Small example on how to use a CustomScoreQuery to influence lucene's ranking.

WeightTest.java

package luceneTest;

import java.io.IOException;
import java.util.HashSet;
import java.util.Set;

import org.apache.lucene.analysis.standard.StandardAnalyzer;
import org.apache.lucene.document.Document;
import org.apache.lucene.document.Field;
import org.apache.lucene.document.FieldType;
import org.apache.lucene.document.StoredField;
import org.apache.lucene.document.StringField;
import org.apache.lucene.index.DirectoryReader;
import org.apache.lucene.index.IndexOptions;
import org.apache.lucene.index.IndexWriter;
import org.apache.lucene.index.IndexWriterConfig;
import org.apache.lucene.index.IndexableField;
import org.apache.lucene.index.LeafReader;
import org.apache.lucene.index.LeafReaderContext;
import org.apache.lucene.queries.CustomScoreProvider;
import org.apache.lucene.queries.CustomScoreQuery;
import org.apache.lucene.queryparser.classic.ParseException;
import org.apache.lucene.queryparser.classic.QueryParser;
import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.search.Query;
import org.apache.lucene.search.ScoreDoc;
import org.apache.lucene.search.TopDocs;
import org.apache.lucene.store.RAMDirectory;

public class WeightTest {

	/**
	 * Make a Document object with an un-indexed title field and an indexed
	 * content field.
	 */
	private static Document createDocument(String title, String content, Float value) {
		Document doc = new Document();

		doc.add(new StringField("title", title, Field.Store.YES));
		doc.add(new StoredField("boost", value));

		FieldType type = new FieldType();
		type.setTokenized(true);
		type.setStoreTermVectors(true);
		type.setStored(false);
		type.setIndexOptions(IndexOptions.DOCS_AND_FREQS_AND_POSITIONS_AND_OFFSETS);
		doc.add(new Field("content", content, type));

		return doc;
	}
	
	private static class MyScoreQuery extends CustomScoreQuery {

		public MyScoreQuery(Query subQuery) {
			super(subQuery);
		}
		
		private class MyScoreProvider extends CustomScoreProvider {

			private LeafReader reader;
			private Set<String> fieldsToLoad;
			
			public MyScoreProvider(LeafReaderContext context) {
				super(context);
				reader = context.reader();
				fieldsToLoad = new HashSet<>();
				fieldsToLoad.add("boost");
			}
			
			@Override
			public float customScore(int doc_id, float currentScore, float valSrcScore) throws IOException {
				Document doc = reader.document(doc_id, fieldsToLoad);
				
				// Get boost value from index
				float influence = 1f;
				IndexableField field = doc.getField("boost");
				Number number = field.numericValue();
				float boost = number.floatValue() * influence;
				
				return currentScore + boost;
			}			
		}
		
		@Override
		public CustomScoreProvider getCustomScoreProvider(LeafReaderContext context) {
			return new MyScoreProvider(context);
		}		
	}

	/**
	 * Searches for the given string in the "content" field
	 */
	private static void search(IndexSearcher searcher, String queryString) throws ParseException, IOException {
		// Build a Query object
		QueryParser parser = new QueryParser("content", new StandardAnalyzer());
		Query query = parser.parse(queryString);
		
		// FunctionScoreQuery fsq = new FunctionScoreQuery(query, DoubleValuesSource.fromLongField("boost"));
		MyScoreQuery msq = new MyScoreQuery(query);

		// Search for the query
		TopDocs hits = searcher.search(msq, 10);

		// Examine the Hits object to see if there were any matches
		int hitCount = hits.totalHits;
		if (hitCount == 0) {
			System.out.println("No matches were found for \"" + queryString + "\"");
		} else {
			System.out.println("Hits for \"" + queryString + "\":");

			// Iterate over the Documents in the Hits object
			for (int i = 0; i < hitCount; i++) {
				ScoreDoc doc = hits.scoreDocs[i];		
				
				System.out.println("  " + (i + 1) + ". " + searcher.doc(doc.doc).get("title") + " - " + doc.score);
			}
		}
		System.out.println();
	}
	

	public static void main(String[] args) throws Exception {
		RAMDirectory idx = new RAMDirectory();

		// Create Index
		IndexWriter writer = new IndexWriter(idx, new IndexWriterConfig(new StandardAnalyzer()));

		// Add some Document objects containing quotes
		writer.addDocument(createDocument("Doc 1", "Some content", 20f));
		writer.addDocument(createDocument("Doc 2", "More content", 1.f));
		writer.addDocument(createDocument("Doc 3", "Even more content ", 10.f));
		
		// Close index
		writer.close();

		// Build an IndexSearcher using the in-memory index
		IndexSearcher searcher = new IndexSearcher(DirectoryReader.open(idx));

		// Run some queries
		search(searcher, "content");
	}

}