深入 Spring Boot：怎样排查 expected single matching bean but found 2 的异常

栏目: Java · 发布时间: 6年前

内容简介：深入 Spring Boot：怎样排查 expected single matching bean but found 2 的异常

写在前面

这个demo来说明怎么排查一个常见的spring expected single matching bean but found 2的异常。

https://github.com/hengyunabc/spring-boot-inside/tree/master/demo-expected-single

调试排查 expected single matching bean but found 2 的错误

把工程导入IDE里，直接启动应用，抛出来的异常信息是：

Caused by: org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'javax.sql.DataSource' available: expected single matching bean but found 2: h2DataSource1,h2DataSource2
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveNamedBean(DefaultListableBeanFactory.java:1041) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBean(DefaultListableBeanFactory.java:345) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBean(DefaultListableBeanFactory.java:340) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1090) ~[spring-context-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.boot.autoconfigure.jdbc.DataSourceInitializer.init(DataSourceInitializer.java:71) ~[spring-boot-autoconfigure-1.4.7.RELEASE.jar:1.4.7.RELEASE]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_112]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_112]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_112]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_112]
    at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor$LifecycleElement.invoke(InitDestroyAnnotationBeanPostProcessor.java:366) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor$LifecycleMetadata.invokeInitMethods(InitDestroyAnnotationBeanPostProcessor.java:311) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor.postProcessBeforeInitialization(InitDestroyAnnotationBeanPostProcessor.java:134) ~[spring-beans-4.3.9.RELEASE.jar:4.3.9.RELEASE]
    ... 30 common frames omitted

很多人碰到这种错误时，就乱配置一通，找不到下手的办法。其实耐心排查下，是很简单的。

抛出异常的原因

异常信息写得很清楚了，在spring context里需要注入/获取到一个DataSource bean，但是现在spring context里出现了两个，它们的名字是：h2DataSource1,h2DataSource2

那么有两个问题：

应用是在哪里要注入/获取到一个DataSource bean？
h2DataSource1,h2DataSource2 是在哪里定义的？

使用 Java Exception Breakpoint

在IDE里，新建一个断点，类型是Java Exception Breakpoint（如果不清楚怎么添加，可以搜索对应IDE的使用文档），异常类是上面抛出来的NoUniqueBeanDefinitionException。

当断点停住时，查看栈，可以很清楚地找到是在DataSourceInitializer.init() line: 71这里要获取DataSource：

Thread [main] (Suspended (exception NoUniqueBeanDefinitionException))
    owns: ConcurrentHashMap<K,V>  (id=49)
    owns: Object  (id=50)
    DefaultListableBeanFactory.resolveNamedBean(Class<T>, Object...) line: 1041
    DefaultListableBeanFactory.getBean(Class<T>, Object...) line: 345
    DefaultListableBeanFactory.getBean(Class<T>) line: 340
    AnnotationConfigEmbeddedWebApplicationContext(AbstractApplicationContext).getBean(Class<T>) line: 1090
    DataSourceInitializer.init() line: 71
    NativeMethodAccessorImpl.invoke0(Method, Object, Object[]) line: not available [native method]
    NativeMethodAccessorImpl.invoke(Object, Object[]) line: 62
    DelegatingMethodAccessorImpl.invoke(Object, Object[]) line: 43
    Method.invoke(Object, Object...) line: 498
    InitDestroyAnnotationBeanPostProcessor$LifecycleElement.invoke(Object) line: 366
    InitDestroyAnnotationBeanPostProcessor$LifecycleMetadata.invokeInitMethods(Object, String) line: 311
    CommonAnnotationBeanPostProcessor(InitDestroyAnnotationBeanPostProcessor).postProcessBeforeInitialization(Object, String) line: 134
    DefaultListableBeanFactory(AbstractAutowireCapableBeanFactory).applyBeanPostProcessorsBeforeInitialization(Object, String) line: 409
    DefaultListableBeanFactory(AbstractAutowireCapableBeanFactory).initializeBean(String, Object, RootBeanDefinition) line: 1620
    DefaultListableBeanFactory(AbstractAutowireCapableBeanFactory).doCreateBean(String, RootBeanDefinition, Object[]) line: 555
    DefaultListableBeanFactory(AbstractAutowireCapableBeanFactory).createBean(String, RootBeanDefinition, Object[]) line: 483
    AbstractBeanFactory$1.getObject() line: 306
    DefaultListableBeanFactory(DefaultSingletonBeanRegistry).getSingleton(String, ObjectFactory<?>) line: 230
    DefaultListableBeanFactory(AbstractBeanFactory).doGetBean(String, Class<T>, Object[], boolean) line: 302
    DefaultListableBeanFactory(AbstractBeanFactory).getBean(String, Class<T>, Object...) line: 220
    DefaultListableBeanFactory.resolveNamedBean(Class<T>, Object...) line: 1018
    DefaultListableBeanFactory.getBean(Class<T>, Object...) line: 345
    DefaultListableBeanFactory.getBean(Class<T>) line: 340
    DataSourceInitializerPostProcessor.postProcessAfterInitialization(Object, String) line: 62
    DefaultListableBeanFactory(AbstractAutowireCapableBeanFactory).applyBeanPostProcessorsAfterInitialization(Object, String) line: 423
    DefaultListableBeanFactory(AbstractAutowireCapableBeanFactory).initializeBean(String, Object, RootBeanDefinition) line: 1633
    DefaultListableBeanFactory(AbstractAutowireCapableBeanFactory).doCreateBean(String, RootBeanDefinition, Object[]) line: 555
    DefaultListableBeanFactory(AbstractAutowireCapableBeanFactory).createBean(String, RootBeanDefinition, Object[]) line: 483
    AbstractBeanFactory$1.getObject() line: 306
    DefaultListableBeanFactory(DefaultSingletonBeanRegistry).getSingleton(String, ObjectFactory<?>) line: 230
    DefaultListableBeanFactory(AbstractBeanFactory).doGetBean(String, Class<T>, Object[], boolean) line: 302
    DefaultListableBeanFactory(AbstractBeanFactory).getBean(String) line: 197
    DefaultListableBeanFactory.preInstantiateSingletons() line: 761
    AnnotationConfigEmbeddedWebApplicationContext(AbstractApplicationContext).finishBeanFactoryInitialization(ConfigurableListableBeanFactory) line: 867
    AnnotationConfigEmbeddedWebApplicationContext(AbstractApplicationContext).refresh() line: 543
    AnnotationConfigEmbeddedWebApplicationContext(EmbeddedWebApplicationContext).refresh() line: 122
    SpringApplication.refresh(ApplicationContext) line: 762
    SpringApplication.refreshContext(ConfigurableApplicationContext) line: 372
    SpringApplication.run(String...) line: 316
    SpringApplication.run(Object[], String[]) line: 1187
    SpringApplication.run(Object, String...) line: 1176
    DemoExpectedSingleApplication.main(String[]) line: 17

