Spring 注解编程IOC
强烈推介IDEA2020.2破解激活,IntelliJ IDEA 注册码,2020.2 IDEA 激活码
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
@Configuration 声明Bean Difinition的配置文件,相当于一个xml文件
@Bean 声明Bean的组件
@Configuration
public class CustomConfig {
@Bean
public Person person() {
return new Person();
}
}
相当于xml bean内容
<beans>
<bean id="person" class="top.felixfly.entity.Person"/>
</beans>
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
@Configuration
@ComponentScan("top.felixfly.spring.annotation")
public class ScanConfiguration {
}
相当于xml component-scan
<beans>
<context:component-scan package="top.felixfly.spring.annotation"/>
</beans>
@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
@Configuration
public class CustomConfig {
@Bean
@Scope("singleton")
public Person person() {
return new Person();
}
}
相当于xml中bean中scope属性
<beans>
<bean id="person" class="top.felixfly.entity.Person" scope="singleton"/>
</beans>
@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
@Configuration
public class CustomConfig {
@Bean
@Lazy
public Person person() {
return new Person();
}
}
相当于xml中bean的lazy-init属性
<beans>
<bean id="person" class="top.felixfly.entity.Person" lazy-init="true"/>
</beans>
@DependsOn
依赖关系注解
@Configuration
public class CustomConfig {
@Bean
@DependsOn("person")
public Manager manager(){
return new Manager();
}
@Bean
public Person person(){
return new Person();
}
}
相当于xml中bean的depends-on属性
<beans>
<bean id="manager" class="top.felixfly.entity.Manager" depends-on="person"/>
</beans>
@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
@Conditional 条件装配Bean
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;
}
}
@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
@Configuration
@Import(Person.class)
public class CustomConfig {
}
public class CustomImportSelector implements ImportSelector {
@Override
public String[] selectImports(AnnotationMetadata annotationMetadata) {
return new String[]{Person.class.getName()};
}
}
@Configuration
@Import(CustomImportSelector.class)
public class CustomConfig {
}
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
<beans>
<bean class="top.felixfly.spring.annotation.entity.Person">
<constructor-arg index="0" value="张三"/>
<constructor-arg index="1" value="27"/>
</bean>
</beans>
@Configuration
@ImportResource("classpath:/spring/application-spring.xml")
public class CustomConfig {
}
@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
@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
1、 根据类型查找,只查询一个直接返回
2、 根据名称查找
@Service
public class PersonService {
@Autowired
private PersonMapper personMapper;
}
可以结合以下注解进行使用
指定名称进行依赖注入
@Service
public class PersonService {
@Autowired
@Qualifier("personMapper")
private PersonMapper personMapper;
}
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
@Service
public class PersonService {
@Resource
private PersonMapper personMapper;
}
@Service
public class PersonService {
// 强制指定Bean
@Resource(name="personMapper2")
private PersonMapper personMapper;
}
@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
<dependency>
<groupId>javax.inject</groupId>
<artifactId>javax.inject</artifactId>
<version>1</version>
</dependency>
@Service
public class PersonService {
@Inject
private PersonMapper personMapper;
}
@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();
}
}
Setter方法注入
public class BeanTwo {
@Autowired
public void setBeanOne(BeanOne beanOne) {
this.beanOne = beanOne;
}
}
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
ApplicationContextAware | ApplicationContext |
---|---|
ApplicationEventPublisherAware | ApplicationContext事件发布器 |
BeanClassLoaderAware | 类加载器 |
BeanFactoryAware | Bean 工厂 |
BeanNameAware | Bean 名称 |
BootstrapContextAware | BootstrapContext |
MessageSourceAware | 国际化管理 |
NotificationPublisherAware Spring | JMX通知发布器 |
ResourceLoaderAware | 资源加载器 |
EmbeddedValueResolverAware | @Value解析器 |
EnvironmentAware | 环境变量 |
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。
@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 class="top.felixfly.spring.annotation.entity.Person" init-method="init" destroy-method="destroy"/>
</beans>
public class Person implements InitializingBean, DisposableBean {
public Person() {
}
@Override
public void afterPropertiesSet() throws Exception {
}
@Override
public void destroy() throws Exception {
}
}
注解使用InitDestroyAnnotationBeanPostProcessor进行解析处理,父类CommonAnnotationBeanPostProcessor
public class Person {
public Person() {
}
@PostConstruct
public void postConstruct(){
}
@PreDestroy
public void preDestroy(){
}
}
BeanPostProcessor
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;
}
}
@Configuration
@Import(CustomBeanPostProcessor.class)
public class CustomConfig {
@Bean
public Person person(){
return new Person();
}
}
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
@Override
public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
throws BeansException {
Object result = existingBean;
for (BeanPostProcessor processor : getBeanPostProcessors()) {
Object current = processor.postProcessBeforeInitialization(result, beanName);
if (current == null) {
return result;
}
result = current;
}
return result;
}
@Override
public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
throws BeansException {
Object result = existingBean;
for (BeanPostProcessor processor : getBeanPostProcessors()) {
Object current = processor.postProcessAfterInitialization(result, beanName);
if (current == null) {
return result;
}
result = current;
}
return result;
}
答:初始化方法执行顺序
销毁方法执行顺序
Multiple lifecycle mechanisms configured for the same bean, with different initialization methods, are called as follows:
Destroy methods are called in the same order:
@Value
属性进行赋值,可以有如下三种写法
public class Person {
@Value("张三")
private String name;
}
public class Person {
@Value("#{20-2}")
private String age;
}
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
@PropertySource("classpath:/person.properties")
public class CustomConfig {
}
相当于xml中的context:property-placeholder
<context:property-placeholder location="classpath:person.properties"/>
@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
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
原文链接:https://gper.club/articles/7e7e7f7ff7g5fgccg67