Application Schema Resolution

To be able to encode XML responses conforming to a GML application schema, the app-schema plugin must be able to locate the application schema files (XSDs) that define the schema. This page describes the schema resolution process.

Schema downloading is now automatic for most users

GeoServer will automatically download and cache (see Cache below) all the schemas it needs the first time it starts if:

  1. All the application schemas you use are accessed via http/https URLs, and
  2. Your GeoServer instance is deployed on a network that permits it to download them.

Note

This is the recommended way of using GeoServer app-schema for most users.

If cached downloading is used, no manual handling of schemas will be required. The rest of this page is for those with more complicated arrangements, or who wish to clear the cache.

Resolution order

The order of sources used to resolve application schemas is:

  1. OASIS Catalog
  2. Classpath
  3. Cache

Every attempt to load a schema works down this list, so imports can be resolved from sources other than that used for the originating document. For example, an application schema in the cache that references a schema found in the catalog will use the version in the catalog, rather than caching it. This allows users to supply unpublished or modified schemas sourced from, for example, the catalog, at the cost of interoperability (how do WFS clients get them?).

OASIS Catalog

An OASIS XML Catalog is a standard configuration file format that instructs an XML processing system how to process entity references. The GeoServer app-schema resolver uses catalog URI semantics to locate application schemas, so uri or rewriteURI entries should be present in your catalog. The optional mapping file catalog element provides the location of the OASIS XML Catalog configuration file, given as a path relative to the mapping file, for example:

<catalog>../../../schemas/catalog.xml</catalog>

Earlier versions of the app-schema plugin required all schemas to be present in the catalog. This is no longer the case. Because the catalog is searched first, existing catalog-based deployments will continue to work as before.

To migrate an existing GeoServer app-schema deployment that uses an OASIS Catalog to instead use cached downloads (see Cache below), remove all catalog elements from your mapping files and restart GeoServer.

Classpath

Java applications such as GeoServer can load resources from the Java classpath. GeoServer app-schema uses a simple mapping from an http or https URL to a classpath resource location. For example, an application schema published at http://schemas.example.org/exampleml/exml.xsd would be found on the classpath if it was stored either:

  • at /org/example/schemas/exampleml/exml.xsd in a JAR file on the classpath (for example, a JAR file in WEB-INF/lib) or,
  • on the local filesystem at WEB-INF/classes/org/example/schemas/exampleml/exml.xsd .

The ability to load schemas from the classpath is intended to support testing, but may be useful to users whose communities supply JAR files containing their application schemas.

Cache

If an application schema cannot be found in the catalog or on the classpath, it is downloaded from the network and stored in a subdirectory app-schema-cache of the GeoServer data directory.

  • Once schemas are downloaded into the cache, they persist indefinitely, including over GeoServer restarts.
  • No attempt will be made to retrieve new versions of cached schemas.
  • To clear the cache, remove the subdirectory app-schema-cache of the GeoServer data directory and restart GeoServer.

GeoServer app-schema uses a simple mapping from an http or https URL to local filesystem path. For example, an application schema published at http://schemas.example.org/exampleml/exml.xsd would be downloaded and stored as app-schema-cache/org/example/schemas/exampleml/exml.xsd . Note that:

  • Only http and https URLs are supported.
  • Port numbers, queries, and fragments are ignored.

If your GeoServer instance is deployed on a network whose firewall rules prevent outgoing TCP connections on port 80 (http) or 443 (https), schema downloading will not work. (For security reasons, some service networks [“demilitarised zones”] prohibit such outgoing connections.) If schema downloading is not permitted on your network, there are three solutions:

  1. Either: Install and configure GeoServer on another network that can make outgoing TCP connections, start GeoServer to trigger schema download, and then manually copy the app-schema-cache directory to the production server. This is the easiest option because GeoServer automatically downloads all the schemas it needs, including dependencies.
  2. Or: Deploy JAR files containing all required schema files on the classpath (see Classpath above).
  3. Or: Use a catalog (see OASIS Catalog above).

Warning

System property “schema.cache.dir” with a cache directory location is required for using a mapping file from a remote URL with ‘http://’ or ‘https://’ protocol.