Spring @ComponentScan – Filter Types

小灰灰 2024-03-25 18:09 40阅读 0赞

There are five types of filters available for `ComponentScan.Filter`  
1、`FilterType.ANNOTATION`  
2、`FilterType.ASSIGNABLE_TYPE`  
3、`FilterType.ASPECTJ`  
4、`FilterType.REGEX`  
5、`FilterType.CUSTOM`

We should note that all these filters can **`include`** or **`exclude`** classes from scanning by using `includeFilters` and `excludeFilters` parameters of the @ComponentScan annotation.

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## 1. FilterType.ANNOTATION ##

@Retention(RetentionPolicy.RUNTIME)
    @Target(ElementType.TYPE)
    public @interface Animal {
         }
    
    @Animal
    public class Elephant {
         }
    
    # Use the FilterType.ANNOTATION to tell Spring to scan for @Animal-annotated classes
    @Configuration
    @ComponentScan(includeFilters = @ComponentScan.Filter(type = FilterType.ANNOTATION, classes = Animal.class))
    public class ComponentScanAnnotationFilterApp {
         }
    
    # 验证
    @Test
    public void whenAnnotationFilterIsUsed_thenComponentScanShouldRegisterBeanAnnotatedWithAnimalAnootation() {
        
        ApplicationContext applicationContext = new AnnotationConfigApplicationContext(ComponentScanAnnotationFilterApp.class)
        List<String> beans = Arrays.stream(applicationContext.getBeanDefinitionNames())
                .filter(bean -> !bean.contains("org.springframework") && !bean.contains("componentScanAnnotationFilterApp"))
                .collect(Collectors.toList());
        assertThat(beans.size(), equalTo(1));
        assertThat(beans.get(0), equalTo("elephant"));
    }

--------------------

## 2. FilterType.ASSIGNABLE\_TYPE ##

public interface Animal {
         }
    public class Elephant implements Animal {
         }
    public class Cat implements Animal {
         }
    
    # Use ASSIGNABLE_TYPE to guide Spring to scan for Animal-implementing classes:
    @Configuration
    @ComponentScan(includeFilters = @ComponentScan.Filter(type = FilterType.ASSIGNABLE_TYPE,classes = Animal.class))
    public class ComponentScanAssignableTypeFilterApp {
         }
    
    @Test
    public void whenAssignableTypeFilterIsUsed_thenComponentScanShouldRegisterBean() {
        
        ApplicationContext applicationContext = new AnnotationConfigApplicationContext(ComponentScanAssignableTypeFilterApp.class);
        List<String> beans = Arrays.stream(applicationContext.getBeanDefinitionNames())
          .filter(bean -> !bean.contains("org.springframework") && !bean.contains("componentScanAssignableTypeFilterApp"))
          .collect(Collectors.toList());
        assertThat(beans.size(), equalTo(2));
        assertThat(beans.contains("cat"), equalTo(true));
        assertThat(beans.contains("elephant"), equalTo(true));
    }

--------------------

## 3. FilterType.REGEX ##

public class Elephant {
         }
    public class Cat {
         }
    public class Lion {
         }
    
    # use FilterType.REGEX which instructs Spring to scan classes that match regex `.*[nt]`.
    @Configuration
    @ComponentScan(includeFilters = @ComponentScan.Filter(type = FilterType.REGEX, pattern = ".*[nt]"))
    public class ComponentScanRegexFilterApp {
         }
    
    @Test
    public void whenRegexFilterIsUsed_thenComponentScanShouldRegisterBeanMatchingRegex() {
        
        ApplicationContext applicationContext = new AnnotationConfigApplicationContext(ComponentScanRegexFilterApp.class);
        List<String> beans = Arrays.stream(applicationContext.getBeanDefinitionNames())
          .filter(bean -> !bean.contains("org.springframework") && !bean.contains("componentScanRegexFilterApp"))
          .collect(Collectors.toList());
        assertThat(beans.size(), equalTo(1));
        assertThat(beans.contains("elephant"), equalTo(true));
    }

--------------------

## 4. FilterType.ASPECTJ ##

public class Elephant {
         }
    public class Cat {
         }
    public class Lion {
         }
    
    @Configuration
    @ComponentScan(includeFilters = @ComponentScan.Filter(type = FilterType.ASPECTJ,
      pattern = "com.componentscan.filter.aspectj.* && !(com.componentscan.filter.aspectj.L* || com.componentscan.filter.aspectj.C*)"))
    public class ComponentScanAspectJFilterApp {
         }
    
    @Test
    public void whenAspectJFilterIsUsed_thenComponentScanShouldRegisterBeanMatchingAspectJCreteria() {
        
        ApplicationContext applicationContext = new AnnotationConfigApplicationContext(ComponentScanAspectJFilterApp.class);
        List<String> beans = Arrays.stream(applicationContext.getBeanDefinitionNames())
          .filter(bean -> !bean.contains("org.springframework") && !bean.contains("componentScanAspectJFilterApp"))
          .collect(Collectors.toList());
        assertThat(beans.size(), equalTo(1));
        assertThat(beans.get(0), equalTo("elephant"));
    }

--------------------

## 5. FilterType.CUSTOM ##

public class ComponentScanCustomFilter implements TypeFilter {
        
        @Override
        public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory) throws IOException {
        
            ClassMetadata classMetadata = metadataReader.getClassMetadata();
            String fullyQualifiedName = classMetadata.getClassName();
            String className = fullyQualifiedName.substring(fullyQualifiedName.lastIndexOf(".") + 1);
            return className.length() > 5 ? true : false;
        }
    }
    
    @Configuration
    @ComponentScan(includeFilters = @ComponentScan.Filter(type = FilterType.CUSTOM, classes = ComponentScanCustomFilter.class))
    public class ComponentScanCustomFilterApp {
         }
    
    @Test
    public void whenCustomFilterIsUsed_thenComponentScanShouldRegisterBeanMatchingCustomFilter() {
        
        ApplicationContext applicationContext = new AnnotationConfigApplicationContext(ComponentScanCustomFilterApp.class);
        List<String> beans = Arrays.stream(applicationContext.getBeanDefinitionNames())
          .filter(bean -> !bean.contains("org.springframework") && !bean.contains("componentScanCustomFilterApp") && !bean.contains("componentScanCustomFilter"))
          .collect(Collectors.toList());
        assertThat(beans.size(), equalTo(1));
        assertThat(beans.get(0), equalTo("elephant"));
    }

--------------------

参考：  
[Spring @ComponentScan – Filter Types][Spring _ComponentScan _ Filter Types]

[Spring _ComponentScan _ Filter Types]: https://www.baeldung.com/spring-componentscan-filter-type