你们都睡了，而我却在写博客，呵呵！我也不知道为什么都夜深了，我却还没一点困意，趁着劲头赶紧把自定义结果集写完，已经拖了2天没更新了，不能让你们等太久，我也要把写博客一直坚持下去。
Collector是什么？还是看源码吧。这也是最权威的解释说明。
/**
* <p>Expert: Collectors are primarily meant to be used to
* gather raw results from a search, and implement sorting
* or custom result filtering, collation, etc. </p>
*
* <p>Lucene's core collectors are derived from {@link Collector}
* and {@link SimpleCollector}. Likely your application can
* use one of these classes, or subclass {@link TopDocsCollector},
* instead of implementing Collector directly:
*
* <ul>
*
* <li>{@link TopDocsCollector} is an abstract base class
* that assumes you will retrieve the top N docs,
* according to some criteria, after collection is
* done. </li>
*
* <li>{@link TopScoreDocCollector} is a concrete subclass
* {@link TopDocsCollector} and sorts according to score +
* docID. This is used internally by the {@link
* IndexSearcher} search methods that do not take an
* explicit {@link Sort}. It is likely the most frequently
* used collector.</li>
*
* <li>{@link TopFieldCollector} subclasses {@link
* TopDocsCollector} and sorts according to a specified
* {@link Sort} object (sort by field). This is used
* internally by the {@link IndexSearcher} search methods
* that take an explicit {@link Sort}.
*
* <li>{@link TimeLimitingCollector}, which wraps any other
* Collector and aborts the search if it's taken too much
* time.</li>
*
* <li>{@link PositiveScoresOnlyCollector} wraps any other
* Collector and prevents collection of hits whose score
* is <= 0.0</li>
*
* </ul>
*
* @lucene.experimental
*/
public interface Collector {
/**
* Create a new {@link LeafCollector collector} to collect the given context.
*
* @param context
* next atomic reader context
*/
LeafCollector getLeafCollector(LeafReaderContext context) throws IOException;
}
Collector系列接口是用来收集查询结果，实现排序，自定义结果集过滤和收集。Collector和LeafCollector是Lucene结果集收集的核心。
TopDocsCollector：是用来收集Top N结果的，
TopScoreDocCollector：它是TopDocsCollector的子类，它返回的结果集会根据评分和docId进行排序，该接口在IndexSearcher类的search方法内部被调用，但search方法并不需要显式的指定一个Sort排序器，TopScoreDocCollector是使用频率最高的一个结果收集器接口。
TopFieldCollector：它也是TopDocsCollector的子类，跟TopScoreDocCollector的区别是，TopScoreDocCollector是根据评分和docId进行排序的，而TopFieldCollector是根据用户指定的域进行排序，在调用IndexSearcher.search方法时需要显式的指定Sort排序器。
TimeLimitingCollector：它是其他Collector的包装器，它的功能是当被包装的Collector耗时超过限制时可以中断收集过程。
PositiveScoresOnlyCollector：从类名就知道它是干嘛的，Positive正数的意思，即只返回score评分大于零的索引文档，它跟TimeLimitingCollector都属于其他Collector的包装器，都使用了装饰者模式。
Collector接口只有一个接口方法：
LeafCollector getLeafCollector(LeafReaderContext context) throws IOException;
根据提供的IndexReader上下文对象返回一个LeafCollector，LeafCollector其实就是对应每个段文件的收集器，每次切换段文件时都会调用一次此接口方法。
其实LeafCollector才是结果收集器接口，Collector只是用来生成每个段文件对应的LeafCollector，在Lucene4,x时代，Collector和LeafCollector并没有分开，现在Lucene5.0中，接口定义粒度更细了，为用户自定义扩展提供了更多的便利。
接着看看LeafCollector的源码说明：
/**
* <p>Collector decouples the score from the collected doc:
* the score computation is skipped entirely if it's not
* needed. Collectors that do need the score should
* implement the {@link #setScorer} method, to hold onto the
* passed {@link Scorer} instance, and call {@link
* Scorer#score()} within the collect method to compute the
* current hit's score. If your collector may request the
* score for a single hit multiple times, you should use
* {@link ScoreCachingWrappingScorer}. </p>
*
* <p><b>NOTE:</b> The doc that is passed to the collect
* method is relative to the current reader. If your
