首先从使用springboot+redis碰到的一个问题说起。在前几篇文章中介绍了用SpringBoot+redis构建了一个个人博客。在刚开始远行的时候发现发了几个请求操作了几次redis之后，后面的就被阻塞了，请求一直在等待返回，我们重现一下问题。
[注意] 该问题只会出现在springboot 2.0之前的版本;2.0之后springboot连接Redis改成了lettuce，并重新实现，问题已经不存在

打开Template的事务支持

POM 配置：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.github.springboot</groupId>
    <artifactId>redis-tx-demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>SpringBoot redis TX demo</name>
    <description>Demo project for Spring Boot with Redis transaction</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.2.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-redis</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-rest</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>


</project>

Redis configuration (EnbaleTransactionSupport设为true):

@Configuration
public class RedisConfiguration {

    @Bean
    public StringRedisTemplate redisTemplate(RedisConnectionFactory redisConnectionFactory) {
        StringRedisTemplate template = new StringRedisTemplate();
        template.setConnectionFactory(redisConnectionFactory);
        template.setEnableTransactionSupport(true); //打开事务支持
        return template;
    }
}

Controller就是简单的set一个key到redis:

@RestController
public class DemoController {
    
    private StringRedisTemplate template;
    
    public DemoController(StringRedisTemplate template) {
        this.template = template;
    }
    
    @GetMapping("/put")
    public String redisSet() {
        int i = (int)(Math.random() * 100);
        template.opsForValue().set("key"+i, "value"+i, 300, TimeUnit.SECONDS);
        return "success "+"key"+i;
    }

}

启动后，我们使用RestClient发送请求http://localhost:8080/put，发送8次之后就会发现没有返回了。这个时候我们查看redis的链接数，发现已经超过8个，springboot对于jedis连接池默认的最大活跃连接数是8，所以看出来是连接池被耗光了。

127.0.0.1:6379> info clients
# Clients
connected_clients:9
client_longest_output_list:0
client_biggest_input_buf:0
blocked_clients:0
127.0.0.1:6379>

还有查看程序的日志可以发现，RedisConnectionUtils只有Opening RedisConnection而没有close。

2018-08-11 11:00:48.889 [DEBUG][http-nio-8080-exec-8]:o.s.data.redis.core.RedisConnectionUtils [doGetConnection:126] Opening RedisConnection
2018-08-11 11:00:50.169 [DEBUG][http-nio-8080-exec-8]:o.s.w.s.m.m.a.RequestResponseBodyMethodProcessor [writeWithMessageConverters:249] Written [success key39] as "text/plain" using [org.springframework.http.converter.StringHttpMessageConverter@766a49c7]
2018-08-11 11:00:50.170 [DEBUG][http-nio-8080-exec-8]:org.springframework.web.servlet.DispatcherServlet [processDispatchResult:1044] Null ModelAndView returned to DispatcherServlet with name 'dispatcherServlet': assuming HandlerAdapter completed request handling
2018-08-11 11:00:50.170 [DEBUG][http-nio-8080-exec-8]:org.springframework.web.servlet.DispatcherServlet [processRequest:1000] Successfully completed request
2018-08-11 11:00:50.170 [DEBUG][http-nio-8080-exec-8]:o.s.boot.web.filter.OrderedRequestContextFilter [doFilterInternal:104] Cleared thread-bound request context: org.apache.catalina.connector.RequestFacade@c03b2d8
2018-08-11 11:00:53.854 [DEBUG][http-nio-8080-exec-9]:o.s.boot.web.filter.OrderedRequestContextFilter [initContextHolders:114] Bound request context to thread: org.apache.catalina.connector.RequestFacade@c03b2d8
2018-08-11 11:00:53.856 [DEBUG][http-nio-8080-exec-9]:org.springframework.web.servlet.DispatcherServlet [doService:865] DispatcherServlet with name 'dispatcherServlet' processing GET request for [/put]
2018-08-11 11:00:53.857 [DEBUG][http-nio-8080-exec-9]:o.s.w.s.m.m.a.RequestMappingHandlerMapping [getHandlerInternal:310] Looking up handler method for path /put
2018-08-11 11:00:53.857 [DEBUG][http-nio-8080-exec-9]:o.s.w.s.m.m.a.RequestMappingHandlerMapping [getHandlerInternal:317] Returning handler method [public java.lang.String com.github.springboot.demo.DemoController.redisSet()]
2018-08-11 11:00:53.858 [DEBUG][http-nio-8080-exec-9]:o.s.b.factory.support.DefaultListableBeanFactory [doGetBean:251] Returning cached instance of singleton bean 'demoController'
2018-08-11 11:00:53.858 [DEBUG][http-nio-8080-exec-9]:org.springframework.web.servlet.DispatcherServlet [doDispatch:951] Last-Modified value for [/put] is: -1
2018-08-11 11:00:53.861 [DEBUG][http-nio-8080-exec-9]:o.s.data.redis.core.RedisConnectionUtils [doGetConnection:126] Opening RedisConnection

