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springboot multi datasource

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/*
 * Copyright 2018 the organization loushi135
 *
 * Licensed 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 com.lsq.springboot.datasource.starter;


import java.util.concurrent.LinkedBlockingDeque;

/**
 * 核心基于ThreadLocal的切换数据源工具类
 *
 * @author TaoYu Kanyuxia
 * @since 1.0.0
 */
public final class MultiDataSourceContextHolder {

    /**
     * 为什么要用链表存储(准确的是栈)
     *      * 为了支持嵌套切换，如ABC三个service都是不同的数据源
     * 其中A的某个业务要调B的方法，B的方法需要调用C的方法。一级一级调用切换，形成了链。
     * 传统的只设置当前线程的方式不能满足此业务需求，必须模拟栈，后进先出。
     * 
     */
    @SuppressWarnings("unchecked")
    private static final ThreadLocal> LOOKUP_KEY_HOLDER = new ThreadLocal() {
        @Override
        protected Object initialValue() {
            return new LinkedBlockingDeque();
        }
    };

    private MultiDataSourceContextHolder() {
    }

    /**
     * 获得当前线程数据源
     *
     * @return 数据源名称
     */
    public static String getDataSourceLookupKey() {
        LinkedBlockingDeque deque = LOOKUP_KEY_HOLDER.get();
        return deque.isEmpty() ? null : deque.getFirst();
    }

    /**
     * 设置当前线程数据源
     *
     * @param dataSourceLookupKey 数据源名称
     */
    public static void setDataSourceLookupKey(String dataSourceLookupKey) {
        LOOKUP_KEY_HOLDER.get().addFirst(dataSourceLookupKey);
    }

    /**
     * 清空当前线程数据源
     * 
     * 如果当前线程是连续切换数据源
     * 只会移除掉当前线程的数据源名称
     * 
     */
    public static void clearDataSourceLookupKey() {
        LinkedBlockingDeque deque = LOOKUP_KEY_HOLDER.get();
        if (deque.isEmpty()) {
            LOOKUP_KEY_HOLDER.remove();
        } else {
            deque.pollFirst();
        }
    }
}