RedisTemplate不太一样的切换库实现
一丶缘由
一个Redis实例有[0-15]共16个database, 默认情况下, redisTemplate只能配置一个database, 当服务应用需要使用另外配置来配置另外的redisTemplate. 由于配置多, 容易出错.这时就出现了"选库"的需求.
二丶RedisTemaplte的执行逻辑
/** * Executes the given action object within a connection that can be exposed or not. Additionally, the connection can * be pipelined. Note the results of the pipeline are discarded (making it suitable for write-only scenarios). * * @param <T> return type * @param action callback object to execute * @param exposeConnection whether to enforce exposure of the native Redis Connection to callback code * @param pipeline whether to pipeline or not the connection for the execution * @return object returned by the action */ @Nullable public <T> T execute(RedisCallback<T> action, boolean exposeConnection, boolean pipeline) { Assert.isTrue(initialized, "template not initialized; call afterPropertiesSet() before using it"); Assert.notNull(action, "Callback object must not be null"); RedisConnectionFactory factory = getRequiredConnectionFactory(); RedisConnection conn = null; try { if (enableTransactionSupport) { // only bind resources in case of potential transaction synchronization conn = RedisConnectionUtils.bindConnection(factory, enableTransactionSupport); } else { conn = RedisConnectionUtils.getConnection(factory); } boolean existingConnection = TransactionSynchronizationManager.hasResource(factory); RedisConnection connToUse = preProcessConnection(conn, existingConnection); boolean pipelineStatus = connToUse.isPipelined(); if (pipeline && !pipelineStatus) { connToUse.openPipeline(); } RedisConnection connToExpose = (exposeConnection ? connToUse : createRedisConnectionProxy(connToUse)); T result = action.doInRedis(connToExpose); // close pipeline if (pipeline && !pipelineStatus) { connToUse.closePipeline(); } // TODO: any other connection processing? return postProcessResult(result, connToUse, existingConnection); } finally { RedisConnectionUtils.releaseConnection(conn, factory, enableTransactionSupport); } }
主要分3步:
1. 获取连接
扫描二维码关注公众号，回复：
8417338 查看本文章
a. 如果开启了事务, 则从事务管理器根据connectionFatory和当前线程获取连接, 如果没有, 则用connectionFactory获取连接
b. 没有开启事务, 直接从connectionFactory获取连接
2. 用connection执行命令
a. preProcessConnection connection前置处理, 一般用于初始化
b. action.doInRedis(connToExpose) 执行当前action
c. postProcessResult(result, connToUse, existingConnection); 后置处理结果
3. 释放连接
RedisConnectionUtils.releaseConnection(conn, factory, enableTransactionSupport);
可以看出,redisTemplate执行主要是围绕connection进行的, 主要是使用RedisConnectionFactory#getConnection()获取连接, 如果每次调用该方法获取到的都是不同的连接, 使用同一个RedisTemplate并不会出现线程安全问题, 然而接口定义并没有指出不同, LettuceConnectionFactory可以创建共享连接, 所以使用同一个RedisTemaplte进行选库操作有可能出现并发问题.LettuceConnection在同步状态下禁止选库操作(会抛出异常).
上图中的配置, 每次进行一次不同的库的操作, 就需要选择一次库, 因为操作一次前就移除了dbIndex
注意: spring boot 2.0 默认使用lettuce连接, 在同步状态下不能进行select(dbIndex)操作
三丶实现二: 创建不同的redisTemplate
直接使用配置创建不同的redisTemplate, 会出现配置过多的问题, 可以利用反射, BeanUtils进行属性复制, 达到相同配置的目的. 需要注意的是, 在RedisTemplate, ConnectionFactory等对象属性, 需要创建不同的对象实例, 以避免并发问题, 因为BeanUtils属性复制, 仅仅进行了引用复制, 还是可能会出现并发问题. 即, 可能出现并发问题的对象, 需要重新创建一份.
