在SpringBoot中注入RedisTemplate实例异常的解决方案
目录
- 注入RedisTemplate实例异常
- 贴出详细的错误日志
- 最后想再验证一个小的问题
注入RedisTemplate实例异常
最近,在项目开发过程中使用了RedisTemplate,进行单元测试时提示
Field redisTemplate in com.example.demo1.dao.RedisDao required a bean of type ‘org.springframework.data.redis.core.RedisTemplate’ that could not be found
翻译过来就是“找不到类型为RedisTemplate的bean”。
当然,仅看这句话我们无法确定为什么会出现这个问题。
贴出详细的错误日志
2018-08-10 14:53:49.761 - Caught exception while allowing TestExecutionListener [org.springframework.test.context.web.ServletTestExecutionListener@5af3afd9] to prepare test instance [com.example.demo1.Demo1ApplicationTests@2361365c]
java.lang.IllegalStateException: Failed to load ApplicationContext
at org.springframework.test.context.cache.DefaultCacheAwareContextLoaderDelegate.loadContext(DefaultCacheAwareContextLoaderDelegate.java:124)
at org.springframework.test.context.support.DefaultTestContext.getApplicationContext(DefaultTestContext.java:83)
at org.springframework.test.context.web.ServletTestExecutionListener.setUpRequestContextIfNecessary(ServletTestExecutionListener.java:189)
at org.springframework.test.context.web.ServletTestExecutionListener.prepareTestInstance(ServletTestExecutionListener.java:131)
at org.springframework.test.context.TestContextManager.prepareTestInstance(TestContextManager.java:230)
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.createTest(SpringJUnit4ClassRunner.java:228)
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner$1.runReflectiveCall(SpringJUnit4ClassRunner.java:287)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.methodBlock(SpringJUnit4ClassRunner.java:289)
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:247)
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:94)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:191)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:675)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)
Caused by: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'redisDao': Unsatisfied dependency expressed through field 'redisTemplate'; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'org.springframework.data.redis.core.RedisTemplate<java.lang.String, java.lang.Object>' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:588)
at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:88)
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:366)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1264)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:553)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:483)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:761)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:867)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:543)
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:693)
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:360)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:303)
at org.springframework.boot.test.context.SpringBootContextLoader.loadContext(SpringBootContextLoader.java:120)
at org.springframework.test.context.cache.DefaultCacheAwareContextLoaderDelegate.loadContextInternal(DefaultCacheAwareContextLoaderDelegate.java:98)
at org.springframework.test.context.cache.DefaultCacheAwareContextLoaderDelegate.loadContext(DefaultCacheAwareContextLoaderDelegate.java:116)
... 25 common frames omitted
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'org.springframework.data.redis.core.RedisTemplate<java.lang.String, java.lang.Object>' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoMatchingBeanFound(DefaultListableBeanFactory.java:1493)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1104)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1066)
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:585)
... 43 common frames omitted
看到这一大段错误日志是不是有点晕,其实我们只需要看关键的错误日志就可以定位到问题。
错误日志中的第二个Caused by打印了关键的错误日志:
No qualifying bean of type ‘org.springframework.data.redis.core.RedisTemplate< java.lang.String, java.lang.Object>
笔主回看写的代码,在注入RedisTemplate< K, V>时指定了具体的类型。
@Component public class RedisDao { /** * 注入时指定了K、V类型 */ @Autowired private RedisTemplate<String, Object> redisTemplate; @Autowired private StringRedisTemplate stringRedisTemplate; @Resource(name="redisTemplate") ValueOperations<String, Object> valOpsObj; @Resource(name="stringRedisTemplate") ValueOperations<String, String> valOpsStr; }
根据错误日志查看DefaultListableBeanFactory这个类的第1493行的代码,源码如下:
/** * 为无法解决的依赖抛出NoSuchBeanDefinitionException或BeanNotOfRequiredTypeException。 * Raise a NoSuchBeanDefinitionException or BeanNotOfRequiredTypeException * for an unresolvable dependency. */ private void raiseNoMatchingBeanFound( Class<?> type, ResolvableType resolvableType, DependencyDescriptor descriptor) throws BeansException { checkBeanNotOfRequiredType(type, descriptor); //抛出NoSuchBeanDefinitionException throw new NoSuchBeanDefinitionException(resolvableType, "expected at least 1 bean which qualifies as autowire candidate. " + "Dependency annotations: " + ObjectUtils.nullSafeToString(descriptor.getAnnotations())); } /** * 为无法解决的依赖抛出BeanNotOfRequiredTypeException,如果适用,例如,bean的目标类型匹配但是公开的代理不匹配。 * * * Raise a BeanNotOfRequiredTypeException for an unresolvable dependency, if applicable, * i.e. if the target type of the bean would match but an exposed proxy doesn't. */ private void checkBeanNotOfRequiredType(Class<?> type, DependencyDescriptor descriptor) { for (String beanName : this.beanDefinitionNames) { RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName); Class<?> targetType = mbd.getTargetType(); if (targetType != null && type.isAssignableFrom(targetType) && isAutowireCandidate(beanName, mbd, descriptor, getAutowireCandidateResolver())) { // Probably a proxy interfering with target type match -> throw meaningful exception. Object beanInstance = getSingleton(beanName, false); Class<?> beanType = (beanInstance != null ? beanInstance.getClass() : predictBeanType(beanName, mbd)); if (!type.isAssignableFrom((beanType))) { //抛出BeanNotOfRequiredTypeException throw new BeanNotOfRequiredTypeException(beanName, type, beanType); } } } BeanFactory parent = getParentBeanFactory(); if (parent instanceof DefaultListableBeanFactory) { ((DefaultListableBeanFactory) parent).checkBeanNotOfRequiredType(type, descriptor); } }
这两个方法说明了没有找到RedisTemplate< String, Object>可以匹配的Bean,那么这个问题该如何解决呢?不妨在使用RedisTemplate< K, V>时不指定具体的类型,修改代码如下:
/** * 注入时不指定K、V的类型 */ @Autowired private RedisTemplate redisTemplate;
重新启动服务,启动日志没有报错,RedisTemplate注入Bean成功了。
为什么RedisTemplate< String, Object>注入Bean会失败呢,很是纳闷。思考很久,想到RedisTemplate在SpringBoot框架中是自动配置的,容器中默认的就是RedisTemplate的实例。
想到这里,就需要翻下官网的文档,看看官网文档有没有什么说明。果然,官方文档第30.1.1章节还是针对RedisTemplate做了说明。
官方文档地址:https://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/
If you add your own @Bean of any of the auto-configured types, it replaces the default (except in the case of RedisTemplate, when the exclusion is based on the bean name, redisTemplate, not its type).
