1. Core Libraries
  2. XML Catalog API
  3. Purpose of XML Catalog API

Purpose of XML Catalog API

The XML Catalog API and the Java XML processors provide an option for developers and system administrators to manage external resources. 

The XML Catalog API provides an implementation of OASIS XML Catalogs v1.1, a standard designed to address issues caused by external resources.

Problems Caused by External Resources

XML, XSD and XSL documents may contain references to external resources that Java XML processors need to retrieve to process the documents. External resources can cause a problem for the applications or the system. The Catalog API and the Java XML processors provide an option for developers and system administrators to manage these external resources.

External resources can cause a problem for the application or the system in these areas:

  • Availability: If a resource is remote, then XML processors must be able to connect to the remote server hosting the resource. Even though connectivity is rarely an issue, it’s still a factor in the stability of an application. Too many connections can be a hazard to servers that hold the resources, and this in turn could affect your applications. See Use Catalog with XML Processors for an example that solves this issue using the XML Catalog API.

  • Performance. Although in most cases connectivity isn’t an issue, a remote fetch can still cause a performance issue for an application. Furthermore, there may be multiple applications on the same system attempting to resolve the same resource, and this would be a waste of system resources.

  • Security: Allowing remote connections can pose a security risk if the application processes untrusted XML sources.

  • Manageability: If a system processes a large number of XML documents, then externally referenced documents, whether local or remote, can become a maintenance hassle.

How XML Catalog API Addresses Problems Caused by External Resources

Application developers can create a local catalog of all external references for the application, and let the Catalog API resolve them for the application. This not only avoids remote connections but also makes it easier to manage these resources.

System administrators can establish a local catalog for the system and configure the Java VM to use the catalog. Then, all of the applications on the system may share the same catalog without any code changes to the applications, assuming that they’re compatible with Java SE 9. To establish a catalog, you may take advantage of existing catalogs such as those included with some Linux distributions.