Lucene in action 笔记 search篇

一. 用lucene怎么完成search

1. 创建IndexSearcher

IndexSearcher searcher = new IndexSearcher(directory);

2. 生成需要搜索的词
Term t = new Term("subject", "ant");

3. 创建查询
Query query = new TermQuery(t);

4. search并得到结果
Hits hits = searcher.search(query);

 

此处的query就简单的由term生成的, 对于复杂的query需要用QueryParser来生成

Query query = QueryParser.parse("+JUNIT +ANT -MOCK", "contents", new SimpleAnalyzer());

static public Query parse(String query, String field, Analyzer analyzer) throws ParseException

query: 需要parse的查询string

field: default的field

analyzer: 处理查询string需要的analyzer, 来处理大小写等

 

二. Using IndexSearcher

1. search

Hits search(Query query)  Straightforward searches needing no filtering.

Hits search(Query query, Filter filter) Searches constrained to a subset of available documents, based on filter criteria.

void search(Query query, HitCollector results) Used only when all documents found from a search will be needed.
HitCollector 和 Hits不同, 会包含所有结果, 所以注意这个函数performance问题

 

2. Working with Hits

Hits应该会记录下所有匹配的结果, 但是只会加载top 100到内存, 因为一般用户也只需要这些. 如果你用doc(n)访问未被cache的文章, 需要先从index里面load, 所以需要时才去调用比较合理.

length() Number of documents in the Hits collection

doc(n) Document instance of the nth top-scoring document
id(n) Document ID of the nth top-scoring document
score(n) Normalized score (based on the score of the topmost document) of the nth topscoring document, guaranteed to be greater than 0 and less than or equal to 1

对于分页显示hits的solution, 推荐每页都从新去做search来生成hits, 并从中取出你所需要的页. 这样符合stateless的服务端的原则

 

3. Reading indexes into memory

如果你内存足够大, 而且index本身是没有变化的时候

你可以把index载入内存, search将飞快...

RAMDirectory ramDir = new RAMDirectory(dir);

 

三. Understanding Lucene scoring

至于怎么排名的就不解释了.

这里有个接口可以查看排名的具体细节, 为什么他就排第一个了?

IndexSearcher searcher = new IndexSearcher(directory);
Hits hits = searcher.search(query);

Explanation explanation = searcher.explain(query, hits.id(0));

System.out.println(explanation.toString());

好了通过打出的各个参数的值, 就能理解他为什么排第一个了

 

四. Creating queries programmatically

用程序的方式取创建查询, 还有一种方法就是用QueryParser去生成查询.

1. Searching by term: TermQuery

Term t = new Term("contents", "java"); Term(field, value)

Query query = new TermQuery(t);

term的value是大小写敏感的, 所以search时的大小写要和index时的一致

 

2. Searching within a range: RangeQuery

begin = new Term("pubmonth","198805");

end = new Term("pubmonth","198810");

RangeQuery query = new RangeQuery(begin, end, true); 最后这个flag是表示是否包含begin和end

QueryParser中的表示为: [begin TO end] or {begin TO end}.

 

3. Searching on a string: PrefixQuery

找前缀, 底下这个意思是找到这个目录, 及其所有子目录

Term term = new Term("category", "/technology/computers/programming");
PrefixQuery query = new PrefixQuery(term);

QueryParser中的表示为:prefix*

 

4. Combining queries: BooleanQuery

TermQuery searchingBooks =new TermQuery(new Term("subject","search"));
RangeQuery currentBooks =new RangeQuery(new Term("pubmonth","200401"), new Term("pubmonth","200412"),true);
BooleanQuery currentSearchingBooks = new BooleanQuery();
currentSearchingBooks.add(searchingBook s, true, false);
currentSearchingBooks.add(currentBooks, true, false);

可见, 可以通过add往booleanquery上加子查询, 并通过最后两个参数来决定与或的关系

两个参数分别是required and prohibited, 就是要求和禁止, 两个不可能全true

false, false: Clause is optional, 即或

true, false: Clause must match, 即与

false, true: Clause must not match, 即非

QueryParser中的表示为: –, +, AND, OR, and NOT

lucene新的接口是:

public void add(Query query, BooleanClause.Occur occur)

where occur can be BooleanClause.Occur.MUST, BooleanClause.Occur.SHOULD or BooleanClause.Occur.MUST_NOT
(AND)BooleanClause.Occur.MUST means exactly that: Only documents matching that clause are considered.
(OR)BooleanClause.Occur.SHOULD means the term is optional.
(NOT)BooleanClause.Occur.MUST_NOT means any documents matching this clause are excluded from the results.

 

5. 后面还有PhraseQuery, WildcardQuery, FuzzyQuery就不一一介绍了, 大家用到再去查吧

 

五. Parsing query expressions: QueryParser

虽然用api去创建query很好, 但有时也需要用human-readable textual query representation.

对于一个已有的query, 我们可以用Query.toString, 得到一个query的human-readable textual query representation.

这个就不具体说了, QueryParser看上去不错, 不过他并不能表示所有的查询, 有些查询必须用api生成. 而且用QueryParser去parse应该是要额外耗费一些时间的. 对于要提供给用户查询UI的应用, QueryParser是非常方便的.