spring注解扫描组件注册

　　最近对单点系统进行微服务拆分，被各个springboot的组件注册搞得云里雾里的。（有的是通过springboot的自动配置进IOC容器的，有的是自己添加构造方法添加进IOC容器。）决定抽时间将spring注解扫描组件注册重新复习一下，好久没写博客了，也该用笔记记录一下自己的学习过程，再不清晰的时候回来看一下加深印象。

一、@Configuration和@Bean给容器注册组件

　　现在我们有如下一个bean，想要将其注入到IOC容器中：

package com.kun.bean;

import org.springframework.beans.factory.annotation.Value;

public class Person {

	private String name;
	private Integer age;
	
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public Integer getAge() {
		return age;
	}
	public void setAge(Integer age) {
		this.age = age;
	}
	
	@Override
	public String toString() {
		return "Person [name=" + name + ", age=" + age "]";
	}

}

　　传统通过配置文件方式定义bean的方式如下：

<bean id="person" class="com.kun.bean.Person">
		<property name="age" value="${}"></property>
		<property name="name" value="zhangsan"></property>
</bean>

　　现在我们通过一个config类来替代原来的配置文件：

package com.kun.config;

import com.kun.bean.Person;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScans;
import org.springframework.context.annotation.Configuration;

@Configuration
public class MainConfig
{
  @Bean({"person"})
  public Person person01()
  {
    return new Person("lisi", Integer.valueOf(20));
  }
}

　　这样，我们就将Person的实例注入到了IOC容器中，测试如下：

package com.kun;

import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.kun.bean.Person;
import com.kun.config.MainConfig;

public class MainTest {
	
	@SuppressWarnings("resource")
	public static void main(String[] args) {
//		ApplicationContext applicationContext = new ClassPathXmlApplicationContext("beans.xml");
//		Person bean = (Person) applicationContext.getBean("person");
//		System.out.println(bean);
		
		ApplicationContext applicationContext = new AnnotationConfigApplicationContext(MainConfig.class);
		Person bean = applicationContext.getBean(Person.class);
		System.out.println(bean);
		
		String[] namesForType = applicationContext.getBeanNamesForType(Person.class);
		for (String name : namesForType) {
			System.out.println(name);
		}
	}
}

　　最终我们能够从IOC容器中获取到注入的Person对象。

　　注意：通过@Configuration和@Bean注册的对象，在IOC容器中的key默认为构造方法的方法名，如果想要改变，则给@Bean注解增加value属性，IOC容器中的key可改为value属性的值。

二、@ComponentScan自动扫描组件

　　传统通过配置文件方式定义bean的方式如下：

<!-- 包扫描、只要标注了@Controller、@Service、@Repository，@Component -->
<context:component-scan base-package="com.kun" default-filters="false"></context:component-scan>

　　现在我们通过一个config类来替代原来的配置文件中的配置：

package com.kun.config;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.FilterType;
import org.springframework.context.annotation.ComponentScan.Filter;
import org.springframework.context.annotation.ComponentScans;

import com.kun.bean.Person;
import org.springframework.core.annotation.Order;

//配置类==配置文件
@Configuration  //告诉Spring这是一个配置类
@Order(2)
@ComponentScans(
		value = {
				@ComponentScan(value= "com.kun",includeFilters = {
/*						@Filter(type=FilterType.ANNOTATION,classes={Controller.class}),
						@Filter(type=FilterType.ASSIGNABLE_TYPE,classes={BookService.class}),*/
						@Filter(type=FilterType.CUSTOM,classes={MyTypeFilter.class})
				},useDefaultFilters = false)
		}
		)
//@ComponentScan  value:指定要扫描的包
//excludeFilters = Filter[] ：指定扫描的时候按照什么规则排除那些组件
//includeFilters = Filter[] ：指定扫描的时候只需要包含哪些组件
//FilterType.ANNOTATION：按照注解
//FilterType.ASSIGNABLE_TYPE：按照给定的类型；
//FilterType.ASPECTJ：使用ASPECTJ表达式
//FilterType.REGEX：使用正则指定
//FilterType.CUSTOM：使用自定义规则
public class MainConfig {
	
	//给容器中注册一个Bean;类型为返回值的类型，id默认是用方法名作为id
	@Bean("person")
	public Person person01(){
		return new Person("lisi", 20);
	}

