Spring @Order注解详解

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