URIs.)

• When entities need to be constructed dynamically, or not through the standard URI resolution scheme. For example, entity text might be the result of a query through some user interface or another computation.

• When the XML source text doesn’t provide usable URIs. SGML-style systems sometimes use system identifiers that aren’t really URIs; they might be relative to some base URI other than the base URI of the appropriate entity (document or DTD). Avoid this practice for XML-based systems; it’s ...