org.apache.commons.dbutils.QueryLoader Maven / Gradle / Ivy
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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.commons.dbutils;
import java.io.IOException;
import java.io.InputStream;
import java.util.HashMap;
import java.util.Map;
import java.util.Properties;
/**
* QueryLoader is a registry for sets of queries so
* that multiple copies of the same queries aren't loaded into memory.
* This implementation loads properties files filled with query name to
* SQL mappings. This class is thread safe.
*/
public class QueryLoader {
/**
* The Singleton instance of this class.
*/
private static final QueryLoader instance = new QueryLoader();
/**
* Return an instance of this class.
* @return The Singleton instance.
*/
public static QueryLoader instance() {
return instance;
}
/**
* Maps query set names to Maps of their queries.
*/
private final Map> queries = new HashMap>();
/**
* QueryLoader constructor.
*/
protected QueryLoader() {
super();
}
/**
* Loads a Map of query names to SQL values. The Maps are cached so a
* subsequent request to load queries from the same path will return
* the cached Map.
*
* @param path The path that the ClassLoader will use to find the file.
* This is not a file system path. If you had a jarred
* Queries.properties file in the com.yourcorp.app.jdbc package you would
* pass "/com/yourcorp/app/jdbc/Queries.properties" to this method.
* @throws IOException if a file access error occurs
* @throws IllegalArgumentException if the ClassLoader can't find a file at
* the given path.
* @return Map of query names to SQL values
*/
public synchronized Map load(String path) throws IOException {
Map queryMap = this.queries.get(path);
if (queryMap == null) {
queryMap = this.loadQueries(path);
this.queries.put(path, queryMap);
}
return queryMap;
}
/**
* Loads a set of named queries into a Map object. This implementation
* reads a properties file at the given path.
* @param path The path that the ClassLoader will use to find the file.
* @throws IOException if a file access error occurs
* @throws IllegalArgumentException if the ClassLoader can't find a file at
* the given path.
* @since DbUtils 1.1
* @return Map of query names to SQL values
*/
protected Map loadQueries(String path) throws IOException {
// Findbugs flags getClass().getResource as a bad practice; maybe we should change the API?
InputStream in = getClass().getResourceAsStream(path);
if (in == null) {
throw new IllegalArgumentException(path + " not found.");
}
Properties props = new Properties();
try {
props.load(in);
} finally {
in.close();
}
// Copy to HashMap for better performance
@SuppressWarnings({ "rawtypes", "unchecked" }) // load() always creates entries
HashMap hashMap = new HashMap(props);
return hashMap;
}
/**
* Removes the queries for the given path from the cache.
* @param path The path that the queries were loaded from.
*/
public synchronized void unload(String path) {
this.queries.remove(path);
}
}