io.cdap.wrangler.registry.SystemDirectiveRegistry Maven / Gradle / Ivy
/*
* Copyright © 2017-2019 Cask Data, Inc.
*
* 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 io.cdap.wrangler.registry;
import io.cdap.wrangler.api.Directive;
import io.cdap.wrangler.api.DirectiveLoadException;
import org.reflections.Reflections;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentSkipListMap;
/**
* This class is implementation of {@link DirectiveRegistry} for maintaining a registry
* of system provided directives. The directives maintained within this registry and
* present and loaded by the Classloader that is responsible for loading this
* class.
*
* In order to load the directives, this class scans through all classes that
* implement the interface {@link Directive}. Instead of scanning entire JAR, it uses the
* package name a starting point for scanning the classes that implement the Directive
* interface.
*
* For every class found, this scan will create a instance of {@link DirectiveInfo}
* object and store it in the registry.
*
* @see UserDirectiveRegistry
* @see CompositeDirectiveRegistry
* @see DirectiveInfo
*/
public final class SystemDirectiveRegistry implements DirectiveRegistry {
// This is the default package in which the directives are searched for.
private static final String PACKAGE = "io.cdap.directives";
private final Map registry;
public SystemDirectiveRegistry() throws DirectiveLoadException {
this(new ArrayList<>());
}
/**
* This constructor uses the user provided namespace as starting pointing
* for scanning classes that implement the interface {@link Directive}.
*
* @param namespaces that is used as starting point for scanning classes.
* @throws DirectiveLoadException thrown if there are any issue loading the directive.
*/
public SystemDirectiveRegistry(List namespaces) throws DirectiveLoadException {
this.registry = new ConcurrentSkipListMap<>();
namespaces.add(PACKAGE);
for (String namespace : namespaces) {
try {
Reflections reflections = new Reflections(namespace);
Set> system = reflections.getSubTypesOf(Directive.class);
for (Class directive : system) {
DirectiveInfo classz = new DirectiveInfo(DirectiveInfo.Scope.SYSTEM, directive);
registry.put(classz.name(), classz);
}
} catch (InstantiationException | IllegalAccessException e) {
throw new DirectiveLoadException(e.getMessage(), e);
}
}
}
/**
* Given the name of the directive, returns the information related to the directive.
*
* @param name of the directive to be retrieved from the registry.
* @return an instance of {@link DirectiveInfo} if found, else null.
*/
@Override
public DirectiveInfo get(String namespace, String name) {
return registry.get(name);
}
@Override
public void reload(String namespace) {
// No-op.
}
/**
* @return Returns an iterator to iterate through all the DirectiveInfo objects
* maintained within the registry.
*/
@Override
public Iterable list(String namespace) {
return registry.values();
}
/**
* Closes any resources acquired during initialization or otherwise.
*/
@Override
public void close() {
// no-op
}
}