/*
* Copyright 2011 The Apache Software Foundation
*
* 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.lealone.dbobject.table;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Iterator;
import java.util.Map;
import java.util.ServiceLoader;
import java.util.concurrent.ConcurrentHashMap;
import org.lealone.api.TableEngine;
import org.lealone.constant.DbSettings;
import org.lealone.message.DbException;
public class TableEngineManager {
private TableEngineManager() {
}
private static Map<String, TableEngine> tableEngines = new ConcurrentHashMap<String, TableEngine>();
private static boolean initialized = false;
public static TableEngine getTableEngine(String name) {
if (!initialized) {
initialize();
}
if (name == null) {
name = DbSettings.getInstance().defaultTableEngine;
//TODO 如果为null怎么办？抛错？还是设个默认值，默认值从哪取？
//if (name == null)
// name = MemoryTableEngine.NAME;
}
TableEngine te = tableEngines.get(name.toUpperCase());
// if (te == null)
// throw DbException.get(ErrorCode.FEATURE_NOT_SUPPORTED_1, name + " store engine not found");
return te;
}
public static void registerTableEngine(TableEngine tableEngine) {
tableEngines.put(tableEngine.getName().toUpperCase(), tableEngine);
}
public static void deregisterTableEngine(TableEngine tableEngine) {
tableEngines.remove(tableEngine.getName().toUpperCase());
}
private static class TableEngineService implements PrivilegedAction<TableEngine> {
@Override
public TableEngine run() {
Iterator<TableEngine> iterator = ServiceLoader.load(TableEngine.class).iterator();
try {
while (iterator.hasNext()) {
//执行next时ServiceLoader内部会自动为每一个实现TableEngine接口的类生成一个新实例
//所以TableEngine接口的实现类必需有一个public的无参数构造函数
iterator.next();
}
} catch (Throwable t) {
DbException.convert(t);
}
return null;
}
}
private synchronized static void initialize() {
if (initialized) {
return;
}
initialized = true;
loadTableEngines();
}
private static void loadTableEngines() {
AccessController.doPrivileged(new TableEngineService());
}
}