spring boot自动装配之@ComponentScan注解用法详解

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

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

 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)

//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;
    }
}

@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)
@Documented
public @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();
	}
 
}

@SpringBootApplication
public class Demo02Application {

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

 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);
        }
    }

context = this.createApplicationContext();

this.prepareContext(context, environment, listeners, applicationArguments, printedBanner);

    this.refreshContext(context);
    this.afterRefresh(context, applicationArguments);