1.@ComponentScan注解作用

@ComponentScan用于类或接口上主要是指定扫描路径,spring会把指定路径下带有指定注解的类自动装配到bean容器里。会被自动装配的注解包括@Controller@Service@Component@Repository等等。与ComponentScan注解相对应的XML配置就是<context:component-scan/>, 根据指定的配置自动扫描package,将符合条件的组件加入到IOC容器中;

XML的配置方式如下:

<context:component-scanbase-package="com.example.test" use-default-filters="false"><context:exclude-filter type="custom"expression="com.example.test.filter.MtyTypeFilter" /></context:component-scan>

2. @ComponentScan注解属性

@ComponentScan有如下常用属性:

  • basePackages和value:指定要扫描的路径(package),如果为空则以@ComponentScan注解的类所在的包为基本的扫描路径。
  • basePackageClasses:指定具体扫描的类。
  • includeFilters:指定满足Filter条件的类。
  • excludeFilters:指定排除Filter条件的类。
  • useDefaultFilters=true/false:指定是否需要使用Spring默认的扫描规则:被@Component, @Repository, @Service, @Controller或者已经声明过@Component自定义注解标记的组件;

在过滤规则Filter中:
FilterType:指定过滤规则,支持的过滤规则有:

  • ANNOTATION:按照注解规则,过滤被指定注解标记的类(默认);
  • ASSIGNABLE_TYPE:按照给定的类型;
  • ASPECTJ:按照ASPECTJ表达式;
  • REGEX:按照正则表达式;
  • CUSTOM:自定义规则,自定义的Filter需要实现TypeFilter接口;

value和classes:指定在该规则下过滤的表达式;

@ComponentScan的常见的配置如下:

@ComponentScan(    excludeFilters = {@Filter(    type = FilterType.CUSTOM,    classes = {TypeExcludeFilter.class}), @Filter(    type = FilterType.CUSTOM,    classes = {AutoConfigurationExcludeFilter.class})})

3. @ComponentScan过滤规则说明

规则表达式说明

 1. 扫描指定类文件   @ComponentScan(basePackageClasses = Person.class) 2. 扫描指定包,使用默认扫描规则,即被@Component, @Repository, @Service, @Controller或者已经声明过@Component自定义注解标记的组件;   @ComponentScan(value = "com.example") 3. 扫描指定包,加载被@Component注解标记的组件和默认规则的扫描(因为useDefaultFilters默认为true@ComponentScan(value = "com.example", includeFilters = { @Filter(type = FilterType.ANNOTATION, value = Component.class) }) 4. 扫描指定包,只加载Person类型的组件   @ComponentScan(value = "com.example", includeFilters = { @Filter(type = FilterType.ASSIGNABLE_TYPE, value = Person.class) }, useDefaultFilters = false) 5. 扫描指定包,过滤掉被@Component标记的组件   @ComponentScan(value = "com.example", excludeFilters = { @Filter(type = FilterType.ANNOTATION, value = Component.class) }) 6. 扫描指定包,自定义过滤规则   @ComponentScan(value = "com.example", includeFilters = { @Filter(type = FilterType.CUSTOM, value = MtyTypeFilter.class) }, useDefaultFilters = true)

4. 自定义扫描过滤规则

  1. 用户自定义扫描过滤规则,需要实现org.springframework.core.type.filter.TypeFilter接口。
//1.自定义类实现TypeFilter接口并重写match()方法public class MtyTypeFilter implements TypeFilter {    /**     *     * @param metadataReader:读取到当前正在扫描的类的信息     * @param metadataReaderFactory:可以获取到其他任何类的信息     * @return     * @throws IOException     */    @Override    public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory) throws IOException {        System.out.println("========MtyTypeFilter===========");        //获取当前类的注解的信息        AnnotationMetadata annotationMetadata = metadataReader.getAnnotationMetadata();        System.out.println("annotationMetadata: "+annotationMetadata);        //输出结果:annotationMetadata: com.example.test.bean.Color        //获取当前正在扫描的类的类信息        ClassMetadata classMetadata = metadataReader.getClassMetadata();        System.out.println("classMetadata: "+classMetadata);        //输出结果: classMetadata: com.example.test.bean.Color        //获取当前类资源(类的路径)        Resource resource = metadataReader.getResource();        System.out.println("resource: "+resource);        //输出结果:resource: file [D:\idea\demo-02\target\classes\com\example\test\bean\Color.class]        //获取类名        String className = classMetadata.getClassName();        System.out.println("className: "+className);        //输出结果:className: com.example.test.bean.Color        Class<?> forName = null;        try {            forName = Class.forName(className);            if (Color.class.isAssignableFrom(forName)) {                // 如果是Color的子类,就加载到IOC容器                return true;            }        } catch (ClassNotFoundException e) {            e.printStackTrace();        }        System.out.println("========MtyTypeFilter===========");        return false;    }}

5. @ComponentScans

可以一次声明多个@ComponentScan

@Retention(RetentionPolicy.RUNTIME)@Target(ElementType.TYPE)@Documented@Repeatable(ComponentScans.class)  //指定ComponentScan可以被ComponentScans作为数组使用public @interface ComponentScan {}  @Retention(RetentionPolicy.RUNTIME)@Target(ElementType.TYPE)@Documentedpublic @interface ComponentScans {    ComponentScan[] value(); }
@ComponentScans(value = { @ComponentScan(value = "com.example.test"),@ComponentScan(value = "com.example.test", includeFilters = {@Filter(type = FilterType.CUSTOM, value = MtyTypeFilter.class) }) })public class MainConfig { @Bean(name = "pers", initMethod = "init", destroyMethod = "destory")public Person person() {return new Person();} }

