注解@Order的作用是定义Spring容器加载Bean的顺序。
源码
@Retention(RetentionPolicy.RUNTIME)@Target({ElementType.TYPE,ElementType.METHOD,ElementType.FIELD})@Documentedpublic@interfaceOrder{/**
* The order value.
* <p>Default is {@link Ordered#LOWEST_PRECEDENCE}.
* @see Ordered#getOrder()
*/intvalue()defaultOrdered.LOWEST_PRECEDENCE;}
publicinterfaceOrdered{/**
* Useful constant for the highest precedence value.
* @see java.lang.Integer#MIN_VALUE
*/int HIGHEST_PRECEDENCE=Integer.MIN_VALUE;/**
* Useful constant for the lowest precedence value.
* @see java.lang.Integer#MAX_VALUE
*/int LOWEST_PRECEDENCE=Integer.MAX_VALUE;/**
* Get the order value of this object.
* <p>Higher values are interpreted as lower priority. As a consequence,
* the object with the lowest value has the highest priority (somewhat
* analogous to Servlet {@code load-on-startup} values).
* <p>Same order values will result in arbitrary sort positions for the
* affected objects.
* @return the order value
* @see #HIGHEST_PRECEDENCE
* @see #LOWEST_PRECEDENCE
*/intgetOrder();}
通过源码解读,我们可以得到以下结论:
- 注解可以作用在类、方法、字段声明(包括枚举常量)
- 注解有一个int类型的参数,可以不传,默认是最低优先级
- 通过常量类的值我们可以推测参数值越小优先级越高;
案例
创建三个pojo类Cat1, Cat2, Cat3,使用@Component注解将其交给Spring容器自动加载,每个类分别加上@Order(1), @Order(2), @Order(3)注解。
@Component@Order(1)publicclassCat1{publicCat1(){System.out.println("Order:1");}}@Component@Order(2)publicclassCat2{publicCat2(){System.out.println("Order:2");}}@Component@Order(3)publicclassCat3{publicCat3(){System.out.println("Order:3");}}
然后启动启动类观察控制台信息输出