我在新项目中使用 Spring + Redis 作为我的缓存组件。 Spring 配置 xml 文件是:

<!-- Jedis Connection --> 
<bean id="jedisConnectionFactory" 
    class="org.springframework.data.redis.connection.jedis.JedisConnectionFactory"
    p:host-name="${redis.ip}" p:port="${redis.port}" p:use-pool="${redis.use-pool}" />

<!-- Redis Template -->
<bean id="redisTemplate" class="org.springframework.data.redis.core.RedisTemplate">
    <property name="connectionFactory" ref="jedisConnectionFactory" />
    <property name="keySerializer">
        <bean class="org.springframework.data.redis.serializer.StringRedisSerializer" />
    </property>
    <property name="valueSerializer">  
        <bean class="org.springframework.data.redis.serializer.JdkSerializationRedisSerializer" />
    </property> 
</bean>

<bean id="cacheManager" class="org.springframework.data.redis.cache.RedisCacheManager" c:template-ref="redisTemplate"/>

<cache:annotation-driven mode="proxy" proxy-target-class="true" cache-manager="cacheManager" />

用法是

    @Cacheable(value = "cacheManager", key="#userId")
public User getUser(String userId) {
    System.out.println("execute==");
    return userAdminMapper.getUser(userId);
}

我的测试用例是:

@Test
public void testCacheUser2() {
    String id = "test";
    User user = userService.getUser(id);
    System.out.println(user);
    user.setUserCreateDate(new Date());
    userService.updateUser(user);
    User user2 = userService.getUser(id);
    System.out.println(user2);
    User user3 = userService.getUser(id);
    System.out.println(user3);
}

如果 Redis 服务器正在运行，则代码运行正确。但我的问题是，如果我关闭 Redis 服务器，它会抛出异常:

org.springframework.data.redis.RedisConnectionFailureException: Cannot get Jedis connection; nested exception is redis.clients.jedis.exceptions.JedisConnectionException: java.net.ConnectException: Connection refused: connect
    at org.springframework.data.redis.connection.jedis.JedisConnectionFactory.fetchJedisConnector(JedisConnectionFactory.java:140)
    at org.springframework.data.redis.connection.jedis.JedisConnectionFactory.getConnection(JedisConnectionFactory.java:229)
    at org.springframework.data.redis.connection.jedis.JedisConnectionFactory.getConnection(JedisConnectionFactory.java:57)
    at org.springframework.data.redis.core.RedisConnectionUtils.doGetConnection(RedisConnectionUtils.java:128)
    at org.springframework.data.redis.core.RedisConnectionUtils.getConnection(RedisConnectionUtils.java:91)
    at org.springframework.data.redis.core.RedisConnectionUtils.getConnection(RedisConnectionUtils.java:78)
    at org.springframework.data.redis.core.RedisTemplate.execute(RedisTemplate.java:177)
    at org.springframework.data.redis.core.RedisTemplate.execute(RedisTemplate.java:152)
    at org.springframework.data.redis.cache.RedisCache.get(RedisCache.java:87)
    at org.springframework.cache.interceptor.CacheAspectSupport.findInCaches(CacheAspectSupport.java:297)
    at org.springframework.cache.interceptor.CacheAspectSupport.findInAnyCaches(CacheAspectSupport.java:287)
    at org.springframework.cache.interceptor.CacheAspectSupport.collectPutRequests(CacheAspectSupport.java:266)
    at org.springframework.cache.interceptor.CacheAspectSupport.execute(CacheAspectSupport.java:199)
    at org.springframework.cache.interceptor.CacheAspectSupport.execute(CacheAspectSupport.java:178)
    at org.springframework.cache.interceptor.CacheInterceptor.invoke(CacheInterceptor.java:60)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:98)
    at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:262)
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:95)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:644)
    at sg.infolab.common.admin.service.impl.UserServiceImpl$$EnhancerBySpringCGLIB$$c7f982a7.getUser(<generated>)
    at sg.infolab.admin.test.RedisServiceTest.testCacheUser2(RedisServiceTest.java:35)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:74)
    at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:83)
    at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:72)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:232)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:89)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
    at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
    at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:71)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:175)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)
Caused by: redis.clients.jedis.exceptions.JedisConnectionException: java.net.ConnectException: Connection refused: connect
    at redis.clients.jedis.Connection.connect(Connection.java:150)
    at redis.clients.jedis.BinaryClient.connect(BinaryClient.java:71)
    at redis.clients.jedis.BinaryJedis.connect(BinaryJedis.java:1783)
    at org.springframework.data.redis.connection.jedis.JedisConnectionFactory.fetchJedisConnector(JedisConnectionFactory.java:137)
    ... 50 more
Caused by: java.net.ConnectException: Connection refused: connect
    at java.net.PlainSocketImpl.socketConnect(Native Method)
    at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:351)
    at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:213)
    at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:200)
    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366)
    at java.net.Socket.connect(Socket.java:529)
    at redis.clients.jedis.Connection.connect(Connection.java:144)
    ... 53 more

