Bean 注册
注册Bean的常用注解有@Component、@Service、@Controller、@Repository,通过扫描包的方式对这些注解进行解析注册Bean。
注解ApplicationContext:AnnotationConfigApplicationContext
常用注解
@Configuration
声明Bean Difinition的配置文件,相当于一个xml文件
@Bean
<code>@Configuration
public class CustomConfig {
@Bean
public Person person() {
return new Person();
}
}
/<code>
相当于xml bean内容
<code><beans>
<bean>
/<beans>
/<code>
bean的名称默认为方法名称,也可以通过@Bean(value="person")或者@Bean("person")进行指定
@ComponentScan
指定扫描路径
<code>@Configuration
@ComponentScan("top.felixfly.spring.annotation")
public class ScanConfiguration {
}
/<code>
相当于xml component-scan
<code><beans>
<component-scan>
/<beans>
/<code>
@ComponentScans
多个扫描路径,值为ComponentScan的数组,1.8以后可以用多个@ComponentScan代替此注解
@Scope
指定Bean的作用域,默认为singleton
- singleton org.springframework.beans.factory.config.ConfigurableBeanFactory#SCOPE_SINGLETON
- prototype org.springframework.beans.factory.config.ConfigurableBeanFactory#SCOPE_PROTOTYPE
- request org.springframework.web.context.WebApplicationContext#SCOPE_REQUEST
- session org.springframework.web.context.WebApplicationContext#SCOPE_SESSION
<code>@Configuration
public class CustomConfig {
@Bean
@Scope("singleton")
public Person person() {
return new Person();
}
}
/<code>
相当于xml中bean中scope属性
<code><beans>
<bean>
/<beans>
/<code>
@Lazy
懒加载,针对singleton Bean进行懒加载,默认情况下单实例Bean直接加载
<code>@Configuration
public class CustomConfig {
@Bean
@Lazy
public Person person() {
return new Person();
}
}
/<code>
相当于xml中bean的lazy-init属性
<code><beans>
<bean>
/<beans>
/<code>
@DependsOn
依赖关系注解
<code>@Configuration
public class CustomConfig {
@Bean
@DependsOn("person")
public Manager manager(){
return new Manager();
}
@Bean
public Person person(){
return new Person();
}
}
/<code>
相当于xml中bean的depends-on属性
<code><beans>
<bean>
/<beans>
/<code>
@Order
Bean的排序,或者说是优先级,两个接口org.springframework.core.Ordered以及org.springframework.core.PriorityOrdered,主要使用优先级的内容
- org.springframework.beans.factory.config.BeanPostProcessor
- org.springframework.http.converter.HttpMessageConverter
@Conditional
条件装配Bean
- 实现org.springframework.context.annotation.Condition接口public class CustomCondition implements Condition { @Override public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) { // true 进行装配,false不进行装配 return false; } }
- Bean上配置@Conditional(Condition.class)@Configuration public class CustomConfig { @Conditional(CustomCondition.class) @Bean public Person person() { return new Person(); } }
当matches方法返回true的时候进行注册当前@Bean,否则不注册。该注解也可以放到配置类上,matches方法返回true的时候进行注册当前配置类,否侧不注册。
@Profile
环境注解,底层使用的是@Conditional
@Import
快捷注册Bean,默认名称为类的全路径
- 直接导入类@Configuration @Import(Person.class) public class CustomConfig { }
- 导入实现org.springframework.context.annotation.ImportSelector类public class CustomImportSelector implements ImportSelector { @Override public String[] selectImports(AnnotationMetadata annotationMetadata) { return new String[]{Person.class.getName()}; } } @Configuration @Import(CustomImportSelector.class) public class CustomConfig { }
- 导入实现org.springframework.context.annotation.ImportBeanDefinitionRegistrar类public class CustomImportBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar { @Override public void registerBeanDefinitions(AnnotationMetadata annotationMetadata, BeanDefinitionRegistry registry) { // 自行注册BeanDefinition RootBeanDefinition beanDefinition = new RootBeanDefinition(Person.class); registry.registerBeanDefinition("person",beanDefinition); } } @Configuration @Import(CustomImportBeanDefinitionRegistrar.class) public class CustomConfig { }