}

　　@ComponentScan注解是一个数组，其中数组中的元素如下：

/*
 * Copyright 2002-2013 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.context.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.beans.factory.support.BeanNameGenerator;
import org.springframework.core.type.filter.TypeFilter;

/**
 * Configures component scanning directives for use with @{@link Configuration} classes.
 * Provides support parallel with Spring XML's {@code <context:component-scan>} element.
 *
 * <p>One of {@link #basePackageClasses()}, {@link #basePackages()} or its alias
 * {@link #value()} may be specified to define specific packages to scan.  If specific
 * packages are not defined scanning will occur from the package of the
 * class with this annotation.
 *
 * <p>Note that the {@code <context:component-scan>} element has an
 * {@code annotation-config} attribute, however this annotation does not. This is because
 * in almost all cases when using {@code @ComponentScan}, default annotation config
 * processing (e.g. processing {@code @Autowired} and friends) is assumed. Furthermore,
 * when using {@link AnnotationConfigApplicationContext}, annotation config processors are
 * always registered, meaning that any attempt to disable them at the
 * {@code @ComponentScan} level would be ignored.
 *
 * <p>See @{@link Configuration}'s javadoc for usage examples.
 *
 * @author Chris Beams
 * @since 3.1
 * @see Configuration
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
public @interface ComponentScan {

	/**
	 * Alias for the {@link #basePackages()} attribute.
	 * Allows for more concise annotation declarations e.g.:
	 * {@code @ComponentScan("org.my.pkg")} instead of
	 * {@code @ComponentScan(basePackages="org.my.pkg")}.
	 */
	String[] value() default {};

	/**
	 * Base packages to scan for annotated components.
	 * <p>{@link #value()} is an alias for (and mutually exclusive with) this attribute.
	 * <p>Use {@link #basePackageClasses()} for a type-safe alternative to String-based package names.
	 */
	String[] basePackages() default {};

	/**
	 * Type-safe alternative to {@link #basePackages()} for specifying the packages
	 * to scan for annotated components. The package of each class specified will be scanned.
	 * <p>Consider creating a special no-op marker class or interface in each package
	 * that serves no purpose other than being referenced by this attribute.
	 */
	Class<?>[] basePackageClasses() default {};

	/**
	 * The {@link BeanNameGenerator} class to be used for naming detected components
	 * within the Spring container.
	 * <p>The default value of the {@link BeanNameGenerator} interface itself indicates
	 * that the scanner used to process this {@code @ComponentScan} annotation should
	 * use its inherited bean name generator, e.g. the default
	 * {@link AnnotationBeanNameGenerator} or any custom instance supplied to the
	 * application context at bootstrap time.
	 * @see AnnotationConfigApplicationContext#setBeanNameGenerator(BeanNameGenerator)
	 */
	Class<? extends BeanNameGenerator> nameGenerator() default BeanNameGenerator.class;

	/**
	 * The {@link ScopeMetadataResolver} to be used for resolving the scope of detected components.
	 */
	Class<? extends ScopeMetadataResolver> scopeResolver() default AnnotationScopeMetadataResolver.class;

	/**
	 * Indicates whether proxies should be generated for detected components, which may be
	 * necessary when using scopes in a proxy-style fashion.
	 * <p>The default is defer to the default behavior of the component scanner used to
	 * execute the actual scan.
	 * <p>Note that setting this attribute overrides any value set for {@link #scopeResolver()}.
	 * @see ClassPathBeanDefinitionScanner#setScopedProxyMode(ScopedProxyMode)
	 */
	ScopedProxyMode scopedProxy() default ScopedProxyMode.DEFAULT;

	/**
	 * Controls the class files eligible for component detection.
	 * <p>Consider use of {@link #includeFilters()} and {@link #excludeFilters()}
	 * for a more flexible approach.
	 */
	String resourcePattern() default ClassPathScanningCandidateComponentProvider.DEFAULT_RESOURCE_PATTERN;

	/**
	 * Indicates whether automatic detection of classes annotated with {@code @Component}
	 * {@code @Repository}, {@code @Service}, or {@code @Controller} should be enabled.
	 */
	boolean useDefaultFilters() default true;

	/**
	 * Specifies which types are eligible for component scanning.
	 * <p>Further narrows the set of candidate components from everything in
	 * {@link #basePackages()} to everything in the base packages that matches
	 * the given filter or filters.
	 * @see #resourcePattern()
	 */
	Filter[] includeFilters() default {};

	/**
	 * Specifies which types are not eligible for component scanning.
	 * @see #resourcePattern()
	 */
	Filter[] excludeFilters() default {};


	/**
	 * Declares the type filter to be used as an {@linkplain ComponentScan#includeFilters()
	 * include filter} or {@linkplain ComponentScan#excludeFilters() exclude filter}.
	 */
	@Retention(RetentionPolicy.RUNTIME)
	@Target({})
	@interface Filter {

		/**
		 * The type of filter to use. Default is {@link FilterType#ANNOTATION}.
		 */
		FilterType type() default FilterType.ANNOTATION;

		/**
		 * The class or classes to use as the filter. In the case of
		 * {@link FilterType#ANNOTATION}, the class will be the annotation itself.
		 * In the case of {@link FilterType#ASSIGNABLE_TYPE}, the class will be the
		 * type that detected components should be assignable to. And in the case
		 * of {@link FilterType#CUSTOM}, the class will be an implementation of
		 * {@link TypeFilter}.
		 * <p>When multiple classes are specified, OR logic is applied, e.g. "include
		 * types annotated with {@code @Foo} OR {@code @Bar}".
		 * <p>Specifying zero classes is permitted but will have no effect on component
		 * scanning.
		 */
		Class<?>[] value();
	}

}

　常用的属性字段有：

　　　value:指定要扫描的包

　　　basePackages：同value

　　　excludeFilters = Filter[] ：指定扫描的时候按照什么规则排除那些组件

　　　includeFilters = Filter[] ：指定扫描的时候只需要包含哪些组件

　Filter常用的枚举如下：

　　FilterType.ANNOTATION：按照注解
　　FilterType.ASSIGNABLE_TYPE：按照给定的类型；
　　FilterType.ASPECTJ：使用ASPECTJ表达式
　　FilterType.REGEX：使用正则指定
　　FilterType.CUSTOM：使用自定义规则

着重看了一下自定义的过滤规则，需要实现TypeFilter接口，复写完match方法，根据方法的返回值来判断是否扫描进IOC容器。

package com.kun.config;

import java.io.IOException;

import org.springframework.core.io.Resource;
import org.springframework.core.type.AnnotationMetadata;
import org.springframework.core.type.ClassMetadata;
import org.springframework.core.type.classreading.MetadataReader;
import org.springframework.core.type.classreading.MetadataReaderFactory;
import org.springframework.core.type.filter.TypeFilter;

public class MyTypeFilter implements TypeFilter {

	/**
	 * metadataReader：读取到的当前正在扫描的类的信息
	 * metadataReaderFactory:可以获取到其他任何类信息的
	 */
	@Override
	public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory)
			throws IOException {
		// TODO Auto-generated method stub
		//获取当前类注解的信息
		AnnotationMetadata annotationMetadata = metadataReader.getAnnotationMetadata();
		//获取当前正在扫描的类的类信息
		ClassMetadata classMetadata = metadataReader.getClassMetadata();
		//获取当前类资源（类的路径）
		Resource resource = metadataReader.getResource();
		
		String className = classMetadata.getClassName();
		System.out.println("--->"+className);
		if(className.contains("er")){
			return true;
		}
		return false;
	}

}

三、@Scope设置组件的作用域

package com.kun.config;

import org.springframework.beans.factory.config.ConfigurableBeanFactory;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Conditional;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;
import org.springframework.context.annotation.Lazy;

import com.kun.bean.Color;
import com.kun.bean.ColorFactoryBean;
import com.kun.bean.Person;
import com.kun.bean.Red;
import com.kun.condition.LinuxCondition;
import com.kun.condition.MyImportBeanDefinitionRegistrar;
import com.kun.condition.MyImportSelector;
import com.kun.condition.WindowsCondition;

//类中组件统一设置。满足当前条件，这个类中配置的所有bean注册才能生效；
@Conditional({WindowsCondition.class})
@Configuration
@Import({Color.class,Red.class,MyImportSelector.class,MyImportBeanDefinitionRegistrar.class})
//@Import导入组件，id默认是组件的全类名
public class MainConfig2 {
	
	//默认是单实例的
	/**
	 * ConfigurableBeanFactory#SCOPE_PROTOTYPE    
	 * @see ConfigurableBeanFactory#SCOPE_SINGLETON  
	 * @see org.springframework.web.context.WebApplicationContext#SCOPE_REQUEST  request
	 * @see org.springframework.web.context.WebApplicationContext#SCOPE_SESSION	 sesssion
	 * @return\
	 * @Scope:调整作用域
	 * prototype：多实例的：ioc容器启动并不会去调用方法创建对象放在容器中。
	 * 					每次获取的时候才会调用方法创建对象；
	 * singleton：单实例的（默认值）：ioc容器启动会调用方法创建对象放到ioc容器中。
	 * 			以后每次获取就是直接从容器（map.get()）中拿，
	 * request：同一次请求创建一个实例
	 * session：同一个session创建一个实例
	 * 
	 * 懒加载：
	 * 		单实例bean：默认在容器启动的时候创建对象；
	 * 		懒加载：容器启动不创建对象。第一次使用(获取)Bean创建对象，并初始化；
	 * 
	 */
//	@Scope("prototype")
	@Bean("person")
	public Person person(){
		System.out.println("给容器中添加Person....");
		return new Person("张三", 25);
	}

}

　　关于@Scope注解没啥可说的，多一句嘴，只有无状态的Bean才可以在多线程环境下共享，在Spring中，绝大部分Bean都可以声明为singleton作用域。
那么对于有状态的bean呢？Spring对一些（如RequestContextHolder、TransactionSynchronizationManager、LocaleContextHolder等）中非线程安全状态的bean采用ThreadLocal进行处理，让它们也成为线程安全的状态，因此有状态的Bean就可以在多线程中共享了。默认Contrller也是单例模式，如果出现线程安全问题需要考虑controller中是否有全局的成员变量被多线程共享，或者将其改成多例模式。

四、@Lazy设置单例bean的懒加载

　　默认的多例bean在IOC容器启动时并不创建，只有在第一次使用(获取)Bean创建对象的时候新生成一个，如果想要单例bean也实现懒加载的策略，此时则需要@Lazy注解。

　　　　@Lazy
　　　　@Bean("person")
　　　　public Person person(){
	　　System.out.println("给容器中添加Person....");
	　　return new Person("张三", 25);
	}

五、@Conditional按照条件注册bean

　　@Conditional注解对类中组件统一设置。满足当前条件，这个类中配置的所有bean注册才能生效。该注解的value为自定义的条件类，该类实现

org.springframework.context.annotation.condition接口，复写其中的matches方法，根据方法的返回值来判断条件是否生效，以决定配置类是否生效。

package com.kun.config;


import org.springframework.context.annotation.Conditional;
import org.springframework.context.annotation.Configuration;

import com.kun.condition.WindowsCondition;

//类中组件统一设置。满足当前条件，这个类中配置的所有bean注册才能生效；
@Conditional({WindowsCondition.class})
@Configuration
public class MainConfig2 {

}

　　自定义的WindowsCondition类如下：

package com.kun.condition;

import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.core.env.Environment;
import org.springframework.core.type.AnnotatedTypeMetadata;

//判断是否windows系统
public class WindowsCondition implements Condition {

	@Override
	public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
		Environment environment = context.getEnvironment();
		String property = environment.getProperty("os.name");
		if(property.contains("Windows")){
			return true;
		}
		return false;
	}

}

六、@Import快速的给IOC容器注册一个组件

package com.kun.config;

import org.springframework.context.annotation.Configuration;

import com.kun.bean.Color;
import com.kun.bean.ColorFactoryBean;
import com.kun.bean.Person;
import com.kun.bean.Red;
import com.kun.condition.LinuxCondition;
import com.kun.condition.MyImportBeanDefinitionRegistrar;
import com.kun.condition.MyImportSelector;
import com.kun.condition.WindowsCondition;

@Configuration
@Import({Color.class,Red.class,MyImportSelector.class,MyImportBeanDefinitionRegistrar.class})
//@Import导入组件，id默认是组件的全类名
public class MainConfig2 {
	
}

　　另外，我们可以实现ImportSelector或者ImportBeanDefinitionRegistrar接口复写相应的方法注册指定的bean：

package com.kun.condition;

import org.springframework.context.annotation.ImportSelector;
import org.springframework.core.type.AnnotationMetadata;

//自定义逻辑返回需要导入的组件
public class MyImportSelector implements ImportSelector {

	//返回值，就是到导入到容器中的组件全类名
	//AnnotationMetadata:当前标注@Import注解的类的所有注解信息
	@Override
	public String[] selectImports(AnnotationMetadata importingClassMetadata) {
		// TODO Auto-generated method stub
		//importingClassMetadata
		//方法不要返回null值
		return new String[]{"com.kun.bean.Blue","com.kun.bean.Yellow"};
	}

}

　　

package com.kun.condition;

import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.RootBeanDefinition;
import org.springframework.context.annotation.ImportBeanDefinitionRegistrar;
import org.springframework.core.type.AnnotationMetadata;

import com.kun.bean.RainBow;

public class MyImportBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar {

	/**
	 * AnnotationMetadata：当前类的注解信息
	 * BeanDefinitionRegistry:BeanDefinition注册类；
	 * 		把所有需要添加到容器中的bean；调用
	 * 		BeanDefinitionRegistry.registerBeanDefinition手工注册进来
	 */
	@Override
	public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
		
		boolean definition = registry.containsBeanDefinition("com.kun.bean.Red");
		boolean definition2 = registry.containsBeanDefinition("com.kun.bean.Blue");
		if(definition && definition2){
			//指定Bean定义信息；（Bean的类型，Bean。。。）
			RootBeanDefinition beanDefinition = new RootBeanDefinition(RainBow.class);
			//注册一个Bean，指定bean名
			registry.registerBeanDefinition("rainBow", beanDefinition);
		}
	}

}

　　这两种方法任选其一即可，如果读过spring源码，那么一定对RootBeanDefinition类很熟悉，Spring通过BeanDefinition将配置文件中的配置信息转换为容器的内部表示，并将这些BeanDefiniton注册到BeanDefinitonRegistry中。Spring容器的BeanDefinitionRegistry就像是Spring配置信息的内存数据库，主要是以map的形式保存，后续操作直接从BeanDefinitionRegistry中读取配置信息。一般情况下，BeanDefinition只在容器启动时加载并解析，除非容器刷新或重启，这些信息不会发生变化，当然如果用户有特殊的需求，也可以通过编程的方式在运行期调整BeanDefinition的定义。因此，第二种方法更好理解一些。

　　最后别忘了通过@Import注解将我们自定义的选择器添加到配置类中，@Import({MyImportSelector.class,MyImportBeanDefinitionRegistrar.class})。

七、通过BeanFactory注册组件

　　实现org.springframework.beans.factory.FactoryBean接口，自定义一个BeanFactory。getObject()中返回的对象会被注册到IOC容器中。

package com.kun.bean;

import org.springframework.beans.factory.FactoryBean;

//创建一个Spring定义的FactoryBean
public class ColorFactoryBean implements FactoryBean<Color> {

	//返回一个Color对象，这个对象会添加到容器中
	@Override
	public Color getObject() throws Exception {
		// TODO Auto-generated method stub
		System.out.println("ColorFactoryBean...getObject...");
		return new Color();
	}

	@Override
	public Class<?> getObjectType() {
		// TODO Auto-generated method stub
		return Color.class;
	}

	//是单例？
	//true：这个bean是单实例，在容器中保存一份
	//false：多实例，每次获取都会创建一个新的bean；
	@Override
	public boolean isSingleton() {
		// TODO Auto-generated method stub
		return false;
	}

}

　　再通过@Bean注解将自定义的FactoryBean注册到IOC容器中。

package com.kun.config;

import org.springframework.beans.factory.config.ConfigurableBeanFactory;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;


import com.kun.bean.Color;
import com.kun.bean.ColorFactoryBean;
import com.kun.bean.Person;
import com.kun.bean.Red;


@Configuration
public class MainConfig2 {
	
	@Bean
	public ColorFactoryBean colorFactoryBean(){
		return new ColorFactoryBean();
	}
	
}

　　注意：默认获取到的是工厂bean调用getObject创建的对象，要获取工厂Bean本身，我们需要给id前面加一个&　　&colorFactoryBean

八、小结

　　给容器中注册组件

　　1）、包扫描+组件标注注解（@Controller/@Service/@Repository/@Component）[自己写的类]

　　2）、@Bean[导入的第三方包里面的组件]

　　3）、@Import[快速给容器中导入一个组件] 

　　　　1）、@Import(要导入到容器中的组件)；容器中就会自动注册这个组件，id默认是全类名

　　　　2）、ImportSelector:返回需要导入的组件的全类名数组；

　　　　3）、ImportBeanDefinitionRegistrar:手动注册bean到容器中

　　4）、使用Spring提供的 FactoryBean（工厂Bean）

　　　　1）、默认获取到的是工厂bean调用getObject创建的对象

　　　　2）、要获取工厂Bean本身，我们需要给id前面加一个&　　&colorFactoryBean