@ComponentScan 详解

蔚落 2022-12-19 09:13 135阅读 0赞

@ComponentScan 的作用就是根据定义的扫描路径，把符合扫描规则的类装配到spring容器中，注解定义如下。

@Retention(RetentionPolicy.RUNTIME)
    @Target({ElementType.TYPE})
    @Documented
    @Repeatable(ComponentScans.class)
    public @interface ComponentScan {
        @AliasFor("basePackages")
        String[] value() default {};
     
        @AliasFor("value")
        String[] basePackages() default {};
     
        Class<?>[] basePackageClasses() default {};
     
        Class<? extends BeanNameGenerator> nameGenerator() default BeanNameGenerator.class;
     
        Class<? extends ScopeMetadataResolver> scopeResolver() default AnnotationScopeMetadataResolver.class;
     
        ScopedProxyMode scopedProxy() default ScopedProxyMode.DEFAULT;
     
        String resourcePattern() default "**/*.class";
        boolean useDefaultFilters() default true;
        ComponentScan.Filter[] includeFilters() default {};
        ComponentScan.Filter[] excludeFilters() default {};
        boolean lazyInit() default false;
        @Retention(RetentionPolicy.RUNTIME)
        @Target({})
        public @interface Filter {
            FilterType type() default FilterType.ANNOTATION;
            @AliasFor("classes")
            Class<?>[] value() default {};
            @AliasFor("value")
            Class<?>[] classes() default {};
            String[] pattern() default {};
        }
    }

basePackages与value:  用于指定包的路径，进行扫描

basePackageClasses: 用于指定某个类的包的路径进行扫描

nameGenerator: bean的名称的生成器

useDefaultFilters: 是否开启对@Component，@Repository，@Service，@Controller的类进行检测

includeFilters: 包含的过滤条件

FilterType.ANNOTATION：按照注解过滤

FilterType.ASSIGNABLE\_TYPE：按照给定的类型

FilterType.ASPECTJ：使用ASPECTJ表达式

FilterType.REGEX：正则

FilterType.CUSTOM：自定义规则

excludeFilters: 排除的过滤条件，用法和includeFilters一样

我的工程结构如下，测试对controller和service的扫描，其中HelloController没有加@Controller等任何注解，就是一个普通类。

![70][]

修改配置类如下：应用默认的过滤器，扫描service包：

1.  `@Configuration`
2.  `@ComponentScan(value = "com.xhx.spring.service",`
3.  `useDefaultFilters = true`
4.  `)`
5.  `public class MyConfig {`
6.  `}`

系统注入了两个service进去

![70 1][]

改成如下所示：HelloController所在的包的类也被扫描了进去

1.  `@Configuration`
2.  `@ComponentScan(value = "com.xhx.spring.service",`
3.  `useDefaultFilters = true,`
4.  `basePackageClasses = HelloController.class`
5.  `)`
6.  `public class MyConfig {`
7.  `}`

系统中会注入下面就给类

![70 2][]

把默认的过滤器关掉，扫描带Controller注解的。

1.  `@Configuration`
2.  `@ComponentScan(value = "com.xhx.spring",`
3.  `useDefaultFilters = false,`
4.  `includeFilters = {`
5.  `@ComponentScan.Filter(type = FilterType.ANNOTATION,classes = {Controller.class})`
6.  `}`
7.  `)`
8.  `public class MyConfig {`
9.  `}`

![70 3][]

按照类的类型扫描，虽然HelloController没有加注解，但是被注入到了spring容器中

1.  `@Configuration`
2.  `@ComponentScan(value = "com.xhx.spring",`
3.  `useDefaultFilters = false,`
4.  `includeFilters = {`
5.  `@ComponentScan.Filter(type = FilterType.ASSIGNABLE_TYPE,classes = {HelloController.class})`
6.  `}`
7.  `)`
8.  `public class MyConfig {`
9.  `}`

![70 4][]

自定义扫描过滤器

package com.xhx.spring.componentscan.config;
     
    import org.springframework.core.type.classreading.MetadataReader;
    import org.springframework.core.type.classreading.MetadataReaderFactory;
    import org.springframework.core.type.filter.TypeFilter;
     
    import java.io.IOException;
     
    /**
     * xuhaixing
     * 2018/9/18 23:07
     **/
    public class MyTypeFilter implements TypeFilter {
        @Override
        public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory) throws IOException {
            String className = metadataReader.getClassMetadata().getClassName();
            if(className.contains("Controller")){
                return true;
            }
            return false;
        }
    }

修改配置类

@Configuration
    @ComponentScan(value = "com.xhx.spring",
            useDefaultFilters = false,
            includeFilters = {
                @ComponentScan.Filter(type = FilterType.CUSTOM,classes = {MyTypeFilter.class})
            }
    )
    public class MyConfig {
    }

输出结果：

![70 5][]

输出spring容器中的bean的测试类：只过滤输出了名字中含有hello的类。

package com.xhx.spring.componentscan;
     
    import com.xhx.spring.componentscan.config.MyConfig;
    import org.junit.Test;
    import org.junit.runner.RunWith;
    import org.springframework.boot.test.context.SpringBootTest;
    import org.springframework.context.annotation.AnnotationConfigApplicationContext;
    import org.springframework.test.context.junit4.SpringRunner;
     
    import java.util.Arrays;
    import java.util.List;
    import java.util.stream.Collectors;
     
    @RunWith(SpringRunner.class)
    @SpringBootTest
    public class ComponentScanApplicationTests {
     
        @Test
        public void testLoads() {
            AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(MyConfig.class);
            List<String> hello = Arrays.stream(context.getBeanDefinitionNames()).collect(Collectors.toList());
            hello.stream().filter(name->name.contains("hello")).peek(System.out::println).count();
        }
     
    }

[70]: /images/20221120/eaad4b15cec24220a718e58213dfcd9a.png
[70 1]: https://img-blog.csdn.net/20180918225846409?watermark/2/text/aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTIzMjY0NjI=/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70
[70 2]: https://img-blog.csdn.net/20180918230026841?watermark/2/text/aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTIzMjY0NjI=/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70
[70 3]: https://img-blog.csdn.net/20180918230451720?watermark/2/text/aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTIzMjY0NjI=/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70
[70 4]: https://img-blog.csdn.net/20180918230600568?watermark/2/text/aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTIzMjY0NjI=/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70
[70 5]: https://img-blog.csdn.net/20180918230913511?watermark/2/text/aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTIzMjY0NjI=/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70