@ImportResource
导入资源xml文件
资源文件名称spring/application-spring.xml
<code><beans>
<bean>
<constructor-arg>
<constructor-arg>
/<bean>
/<beans>
/<code>
<code>@Configuration
@ImportResource("classpath:/spring/application-spring.xml")
public class CustomConfig {
}
/<code>
常见问题
@Configuration、其他注解与@Bean结合使用有什么不同
答:@Configuration注解使用的其实也是一个Bean,但本身是BeanFatory,是经过CGLIB进行增强的Bean,其他注解(@Component、@Service、@Controller、@Repository)使用的就是一个简单的Bean
Bean 依赖注入
常用注解
@Autowired
Spring自带的自动注入,注解的属性required来支持是否必须要进行依赖注入。根据以下规则进行查找进行注入
- 根据类型查找,只查询一个直接返回
- 根据名称查找
<code>@Service
public class PersonService {
@Autowired
private PersonMapper personMapper;
}
/<code>
可以结合以下注解进行使用
- @Qualifier指定名称进行依赖注入@Service public class PersonService { @Autowired @Qualifier("personMapper") private PersonMapper personMapper; }
- @Primary指定优先进行依赖注入@Service public class PersonService { @Autowired private PersonMapper personMapper; } @Configuration @ComponentScan({"top.felixfly.spring.annotation.mapper","top.felixfly.spring.annotation.service"}) public class CustomConfig { // 优先注入 @Bean("personMapper2") @Primary public PersonMapper personMapper(){ return new PersonMapper(); } }
只有一个有参构造器时,@Autowired可以省略,可以自动进行注入
@Resource
Java规范(JSR250)的注解,默认按照属性的名称进行依赖查找匹配,也可以用属性name进行强制指定,但不支持与@Primary注解结合使用和required是否必须要进行依赖注入
<code>@Service
public class PersonService {
@Resource
private PersonMapper personMapper;
}
@Service
public class PersonService {
\t// 强制指定Bean
@Resource(name="personMapper2")
private PersonMapper personMapper;
}
/<code>
@Inject
Java规范的注解(JSR330),功能与@Autowired一样,但不支持required是否必须要进行依赖注入。需要引入javax.inject
<code><dependency>
<groupid>javax.inject/<groupid>
<artifactid>javax.inject/<artifactid>
<version>1/<version>
/<dependency>
/<code>
<code>@Service
public class PersonService {
@Inject
private PersonMapper personMapper;
}
/<code>
注入方式
构造器注入
<code>@Configuration
public class AppConfig {
@Bean
public BeanOne beanOne() {
// 构造器注入
return new BeanOne(beanTwo());
}
@Bean
public BeanOne beanThree(BeanTwo beanTwo) {
// 构造器注入
return new BeanOne(beanTwo);
}
@Bean
public BeanTwo beanTwo() {
return new BeanTwo();
}
}
/<code>
Setter方法注入
<code>public class BeanTwo {
@Autowired
public void setBeanOne(BeanOne beanOne) {
this.beanOne = beanOne;
}
}
/<code>
Aware接口
自定义组件注入Spring底层的组件,比如ApplicationContext,这些Aware接口一般通过Processor进行处理。ApplicationContextAwareProcessor处理EnvironmentAware、EmbeddedValueResolverAware、ResourceLoaderAware、ApplicationEventPublisherAware、MessageSourceAware、ApplicationContextAware
ApplicationContextAwareApplicationContextApplicationEventPublisherAwareApplicationContext事件发布器BeanClassLoaderAware类加载器BeanFactoryAwareBean 工厂BeanNameAwareBean 名称BootstrapContextAwareBootstrapContextMessageSourceAware国际化管理NotificationPublisherAwareSpring JMX通知发布器ResourceLoaderAware资源加载器EmbeddedValueResolverAware@Value解析器EnvironmentAware环境变量
常见问题
循环依赖的问题
答:循环依赖的产生,BeanA依赖BeanB,BeanB依赖BeanC,而BeanC又依赖于BeanA,这时候就会产生循环依赖的问题,单例Bean中通过构造器注入会产生循环依赖的问题,会产生BeanCurrentlyInCreationException,通过Setter方法注入不会产生异常,可以解决循环依赖问题。原型@Bean通过Setter方法注入依然会产生BeanCurrentlyInCreationException,没办法解决循环依赖问题。
Bean 生命周期
Bean的生命周期包含实例化–>初始化–>销毁,单实例Bean实例化在容器创建的时候进行实例化以及初始化,销毁在容器关闭的时候进行调用;多实例Bean在获取Bean的时候进行实例化以及初始化,销毁需要自行进行调用。
初始化和销毁常用方法
