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Apache Solr (module: core)
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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;

import java.io.IOException;
import java.io.Writer;
import org.apache.solr.request.SolrQueryRequest;
import org.apache.solr.util.plugin.NamedListInitializedPlugin;

/**
 * Implementations of QueryResponseWriter are used to format responses to query
 * requests.
 *
 * Different QueryResponseWriters are registered with the SolrCore. One
 * way to register a QueryResponseWriter with the core is through the solrconfig.xml
 * file.
 *
 * 
Example solrconfig.xml entry to register a QueryResponseWriter
 * implementation to handle all queries with a writer type of "simple":
 *
 * 

 *    <queryResponseWriter name="simple" class="foo.SimpleResponseWriter" />
 * 
 *
 * 
A single instance of any registered QueryResponseWriter is created via the default constructor
 * and is reused for all relevant queries.
 */
public interface QueryResponseWriter extends NamedListInitializedPlugin {
  public static String CONTENT_TYPE_XML_UTF8 = "application/xml; charset=UTF-8";
  public static String CONTENT_TYPE_TEXT_UTF8 = "text/plain; charset=UTF-8";
  public static String CONTENT_TYPE_TEXT_ASCII = "text/plain; charset=US-ASCII";

  /**
   * Write a SolrQueryResponse, this method must be thread save.
   *
   * 
Information about the request (in particular: formatting options) may be obtained from
   * req but the dominant source of information should be rsp.
   *
   * 
There are no mandatory actions that write must perform. An empty write implementation would
   * fulfill all interface obligations.
   */
  public void write(Writer writer, SolrQueryRequest request, SolrQueryResponse response)
      throws IOException;

  /**
   * Return the applicable Content Type for a request, this method must be thread safe.
   *
   * QueryResponseWriter's must implement this method to return a valid HTTP Content-Type header
   * for the request, that will logically correspond with the output produced by the write method.
   *
   * @return a Content-Type string, which may not be null.
   */
  public String getContentType(SolrQueryRequest request, SolrQueryResponse response);
}