Lucene example source code file (AttributeSource.java)

This example Lucene source code file (AttributeSource.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Lucene tags/keywords

attribute, attribute, attributefactory, attributeimpl, attributeimpl, attributesource, attributesource, class, illegalargumentexception, iterator, override, state, state, util, weakreference

The Lucene AttributeSource.java source code

package org.apache.lucene.util;

/**
 * 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.
 */

import java.lang.ref.WeakReference;
import java.util.Collections;
import java.util.NoSuchElementException;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.WeakHashMap;
import java.util.LinkedList;
import java.util.Map;
import java.util.Map.Entry;

import org.apache.lucene.analysis.TokenStream; // for javadocs
import org.apache.lucene.analysis.tokenattributes.TermAttribute;
import org.apache.lucene.analysis.tokenattributes.CharTermAttributeImpl;

/**
 * An AttributeSource contains a list of different {@link AttributeImpl}s,
 * and methods to add and get them. There can only be a single instance
 * of an attribute in the same AttributeSource instance. This is ensured
 * by passing in the actual type of the Attribute (Class<Attribute>) to 
 * the {@link #addAttribute(Class)}, which then checks if an instance of
 * that type is already present. If yes, it returns the instance, otherwise
 * it creates a new instance and returns it.
 */
public class AttributeSource {
  /**
   * An AttributeFactory creates instances of {@link AttributeImpl}s.
   */
  public static abstract class AttributeFactory {
    /**
     * returns an {@link AttributeImpl} for the supplied {@link Attribute} interface class.
     */
    public abstract AttributeImpl createAttributeInstance(Class<? extends Attribute> attClass);
    
    /**
     * This is the default factory that creates {@link AttributeImpl}s using the
     * class name of the supplied {@link Attribute} interface class by appending <code>Impl to it.
     */
    public static final AttributeFactory DEFAULT_ATTRIBUTE_FACTORY = new DefaultAttributeFactory();
    
    private static final class DefaultAttributeFactory extends AttributeFactory {
      private static final WeakHashMap<Class>> attClassImplMap =
        new WeakHashMap<Class>>();
      
      private DefaultAttributeFactory() {}
    
      @Override
      public AttributeImpl createAttributeInstance(Class<? extends Attribute> attClass) {
        try {
          return getClassForInterface(attClass).newInstance();
        } catch (InstantiationException e) {
          throw new IllegalArgumentException("Could not instantiate implementing class for " + attClass.getName());
        } catch (IllegalAccessException e) {
          throw new IllegalArgumentException("Could not instantiate implementing class for " + attClass.getName());
        }
      }
      
      private static Class<? extends AttributeImpl> getClassForInterface(Class attClass) {
        synchronized(attClassImplMap) {
          final WeakReference<Class ref = attClassImplMap.get(attClass);
          Class<? extends AttributeImpl> clazz = (ref == null) ? null : ref.get();
          if (clazz == null) {
            try {
              // TODO: Remove when TermAttribute is removed!
              // This is a "sophisticated backwards compatibility hack"
              // (enforce new impl for this deprecated att):
              if (TermAttribute.class.equals(attClass)) {
                clazz = CharTermAttributeImpl.class;
              } else {
                clazz = Class.forName(attClass.getName() + "Impl", true, attClass.getClassLoader())
                  .asSubclass(AttributeImpl.class);
              }
              attClassImplMap.put(attClass,
                new WeakReference<Class(clazz)
              );
            } catch (ClassNotFoundException e) {
              throw new IllegalArgumentException("Could not find implementing class for " + attClass.getName());
            }
          }
          return clazz;
        }
      }
    }
  }
      
  /**
   * This class holds the state of an AttributeSource.
   * @see #captureState
   * @see #restoreState
   */
  public static final class State implements Cloneable {
    AttributeImpl attribute;
    State next;
    
    @Override
    public Object clone() {
      State clone = new State();
      clone.attribute = (AttributeImpl) attribute.clone();
      
      if (next != null) {
        clone.next = (State) next.clone();
      }
      
      return clone;
    }
  }
    
  // These two maps must always be in sync!!!
  // So they are private, final and read-only from the outside (read-only iterators)
  private final Map<Class attributes;
  private final Map<Class attributeImpls;
  private final State[] currentState;

  private AttributeFactory factory;
  
  /**
   * An AttributeSource using the default attribute factory {@link AttributeSource.AttributeFactory#DEFAULT_ATTRIBUTE_FACTORY}.
   */
  public AttributeSource() {
    this(AttributeFactory.DEFAULT_ATTRIBUTE_FACTORY);
  }
  
