Spring笔记-@Order注解和Ordered接口解析

目录

• @Order注解和Ordered接口
• 1.OrderUtils
• 2.Ordered接口
• 3.OrderComparator
• 4.AnnotationAwareOrderComparator
• 5.Bean注册顺序
• Spring的Orderd接口及@Order,@Primary,@Priority三个注解介绍
• 1.如何发现Orderd接口及@Order、@Primary、@Priority
• 2.Orderd、@Order、@Priority、@Primary
• 3.测试

@Order注解和Ordered接口

Order注解用于排序

public @interface Order {
 
    /**
     * The order value.
     * 
Default is {@link Ordered#LOWEST_PRECEDENCE}.
     * @see Ordered#getOrder()
     */
    int value() default Ordered.LOWEST_PRECEDENCE;
 
}

1.OrderUtils

Spring提供了OrderUtils来获取Class的Order注解排序信息

扩展：Priority注解为javax扩展注解,功能与Order相同

public class OrderUtilsTests {
 
    @Test
    public void getSimpleOrder() {
        assertEquals(Integer.valueOf(50), OrderUtils.getOrder(SimpleOrder.class, null));
    }
 
    @Test
    public void getPriorityOrder() {
        assertEquals(Integer.valueOf(55), OrderUtils.getOrder(SimplePriority.class, null));
    }
 
    @Order(50)
    private static class SimpleOrder {}
 
    @Priority(55)
    private static class SimplePriority {}
}

2.Ordered接口

对象排序的另一种实现

public interface Ordered {
    int getOrder();
}

3.OrderComparator

使用OrderComparator来比较2个对象的排序顺序

public final class OrderComparatorTests {
 
    private final OrderComparator comparator = new OrderComparator();
 
    @Test
    public void compareOrderedInstancesBefore() {
        assertEquals(-1, this.comparator.compare(
                new StubOrdered(100), new StubOrdered(2000)));
    }
 
    @Test
    public void compareOrderedInstancesSame() {
        assertEquals(0, this.comparator.compare(
                new StubOrdered(100), new StubOrdered(100)));
    }
 
    @Test
    public void compareOrderedInstancesAfter() {
        assertEquals(1, this.comparator.compare(
                new StubOrdered(982300), new StubOrdered(100)));
    }
 
    private static final class StubOrdered implements Ordered {
 
        private final int order;
 
        public StubOrdered(int order) {
            this.order = order;
        }
 
        @Override
        public int getOrder() {
            return this.order;
        }
    }
 
}

其内部比较逻辑

return (i1 < i2) ? -1 : (i1 > i2) ? 1 : 0;

• i1比i2小则返回-1
• i1比i2大则返回1
• i1等于i2则返回0

4.AnnotationAwareOrderComparator

AnnotationAwareOrderComparator继承自OrderComparator

其可以同时处理对象实现Ordered接口或@Order注解

其提供了静态方法sort,可以对List进行排序

public class AnnotationAwareOrderComparator extends OrderComparator {
}

测试代码

public class AnnotationAwareOrderComparatorTests {
 
    @Test
    public void sortInstances() {
        List