spring data redis源码框架分析

杨叔叔

　　redis是由Salvatore Sanfilippo用C语言编写的一个缓存系统，与memcached相比，提供了更多的处理复杂数据结构的方法；性能也非常的突出。
　　由于项目需要，自己简单地看了下spring新加入的模块spring data redis，spring data redis对jedis, jredis, rjc等redis的java客户端接口进行了进一部的抽象，类似于jdbcTemplate的实现。具体spring配置方式如下：
　　

<?xml version="1.0" encoding="UTF-8"?><beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:p="http://www.springframework.org/schema/p"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
<bean id="connectionFactory" class="org.springframework.data.redis.connection.jedis.JedisConnectionFactory"
p:host-name="${redis.host}" p:port="${redis.port}" p:password="${redis.pass}"/>
<!-- Configurer that replaces ${...} placeholders with values from a properties file -->
<context:property-placeholder location="classpath:redis.properties"/>
<context:annotation-config />
<context:component-scan base-package="org.springframework.data.redis.samples"/>
<bean id="redisTemplate" class="org.springframework.data.redis.core.StringRedisTemplate"
p:connection-factory-ref="connectionFactory"/>
</beans>
　　connectionFactory功能类似于spring 数据库连接的datasource，提供对远程redis server的连接访问；  redisTemplate类似于SqlMapClientTemplate，提供对redis server访问的模板方法。 
　　下面是spring data redis class diagram 

　　结合下面的代码我们进行分析：

public class Example{
@autowired
private RedisTemplate<String,String> template;
public void addLink(String userId, URL url){
template.opsForList.leftPush(userId, url.toExternalForm);
}
}
 　　spring data redis根据数据的类型进行了接口方法的拆分，如ValueOperations，ListOperations，SetOperations，ZSetOperations。template调用opsForList拿到具体的对哪种数据结构进行操作的对象，进而调用相应的操作方法。DefaultListOperations等对象使用回调函数的方法向redis server进行请求。 

public Long leftPush(K key, V value) {
final byte[] rawKey = rawKey(key);
final byte[] rawValue = rawValue(value);
return execute(new RedisCallback<Long>() {
public Long doInRedis(RedisConnection connection) {
return connection.lPush(rawKey, rawValue);
}
}, true);
}
 　　在RedisTemplate中，有一个重要的方法execute对connection进行预处理，包括是否使用pipeline，是否expose(暴露)connection等，对server进行请求后的返回结果进行后续的处理等。 

/**
* 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
*/
public <T> T execute(RedisCallback<T> action, boolean exposeConnection, boolean pipeline) {
Assert.notNull(action, "Callback object must not be null");
RedisConnectionFactory factory = getConnectionFactory();
//由spring中配置的JedisConnectionFactory创建连接
RedisConnection conn = RedisConnectionUtils.getConnection(factory);
boolean existingConnection = TransactionSynchronizationManager.hasResource(factory);
preProcessConnection(conn, existingConnection);//调用StringRedisTemplate的preProcessConnection方法
//拿到了DefaultStringRedisConnection
boolean pipelineStatus = conn.isPipelined();//判断是否打开pipeline
if (pipeline && !pipelineStatus) {
conn.openPipeline();
}
try {
RedisConnection connToExpose = (exposeConnection ? conn : createRedisConnectionProxy(conn));
T result = action.doInRedis(connToExpose);
// TODO: any other connection processing?
// 对后续结果进行处理，但postProcessResult还是直接返回result的，不知为何？
return postProcessResult(result, conn, existingConnection);
} finally {
try {
if (pipeline && !pipelineStatus) {
conn.closePipeline();
}
} finally {
RedisConnectionUtils.releaseConnection(conn, factory);
}
}
}