org.apache.solr.response.transform.DocTransformer.java Source code

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Here is the source code for org.apache.solr.response.transform.DocTransformer.java

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/*
 * 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.
 */
package org.apache.solr.response.transform;

import java.io.IOException;

import org.apache.solr.common.SolrDocument;
import org.apache.solr.response.QueryResponseWriter;
import org.apache.solr.response.ResultContext;
import org.apache.solr.search.SolrIndexSearcher;

/**
 * A DocTransformer can add, remove or alter a Document before it is written out to the Response.  For instance, there are implementations
 * that can put explanations inline with a document, add constant values and mark items as being artificially boosted (see {@link org.apache.solr.handler.component.QueryElevationComponent})
 *
 * <p>
 * New instance for each request
 *
 * @see TransformerFactory
 *
 */
public abstract class DocTransformer {
    protected ResultContext context;

    /**
     *
     * @return The name of the transformer
     */
    public abstract String getName();

    /**
     * This is called before {@link #transform} to provide context for any subsequent transformations.
     *
     * @param context The {@link ResultContext} stores information about how the documents were produced.
     * @see #needsSolrIndexSearcher
     */
    public void setContext(ResultContext context) {
        this.context = context;

    }

    /**
     * Indicates if this transformer requires access to the underlying index to perform it's functions.
     *
     * In some situations (notably RealTimeGet) this method <i>may</i> be called before {@link #setContext} 
     * to determine if the transformer must be given a "full" ResultContext and accurate docIds 
     * that can be looked up using {@link ResultContext#getSearcher}, or if optimizations can be taken 
     * advantage of such that {@link ResultContext#getSearcher} <i>may</i> return null, and docIds passed to 
     * {@link #transform} <i>may</i> be negative.
     *
     * The default implementation always returns <code>false</code>.
     * 
     * @see ResultContext#getSearcher
     * @see #transform
     */
    public boolean needsSolrIndexSearcher() {
        return false;
    }

    /**
     * This is where implementations do the actual work.
     * If implementations require a valid docId and index access, the {@link #needsSolrIndexSearcher} 
     * method must return true
     *
     * Default implementation calls {@link #transform(SolrDocument, int)}.
     *
     * @param doc The document to alter
     * @param docid The Lucene internal doc id, or -1 in cases where the <code>doc</code> did not come from the index
     * @param score the score for this document
     * @throws IOException If there is a low-level I/O error.
     * @see #needsSolrIndexSearcher
     */
    public void transform(SolrDocument doc, int docid, float score) throws IOException {
        transform(doc, docid);
    }

    /**
     * This is where implementations do the actual work.
     * If implementations require a valid docId and index access, the {@link #needsSolrIndexSearcher} 
     * method must return true
     *
     * @param doc The document to alter
     * @param docid The Lucene internal doc id, or -1 in cases where the <code>doc</code> did not come from the index
     * @throws IOException If there is a low-level I/O error.
     * @see #needsSolrIndexSearcher
     */
    public abstract void transform(SolrDocument doc, int docid) throws IOException;

    /**
     * When a transformer needs access to fields that are not automatically derived from the
     * input fields names, this option lets us explicitly say the field names that we hope
     * will be in the SolrDocument.  These fields will be requested from the
     * {@link SolrIndexSearcher} but may or may not be returned in the final
     * {@link QueryResponseWriter}
     * 
     * @return a list of extra lucene fields
     */
    public String[] getExtraRequestFields() {
        return null;
    }

    @Override
    public String toString() {
        return getName();
    }

    /**
     * Trivial Impl that ensure that the specified field is requested as an "extra" field,
     * but then does nothing during the transformation phase.
     */
    public static final class NoopFieldTransformer extends DocTransformer {
        final String field;

        public NoopFieldTransformer() {
            this.field = null;
        }

        public NoopFieldTransformer(String field) {
            this.field = field;
        }

        public String getName() {
            return "noop";
        }

        public String[] getExtraRequestFields() {
            return this.field == null ? null : new String[] { field };
        }

        public void transform(SolrDocument doc, int docid) {
            // No-Op
        }
    }
}