lucene/analysis/common/src/java/org/apache/lucene/analysis/util/ClasspathResourceLoader.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.lucene.analysis.util;


import java.io.IOException;
import java.io.InputStream;

import org.apache.lucene.util.SuppressForbidden;

/**
 * Simple {@link ResourceLoader} that uses {@link ClassLoader#getResourceAsStream(String)}
 * and {@link Class#forName(String,boolean,ClassLoader)} to open resources and
 * classes, respectively.
 */
public final class ClasspathResourceLoader implements ResourceLoader {
  private final Class<?> clazz;
  private final ClassLoader loader;
  
  /**
   * Creates an instance using the context classloader to load resources and classes.
   * Resource paths must be absolute.
   * 
   * @deprecated You should not use this ctor, because it uses the thread's context
   * class loader, which is bad programming style. Please specify a reference class or
   * a {@link ClassLoader} instead.
   * @see #ClasspathResourceLoader(ClassLoader)
   * @see #ClasspathResourceLoader(Class)
   */
  @Deprecated
  @SuppressForbidden(reason = "Deprecated method uses thread's context classloader, but there for backwards compatibility")
  public ClasspathResourceLoader() {
    this(Thread.currentThread().getContextClassLoader());
  }

  /**
   * Creates an instance using the given classloader to load Resources and classes.
   * Resource paths must be absolute.
   */
  public ClasspathResourceLoader(ClassLoader loader) {
    this(null, loader);
  }

  /**
   * Creates an instance using the context classloader to load Resources and classes
   * Resources are resolved relative to the given class, if path is not absolute.
   */
  public ClasspathResourceLoader(Class<?> clazz) {
    this(clazz, clazz.getClassLoader());
  }

  private ClasspathResourceLoader(Class<?> clazz, ClassLoader loader) {
    this.clazz = clazz;
    this.loader = loader;
  }

  @Override
  public InputStream openResource(String resource) throws IOException {
    final InputStream stream = (clazz != null) ?
      clazz.getResourceAsStream(resource) :
      loader.getResourceAsStream(resource);
    if (stream == null)
      throw new IOException("Resource not found: " + resource);
    return stream;
  }
  
  @Override
  public <T> Class<? extends T> findClass(String cname, Class<T> expectedType) {
    try {
      return Class.forName(cname, true, loader).asSubclass(expectedType);
    } catch (Exception e) {
      throw new RuntimeException("Cannot load class: " + cname, e);
    }
  }

  @Override
  public <T> T newInstance(String cname, Class<T> expectedType) {
    Class<? extends T> clazz = findClass(cname, expectedType);
    try {
      return clazz.newInstance();
    } catch (Exception e) {
      throw new RuntimeException("Cannot create instance: " + cname, e);
    }
  }
}