AbstractLoader.java
/*
* Portions of this software was developed by employees of the National Institute
* of Standards and Technology (NIST), an agency of the Federal Government and is
* being made available as a public service. Pursuant to title 17 United States
* Code Section 105, works of NIST employees are not subject to copyright
* protection in the United States. This software may be subject to foreign
* copyright. Permission in the United States and in foreign countries, to the
* extent that NIST may hold copyright, to use, copy, modify, create derivative
* works, and distribute this software and its documentation without fee is hereby
* granted on a non-exclusive basis, provided that this notice and disclaimer
* of warranty appears in all copies.
*
* THE SOFTWARE IS PROVIDED 'AS IS' WITHOUT ANY WARRANTY OF ANY KIND, EITHER
* EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING, BUT NOT LIMITED TO, ANY WARRANTY
* THAT THE SOFTWARE WILL CONFORM TO SPECIFICATIONS, ANY IMPLIED WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND FREEDOM FROM
* INFRINGEMENT, AND ANY WARRANTY THAT THE DOCUMENTATION WILL CONFORM TO THE
* SOFTWARE, OR ANY WARRANTY THAT THE SOFTWARE WILL BE ERROR FREE. IN NO EVENT
* SHALL NIST BE LIABLE FOR ANY DAMAGES, INCLUDING, BUT NOT LIMITED TO, DIRECT,
* INDIRECT, SPECIAL OR CONSEQUENTIAL DAMAGES, ARISING OUT OF, RESULTING FROM,
* OR IN ANY WAY CONNECTED WITH THIS SOFTWARE, WHETHER OR NOT BASED UPON WARRANTY,
* CONTRACT, TORT, OR OTHERWISE, WHETHER OR NOT INJURY WAS SUSTAINED BY PERSONS OR
* PROPERTY OR OTHERWISE, AND WHETHER OR NOT LOSS WAS SUSTAINED FROM, OR AROSE OUT
* OF THE RESULTS OF, OR USE OF, THE SOFTWARE OR SERVICES PROVIDED HEREUNDER.
*/
package gov.nist.secauto.metaschema.core.model.xml;
import gov.nist.secauto.metaschema.core.model.MetaschemaException;
import gov.nist.secauto.metaschema.core.util.CollectionUtil;
import gov.nist.secauto.metaschema.core.util.ObjectUtils;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import java.io.File;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URI;
import java.net.URISyntaxException;
import java.net.URL;
import java.nio.file.Path;
import java.util.Collection;
import java.util.Deque;
import java.util.LinkedHashMap;
import java.util.LinkedList;
import java.util.Map;
import java.util.stream.Collectors;
import edu.umd.cs.findbugs.annotations.NonNull;
public abstract class AbstractLoader<T> {
private static final Logger LOGGER = LogManager.getLogger(ConstraintLoader.class);
@NonNull
private final Map<URI, T> cache = new LinkedHashMap<>(); // NOPMD - intentional
/**
* Retrieve the set of loaded resources.
*
* @return the set of loaded resources
*/
@NonNull
public Collection<T> getLoadedResources() {
return CollectionUtil.unmodifiableCollection(ObjectUtils.notNull(cache.values()));
}
/**
* Retrieve a mapping of resource URIs to the associated loaded resource.
*
* @return the mapping
*/
@NonNull
protected Map<URI, T> getCachedEntries() {
return CollectionUtil.unmodifiableMap(cache);
}
/**
* Load a resource from the specified URI.
*
* @param resource
* the resource to load
* @return the loaded instance for the specified resource
* @throws MetaschemaException
* if an error occurred while processing the resource
* @throws IOException
* if an error occurred parsing the resource
*/
@NonNull
public T load(@NonNull URI resource) throws MetaschemaException, IOException {
if (!resource.isAbsolute()) {
throw new IllegalArgumentException(String.format("The URI '%s' must be absolute.", resource.toString()));
}
return loadInternal(resource, new LinkedList<>());
}
/**
* Load a resource from the specified path.
*
* @param path
* the resource to load
* @return the loaded instance for the specified resource
* @throws MetaschemaException
* if an error occurred while processing the resource
* @throws IOException
* if an error occurred parsing the resource
*/
@NonNull
public T load(@NonNull Path path) throws MetaschemaException, IOException {
return loadInternal(ObjectUtils.notNull(path.toAbsolutePath().normalize().toUri()), new LinkedList<>());
}
/**
* Load a resource from the specified file.
*
* @param file
* the resource to load
* @return the loaded instance for the specified resource
* @throws MetaschemaException
* if an error occurred while processing the resource
* @throws IOException
* if an error occurred parsing the resource
*/
@NonNull
public T load(@NonNull File file) throws MetaschemaException, IOException {
return load(file.toPath());
}
/**
* Loads a resource from the specified URL.
*
* @param url
* the URL to load the resource from
* @return the loaded instance for the specified resource
* @throws MetaschemaException
* if an error occurred while processing the resource
* @throws IOException
* if an error occurred parsing the resource
*/
@NonNull
public T load(@NonNull URL url) throws MetaschemaException, IOException {
try {
URI resource = url.toURI();
return loadInternal(ObjectUtils.notNull(resource), new LinkedList<>());
} catch (URISyntaxException ex) {
// this should not happen
LOGGER.error("Invalid url", ex);
throw new IOException(ex);
}
}
/**
* Loads a resource from the provided URI.
* <p>
* If the resource imports other resources, the provided
* {@code visitedResources} can be used to track circular imports. This is
* useful when this method recurses into included resources.
* <p>
* Previously loaded resources are provided by the cache. This method will add
* the resource to the cache after all imported resources have been loaded.
*
* @param resource
* the resource to load
* @param visitedResources
* a LIFO queue representing previously visited resources in an import
* chain
* @return the loaded resource
* @throws MetaschemaException
* if an error occurred while processing the resource
* @throws MalformedURLException
* if the provided URI is malformed
* @throws IOException
* if an error occurred parsing the resource
*/
@NonNull
protected T loadInternal(@NonNull URI resource, @NonNull Deque<URI> visitedResources)
throws MetaschemaException, MalformedURLException, IOException {
// first check if the current resource has been visited to prevent cycles
if (visitedResources.contains(resource)) {
throw new MetaschemaException("Cycle detected in metaschema includes for '" + resource + "'. Call stack: '"
+ visitedResources.stream().map(n -> n.toString()).collect(Collectors.joining(",")));
}
T retval = cache.get(resource);
if (retval == null) {
LOGGER.info("Loading module '{}'", resource);
try {
visitedResources.push(resource);
retval = parseResource(resource, visitedResources);
} finally {
visitedResources.pop();
}
cache.put(resource, retval);
} else {
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("Found metaschema in cache '{}'", resource);
}
}
return ObjectUtils.notNull(retval);
}
/**
* Parse the provided {@code resource}.
*
* @param resource
* the resource to parse
* @param visitedResources
* a stack representing previously parsed resources imported by the
* provided {@code resource}
* @return the parsed resource
* @throws IOException
* if an error occurred while parsing the resource
*/
protected abstract T parseResource(@NonNull URI resource, @NonNull Deque<URI> visitedResources)
throws IOException;
}