关闭template的事务支持

接下来我们修改一下RedisConfiguration的配置，不启用事务管理，

@Bean
    public StringRedisTemplate redisTemplate(RedisConnectionFactory redisConnectionFactory) {
        StringRedisTemplate template = new StringRedisTemplate();
        template.setConnectionFactory(redisConnectionFactory);
//      template.setEnableTransactionSupport(true);   //禁用事务支持
        return template;
    }

重新测试一下，发现是正常的，redis的client链接数一直保持在2。程序日志里的也可以看到Redis Connection关闭的日志。

2018-08-11 15:55:19.975 [DEBUG][http-nio-8080-exec-1]:o.s.data.redis.core.RedisConnectionUtils [doGetConnection:126] Opening RedisConnection
2018-08-11 15:55:20.029 [DEBUG][http-nio-8080-exec-1]:o.s.data.redis.core.RedisConnectionUtils [releaseConnection:210] Closing Redis Connection
2018-08-11 15:55:20.056 [DEBUG][http-nio-8080-exec-1]:o.s.w.s.m.m.a.RequestResponseBodyMethodProcessor [writeWithMessageConverters:249] Written [success key72] as "text/plain" using [org.springframework.http.converter.StringHttpMessageConverter@51ab1ee3]

也就是说，如果我们把事务的支持打开，spring在每次操作之后是不会主动关闭连接的。我们去RedisTemplate的源码中找下原因。

public ValueOperations<K, V> opsForValue() {
        if (valueOps == null) {
            valueOps = new DefaultValueOperations<K, V>(this);
        }
        return valueOps;
}

可以发现template.opsForValue().set()操作最终是调用的DefaultValueOperations中的set()方法，继续跟进去最终调用的RedisTemplate中的execute(RedisCallback<T> action, boolean exposeConnection, boolean pipeline)方法。

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 = getConnectionFactory();
        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);
        }
    }

可以看到获取连接的操作也针对打开事务支持的template有特殊的处理逻辑。这里我们先跳过，先看看最终肯定会走到的RedisConnectionUtils.releaseConnection(conn, factory)这一步。

/**
     * Closes the given connection, created via the given factory if not managed externally (i.e. not bound to the
     * thread).
     * 
     * @param conn the Redis connection to close
     * @param factory the Redis factory that the connection was created with
     */
    public static void releaseConnection(RedisConnection conn, RedisConnectionFactory factory) {

        if (conn == null) {
            return;
        }

        RedisConnectionHolder connHolder = (RedisConnectionHolder) TransactionSynchronizationManager.getResource(factory);

        if (connHolder != null && connHolder.isTransactionSyncronisationActive()) {
            if (log.isDebugEnabled()) {
                log.debug("Redis Connection will be closed when transaction finished.");
            }
            return;
        }

        // release transactional/read-only and non-transactional/non-bound connections.
        // transactional connections for read-only transactions get no synchronizer registered
        if (isConnectionTransactional(conn, factory)
                && TransactionSynchronizationManager.isCurrentTransactionReadOnly()) {
            unbindConnection(factory);
        } else if (!isConnectionTransactional(conn, factory)) {
            if (log.isDebugEnabled()) {
                log.debug("Closing Redis Connection");
            }
            conn.close();
        }
    }