请问如果客户端连接不上Redis Server，为什么会抛出异常？我们可以这样配置场景吗——如果缓存层(Redis Server)无法连接(可能是崩溃了或者网络不通)，它应该直接连接到数据库并获取数据。

最佳答案

我遇到了同样的问题。我正在针对数据库开发一些数据服务，通过 Spring Caching 注释使用 Redis 作为缓存存储。如果 Redis 服务器变得不可用，我希望服务像未缓存一样继续运行，而不是抛出异常。

一开始我尝试了一个自定义的CacheErrorHandler，这是Spring提供的一种机制。它不是很有效，因为它只处理 RuntimeExceptions，并且仍然让 java.net.ConnectException 之类的东西爆炸。

最后我所做的是扩展 RedisTemplate，覆盖一些 execute() 方法，以便它们记录警告而不是传播异常。这似乎有点 hack，我可能重写了太少或太多的 execute() 方法，但它在我所有的测试用例中都很有效。

不过，这种方法有一个重要的操作方面。如果 Redis 服务器变得不可用，您必须在使其再次可用之前刷新它(清除条目)。否则，您可能会因为同时发生的更新而开始检索具有不正确数据的缓存条目。

下面是来源。随意使用它。希望对您有所帮助。

import java.util.List;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.data.redis.core.RedisCallback;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.SessionCallback;
import org.springframework.data.redis.core.script.RedisScript;
import org.springframework.data.redis.serializer.RedisSerializer;


/**
 * An extension of RedisTemplate that logs exceptions instead of letting them propagate.
 * If the Redis server is unavailable, cache operations are always a "miss" and data is fetched from the database.
 */
public class LoggingRedisTemplate<K, V> extends RedisTemplate<K, V> {

    private static final Logger logger = LoggerFactory.getLogger(LoggingRedisTemplate.class);


    @Override
    public <T> T execute(final RedisCallback<T> action, final boolean exposeConnection, final boolean pipeline) {
        try {
            return super.execute(action, exposeConnection, pipeline);
        }
        catch(final Throwable t) {
            logger.warn("Error executing cache operation: {}", t.getMessage());
            return null;
        }
    }


    @Override
    public <T> T execute(final RedisScript<T> script, final List<K> keys, final Object... args) {
        try {
            return super.execute(script, keys, args);
        }
        catch(final Throwable t) {
            logger.warn("Error executing cache operation: {}", t.getMessage());
            return null;
        }
    }


    @Override
    public <T> T execute(final RedisScript<T> script, final RedisSerializer<?> argsSerializer, final RedisSerializer<T> resultSerializer, final List<K> keys, final Object... args) {
        try {
            return super.execute(script, argsSerializer, resultSerializer, keys, args);
        }
        catch(final Throwable t) {
            logger.warn("Error executing cache operation: {}", t.getMessage());
            return null;
        }
    }


    @Override
    public <T> T execute(final SessionCallback<T> session) {
        try {
            return super.execute(session);
        }
        catch(final Throwable t) {
            logger.warn("Error executing cache operation: {}", t.getMessage());
            return null;
        }
    }
}

关于error-handling - Spring Redis 错误处理，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/26021991/