如果针对自动配置类型添加自己的Bean,它将取代默认的。我的代码好像写的没问题啊,等等…括号中这句话才是重点啊。翻译一波,在RedisTemplate的情况下除外,当排除基于Bean的名称,而不是它的类型。英文不太好,怎么翻译好像都不大通顺。
现在好像明白了,刚才的RedisTemplate< String, Object>注入时用到了@Autowired,@Autowired默认按照类型装配的。也就是说,想要获取RedisTemplate< String, Object>的Bean,要根据名字装配。那么自然想到使用@Resource,它默认按照名字装配。
再次修改代码如下:
/** * 注入时指定了K、V类型 */ @Resource private RedisTemplate<String, Object> redisTemplate;
再次重新启动服务,启动日志没有报错,RedisTemplate< String, Object>注入Bean成功了。通过这个错误,学习到SpringBoot框架中自动配置类的一个特性。同时,也反映出学习一门技术要从官网开始,避免踩坑。
在实际开发过程中,使用RedisTemplate< K, V>不是必须指定K、V的类型,使用默认的Bean就能满足需求。
最后想再验证一个小的问题
再次修改代码如下:
/** * Redis访问工具类 * @author zhaoheng * @date 2018年8月10日 */ @Component public class RedisDao { /** * 注入时指定K、V类型都为String */ @Autowired private RedisTemplate<String, String> redisTemplate; @Autowired private StringRedisTemplate stringRedisTemplate; /** * 比较两个对象是否是同一个对象 */ public boolean compare () { LOG.info("redisTemplate的hashcode:{}", redisTemplate.hashCode()); LOG.info("stringRedisTemplate的hashcode:{}", stringRedisTemplate.hashCode()); LOG.info("equal()的结果:{}", redisTemplate.equals(stringRedisTemplate)); return redisTemplate == stringRedisTemplate; } } /** * 单元测试类 * @author zhaoheng * @date 2018年8月10日 */ @RunWith(SpringRunner.class) @SpringBootTest public class Demo1ApplicationTests { private static final Logger LOG = LoggerFactory.getLogger(Demo1ApplicationTests.class); @Autowired private RedisDao redisDao; @Test public void contextLoads() { boolean flag = redisDao.compare(); LOG.info("redisTemplate和stringRedisTemplate的比较结果:{}", flag); } }
上边这段代码在注入RedisTemplate时指定K、V都为String类型,在compare()方法中比较redisTemplate和stringRedisTemplate是否是同一个对象。运行下单元测试类,测试结果如下:
2018-08-10 18:30:57.075 - Started Demo1ApplicationTests in 15.58 seconds (JVM running for 16.974)
2018-08-10 18:30:57.360 - redisTemplate的hashcode:1996087296
2018-08-10 18:30:57.360 - stringRedisTemplate的hashcode:1996087296
2018-08-10 18:30:57.363 - equal()的结果:true
2018-08-10 18:30:57.364 - redisTemplate和stringRedisTemplate的比较结果:true
测试结果表明redisTemplate和stringRedisTemplate是同一个对象。等等…这次注入RedisTemplate时指定K、V都为String为什么没有错呢?而且,两个对象竟然是同一个对象。还是来看下StringRedisTemplate的源码吧。
public class StringRedisTemplate extends RedisTemplate<String, String> { /** * Constructs a new <code>StringRedisTemplate</code> instance. {@link #setConnectionFactory(RedisConnectionFactory)} * and {@link #afterPropertiesSet()} still need to be called. */ public StringRedisTemplate() { RedisSerializer<String> stringSerializer = new StringRedisSerializer(); setKeySerializer(stringSerializer); setValueSerializer(stringSerializer); setHashKeySerializer(stringSerializer); setHashValueSerializer(stringSerializer); } /** * Constructs a new <code>StringRedisTemplate</code> instance ready to be used. * * @param connectionFactory connection factory for creating new connections */ public StringRedisTemplate(RedisConnectionFactory connectionFactory) { this(); setConnectionFactory(connectionFactory); afterPropertiesSet(); } protected RedisConnection preProcessConnection(RedisConnection connection, boolean existingConnection) { return new DefaultStringRedisConnection(connection); } }
看了源码是不是理解了,因为StringRedisTemplate类的父类就是RedisTemplate< String, String>,而Bean默认是单例的,两个是自然是同一个对象了。
以上为个人经验,希望能给大家一个参考,也希望大家多多支持我们。