《Spring Recipes》第一章笔记：Scanning Components from ...

问题

当需要注入的bean太多时，手工进行配置太费时费力，Spring容器提供了指定扫描功能。

解决方案

使用Spring的component scanning功能。可以通过@Component，@Repository, @Service , 和@Controller注解，使Spring容器指定扫描bean配置，进行注入。

@Repository
public class SequenceDaoImpl implements SequenceDao {
... ...
}

可以在使用component scan的同时，使用@Autowired进行注入

@Service 
public class SequenceService {
    @Autowired
    private SequenceDao sequenceDao;
... ...
}

配置文件：

需要配置<context:component-scan base-package="com.apress.springrecipes.sequence">，base-package指定了容器需要扫描的类路径。

<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.0.xsd">
<context:component-scan base-package="com.apress.springrecipes.sequence" />
</beans>

Filtering Components

Spring容器运行用户对需要进行扫描的bean进行过滤。

通过context:include-filter和context:exclude-filter标签进行配置。

Table 4.5. Filter Types

Filter Type	Example Expression	Description
annotation	org.example.SomeAnnotation	An annotation to be present at the type level in target components.
assignable	org.example.SomeClass	A class (or interface) that the target components are assignable to (extend/implement).
aspectj	org.example..*Service+	An AspectJ type expression to be matched by the target components.
regex	org\.example\.Default.*	A regex expression to be matched by the target components class names.
custom	org.example.MyTypeFilter	A custom implementation of the org.springframework.core.type .TypeFilter interface.

例：

<beans ...>
  <context:component-scan base-package="com.apress.springrecipes.sequence">
    <context:include-filter type="regex"
    expression="com\.apress\.springrecipes\.sequence\..*Dao.*" />
    <context:include-filter type="regex"
    expression="com\.apress\.springrecipes\.sequence\..*Service.*" />
    <context:exclude-filter type="annotation"
    expression="org.springframework.stereotype.Controller" />
  </context:component-scan>
</beans>

对扫描到的Componet进行命名

Spring容器默认情况下，对扫描到的bean的命名方式为：将bean的类名的首字母小写，例如

@Repository
public class SequenceDaoImpl implements SequenceDao {
... ...
}

在容器中的名称为sequenceDaoImpl。

用户也可以自行进行指定：

@Service("sequenceService")
public class SequenceService {
...
}

@Repository("sequenceDao")
public class SequenceDaoImpl implements SequenceDao {
...
}

并且用户可以通过设置<context:component-scan>元素的name-generator属性来指定component默认名称生成规则。

<beans>
<context:component-scan base-package="org.example"
    name-enerator="org.example.MyNameGenerator"/>
</beans>

指定Component的Scope

使用@Scope注解设定。

@Scope("prototype")
@Repository
public class MovieFinderImpl implements MovieFinder {
  // ...
}

Table 4.3. Bean scopes

Scope	Description
singleton	(Default) Scopes a single bean definition to a single object instance per Spring IoC container.
prototype	Scopes a single bean definition to any number of object instances.
request	Scopes a single bean definition to the lifecycle of a single HTTP request; that is, each HTTP request has its own instance of a bean created off the back of a single bean definition. Only valid in the context of a web-aware Spring ApplicationContext.
session	Scopes a single bean definition to the lifecycle of an HTTP Session. Only valid in the context of a web-aware Spring ApplicationContext.
global session	Scopes a single bean definition to the lifecycle of a global HTTP Session. Typically only valid when used in a portlet context. Only valid in the context of a web-aware Spring ApplicationContext.