* collector needs to resolve this to the docID space of the
* Multi*Reader, you must re-base it by recording the
* docBase from the most recent setNextReader call. Here's
* a simple example showing how to collect docIDs into a
* BitSet:</p>
*
* <pre class="prettyprint">
* IndexSearcher searcher = new IndexSearcher(indexReader);
* final BitSet bits = new BitSet(indexReader.maxDoc());
* searcher.search(query, new Collector() {
*
* public LeafCollector getLeafCollector(LeafReaderContext context)
* throws IOException {
* final int docBase = context.docBase;
* return new LeafCollector() {
*
* <em>// ignore scorer</em>
* public void setScorer(Scorer scorer) throws IOException {
* }
*
* public void collect(int doc) throws IOException {
* bits.set(docBase + doc);
* }
*
* };
* }
*
* });
* </pre>
*
* <p>Not all collectors will need to rebase the docID. For
* example, a collector that simply counts the total number
* of hits would skip it.</p>
*
* @lucene.experimental
*/
public interface LeafCollector {
/**
* Called before successive calls to {@link #collect(int)}. Implementations
* that need the score of the current document (passed-in to
* {@link #collect(int)}), should save the passed-in Scorer and call
* scorer.score() when needed.
*/
void setScorer(Scorer scorer) throws IOException;
/**
* Called once for every document matching a query, with the unbased document
* number.
* <p>Note: The collection of the current segment can be terminated by throwing
* a {@link CollectionTerminatedException}. In this case, the last docs of the
* current {@link org.apache.lucene.index.LeafReaderContext} will be skipped and {@link IndexSearcher}
* will swallow the exception and continue collection with the next leaf.
* <p>
* Note: This is called in an inner search loop. For good search performance,
* implementations of this method should not call {@link IndexSearcher#doc(int)} or
* {@link org.apache.lucene.index.IndexReader#document(int)} on every hit.
* Doing so can slow searches by an order of magnitude or more.
*/
void collect(int doc) throws IOException;
}
LeafCollector将打分操作从文档收集中分离出去了，如果你不需要打分操作，你可以完全跳过。
如果你需要打分操作，你需要实现setScorer方法并传入一个Scorer对象，然后在collect方法中
通过调用Scorer.score方法完成对当前命中文档的打分操作。如果你的LeafCollector在collect
方法中需要对命中的某个索引文档调用多次score方法的话，请你使用ScoreCachingWrappingScorer
对象包装你的Scorer对象。(利用缓存防止多次进行重复打分)
collect方法中的doc参数是相对于当前IndexReader的，如果你需要把doc解析成docId(索引文档ID),
你需要调用setNextReader方法来重新计算IndexReader的docBase值。
并不是所有的Collector都需要计算docID基数的，比如对于只需要收集总的命中结果数量的Collector来说，
可以跳过这个操作。
通过以上的理解，我们可以总结出：通过Collector接口生产LeafCollector，然后通过LeafCollector接口
去完成结果收集和命中结果的打分操作。即底下真正干活的是LeafCollector。
void collect(int doc) throws IOException;
这里collect方法用来收集每个索引文档，提供的doc参数表示段文件编号，如果你要获取索引文档的编号，请加上当前段文件Reader的docBase基数，如leafReaderContext.reader().docBase + doc;
如果你需要自定义打分器，请继承实现自己的Scorer，那这个setScorer什么时候调用呢，这个通过阅读IndexSearcher的search方法顺藤摸瓜从而知晓，看图：
其实内部是先把Query对象包装成Filter，然后通过调用createNormalizedWeight方法生成Weight(权重类)，观摩Weight接口你会发现，其中有个Scorer scorer接口方法：
至此我们就弄清楚了，我们的LeafCollector不用关心Scorer是怎么创建并传入到LeafCollector中的，我们只需要实现自己的Scorer即可，我们在IndexSearcher.search方法时内部会首先创建Weight,通过Weight来生成Scorer，我们在调用search方法时需要传入collector接口，那自然scorer接口就被传入了leafCollector中。
如果实现了自己的Scorer则必然需要也要实现自己的Weight并通过自定义Weight来生成自定义Scorer，特此提醒，为了简便起见，这里就没有自定义Scorer。
下面是一个自定义Collector的简单示例，希望能抛砖引玉，为大家排忧解惑，如果代码有任何BUG或纰漏，还望大家告知我。
package com.yida.framework.lucene5.collector;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import org.apache.lucene.index.LeafReaderContext;