  /**
   * An AttributeSource that uses the same attributes as the supplied one.
   */
  public AttributeSource(AttributeSource input) {
    if (input == null) {
      throw new IllegalArgumentException("input AttributeSource must not be null");
    }
    this.attributes = input.attributes;
    this.attributeImpls = input.attributeImpls;
    this.currentState = input.currentState;
    this.factory = input.factory;
  }
  
  /**
   * An AttributeSource using the supplied {@link AttributeFactory} for creating new {@link Attribute} instances.
   */
  public AttributeSource(AttributeFactory factory) {
    this.attributes = new LinkedHashMap<Class();
    this.attributeImpls = new LinkedHashMap<Class();
    this.currentState = new State[1];
    this.factory = factory;
  }
  
  /**
   * returns the used AttributeFactory.
   */
  public AttributeFactory getAttributeFactory() {
    return this.factory;
  }
  
  /** Returns a new iterator that iterates the attribute classes
   * in the same order they were added in.
   */
  public Iterator<Class getAttributeClassesIterator() {
    return Collections.unmodifiableSet(attributes.keySet()).iterator();
  }
  
  /** Returns a new iterator that iterates all unique Attribute implementations.
   * This iterator may contain less entries that {@link #getAttributeClassesIterator},
   * if one instance implements more than one Attribute interface.
   */
  public Iterator<AttributeImpl> getAttributeImplsIterator() {
    final State initState = getCurrentState();
    if (initState != null) {
      return new Iterator<AttributeImpl>() {
        private State state = initState;
      
        public void remove() {
          throw new UnsupportedOperationException();
        }
        
        public AttributeImpl next() {
          if (state == null)
            throw new NoSuchElementException();
          final AttributeImpl att = state.attribute;
          state = state.next;
          return att;
        }
        
        public boolean hasNext() {
          return state != null;
        }
      };
    } else {
      return Collections.<AttributeImpl>emptySet().iterator();
    }
  }
  
  /** a cache that stores all interfaces for known implementation classes for performance (slow reflection) */
  private static final WeakHashMap<Class>>> knownImplClasses =
    new WeakHashMap<Class>>>();
  
  static LinkedList<WeakReference> getAttributeInterfaces(final Class clazz) {
    synchronized(knownImplClasses) {
      LinkedList<WeakReference> foundInterfaces = knownImplClasses.get(clazz);
      if (foundInterfaces == null) {
        // we have a strong reference to the class instance holding all interfaces in the list (parameter "att"),
        // so all WeakReferences are never evicted by GC
        knownImplClasses.put(clazz, foundInterfaces = new LinkedList<WeakReference>());
        // find all interfaces that this attribute instance implements
        // and that extend the Attribute interface
        Class<?> actClazz = clazz;
        do {
          for (Class<?> curInterface : actClazz.getInterfaces()) {
            if (curInterface != Attribute.class && Attribute.class.isAssignableFrom(curInterface)) {
              foundInterfaces.add(new WeakReference<Class(curInterface.asSubclass(Attribute.class)));
            }
          }
          actClazz = actClazz.getSuperclass();
        } while (actClazz != null);
      }
      return foundInterfaces;
    }
  }
  
  /** <b>Expert: Adds a custom AttributeImpl instance with one or more Attribute interfaces.
   * <p>Please note: It is not guaranteed, that att is added to
   * the <code>AttributeSource, because the provided attributes may already exist.
   * You should always retrieve the wanted attributes using {@link #getAttribute} after adding
   * with this method and cast to your class.
   * The recommended way to use custom implementations is using an {@link AttributeFactory}.
   * </font>

   */
  public void addAttributeImpl(final AttributeImpl att) {
    final Class<? extends AttributeImpl> clazz = att.getClass();
    if (attributeImpls.containsKey(clazz)) return;
    final LinkedList<WeakReference> foundInterfaces =
      getAttributeInterfaces(clazz);
    
    // add all interfaces of this AttributeImpl to the maps
    for (WeakReference<Class curInterfaceRef : foundInterfaces) {
      final Class<? extends Attribute> curInterface = curInterfaceRef.get();
      assert (curInterface != null) :
        "We have a strong reference on the class holding the interfaces, so they should never get evicted";
      // Attribute is a superclass of this interface
      if (!attributes.containsKey(curInterface)) {
        // invalidate state to force recomputation in captureState()
        this.currentState[0] = null;
        attributes.put(curInterface, att);
        attributeImpls.put(clazz, att);
      }
    }
  }
  
