spring提供了一个基于条件创建bean的注解@Conditional。
@Conditional注解定义:
//1.可作用于类(接口)、方法上
@Target({
ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Conditional {
//2.需要传入Condition类型的参数(继承Condition接口)
Class<? extends Condition>[] value();
}
@Conditional注解使用:
1、定义一个类实现Condition接口,返回true则会创建bean,false则不会创建
public class MyCondition implements Condition {
@Override
public boolean matches(ConditionContext conditionContext, AnnotatedTypeMetadata annotatedTypeMetadata) {
return true;
}
}
2,定义java配置类
@Configuration
public class BeanConfig {
@Bean
@Conditional({
MyCondition.class})
public User user(){
User user = new User();
user.setName("小明");
return user;
}
}
3、获取bean
@Test
public void test(){
AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(BeanConfig.class);
//获取bean,如果MyCondition返回flase则会报NoSuchBeanDefinitionException,注解注入@Autowired(required = false)
User u = (User) context.getBean("user");
System.out.println(u.toString());
}
@Conditional注解常用子注解: springboot封装conditional注解,在包org.springframework.boot.autoconfigure.condition下。
1、ConditionalOnProperty :当配置文件熟悉值与注解配置的值一致时才会创建bean。prefix配置文件的前缀,name字段名,havingValue字段值
//当配置文件 user.enable=1时才会创建bean,否则不会创建
@ConditionalOnProperty(prefix = "user", name = "enable",havingValue = "1")
@Bean
public User user(){
User user = new User();
user.setName("name");
return user;
}
2、ConditionalOnBean 和 ConditionalOnMissingBean:当某一个bean存在或不存在时才会创建bean。
@Bean
public Dept dept(){
return new Dept();
}
/**
* ConditionalOnBean 和 ConditionalOnMissingBean 跟bean的创建顺序有关,
* 如果先创建了则ConditionalOnBean修饰的bean被创建,后创建传入的bean类型则ConditionalOnMissingBean修饰的bean被创建
* @return
*/
@ConditionalOnBean(Dept.class)
@Bean
public User user(){
User user = new User();
user.setName("name");
return user;
}
@ConditionalOnMissingBean(Dept.class)
@Bean
public User user1(){
User user = new User();
user.setName("name-1");
return user;
}
3、ConditionalOnExpression:多个条件判断,满足则创建bean,可以用and 和 or。
/**
* 多个条件判断
* @return
*/
//@ConditionalOnExpression("'${user.enable}' == '1' and '${user.open}' == '2'")
@ConditionalOnExpression("'${user.enable}' == '1' or '${user.open}' == '2'")
@Bean
public User user(){
User user = new User();
user.setName("name");
return user;
}