lang/java/reef-tang/tang/src/main/java/org/apache/reef/tang/Tang.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.reef.tang;

import org.apache.reef.tang.exceptions.BindException;
import org.apache.reef.tang.implementation.TangImpl;

import java.net.URL;

/**
 * The root factory interface for Tang.  This interface allows callers to
 * instantiate Tang's core API, and is responsible for memoization and other
 * runtime optimizations.
 */
public interface Tang {

  /**
   * Returns an Injector for the given Configurations.
   *
   * @param confs a configuration
   * @return an injector
   * @throws BindException If the confs conflict, a BindException will be thrown.
   */
  Injector newInjector(Configuration... confs) throws BindException;

  /**
   * Returns an Injector for the given Configuration.
   *
   * @param confs a configuration
   * @return an injector
   */
  Injector newInjector(Configuration confs);

  /**
   * Returns an Injector based on an empty Configuration.

   * @return an injector
   */
  Injector newInjector();

  /**
   * Return a new ConfigurationBuilder that is backed by the provided
   * ClassHierarchy object.
   *
   * @param ch Any valid Tang ClassHierarchy, including ones derived from non-Java application binaries.
   * @return an instance of ConfigurationBuilder.  In Tang's default implementation this returns an instance
   * or JavaConfigurationBuilder if ch is backed by a Java classloader.
   */
  ConfigurationBuilder newConfigurationBuilder(ClassHierarchy ch);

  /**
   * Create a new ConfigurationBuilder that is backed by the default
   * classloader and the provided jars.  Following standard Java's semantics,
   * when looking up a class, Tang will consult the default classloader first,
   * then the first classpath entry / jar passed to this method, then the
   * second, and so on.
   *
   * @param jars the locations of jar files
   * @return a new JavaConfigurationBuilder
   */
  JavaConfigurationBuilder newConfigurationBuilder(URL... jars);

  /**
   * Merge a set of configurations into a new JavaConfiurationBuilder.  If
   * the configurations conflict, this method will throw a bind exception.
   * <p>
   * The underlying ClassHierarchies and parameter parsers of the
   * configurations will be checked for consistency.  The returned
   * configuration builder will be backed by a ClassHierachy that incorporates
   * the classpath and parsers from all of the provided Configurations.
   *
   * @param confs configurations
   * @return a new ConfigurationBuilder
   * @throws BindException if any of the configurations contain duplicated or
   *                       conflicting bindings, or if the backing ClassHierarchy objects conflict
   *                       in some way.
   */
  JavaConfigurationBuilder newConfigurationBuilder(Configuration... confs)
      throws BindException;

  /**
   * Create an empty JavaConfigurationBuilder that is capable of parsing
   * application-specific configuration values.  The returned
   * JavaConfigurationBuilder will be backed by the default classloader.
   *
   * @param parameterParsers the parsers for parameters
   * @return a new ConfigurationBuilder
   * @throws BindException if any of the configurations contain duplicated or
   *                       conflicting bindings, or if the backing ClassHierarchy objects conflict
   *                       in some way.
   */
  JavaConfigurationBuilder newConfigurationBuilder(
      @SuppressWarnings("unchecked") Class<? extends ExternalConstructor<?>>... parameterParsers)
      throws BindException;

  /**
   * Create a new JavaConfiguration builder that has additional jars,
   * incorporates existing configuration data and / or can parse
   * application-specific types.
   *
   * See the documentation for the other newConfigurationBuilder methods in
   * this class for detailed information about each of the parameters to
   * this method.
   *
   * @param jars the locations of jar files
   * @param confs configurations
   * @param parameterParsers the parsers for parameters
   * @return a configuration builder
   */
  JavaConfigurationBuilder newConfigurationBuilder(
      URL[] jars, Configuration[] confs, Class<? extends ExternalConstructor<?>>[] parameterParsers)
      throws BindException;

  /**
   * Create a new empty ConfigurationBuilder that is backed by the default
   * classloader.
   *
   * @return a configuration builder
   */
  JavaConfigurationBuilder newConfigurationBuilder();

  /**
   * @return an instance of JavaClassHierarchy that is backed by the default
   * Java classloader.  ClassHierarchy objects are immutable, so multiple
   * invocations of this method may return the same instance.
   */
  JavaClassHierarchy getDefaultClassHierarchy();

  /**
   * Get a default class hierarchy.
   *
   * @param jars the locations of jar files
   * @param parsers the parsers
   * @return a custom instance of JavaClassHierarchy.  ClassHierarchy objects
   * are immutable, so multiple invocations of this method may return the
   * same instance.
   * TODO Is the class hierarchy returned here backed by the default
   * classloader or not?  If not, then callers will need to merge it with
   * getDefaultClassHierarchy().  If so, we should add a new method like
   * getNonDefaultClassHiearchy() that takes the same options as this one.
   */
  JavaClassHierarchy getDefaultClassHierarchy(URL[] jars, Class<? extends ExternalConstructor<?>>[] parsers);

  /**
   * A factory that returns the default implementation of the Tang interface.
   */
  class Factory {
    /**
     * Return an instance of the default implementation of Tang.
     *
     * @return an instance of Tang.
     */
    public static Tang getTang() {
      return new TangImpl();
    }

    /**
     * Empty private constructor to prohibit instantiation of utility class.
     */
    private Factory() {
    }
  }
}