可以看到针对打开事务支持的template,只是解绑了连接，根本没有做close的操作。关于什么是解绑，其实这个方法的注释中已经说的比较清楚了，对于开启了事务的Template，由于已经绑定了线程中连接，所以这里是不会关闭的，只是做了解绑的操作。
到这里原因就很清楚了，就是只要template开启了事务支持，spring就认为只要使用这个template就会包含在事务当中，因为一个事务中的操作必须在同一个连接中完成，所以在每次get/set之后，template是不会关闭链接的，因为它不知道事务有没有结束。

使用@Transanctional注解支持Redis事务

既然RedisTemlate在setEnableTransactionSupport会造成连接不关闭，那怎么样才能正常关闭呢？我们将事务支持开关和@Transanctional结合起来用看看会怎么样。
spring中要使用@Transanctional首先要配transactionManager，但是spring没有专门针对Redis的事务管理器实现，而是所有调用RedisTemplate的方法最终都会调用到RedisConnctionUtils这个类的方法上面，在这个类里面会判断是不是进入到事务里面，也就是说Redis的事务管理的功能是由RedisConnctionUtils内部实现的。
根据官方文档，我只想用Redis事务，也必须把JDBC捎上。当然反过来讲，不依赖数据的项目确实不多，貌似这么实现影响也不大。下面我们先根据官方文档配置一下看看效果。
首先修改POM配置，添加两个依赖。如果项目里本来已经使用了数据库，那这一步就不需要了。

<dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-jdbc</artifactId>
</dependency>
<dependency>
        <groupId>com.h2database</groupId>
        <artifactId>h2</artifactId>
        <scope>runtime</scope>
</dependency>

然后修改RedisConfiguration

@Bean
    public StringRedisTemplate redisTemplate(RedisConnectionFactory redisConnectionFactory) {
        StringRedisTemplate template = new StringRedisTemplate();
        template.setConnectionFactory(redisConnectionFactory);
        template.setEnableTransactionSupport(true);//打开事务支持
        return template;
    }

    //配置事务管理器
    @Bean
    public PlatformTransactionManager transactionManager(DataSource dataSource) throws SQLException {
        return new DataSourceTransactionManager(dataSource);
    }

我们新建一个RedisService，将原来的数据操作移到service里面。同时将Service方法加上@Transactional注解。

@Service
public class RedisService {
    
    private StringRedisTemplate template;
    
    public RedisService(StringRedisTemplate template) {
        this.template = template;
    }

    @Transactional
    public String put() {
        int i = (int)(Math.random() * 100);
        template.opsForValue().set("key"+i, "value"+i, 300, TimeUnit.SECONDS);
        return "success "+"key"+i;
    }
}
//-----------------------------------------------------------
//controller里面加一个新的方法，调用Service
@GetMapping("/puttx")
public String redisTxSet() {
    return redisService.put();
}

完成这些工作之后，再往http://localhost:8080/puttx发送请求，无论点多少次，Redis的连接数始终维持在1个不变。在看程序的输出日志里面我们也发现了，事务结束后连接被正常释放。因为使用了JDBC的事务管理器，所以还顺便做了一次数据库事务的开启和提交。还有一点值得注意的是，跟数据库一样，使用注解来做事务管理，spring也会主动管理redis事务的提交和回滚，也就是在之前发送一条MULTI命令，成功后发送EXEC，失败后发送DISCARD。