import org.apache.lucene.index.SortedDocValues;
import org.apache.lucene.search.Collector;
import org.apache.lucene.search.LeafCollector;
import org.apache.lucene.search.ScoreDoc;
import org.apache.lucene.search.Scorer;
/**
* 自定义Collector结果收集器
* @author Lanxiaowei
*
*/
public class GroupCollector implements Collector, LeafCollector {
/**评分计算器*/
private Scorer scorer;
/**段文件的编号*/
private int docBase;
private String fieldName;
private SortedDocValues sortedDocValues;
private List<ScoreDoc> scoreDocs = new ArrayList<ScoreDoc>();
public LeafCollector getLeafCollector(LeafReaderContext context)
throws IOException {
this.sortedDocValues = context.reader().getSortedDocValues(fieldName);
return this;
}
public void setScorer(Scorer scorer) throws IOException {
this.scorer = scorer;
}
public void collect(int doc) throws IOException {
// scoreDoc:docId和评分
this.scoreDocs.add(new ScoreDoc(this.docBase + doc, this.scorer.score()));
}
public GroupCollector(String fieldName) {
super();
this.fieldName = fieldName;
}
public int getDocBase() {
return docBase;
}
public void setDocBase(int docBase) {
this.docBase = docBase;
}
public String getFieldName() {
return fieldName;
}
public void setFieldName(String fieldName) {
this.fieldName = fieldName;
}
public SortedDocValues getSortedDocValues() {
return sortedDocValues;
}
public void setSortedDocValues(SortedDocValues sortedDocValues) {
this.sortedDocValues = sortedDocValues;
}
public List<ScoreDoc> getScoreDocs() {
return scoreDocs;
}
public void setScoreDocs(List<ScoreDoc> scoreDocs) {
this.scoreDocs = scoreDocs;
}
public Scorer getScorer() {
return scorer;
}
}
package com.yida.framework.lucene5.collector;
import java.io.IOException;
import java.nio.file.Paths;
import java.util.List;
import org.apache.lucene.document.Document;
import org.apache.lucene.index.DirectoryReader;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;
import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.search.ScoreDoc;
import org.apache.lucene.search.TermQuery;
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.FSDirectory;
/**
* 自定义Collector测试
* @author Lanxiaowei
*
*/
public class GroupCollectorTest {
public static void main(String[] args) throws IOException {
String indexDir = "C:/lucenedir";
Directory directory = FSDirectory.open(Paths.get(indexDir));
IndexReader reader = DirectoryReader.open(directory);
IndexSearcher searcher = new IndexSearcher(reader);
TermQuery termQuery = new TermQuery(new Term("title", "lucene"));
GroupCollector collector = new GroupCollector("title2");
searcher.search(termQuery, null, collector);
List<ScoreDoc> docs = collector.getScoreDocs();
for (ScoreDoc scoreDoc : docs) {
int docID = scoreDoc.doc;
Document document = searcher.doc(docID);
String title = document.get("title");
float score = scoreDoc.score;
System.out.println(docID + ":" + title + " " + score);
}
reader.close();
directory.close();
}
}
这里仅仅是一个简单的示例，如果你需要更严格的干预索引文档，请在collect方法里实现的代码逻辑，如果你需要更细粒度的干预文档打分过程，请继承Scorer抽象类自定义的实现并继承Weight抽象类自定义的实现，然后调用IndexSearch的这个方法即可：
protected TopFieldDocs search(Weight weight, FieldDoc after, int nDocs,
Sort sort, boolean fillFields,
boolean doDocScores, boolean doMaxScore)
throws IOException
一如既往的，demo源码会上传到底下的附件里，至于有童鞋要求我的demo不要使用Maven构建，I am very sorry,I can't meet your requirments.如果你不会Maven，还是花时间去学下吧。OK，凌晨一点多了，我该搁笔就寝咯！
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