创建Spring项目
若创建的是Java项目，向其加入Spring包；若创建的是Maven项目，添加如下依赖：
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
<version>5.1.9.RELEASE</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-beans</artifactId>
<version>5.1.9.RELEASE</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
<version>5.1.9.RELEASE</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-expression</artifactId>
<version>5.1.9.RELEASE</version>
</dependency>创建配置类
在类上加@Configuration注解，这个类就是配置类
@Configuration
public class BeanConfig {
}一、@Bean
public class Red {
}在配置类中，使用@Bean注解，注册Bean，把Red注册到容器中
@Configuration
public class BeanConfig {
@Bean
public Red red() {
return new Red();
}
}二、@Import
1.@Import(组件)
@Import(组件)，容器中就会自动注册这个组件
public class Green {
}配置类：
@Configuration
@Import({Green.class})
public class BeanConfig {
@Bean
public Red red() {
return new Red();
}
}2.ImportSelector
public class Blue {
}ColorImportSelector实现ImportSelector接口，返回需要导入的组件的全类名数组
// 自定义逻辑和需要导入的组件
public class ColorImportSelector implements ImportSelector {
// 返回值，就是要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) {
return new String[] {"com.example.entity.Blue"};
}
}配置类：
@Configuration
@Import({Green.class, ColorImportSelector.class})
public class BeanConfig {
@Bean
public Red red() {
return new Red();
}
}3.ImportBeanDefinitionRegistrar
public class Gray {
}ColorImportBeanDefinitionRegistrar实现ImportBeanDefinitionRegistrar接口，手动注册bean到容器中
public class ColorImportBeanDefinitionRegistrar 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) {
// 指定Bean定义信息（Bean的类型，Bean...）
RootBeanDefinition beanDefinition = new RootBeanDefinition(Gray.class);
// 注册一个Bean，指定bean名
registry.registerBeanDefinition("gray", beanDefinition);
}
}配置类：
@Configuration
@Import({Green.class, ColorImportSelector.class, ColorImportBeanDefinitionRegistrar.class})
public class BeanConfig {
@Bean
public Red red() {
return new Red();
}
}三、FactoryBean
public class Yellow {
}使用Spring提供的FactoryBean（工厂Bean），默认获取到工厂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&
public class ColorFactoryBean implements FactoryBean<Yellow> {
// 返回一个Yellow对象，这个对象会添加到容器中
@Override
public Yellow getObject() throws Exception {
return new Yellow();
}
@Override
public Class<?> getObjectType() {
return Yellow.class;
}
// 返回true，表示单实例
@Override
public boolean isSingleton() {
return true;
}
}配置类：
@Configuration
@Import({Green.class, ColorImportSelector.class, ColorImportBeanDefinitionRegistrar.class})
public class BeanConfig {
@Bean
public Red red() {
return new Red();
}
@Bean
public ColorFactoryBean colorFactoryBean(){
return new ColorFactoryBean();
}
}四、测试
public class MyMain {
public static void main(String[] args) {
ApplicationContext applicationContext = new AnnotationConfigApplicationContext(BeanConfig.class);
String[] definitionNames = applicationContext.getBeanDefinitionNames();
for (String name : definitionNames) {
Object bean = applicationContext.getBean(name);
System.out.println("- - -");
System.out.println("name: " + name);
System.out.println("bean: " + bean.getClass());
}
System.out.println("\n- - - - - -\n");
// 对于 FactoryBean
List<String> list = Arrays.asList("colorFactoryBean", "&colorFactoryBean");
for (String name : list) {
Object bean = applicationContext.getBean(name);
System.out.println("- - -");
System.out.println("name: " + name);
System.out.println("bean: " + bean.getClass());
}
}
}结果：
DefaultListableBeanFactory 的 Map<String, Object> singletonObjects 中记录：
key: colorFactoryBean
value: ColorFactoryBean
- - -
name: org.springframework.context.annotation.internalConfigurationAnnotationProcessor
bean: class org.springframework.context.annotation.ConfigurationClassPostProcessor
- - -
name: org.springframework.context.annotation.internalAutowiredAnnotationProcessor
bean: class org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor
- - -
name: org.springframework.context.annotation.internalCommonAnnotationProcessor
bean: class org.springframework.context.annotation.CommonAnnotationBeanPostProcessor
- - -
name: org.springframework.context.event.internalEventListenerProcessor
bean: class org.springframework.context.event.EventListenerMethodProcessor
- - -
name: org.springframework.context.event.internalEventListenerFactory
bean: class org.springframework.context.event.DefaultEventListenerFactory
- - -
name: beanConfig
bean: class com.example.config.BeanConfig$$EnhancerBySpringCGLIB$$eb0e8d2e
- - -
name: com.example.entity.Green
bean: class com.example.entity.Green
- - -
name: com.example.entity.Blue
bean: class com.example.entity.Blue
- - -
name: red
bean: class com.example.entity.Red
- - -
name: colorFactoryBean
bean: class com.example.entity.Yellow
- - -
name: gray
bean: class com.example.entity.Gray
- - - - - -
- - -
name: colorFactoryBean
bean: class com.example.entity.Yellow
- - -
name: &colorFactoryBean
bean: class com.example.config.ColorFactoryBean总结：
1.
@Configuration
public class BeanConfig {
}
生成
name: beanConfig
bean: class com.example.config.BeanConfig$$EnhancerBySpringCGLIB$$eb0e8d2e
2.
@Import({Green.class})
生成
name: com.example.entity.Green
bean: class com.example.entity.Green
3.
@Import({ColorImportSelector.class})
生成
name: com.example.entity.Blue
bean: class com.example.entity.Blue
4.
@Bean
public Red red() {
return new Red();
}
生成
name: red
bean: class com.example.entity.Red
5.
@Bean
public ColorFactoryBean colorFactoryBean(){
return new ColorFactoryBean();
}
生成
name: colorFactoryBean
bean: class com.example.entity.Yellow
name: &colorFactoryBean
bean: class com.example.config.ColorFactoryBean
6.
@Import({ColorImportBeanDefinitionRegistrar.class})
name: gray
bean: class com.example.entity.Gray