2018-08-11 20:57:04.990 [DEBUG][http-nio-8080-exec-1]:o.s.data.redis.core.RedisConnectionUtils [doGetConnection:126] Opening RedisConnection
2018-08-11 20:57:04.990 [DEBUG][http-nio-8080-exec-1]:o.springframework.aop.framework.JdkDynamicAopProxy [getProxy:118] Creating JDK dynamic proxy: target source is SingletonTargetSource for target object [org.springframework.data.redis.connection.jedis.JedisConnection@20f2be3c]
2018-08-11 20:57:04.990 [DEBUG][http-nio-8080-exec-1]:o.s.data.redis.core.RedisConnectionUtils [intercept:337] Invoke 'multi' on bound conneciton
2018-08-11 20:57:04.991 [DEBUG][http-nio-8080-exec-1]:o.s.data.redis.core.RedisConnectionUtils [intercept:337] Invoke 'isPipelined' on bound conneciton
2018-08-11 20:57:04.991 [DEBUG][http-nio-8080-exec-1]:o.s.data.redis.core.RedisConnectionUtils [intercept:337] Invoke 'setEx' on bound conneciton
2018-08-11 20:57:04.991 [DEBUG][http-nio-8080-exec-1]:o.s.data.redis.core.RedisConnectionUtils [releaseConnection:198] Redis Connection will be closed when transaction finished.
2018-08-11 20:57:04.991 [DEBUG][http-nio-8080-exec-1]:o.s.jdbc.datasource.DataSourceTransactionManager [processCommit:759] Initiating transaction commit
2018-08-11 20:57:04.991 [DEBUG][http-nio-8080-exec-1]:o.s.jdbc.datasource.DataSourceTransactionManager [doCommit:310] Committing JDBC transaction on Connection [ProxyConnection[PooledConnection[conn9: url=jdbc:h2:mem:testdb user=SA]]]
2018-08-11 20:57:04.992 [DEBUG][http-nio-8080-exec-1]:o.s.data.redis.core.RedisConnectionUtils [intercept:337] Invoke 'exec' on bound conneciton
2018-08-11 20:57:04.992 [DEBUG][http-nio-8080-exec-1]:o.s.data.redis.core.RedisConnectionUtils [afterCompletion:306] Closing bound connection after transaction completed with 0
2018-08-11 20:57:04.992 [DEBUG][http-nio-8080-exec-1]:o.s.data.redis.core.RedisConnectionUtils [intercept:337] Invoke 'close' on bound conneciton
2018-08-11 20:57:04.993 [DEBUG][http-nio-8080-exec-1]:o.s.jdbc.datasource.DataSourceTransactionManager [doCleanupAfterCompletion:368] Releasing JDBC Connection [ProxyConnection[PooledConnection[conn9: url=jdbc:h2:mem:testdb user=SA]]] after transaction
2018-08-11 20:57:04.993 [DEBUG][http-nio-8080-exec-1]:o.springframework.jdbc.datasource.DataSourceUtils [doReleaseConnection:327] Returning JDBC Connection to DataSource

总结

在spring中要使用Redis注解式事务，首先要设置RedisTemplate的enableTransactionSupport属性为true，然后配置一个jdbc的事务管理器。
这里有一点非常重要，一旦这样配置，所有使用这个template的redis操作都必须走注解式事务，要不然会导致连接一直占用，不关闭。

建议

• 升级到springboot 2.0以上版本，如果因为项目原因无法升级看下面的建议
• 如果使用Redis事务的场景不多，完全可以自己管理，不需要使用spring的注解式事务。如下面这样使用：

List<Object> txResults = redisTemplate.execute(new SessionCallback<List<Object>>() {
  public List<Object> execute(RedisOperations operations) throws DataAccessException {
    operations.multi();
    operations.opsForSet().add("key", "value1");
    // This will contain the results of all ops in the transaction
    return operations.exec();
  }
});

• 如果一定要使用spring提供的注解式事务，建议初始化两个RedisTemplate Bean，分别设置enableTransactionSupport属性为true和false。针对需要事务和不需要事务的操作使用不同的template。
• 从个人角度，我不建议使用redis事务，因为redis对于事务的支持并不是关系型数据库那样满足ACID。Redis事务只能保证ACID中的隔离性和一致性，无法保证原子性和持久性。而我们使用事务最重要的一个理由就是原子性，这一点无法保证，事务的意义就去掉一大半了。所以事务的场景可以尝试通过业务代码来实现。

本篇博客使用的代码：https://github.com/chilexun/springboot-demo.git