定位哪里要注入/使用DataSource

要获取DataSource具体的代码是：

//org.springframework.boot.autoconfigure.jdbc.DataSourceInitializer.init()
    @PostConstruct
    public void init() {
        if (!this.properties.isInitialize()) {
            logger.debug("Initialization disabled (not running DDL scripts)");
            return;
        }
        if (this.applicationContext.getBeanNamesForType(DataSource.class, false,
                false).length > 0) {
            this.dataSource = this.applicationContext.getBean(DataSource.class);
        }
        if (this.dataSource == null) {
            logger.debug("No DataSource found so not initializing");
            return;
        }
        runSchemaScripts();
    }

this.applicationContext.getBean(DataSource.class); 要求spring context里只有一个DataSource的bean，但是应用里有两个，所以抛出了NoUniqueBeanDefinitionException。

从BeanDefinition获取bean具体定义的代码

我们再来看 h2DataSource1,h2DataSource2 是在哪里定义的？

上面进程断在了DefaultListableBeanFactory.resolveNamedBean(Class<T>, Object…) 函数里的 throw new NoUniqueBeanDefinitionException(requiredType, candidates.keySet()); 这一行。

那么我们在这里执行一下（如果不清楚，先搜索下IDE怎么在断点情况下执行代码）：

this.getBeanDefinition("h2DataSource1")

返回的信息是：

Root bean: class [null]; scope=; abstract=false; lazyInit=false; autowireMode=3; dependencyCheck=0; autowireCandidate=true; primary=false; factoryBeanName=demoExpectedSingleApplication; factoryMethodName=h2DataSource1; initMethodName=null; destroyMethodName=(inferred);
defined in com.example.demo.expected.single.DemoExpectedSingleApplication

可以很清楚地定位到h2DataSource1这个bean是在 com.example.demo.expected.single.DemoExpectedSingleApplication里定义的。

所以上面两个问题的答案是：

是spring boot代码里的DataSourceInitializer.init() line: 71这里要获取DataSource，并且只允许有一个DataSource实例
h2DataSource1,h2DataSource2 是在com.example.demo.expected.single.DemoExpectedSingleApplication里定义的

解决问题

上面排查到的原因是：应用定义了两个DataSource实例，但是spring boot却要求只有一个。那么有两种办法来解决：

使用@Primary来指定一个优先使用的DataSource，这样子spring boot里自动初始的代码会获取到@Primary的bean
把spring boot自动初始化DataSource相关的代码禁止掉，应用自己来控制所有的DataSource相关的bean

禁止的办法有两种：

在main函数上配置exclude

@SpringBootApplication(exclude = { DataSourceAutoConfiguration.class, DataSourceTransactionManagerAutoConfiguration.class })

在application.properties里配置：

spring.autoconfigure.exclude=org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration,org.springframework.boot.autoconfigure.jdbc.DataSourceTransactionManagerAutoConfiguration

总结

排查spring初始化问题时，灵活使用Java Exception Breakpoint
从异常栈上，可以很容易找到哪里要注入/使用bean
从BeanDefinition可以找到bean是在哪里定义的（哪个Configuration类/xml）

以上所述就是小编给大家介绍的《深入 Spring Boot：怎样排查 expected single matching bean but found 2 的异常》，希望对大家有所帮助，如果大家有任何疑问请给我留言，小编会及时回复大家的。在此也非常感谢大家对码农网的支持！

查看所有标签

猜你喜欢:

本站部分资源来源于网络，本站转载出于传递更多信息之目的，版权归原作者或者来源机构所有，如转载稿涉及版权问题，请联系我们。

码农书籍

Web Data Mining

Bing Liu / Springer / 2011-6-26 / CAD 61.50

Web mining aims to discover useful information and knowledge from Web hyperlinks, page contents, and usage data. Although Web mining uses many conventional data mining techniques, it is not purely an ......一起来看看《Web Data Mining》这本书的介绍吧!

码农工具