MountPointResources.java

/***************************************************************************
   Copyright 2013 Emily Estes

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
***************************************************************************/
package net.metanotion.simpletemplate;


/** This resource factory wraps another resource factory and prepends a prefix to all resource requests. i.e. requests
for a resource with a prefix like "/prefix" for "/prefix/foo" get passed on the wrapped resource factory as "/foo".
*/
public final class MountPointResources implements ResourceFactory {
    private final String prefix;
    private final ResourceFactory delegate;
    private final ResourceFactory parent;

    /** Create a new prefixed resource factory.
        @param delegate The resource factory to use for the prefix
        @param prefixPath The path to strip from all requests against delegate.
    */
    public MountPointResources(final ResourceFactory delegate, final String prefixPath) {
        this(delegate, prefixPath, NullTemplateHelper.INSTANCE);
    }

    /** Create a new prefixed resource factory that delegates all unmatched requests to another resource factory.
        @param delegate The resource factory to use for the prefix
        @param prefixPath The path to strip from all requests against delegate.
        @param parent The resource factroy to delegate all unmatched prefixes to.
    */
    public MountPointResources(final ResourceFactory delegate, final String prefixPath, final ResourceFactory parent) {
        this.prefix = prefixPath;
        this.delegate = delegate;
        this.parent = parent;
    }

    @Override public Resource get(final String urn) {
        if(!urn.startsWith(prefix)) {
            return parent.get(urn);
        } else {
            return delegate.get(urn.substring(prefix.length()));
        }
    }
}