  /**
   * The caller must pass in a Class<? extends Attribute> value.
   * This method first checks if an instance of that class is 
   * already in this AttributeSource and returns it. Otherwise a
   * new instance is created, added to this AttributeSource and returned. 
   */
  public <A extends Attribute> A addAttribute(Class attClass) {
    AttributeImpl attImpl = attributes.get(attClass);
    if (attImpl == null) {
      if (!(attClass.isInterface() && Attribute.class.isAssignableFrom(attClass))) {
        throw new IllegalArgumentException(
          "addAttribute() only accepts an interface that extends Attribute, but " +
          attClass.getName() + " does not fulfil this contract."
        );
      }
      addAttributeImpl(attImpl = this.factory.createAttributeInstance(attClass));
    }
    return attClass.cast(attImpl);
  }
  
  /** Returns true, iff this AttributeSource has any attributes */
  public boolean hasAttributes() {
    return !this.attributes.isEmpty();
  }

  /**
   * The caller must pass in a Class<? extends Attribute> value. 
   * Returns true, iff this AttributeSource contains the passed-in Attribute.
   */
  public boolean hasAttribute(Class<? extends Attribute> attClass) {
    return this.attributes.containsKey(attClass);
  }

  /**
   * The caller must pass in a Class<? extends Attribute> value. 
   * Returns the instance of the passed in Attribute contained in this AttributeSource
   * 
   * @throws IllegalArgumentException if this AttributeSource does not contain the
   *         Attribute. It is recommended to always use {@link #addAttribute} even in consumers
   *         of TokenStreams, because you cannot know if a specific TokenStream really uses
   *         a specific Attribute. {@link #addAttribute} will automatically make the attribute
   *         available. If you want to only use the attribute, if it is available (to optimize
   *         consuming), use {@link #hasAttribute}.
   */
  public <A extends Attribute> A getAttribute(Class attClass) {
    AttributeImpl attImpl = attributes.get(attClass);
    if (attImpl == null) {
      throw new IllegalArgumentException("This AttributeSource does not have the attribute '" + attClass.getName() + "'.");
    }
    return attClass.cast(attImpl);
  }
    
  private State getCurrentState() {
    State s  = currentState[0];
    if (s != null || !hasAttributes()) {
      return s;
    }
    State c = s = currentState[0] = new State();
    final Iterator<AttributeImpl> it = attributeImpls.values().iterator();
    c.attribute = it.next();
    while (it.hasNext()) {
      c.next = new State();
      c = c.next;
      c.attribute = it.next();
    }
    return s;
  }
  
  /**
   * Resets all Attributes in this AttributeSource by calling
   * {@link AttributeImpl#clear()} on each Attribute implementation.
   */
  public void clearAttributes() {
    for (State state = getCurrentState(); state != null; state = state.next) {
      state.attribute.clear();
    }
  }
  
  /**
   * Captures the state of all Attributes. The return value can be passed to
   * {@link #restoreState} to restore the state of this or another AttributeSource.
   */
  public State captureState() {
    final State state = this.getCurrentState();
    return (state == null) ? null : (State) state.clone();
  }
  
  /**
   * Restores this state by copying the values of all attribute implementations
   * that this state contains into the attributes implementations of the targetStream.
   * The targetStream must contain a corresponding instance for each argument
   * contained in this state (e.g. it is not possible to restore the state of
   * an AttributeSource containing a TermAttribute into a AttributeSource using
   * a Token instance as implementation).
   * <p>
   * Note that this method does not affect attributes of the targetStream
   * that are not contained in this state. In other words, if for example
   * the targetStream contains an OffsetAttribute, but this state doesn't, then
   * the value of the OffsetAttribute remains unchanged. It might be desirable to
   * reset its value to the default, in which case the caller should first
   * call {@link TokenStream#clearAttributes()} on the targetStream.   
   */
  public void restoreState(State state) {
    if (state == null)  return;
    
    do {
      AttributeImpl targetImpl = attributeImpls.get(state.attribute.getClass());
      if (targetImpl == null) {
        throw new IllegalArgumentException("State contains AttributeImpl of type " +
          state.attribute.getClass().getName() + " that is not in in this AttributeSource");
      }
      state.attribute.copyTo(targetImpl);
      state = state.next;
    } while (state != null);
  }

  @Override
  public int hashCode() {
    int code = 0;
    for (State state = getCurrentState(); state != null; state = state.next) {
      code = code * 31 + state.attribute.hashCode();
    }
    return code;
  }
  
  @Override
  public boolean equals(Object obj) {
    if (obj == this) {
      return true;
    }

    if (obj instanceof AttributeSource) {
      AttributeSource other = (AttributeSource) obj;  
    
      if (hasAttributes()) {
        if (!other.hasAttributes()) {
          return false;
        }
        
        if (this.attributeImpls.size() != other.attributeImpls.size()) {
          return false;
        }
  
        // it is only equal if all attribute impls are the same in the same order
        State thisState = this.getCurrentState();
        State otherState = other.getCurrentState();
        while (thisState != null && otherState != null) {
          if (otherState.attribute.getClass() != thisState.attribute.getClass() || !otherState.attribute.equals(thisState.attribute)) {
            return false;
          }
          thisState = thisState.next;
          otherState = otherState.next;
        }
        return true;
      } else {
        return !other.hasAttributes();
      }
    } else
      return false;
  }
  
  /**
   * Returns a string representation of the object. In general, the {@code toString} method
   * returns a string that "textually represents" this object.
   *
   * <p>WARNING: For backwards compatibility this method is implemented as
   * in Lucene 2.9/3.0. In Lucene 4.0 this default implementation
   * will be removed.
   *
   * <p>It is recommeneded to use {@link #reflectAsString} or {@link #reflectWith}
   * to get a well-defined output of AttributeSource's internals.
   */
  // TODO: @deprecated remove this method in 4.0
  @Override
  public String toString() {
    final StringBuilder sb = new StringBuilder().append('(');
    if (hasAttributes()) {
      for (State state = getCurrentState(); state != null; state = state.next) {
        if (sb.length() > 1) sb.append(',');
        sb.append(state.attribute.toString());
      }
    }
    return sb.append(')').toString();
  }
  
  /**
   * This method returns the current attribute values as a string in the following format
   * by calling the {@link #reflectWith(AttributeReflector)} method:
   * 
   * <ul>
   * <li>iff {@code prependAttClass=true}: {@code "AttributeClass#key=value,AttributeClass#key=value"}
   * <li>iff {@code prependAttClass=false}: {@code "key=value,key=value"}
   * </ul>
   *
   * @see #reflectWith(AttributeReflector)
   */
  public final String reflectAsString(final boolean prependAttClass) {
    final StringBuilder buffer = new StringBuilder();
    reflectWith(new AttributeReflector() {
      public void reflect(Class<? extends Attribute> attClass, String key, Object value) {
        if (buffer.length() > 0) {
          buffer.append(',');
        }
        if (prependAttClass) {
          buffer.append(attClass.getName()).append('#');
        }
        buffer.append(key).append('=').append((value == null) ? "null" : value);
      }
    });
    return buffer.toString();
  }
  
  /**
   * This method is for introspection of attributes, it should simply
   * add the key/values this AttributeSource holds to the given {@link AttributeReflector}.
   *
   * <p>This method iterates over all Attribute implementations and calls the
   * corresponding {@link AttributeImpl#reflectWith} method.</p>
   *
   * @see AttributeImpl#reflectWith
   */
  public final void reflectWith(AttributeReflector reflector) {
    for (State state = getCurrentState(); state != null; state = state.next) {
      state.attribute.reflectWith(reflector);
    }
  }

  /**
   * Performs a clone of all {@link AttributeImpl} instances returned in a new
   * {@code AttributeSource} instance. This method can be used to e.g. create another TokenStream
   * with exactly the same attributes (using {@link #AttributeSource(AttributeSource)}).
   * You can also use it as a (non-performant) replacement for {@link #captureState}, if you need to look
   * into / modify the captured state.
   */
  public AttributeSource cloneAttributes() {
    final AttributeSource clone = new AttributeSource(this.factory);
    
    if (hasAttributes()) {
      // first clone the impls
      for (State state = getCurrentState(); state != null; state = state.next) {
        clone.attributeImpls.put(state.attribute.getClass(), (AttributeImpl) state.attribute.clone());
      }
      
      // now the interfaces
      for (Entry<Class entry : this.attributes.entrySet()) {
        clone.attributes.put(entry.getKey(), clone.attributeImpls.get(entry.getValue().getClass()));
      }
    }
    
    return clone;
  }
  
  /**
   * Copies the contents of this {@code AttributeSource} to the given target {@code AttributeSource}.
   * The given instance has to provide all {@link Attribute}s this instance contains. 
   * The actual attribute implementations must be identical in both {@code AttributeSource} instances;
   * ideally both AttributeSource instances should use the same {@link AttributeFactory}.
   * You can use this method as a replacement for {@link #restoreState}, if you use
   * {@link #cloneAttributes} instead of {@link #captureState}.
   */
  public final void copyTo(AttributeSource target) {
    for (State state = getCurrentState(); state != null; state = state.next) {
      final AttributeImpl targetImpl = target.attributeImpls.get(state.attribute.getClass());
      if (targetImpl == null) {
        throw new IllegalArgumentException("This AttributeSource contains AttributeImpl of type " +
          state.attribute.getClass().getName() + " that is not in the target");
      }
      state.attribute.copyTo(targetImpl);
    }
  }

}