- @Bean指定initMethod和destroyMethod@Configuration public class CustomConfig { @Bean(initMethod = "init",destroyMethod = "destroy") public Person person(){ return new Person(); } } 相当于xml中配置init-method和destroy-method属性<beans> <bean> /<beans>
- 实现InitializingBean和DisposableBeanpublic class Person implements InitializingBean, DisposableBean { public Person() { } @Override public void afterPropertiesSet () throws Exception { } @Override public void destroy() throws Exception { } }
- 使用@PostConstruct和@PreDestroy注解使用InitDestroyAnnotationBeanPostProcessor进行解析处理,父类CommonAnnotationBeanPostProcessorpublic class Person { public Person() { } @PostConstruct public void postConstruct(){ } @PreDestroy public void preDestroy(){ } }
BeanPostProcessor
- postProcessBeforeInitialization 初始化之前执行方法
- postProcessAfterInitialization 初始化之后执行方法
<code>public class CustomBeanPostProcessor implements BeanPostProcessor {
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
return bean;
}
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
return bean;
}
}
/<code>
<code>@Configuration
@Import(CustomBeanPostProcessor.class)
public class CustomConfig {
@Bean
public Person person(){
return new Person();
}
}
/<code>
执行方法若是返回null值,后续的BeanPostProcessor不会进行执行,源代码执行如下:
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory
<code>@Override
\tpublic Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
\t\t\tthrows BeansException {
\t\tObject result = existingBean;
\t\tfor (BeanPostProcessor processor : getBeanPostProcessors()) {
\t\t\tObject current = processor.postProcessBeforeInitialization(result, beanName);
\t\t\tif (current == null) {
\t\t\t\treturn result;
\t\t\t}
\t\t\tresult = current;
\t\t}
\t\treturn result;
\t}
\t@Override
\tpublic Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
\t\t\tthrows BeansException {
\t\tObject result = existingBean;
\t\tfor (BeanPostProcessor processor : getBeanPostProcessors()) {
\t\t\tObject current = processor.postProcessAfterInitialization(result, beanName);
\t\t\tif (current == null) {
\t\t\t\treturn result;
\t\t\t}
\t\t\tresult = current;
\t\t}
\t\treturn result;
\t}
/<code>
常见问题
生命周期执行方法顺序
答:初始化方法执行顺序
- @PostConstruct
- 实现InitializingBean接口的方法
- @Bean指定initMethod
销毁方法执行顺序
- @PreDestroy
- 实现DisposableBean接口的方法
- @Bean指定destroyMethod
Multiple lifecycle mechanisms configured for the same bean, with different initialization methods, are called as follows:
Methods annotated with @PostConstructafterPropertiesSet() as defined by the InitializingBean callback interfaceA custom configured init() method
Destroy methods are called in the same order:
Methods annotated with @PreDestroydestroy() as defined by the DisposableBean callback interfaceA custom configured destroy() method
资源属性赋值
常用注解
@Value
属性进行赋值,可以有如下三种写法
- 直接赋值public class Person { @Value("张三") private String name; }
- SpEL表达式 #{}public class Person { @Value("#{20-2}") private String age; }
- ${} 文件属性赋值(通常在环境变量Enviroment中),要配合@PropertySource使用public class Person { @Value("${person.age}") private String age; }
@PropertySource
引入配置文件,配置文件下根路径下person.properties
<code>@PropertySource("classpath:/person.properties")
public class CustomConfig {
}
/<code>
相当于xml中的context:property-placeholder
<code><property-placeholder>
/<code>
@PropertySources
多个配置文件引入,值为PropertySource的数组,1.8以后可以用多个@PropertySource代替此注解
常见问题
配置文件属性乱码
答:注解@PropertySource通过属性encoding进行配置文件编码,该配置在4.3版本引入;xml配置文件中通过属性file-encoding配置文件编码
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