有时候我们在做lucene的结果展示的时候可能需要对多个列的内容进行计算，根据多个field对应的值做数值方面的运算。
lucene自4.6版本起，提供了用于运算的expression模块；
expression分为两部分：
org.apache.lucene.expressions：提供了字段绑定和相关的表达式参数传递的功能；org.apache.lucene.expressions.js:提供了表达式定义的功能。
Expression类使用示例
Expression是提供document的运算的支持类；
我们的运算表达式和其绑定内容通常类似于如下：
// compile an expression:
Expression expr = JavascriptCompiler.compile("sqrt(_score) + ln(popularity)");
// SimpleBindings just maps variables to SortField instances
SimpleBindings bindings = new SimpleBindings();
bindings.add(new SortField("_score", SortField.Type.SCORE));
bindings.add(new SortField("popularity", SortField.Type.INT));
// create a sort field and sort by it (reverse order)
Sort sort = new Sort(expr.getSortField(bindings, true));
Query query = new TermQuery(new Term("body", "contents"));
searcher.search(query, null, 10, sort);
如上所示，我们对document中的_score和popularity两个字段进行值的运算，这里是对_score开平方之后和popularity的对数运算求和，运算方式的定义在第一行；
下边有定义了SimpleBindings，binding主要是对运算的数据进行数据绑定；
最终的查询结果是根据以上的运算结果采取倒排序的方式
表达式说明
表达式的构造可以采用如下的几种来进行组合：
- 数值型的
- + - * / %等运算符
- 移位运算符：| & ^ ~ << >> >>>
- 布尔运算符（包括三目运算符）：
&& || ! ?: - 比较运算符：< <= == >= >
- 数学运算函数：abs ceil exp floor ln log10 logn max min sqrt pow
- 三角运算函数：acosh acos asinh asin atanh atan atan2 cosh cos sinh sin tanh tan
- haversin公式
- min,max函数
代码示例
我写了一个测试程序，模拟长方形的运算并排序；
面积倒序排序；
当面积相同时，按宽度倒序，长度倒序；
周长倒序排序；
周长相同时，按宽度倒序，长度倒序；
示例程序如下：
package com.lucene.expression;
import java.io.IOException;
import java.nio.file.Paths;
import java.text.ParseException;
import org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.analysis.standard.StandardAnalyzer;
import org.apache.lucene.document.Document;
import org.apache.lucene.document.Field;
import org.apache.lucene.document.IntField;
import org.apache.lucene.document.NumericDocValuesField;
import org.apache.lucene.expressions.Expression;
import org.apache.lucene.expressions.SimpleBindings;
import org.apache.lucene.expressions.js.JavascriptCompiler;
import org.apache.lucene.index.DirectoryReader;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.IndexWriter;
import org.apache.lucene.index.IndexWriterConfig;
import org.apache.lucene.index.IndexWriterConfig.OpenMode;
import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.search.MatchAllDocsQuery;
import org.apache.lucene.search.Query;
import org.apache.lucene.search.ScoreDoc;
import org.apache.lucene.search.Sort;
import org.apache.lucene.search.SortField;
import org.apache.lucene.search.TopDocs;
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.FSDirectory;
import org.junit.Test;
public class LuceneExpressionTest{
@Test
public void index(){
try {
Directory directory = FSDirectory.open(Paths.get("index"));
Analyzer analyzer = new StandardAnalyzer();
IndexWriterConfig config = new IndexWriterConfig(analyzer);
config.setOpenMode(OpenMode.CREATE_OR_APPEND);
IndexWriter writer = new IndexWriter(directory, config);
Document doc = new Document();
//模拟长方形
doc.add(new IntField("width", 3,Field.Store.YES));
doc.add(new IntField("longth", 4,Field.Store.YES));
doc.add(new NumericDocValuesField("width", 3));
doc.add(new NumericDocValuesField("longth", 4));
writer.addDocument(doc);
Document doc1 = new Document();
doc1.add(new IntField("width", 2,Field.Store.YES));
doc1.add(new IntField("longth", 5,Field.Store.YES));
doc1.add(new NumericDocValuesField("width", 2));
doc1.add(new NumericDocValuesField("longth", 5));
writer.addDocument(doc1);
Document doc2 = new Document();
doc2.add(new IntField("width", 2,Field.Store.YES));
doc2.add(new IntField("longth", 6,Field.Store.YES));
doc2.add(new NumericDocValuesField("width", 2));
doc2.add(new NumericDocValuesField("longth", 6));
writer.addDocument(doc2);
writer.commit();
writer.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
/**
* 面积比较
*/
@Test
public void testAcreage(){
try {
Expression expr = JavascriptCompiler.compile("width*longth");
SimpleBindings bindings = new SimpleBindings();
bindings.add(new SortField("width", SortField.Type.INT));
bindings.add(new SortField("longth", SortField.Type.INT));
Sort sort = new Sort(expr.getSortField(bindings, true));
Query query = new MatchAllDocsQuery();
Directory directory = FSDirectory.open(Paths.get("index"));
IndexReader reader = DirectoryReader.open(directory);
IndexSearcher searcher = new IndexSearcher(reader);
TopDocs docs = searcher.search(query, 10, sort);
for (ScoreDoc scoreDoc : docs.scoreDocs) {
System.out.println(searcher.doc(scoreDoc.doc));
}
} catch (ParseException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
/**
* 周长比较
*/
@Test
public void testCircum(){
try {
Expression expr = JavascriptCompiler.compile("width+longth+sqrt(pow(width,2)+pow(longth,2))");
SimpleBindings bindings = new SimpleBindings();
bindings.add(new SortField("width", SortField.Type.INT));
bindings.add(new SortField("longth", SortField.Type.INT));
Sort sort = new Sort(expr.getSortField(bindings, true));
Query query = new MatchAllDocsQuery();
Directory directory = FSDirectory.open(Paths.get("index"));
IndexReader reader = DirectoryReader.open(directory);
IndexSearcher searcher = new IndexSearcher(reader);
TopDocs docs = searcher.search(query, 10, sort);
for (ScoreDoc scoreDoc : docs.scoreDocs) {
System.out.println(searcher.doc(scoreDoc.doc));
}
} catch (ParseException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
面积的比较运行结果为：
Document<stored<width:3> stored<longth:4>> Document<stored<width:2> stored<longth:6>> Document<stored<width:2> stored<longth:5>>
同样的，周长比较的运行结果为：
Document<stored<width:2> stored<longth:6>> Document<stored<width:2> stored<longth:5>> Document<stored<width:3> stored<longth:4>>
以上是lucene的expression的应用，源代码会在明天放出；
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时间： 2024-08-05 01:51:10