Source Code Cross Referenced for QueryLoader.java in  » Database-JDBC-Connection-Pool » Database-Utilities » org » apache » commons » dbutils » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » Database JDBC Connection Pool » Database Utilities » org.apache.commons.dbutils 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


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 Map queries = new HashMap();
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 load(String path) throws IOException {
073:
074:                Map queryMap = (Map) 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 loadQueries(String path) throws IOException {
095:                InputStream in = getClass().getResourceAsStream(path);
096:
097:                if (in == null) {
098:                    throw new IllegalArgumentException(path + " not found.");
099:                }
100:
101:                Properties props = new Properties();
102:                props.load(in);
103:
104:                // Copy to HashMap for better performance
105:                return new HashMap(props);
106:            }
107:
108:            /**
109:             * Removes the queries for the given path from the cache.
110:             * @param path The path that the queries were loaded from.
111:             */
112:            public synchronized void unload(String path) {
113:                this.queries.remove(path);
114:            }
115:
116:        }
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