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[资料] SpringBoot中注入RedisTemplate实例异常解决

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发表于 2019-3-11 13:25:56 | 显示全部楼层
zu
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。现在,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。


  1. @Component
  2. public class RedisDao {

  3.     /**
  4.      * 注入时指定了K、V类型
  5.      */
  6.     @Autowired
  7.     private RedisTemplate<String, Object> redisTemplate;

  8.     @Autowired
  9.     private StringRedisTemplate stringRedisTemplate;

  10.     @Resource(name="redisTemplate")
  11.     ValueOperations<String, Object> valOpsObj;

  12.     @Resource(name="stringRedisTemplate")
  13.     ValueOperations<String, String> valOpsStr;  
  14. }
复制代码
根据错误日志查看DefaultListableBeanFactory这个类的第1493行的代码,源码如下:

  1. /**
  2.      * 为无法解决的依赖抛出NoSuchBeanDefinitionException或BeanNotOfRequiredTypeException。
  3.      * Raise a NoSuchBeanDefinitionException or BeanNotOfRequiredTypeException
  4.      * for an unresolvable dependency.
  5.      */
  6.     private void raiseNoMatchingBeanFound(
  7.             Class<?> type, ResolvableType resolvableType, DependencyDescriptor descriptor) throws BeansException {

  8.         checkBeanNotOfRequiredType(type, descriptor);
  9.         //抛出NoSuchBeanDefinitionException
  10.         throw new NoSuchBeanDefinitionException(resolvableType,
  11.                 "expected at least 1 bean which qualifies as autowire candidate. " +
  12.                 "Dependency annotations: " + ObjectUtils.nullSafeToString(descriptor.getAnnotations()));
  13.     }

  14.    /**
  15.      * 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。
  16.      *
  17.      *
  18.      * Raise a BeanNotOfRequiredTypeException for an unresolvable dependency, if applicable,
  19.      * i.e. if the target type of the bean would match but an exposed proxy doesn't.
  20.      */
  21.     private void checkBeanNotOfRequiredType(Class<?> type, DependencyDescriptor descriptor) {
  22.         for (String beanName : this.beanDefinitionNames) {
  23.             RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
  24.             Class<?> targetType = mbd.getTargetType();
  25.             if (targetType != null && type.isAssignableFrom(targetType) &&
  26.                     isAutowireCandidate(beanName, mbd, descriptor, getAutowireCandidateResolver())) {
  27.                 // Probably a proxy interfering with target type match -> throw meaningful exception.
  28.                 Object beanInstance = getSingleton(beanName, false);
  29.                 Class<?> beanType = (beanInstance != null ? beanInstance.getClass() : predictBeanType(beanName, mbd));
  30.                 if (!type.isAssignableFrom((beanType))) {
  31.                     //抛出BeanNotOfRequiredTypeException
  32.                     throw new BeanNotOfRequiredTypeException(beanName, type, beanType);
  33.                 }
  34.             }
  35.         }

  36.         BeanFactory parent = getParentBeanFactory();
  37.         if (parent instanceof DefaultListableBeanFactory) {
  38.             ((DefaultListableBeanFactory) parent).checkBeanNotOfRequiredType(type, descriptor);
  39.         }
  40.     }
复制代码
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:

  1. /**
  2. * 注入时不指定K、V的类型
  3. */
  4. @Autowired
  5. private RedisTemplate redisTemplate;
复制代码
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-bo ... ference/htmlsingle/


QQ截图20190311132200.jpg

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:


  1. /**
  2.      * 注入时指定了K、V类型
  3.      */
  4.     @Resource
  5.     private RedisTemplate<String, Object> redisTemplate;
复制代码
注解由@Autowired改成了@Resource 项目启动不报错了,完美解决!

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:


  1. /**
  2. * Redis访问工具类
  3. * @author zhaoheng
  4. * @date   2018年8月10日
  5. */
  6. @Component
  7. public class RedisDao {

  8.     /**
  9.      * 注入时指定K、V类型都为String
  10.      */
  11.     @Autowired
  12.     private RedisTemplate<String, String> redisTemplate;

  13.     @Autowired
  14.     private StringRedisTemplate stringRedisTemplate;

  15.     /**
  16.      * 比较两个对象是否是同一个对象
  17.      */
  18.     public boolean compare () {
  19.         LOG.info("redisTemplate的hashcode:{}", redisTemplate.hashCode());
  20.         LOG.info("stringRedisTemplate的hashcode:{}", stringRedisTemplate.hashCode());
  21.         LOG.info("equal()的结果:{}", redisTemplate.equals(stringRedisTemplate));
  22.         return redisTemplate == stringRedisTemplate;
  23.     }   
  24. }

  25. /**
  26. * 单元测试类
  27. * @author zhaoheng
  28. * @date   2018年8月10日
  29. */
  30. @RunWith(SpringRunner.class)
  31. @SpringBootTest
  32. public class Demo1ApplicationTests {

  33.     private static final Logger LOG = LoggerFactory.getLogger(Demo1ApplicationTests.class);

  34.     @Autowired
  35.     private RedisDao redisDao;

  36.     @Test
  37.     public void contextLoads() {
  38.         boolean flag = redisDao.compare();
  39.         LOG.info("redisTemplate和stringRedisTemplate的比较结果:{}", flag);

  40.     }
  41. }
复制代码
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。

  1. public class StringRedisTemplate extends RedisTemplate<String, String> {

  2.     /**
  3.      * Constructs a new <code>StringRedisTemplate</code> instance. {@link #setConnectionFactory(RedisConnectionFactory)}
  4.      * and {@link #afterPropertiesSet()} still need to be called.
  5.      */
  6.     public StringRedisTemplate() {
  7.         RedisSerializer<String> stringSerializer = new StringRedisSerializer();
  8.         setKeySerializer(stringSerializer);
  9.         setValueSerializer(stringSerializer);
  10.         setHashKeySerializer(stringSerializer);
  11.         setHashValueSerializer(stringSerializer);
  12.     }

  13.     /**
  14.      * Constructs a new <code>StringRedisTemplate</code> instance ready to be used.
  15.      *
  16.      * @param connectionFactory connection factory for creating new connections
  17.      */
  18.     public StringRedisTemplate(RedisConnectionFactory connectionFactory) {
  19.         this();
  20.         setConnectionFactory(connectionFactory);
  21.         afterPropertiesSet();
  22.     }

  23.     protected RedisConnection preProcessConnection(RedisConnection connection, boolean existingConnection) {
  24.         return new DefaultStringRedisConnection(connection);
  25.     }
  26. }
复制代码
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。




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