關於context:component-scan配置中use-default-filters參數的做用

參考了多篇文章都說明了use-default-filters參數的基本用途，但有些主要點沒有說到，這裏補充記錄下：

<context:component-scan base-package="com.jaamy"  use-default-filters="false">
         <context:include-filter type="annotation"  expression="org.springframework.stereotype.Controller" />
</context:component-scan>

 這個只掃描com.jaamy包下的@Controller，不會掃描@Service、@Repository

 

<context:component-scan base-package="com.jaamy">
         <context:include-filter type="annotation"  expression="org.springframework.stereotype.Controller" />
</context:component-scan>

 這個不但掃描com.jaamy包下的@Controller，同時也會掃描@Service、@Repository，注意這裏沒有添加use-default-filters參數

 

下面配合源碼說明下use-default-filters參數的做用以及和context:include-filter、exclude-filter的關係。

代碼中是根據use-default-filters的值來肯定是否須要調用registerDefaultFilters來添加默認的filters到includeFilters中，看下面的代碼：

org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider

public ClassPathScanningCandidateComponentProvider(boolean useDefaultFilters, Environment environment) {
        if (useDefaultFilters) {
            registerDefaultFilters();
        }
        Assert.notNull(environment, "Environment must not be null");
        this.environment = environment;
    }

 

use-default-filters爲true時調用了下面的代碼，在includeFilters列表中添加了Component、ManagedBean和Named，所以use-default-filters的值直接影響includeFilters的內容，而includeFilters的容直接影響了要掃描的內容，所以use-default-filters的值是否配置也就決定了總體要掃描的內容。

protected void registerDefaultFilters() {
        this.includeFilters.add(new AnnotationTypeFilter(Component.class));
        ClassLoader cl = ClassPathScanningCandidateComponentProvider.class.getClassLoader();
        try {
            this.includeFilters.add(new AnnotationTypeFilter(
                    ((Class<? extends Annotation>) ClassUtils.forName("javax.annotation.ManagedBean", cl)), false));
            logger.debug("JSR-250 'javax.annotation.ManagedBean' found and supported for component scanning");
        }
        catch (ClassNotFoundException ex) {
            // JSR-250 1.1 API (as included in Java EE 6) not available - simply skip.
        }
        try {
            this.includeFilters.add(new AnnotationTypeFilter(
                    ((Class<? extends Annotation>) ClassUtils.forName("javax.inject.Named", cl)), false));
            logger.debug("JSR-330 'javax.inject.Named' annotation found and supported for component scanning");
        }
        catch (ClassNotFoundException ex) {
            // JSR-330 API not available - simply skip.
        }
    }

 

關於include-filter、exclude-filter的做用主要是用來過濾掃描到的bean是否合法：

首先經過exclude-filter進行黑名單過濾；

而後經過include-filter進行白名單過濾；

不然默認排除。 看下面的代碼：

protected boolean isCandidateComponent(MetadataReader metadataReader) throws IOException {
        for (TypeFilter tf : this.excludeFilters) {
            if (tf.match(metadataReader, this.metadataReaderFactory)) {
                return false;
            }
        }
        for (TypeFilter tf : this.includeFilters) {
            if (tf.match(metadataReader, this.metadataReaderFactory)) {
                return isConditionMatch(metadataReader);
            }
        }
        return false;
    }

 

總結：

<context:component-scan base-package="com.jaamy"  use-default-filters="false">
         <context:include-filter type="annotation"  expression="org.springframework.stereotype.Controller" />
</context:component-scan>

針對上面的配置，use-default-filters的做用以下：

use-default-filters不配置或者是配置爲true時：

不但要掃描include配置的com.jaamy包下的@Controller，並且還要掃描@Service和@Repository

use-default-filters配置爲false時：

只掃描include配置的com.jaamy包下的@Controller，不掃描@Service和@Repository

 

參考地址：http://jinnianshilongnian.iteye.com/blog/1762632