/** * 其他选库实现 https://www.jianshu.com/p/9d78cd1c46b6 * * * 本类用于创建restTemplate相同配置,但dbIndex不同的RestTemplate, 可以理解为选库 * * @author TimFruit * @date 20-1-2 下午2:31 */ public class RedisDbSelectFactory { /** * 创建restTemplate相同配置,但dbIndex不同的RestTemplate, 可以理解为选库 * * @param redisTemplate * @param dbIndex redis库 * @return */ public static RedisTemplate selectDb(RedisTemplate redisTemplate, int dbIndex){ try { RedisTemplate dbSelectRedisTemplate=redisTemplate.getClass().getConstructor().newInstance(); BeanUtils.copyProperties(redisTemplate, dbSelectRedisTemplate); RedisConnectionFactory connectionFactory=dbSelectRedisTemplate.getConnectionFactory(); RedisConnectionFactory dbSelectConnectionFactory=null; if(connectionFactory instanceof LettuceConnectionFactory){ dbSelectConnectionFactory= createLettuceDbSelectFactory((LettuceConnectionFactory)connectionFactory, dbIndex); }else if(connectionFactory instanceof JedisConnectionFactory){ dbSelectConnectionFactory= createJedisDbSelectFactory((JedisConnectionFactory) connectionFactory, dbIndex); }else { throw new RuntimeException("不能识别类型"+connectionFactory.getClass()); } dbSelectRedisTemplate.setConnectionFactory(dbSelectConnectionFactory); dbSelectRedisTemplate.afterPropertiesSet(); return dbSelectRedisTemplate; } catch (InstantiationException e) { throw new RuntimeException(e); } catch (IllegalAccessException e) { throw new RuntimeException(e); } catch (InvocationTargetException e) { throw new RuntimeException(e); } catch (NoSuchMethodException e) { throw new RuntimeException(e); } } // -------------------------------------- // jedisConnectionFactory private static JedisConnectionFactory createJedisDbSelectFactory(JedisConnectionFactory connectionFactory, int dbIndex){ JedisConnectionFactory dbSelectConnectionFactory=new JedisDbSelectConnectionFactory(dbIndex); BeanUtils.copyProperties(connectionFactory, dbSelectConnectionFactory); dbSelectConnectionFactory.afterPropertiesSet(); return dbSelectConnectionFactory; } @Slf4j private static class JedisDbSelectConnectionFactory extends JedisConnectionFactory{ private int pointDbIndex; public JedisDbSelectConnectionFactory(int pointDbIndex) { this.pointDbIndex = pointDbIndex; } /** * 替换原配置的dbIndex * @return */ @Override public int getDatabase() { log.info("使用redis库{}",pointDbIndex); return pointDbIndex; } } // -------------------------------------- // lettuceConnectionFactory, 创建后的connection在同步状态下不支持选择库 (connection#select), private static LettuceConnectionFactory createLettuceDbSelectFactory(LettuceConnectionFactory connectionFactory, int dbIndex){ LettuceConnectionFactory dbSelectConnectionFactory=new LettuceDbSelectConnectionFactory(dbIndex); BeanUtils.copyProperties(connectionFactory, dbSelectConnectionFactory); dbSelectConnectionFactory.afterPropertiesSet(); return dbSelectConnectionFactory; } @Slf4j private static class LettuceDbSelectConnectionFactory extends LettuceConnectionFactory{ private int pointDbIndex; public LettuceDbSelectConnectionFactory(int pointDbIndex) { this.pointDbIndex = pointDbIndex; } /** * 替换原配置的dbIndex * @return */ @Override public int getDatabase() { log.info("使用redis库{}",pointDbIndex); return pointDbIndex; } } }
配置使用不同的库:
/** * key是String, value是json * 使用3号库 * @param defaultRedisTemplate * @return */ @Bean("default3RedisManager") public RedisManager<String, Object> default3RedisManager(RedisTemplate<String,Object> defaultRedisTemplate){ RedisTemplate<String,Object> default3RedisTemplate=RedisDbSelectFactory.selectDb(defaultRedisTemplate, 3); return new RedisManager<>(default3RedisTemplate); }
上图可以看出, keySerializer是同一个对象, connectionFactory则是不同的对象
四丶后记
每次实现都有它的适用场景和短板, 需要使用得当, 否则会出现问题.
学习资料: