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