6. spring boot处理@ComponentScan源码分析

spring创建bean对象的基本流程是先创建对应的BeanDefinition对象,然后在基于BeanDefinition对象来创建Bean对象,SpringBoot也是如此,只不过通过注解创建BeanDefinition对象的时机和解析方式不同而已。SpringBoot是通过ConfigurationClassPostProcessor这个BeanFactoryPostProcessor类来处理。

本演示的demo涉及到4个演示类,分别是:

  1. 带有@SpringBootApplication注解的启动类Demo02Application。
  2. 带有@RestController注解的类HelloController。
  3. 带有@Configuration注解且有通过@Bean注解来创建addInterceptors的方法的MyMvcConfig类。
  4. Account实体类无任何注解。

本文的最后会贴出所有代码。 先从启动类为入口,SpringBoot启动类如下:

@SpringBootApplicationpublic class Demo02Application {    public static void main(String[] args) {        //1、返回我们IOC容器        ConfigurableApplicationContext run = SpringApplication.run(Demo02Application.class, args);}}

SpringApplication.run(Demo02Application.class, args);一路断点到核心方法SpringApplication.ConfigurableApplicationContext run(String... args)方法

run方法干了两件事:

  • 创建SpringApplication对象
  • 利用创建好的SpringApplication对象调用run方法
 public ConfigurableApplicationContext run(String... args) {        long startTime = System.nanoTime();        DefaultBootstrapContext bootstrapContext = this.createBootstrapContext();        ConfigurableApplicationContext context = null;        this.configureHeadlessProperty();        //初始化监听器        SpringApplicationRunListeners listeners = this.getRunListeners(args);        //发布ApplicationStartingEven        listeners.starting(bootstrapContext, this.mainApplicationClass);        try {         //装配参数和环境            ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);            //发布ApplicationEnvironmentPreparedEvent            ConfigurableEnvironment environment = this.prepareEnvironment(listeners, bootstrapContext, applicationArguments);            this.configureIgnoreBeanInfo(environment);            Banner printedBanner = this.printBanner(environment);            //创建ApplicationContext,并装配            context = this.createApplicationContext();            context.setApplicationStartup(this.applicationStartup);            //发布ApplicationPreparedEvent            this.prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);            this.refreshContext(context);            this.afterRefresh(context, applicationArguments);            Duration timeTakenToStartup = Duration.ofNanos(System.nanoTime() - startTime);            if (this.logStartupInfo) {                (new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), timeTakenToStartup);            }//发布ApplicationStartedEven            listeners.started(context, timeTakenToStartup);            //执行Spring中@Bean下的一些操作,如静态方法            this.callRunners(context, applicationArguments);        } catch (Throwable var12) {            this.handleRunFailure(context, var12, listeners);            throw new IllegalStateException(var12);        }        try {            Duration timeTakenToReady = Duration.ofNanos(System.nanoTime() - startTime);            listeners.ready(context, timeTakenToReady);            return context;        } catch (Throwable var11) {            this.handleRunFailure(context, var11, (SpringApplicationRunListeners)null);            throw new IllegalStateException(var11);        }    }
  • 重点方法一:本方法法实现的重点功能:
  1. demoweb工程,springboot通过反射创建上下文context:AnnotationConfigServletWebServerApplicationContext
  2. 在构建context的无参构造方法中构建成员变量reader=new AnnotatedBeanDefinitionReader(this),在AnnotatedBeanDefinitionReader的无参构造方法中会beanFactory对象,并向beanFactory中注册5个BeanDefinition对象,重点关注ConfigurationClassPostProcessor。
context = this.createApplicationContext();
  • 重点方法二:本方法实现的重点功能
    本方法会构建启动类Demo02Application对应的BeanDefinition对象,并注册到beanFactory中,此时的context对象可见下图
   this.prepareContext(context, environment, listeners, applicationArguments, printedBanner);
  • 重点方法三:本方法实现的重点功能
    该方法实际调用applicationContext的refresh方法,代码分析详见我的另一篇博客,本文后面只会分析ConfigurationClassPostProcessor对象的创建和postProcessBeanDefinitionRegistry方法的执行
    this.refreshContext(context);    this.afterRefresh(context, applicationArguments);

this.prepareContext(context, environment, listeners, applicationArguments, printedBanner);代码执行后的截图如下:

ConfigurationClassPostProcessor实现BeanFactoryPostProcessor,关于BeanFactoryPostProcessor扩展接口的作用在《spring初始化源码浅析之关键类和扩展接口》一文中有详细介绍。

ConfigurationClassPostProcessor对象的创建和方法执行的断点如下:
this.refreshContext(context);–> AbstractApplicationContext.refresh() –> invokeBeanFactoryPostProcessors() –>PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors()->invokeBeanDefinitionRegistryPostProcessors()

下面重点看ConfigurationClassPostProcessor类的postProcessBeanDefinitionRegistry()方法如何处理@ComponentScan注解:

同过源代码发现最终是由ConfigurationClassParser的解析类来处理,继续查看ConfigurationClassParser.doProcessConfigurationClass

原来在这里对@ComponentScan注解做了判断,上面一段代码做了核心的几件事:

  1. 扫描@ComponentScan注解包下面的所有的可自动装备类,生成BeanDefinition对象,并注册到beanFactory对象中。
  2. 通过DeferredImportSelectorHandler处理@EnableAutoConfiguration注解,后续会有专文介绍。
  3. 将带有@Configuration 注解的类解析成ConfigurationClass对象并缓存,后面创建@Bean注解的Bean对象所对应的BeanDefinition时会用到
    到此为止MyFilter2对应的BeanDefinition已创建完毕,如下图: