--- /dev/null
+package org.apache.lucene.analysis;
+
+/**
+ * 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.io.IOException;
+import java.io.Closeable;
+import java.lang.reflect.Modifier;
+
+import org.apache.lucene.document.Document;
+import org.apache.lucene.document.Field;
+import org.apache.lucene.index.IndexWriter;
+import org.apache.lucene.util.Attribute;
+import org.apache.lucene.util.AttributeImpl;
+import org.apache.lucene.util.AttributeSource;
+
+/**
+ * A <code>TokenStream</code> enumerates the sequence of tokens, either from
+ * {@link Field}s of a {@link Document} or from query text.
+ * <p>
+ * This is an abstract class; concrete subclasses are:
+ * <ul>
+ * <li>{@link Tokenizer}, a <code>TokenStream</code> whose input is a Reader; and
+ * <li>{@link TokenFilter}, a <code>TokenStream</code> whose input is another
+ * <code>TokenStream</code>.
+ * </ul>
+ * A new <code>TokenStream</code> API has been introduced with Lucene 2.9. This API
+ * has moved from being {@link Token}-based to {@link Attribute}-based. While
+ * {@link Token} still exists in 2.9 as a convenience class, the preferred way
+ * to store the information of a {@link Token} is to use {@link AttributeImpl}s.
+ * <p>
+ * <code>TokenStream</code> now extends {@link AttributeSource}, which provides
+ * access to all of the token {@link Attribute}s for the <code>TokenStream</code>.
+ * Note that only one instance per {@link AttributeImpl} is created and reused
+ * for every token. This approach reduces object creation and allows local
+ * caching of references to the {@link AttributeImpl}s. See
+ * {@link #incrementToken()} for further details.
+ * <p>
+ * <b>The workflow of the new <code>TokenStream</code> API is as follows:</b>
+ * <ol>
+ * <li>Instantiation of <code>TokenStream</code>/{@link TokenFilter}s which add/get
+ * attributes to/from the {@link AttributeSource}.
+ * <li>The consumer calls {@link TokenStream#reset()}.
+ * <li>The consumer retrieves attributes from the stream and stores local
+ * references to all attributes it wants to access.
+ * <li>The consumer calls {@link #incrementToken()} until it returns false
+ * consuming the attributes after each call.
+ * <li>The consumer calls {@link #end()} so that any end-of-stream operations
+ * can be performed.
+ * <li>The consumer calls {@link #close()} to release any resource when finished
+ * using the <code>TokenStream</code>.
+ * </ol>
+ * To make sure that filters and consumers know which attributes are available,
+ * the attributes must be added during instantiation. Filters and consumers are
+ * not required to check for availability of attributes in
+ * {@link #incrementToken()}.
+ * <p>
+ * You can find some example code for the new API in the analysis package level
+ * Javadoc.
+ * <p>
+ * Sometimes it is desirable to capture a current state of a <code>TokenStream</code>,
+ * e.g., for buffering purposes (see {@link CachingTokenFilter},
+ * {@link TeeSinkTokenFilter}). For this usecase
+ * {@link AttributeSource#captureState} and {@link AttributeSource#restoreState}
+ * can be used.
+ * <p>The {@code TokenStream}-API in Lucene is based on the decorator pattern.
+ * Therefore all non-abstract subclasses must be final or have at least a final
+ * implementation of {@link #incrementToken}! This is checked when Java
+ * assertions are enabled.
+ */
+public abstract class TokenStream extends AttributeSource implements Closeable {
+
+ /**
+ * A TokenStream using the default attribute factory.
+ */
+ protected TokenStream() {
+ super();
+ assert assertFinal();
+ }
+
+ /**
+ * A TokenStream that uses the same attributes as the supplied one.
+ */
+ protected TokenStream(AttributeSource input) {
+ super(input);
+ assert assertFinal();
+ }
+
+ /**
+ * A TokenStream using the supplied AttributeFactory for creating new {@link Attribute} instances.
+ */
+ protected TokenStream(AttributeFactory factory) {
+ super(factory);
+ assert assertFinal();
+ }
+
+ private boolean assertFinal() {
+ try {
+ final Class<?> clazz = getClass();
+ if (!clazz.desiredAssertionStatus())
+ return true;
+ assert clazz.isAnonymousClass() ||
+ (clazz.getModifiers() & (Modifier.FINAL | Modifier.PRIVATE)) != 0 ||
+ Modifier.isFinal(clazz.getMethod("incrementToken").getModifiers()) :
+ "TokenStream implementation classes or at least their incrementToken() implementation must be final";
+ return true;
+ } catch (NoSuchMethodException nsme) {
+ return false;
+ }
+ }
+
+ /**
+ * Consumers (i.e., {@link IndexWriter}) use this method to advance the stream to
+ * the next token. Implementing classes must implement this method and update
+ * the appropriate {@link AttributeImpl}s with the attributes of the next
+ * token.
+ * <P>
+ * The producer must make no assumptions about the attributes after the method
+ * has been returned: the caller may arbitrarily change it. If the producer
+ * needs to preserve the state for subsequent calls, it can use
+ * {@link #captureState} to create a copy of the current attribute state.
+ * <p>
+ * This method is called for every token of a document, so an efficient
+ * implementation is crucial for good performance. To avoid calls to
+ * {@link #addAttribute(Class)} and {@link #getAttribute(Class)},
+ * references to all {@link AttributeImpl}s that this stream uses should be
+ * retrieved during instantiation.
+ * <p>
+ * To ensure that filters and consumers know which attributes are available,
+ * the attributes must be added during instantiation. Filters and consumers
+ * are not required to check for availability of attributes in
+ * {@link #incrementToken()}.
+ *
+ * @return false for end of stream; true otherwise
+ */
+ public abstract boolean incrementToken() throws IOException;
+
+ /**
+ * This method is called by the consumer after the last token has been
+ * consumed, after {@link #incrementToken()} returned <code>false</code>
+ * (using the new <code>TokenStream</code> API). Streams implementing the old API
+ * should upgrade to use this feature.
+ * <p/>
+ * This method can be used to perform any end-of-stream operations, such as
+ * setting the final offset of a stream. The final offset of a stream might
+ * differ from the offset of the last token eg in case one or more whitespaces
+ * followed after the last token, but a {@link WhitespaceTokenizer} was used.
+ *
+ * @throws IOException
+ */
+ public void end() throws IOException {
+ // do nothing by default
+ }
+
+ /**
+ * Resets this stream to the beginning. This is an optional operation, so
+ * subclasses may or may not implement this method. {@link #reset()} is not needed for
+ * the standard indexing process. However, if the tokens of a
+ * <code>TokenStream</code> are intended to be consumed more than once, it is
+ * necessary to implement {@link #reset()}. Note that if your TokenStream
+ * caches tokens and feeds them back again after a reset, it is imperative
+ * that you clone the tokens when you store them away (on the first pass) as
+ * well as when you return them (on future passes after {@link #reset()}).
+ */
+ public void reset() throws IOException {}
+
+ /** Releases resources associated with this stream. */
+ public void close() throws IOException {}
+
+}
fnp / pylucene.git / blobdiff