Why @Qualifier not work

Question

I used spring boot + jdbctemplate and I have to use multi datasource, e.g.

@Configuration
public class MultiDBConfig {

    @Bean(name = "fooDb")
    @ConfigurationProperties(prefix = "foo.datasource")
    public DataSource fooDataSource() {
        return DataSourceBuilder.create().build();
    }

    @Bean(name = "fooJdbcTemplate")
    public JdbcTemplate fooJdbcTemplate(@Qualifier("fooDb") DataSource ds) {
        return new JdbcTemplate(ds);
    }

    @Bean(name = "barDb")
    @ConfigurationProperties(prefix = "bar.datasource")
    public DataSource barDataSource() {
        return DataSourceBuilder.create().build();
    }

    @Bean(name = "barJdbcTemplate")
    public JdbcTemplate barJdbcTemplate(@Qualifier("barDb") DataSource ds) {
        return new JdbcTemplate(ds);
    }

}

when start my application, it failed and have below error info

Parameter 0 of method fooJdbcTemplate in com.example.multidatasourcedemo.MultiDBConfig required a single bean, but 3 were found:
    - fooDb: defined by method 'fooDataSource' in class path resource [com/example/multidatasourcedemo/MultiDBConfig.class]
    - barDb: defined by method 'barDataSource' in class path resource [com/example/multidatasourcedemo/MultiDBConfig.class]
    - testDb: defined by method 'testDataSource' in class path resource [com/example/multidatasourcedemo/MultiDBConfig.class]


Action:

Consider marking one of the beans as @Primary, updating the consumer to accept multiple beans, or using @Qualifier to identify the bean that should be consumed

But I obviously have used @Qualifier to identify the bean , e.g.

@Bean(name = "fooJdbcTemplate")
public JdbcTemplate fooJdbcTemplate(@Qualifier("fooDb") DataSource ds)

Why doesn't @Qualifier work here?

Answer 1

So I've done some debugging and found something which might explain what's happening. At this point I'm not sure if it's a bug (could be this one), but I have not been able to find any other documentation to clarify this either.

For reference this is spring-boot 1.5.4.

---

I started from the log, you can find below an excerpt, more specifically the line regarding DataSourceInitializer.init (below with ==> at the beginning):

org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'javax.sql.DataSource' available: expected single matching bean but found 3: fooDb,barDb,testDb
    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:77) ~[spring-boot-autoconfigure-1.5.4.RELEASE.jar:1.5.4.RELEASE]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_45]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_45]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_45]
    at java.lang.reflect.Method.invoke(Method.java:497) ~[na:1.8.0_45]
    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
    ...

What happens is, when initialising the data sources, spring-boot tries to initialise the DB as well, feature which is enabled by default according to the docs:

Spring JDBC has a DataSource initializer feature. Spring Boot enables it by default and loads SQL from the standard locations schema.sql and data.sql (in the root of the classpath).

This takes place in the @PostConstruct section of org.springframework.boot.autoconfigure.jdbc.DataSourceInitializer:

@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();
}

As you can see, it tries to get the DataSource to execute the DB initialisation using the class this.dataSource = this.applicationContext.getBean(DataSource.class); and since there are 3 instances and no primary, it fails as per the expected behaviour of getBean(class)

<T> T getBean(Class<T> requiredType) throws BeansException
Return the bean instance that uniquely matches the given object type, if any.
This method goes into ListableBeanFactory by-type lookup territory but may also be translated into a conventional by-name lookup based on the name of the given type. For more extensive retrieval operations across sets of beans, use ListableBeanFactory and/or BeanFactoryUtils.

Parameters:
requiredType - type the bean must match; can be an interface or superclass. null is disallowed.

Returns:
an instance of the single bean matching the required type

Throws:
NoSuchBeanDefinitionException - if no bean of the given type was found
==> NoUniqueBeanDefinitionException - if more than one bean of the given type was found
BeansException - if the bean could not be created

---

So, bottom line, this happens before even trying to autowire your @Qualifier("fooDb") bean in the method, and I believe you have at lease these 2 choices, and in both cases your @Qualifier will be taken into account at the time when your JdbcTemplate is created:

• if you need to execute some scripts to initialise your DB, then use @Primary to indicate which DataSource could be used for the task
• otherwise, you can disable this implicit feature by adding spring.datasource.initialize=false in your application.properties (see here a list of common properties that can be configured)