001 /*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements. See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License. You may obtain a copy of the License at
008 *
009 * http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017 package org.apache.commons.dbutils;
018
019 import java.io.IOException;
020 import java.io.InputStream;
021 import java.util.HashMap;
022 import java.util.Map;
023 import java.util.Properties;
024
025 /**
026 * <code>QueryLoader</code> is a registry for sets of queries so
027 * that multiple copies of the same queries aren't loaded into memory.
028 * This implementation loads properties files filled with query name to
029 * SQL mappings. This class is thread safe.
030 */
031 public class QueryLoader {
032
033 /**
034 * The Singleton instance of this class.
035 */
036 private static final QueryLoader instance = new QueryLoader();
037
038 /**
039 * Return an instance of this class.
040 * @return The Singleton instance.
041 */
042 public static QueryLoader instance() {
043 return instance;
044 }
045
046 /**
047 * Maps query set names to Maps of their queries.
048 */
049 private final Map<String, Map<String, String>> queries = new HashMap<String, Map<String, String>>();
050
051 /**
052 * QueryLoader constructor.
053 */
054 protected QueryLoader() {
055 super();
056 }
057
058 /**
059 * Loads a Map of query names to SQL values. The Maps are cached so a
060 * subsequent request to load queries from the same path will return
061 * the cached Map.
062 *
063 * @param path The path that the ClassLoader will use to find the file.
064 * This is <strong>not</strong> a file system path. If you had a jarred
065 * Queries.properties file in the com.yourcorp.app.jdbc package you would
066 * pass "/com/yourcorp/app/jdbc/Queries.properties" to this method.
067 * @throws IOException if a file access error occurs
068 * @throws IllegalArgumentException if the ClassLoader can't find a file at
069 * the given path.
070 * @return Map of query names to SQL values
071 */
072 public synchronized Map<String, String> load(String path) throws IOException {
073
074 Map<String, String> queryMap = this.queries.get(path);
075
076 if (queryMap == null) {
077 queryMap = this.loadQueries(path);
078 this.queries.put(path, queryMap);
079 }
080
081 return queryMap;
082 }
083
084 /**
085 * Loads a set of named queries into a Map object. This implementation
086 * reads a properties file at the given path.
087 * @param path The path that the ClassLoader will use to find the file.
088 * @throws IOException if a file access error occurs
089 * @throws IllegalArgumentException if the ClassLoader can't find a file at
090 * the given path.
091 * @since DbUtils 1.1
092 * @return Map of query names to SQL values
093 */
094 protected Map<String, String> loadQueries(String path) throws IOException {
095 // Findbugs flags getClass().getResource as a bad practice; maybe we should change the API?
096 InputStream in = getClass().getResourceAsStream(path);
097
098 if (in == null) {
099 throw new IllegalArgumentException(path + " not found.");
100 }
101
102 Properties props = new Properties();
103 try {
104 props.load(in);
105 } finally {
106 in.close();
107 }
108
109 // Copy to HashMap for better performance
110
111 @SuppressWarnings({ "rawtypes", "unchecked" }) // load() always creates <String,String> entries
112 HashMap<String, String> hashMap = new HashMap(props);
113 return hashMap;
114 }
115
116 /**
117 * Removes the queries for the given path from the cache.
118 * @param path The path that the queries were loaded from.
119 */
120 public synchronized void unload(String path) {
121 this.queries.remove(path);
122 }
123
124 }