巧用Spring中的@Order進行排序

更新時間：2022年08月17日 14:59:47 作者：Jon Kee

這篇文章主要介紹了巧用Spring中的@Order進行排序，具有很好的參考價值，希望對大家有所幫助。如有錯誤或未考慮完全的地方，望不吝賜教

Spring @Order進行排序

直接上代碼

public class OrderAnnotationTest {
?? ?public static void main(String[] args) {
?? ??? ?A a = new A();
?? ??? ?B b = new B();
?? ??? ?C c = new C();
?? ??? ?List<Object> orderList = new ArrayList<>(3);
?? ??? ?orderList.add(a);
?? ??? ?orderList.add(b);
?? ??? ?orderList.add(c);
?? ??? ?orderList.sort(AnnotationAwareOrderComparator.INSTANCE);
?? ??? ?System.out.println(orderList);
?? ?}
?? ?@Order(0)
?? ?static class A {
?? ??? ?@Override
?? ??? ?public String toString() {
?? ??? ??? ?return "A";
?? ??? ?}
?? ?}
?? ?@Order(-1)
?? ?static class B {
?? ??? ?@Override
?? ??? ?public String toString() {
?? ??? ??? ?return "B";
?? ??? ?}
?? ?}
?? ?@Order(2)
?? ?static class C {
?? ??? ?@Override
?? ??? ?public String toString() {
?? ??? ??? ?return "C";
?? ??? ?}
?? ?}
}

結(jié)果如下：

[B, A, C]

原理解析：

AnnotationAwareOrderComparator繼承自O(shè)rderComparator

實際比較的方法如下

private int doCompare(@Nullable Object o1, @Nullable Object o2, @Nullable OrderSourceProvider sourceProvider) {
?? ?boolean p1 = (o1 instanceof PriorityOrdered);
?? ?boolean p2 = (o2 instanceof PriorityOrdered);
?? ?if (p1 && !p2) {
?? ??? ?return -1;
?? ?}
?? ?else if (p2 && !p1) {
?? ??? ?return 1;
?? ?}
?? ?int i1 = getOrder(o1, sourceProvider);
?? ?int i2 = getOrder(o2, sourceProvider);
?? ?return Integer.compare(i1, i2);
}

Spring中關(guān)于Order的那點事

本文閱讀源碼版本為spring5.3.1

為啥要用Order

spring是一個大量使用策略設(shè)計模式的框架，這意味著有很多相同接口的實現(xiàn)類，如果不手動指定順序的話，那么使用時肯定會有問題。而Order給我們提供了一種編碼設(shè)置順序的可能。

關(guān)于Order

spring中提供了多種方式來設(shè)置優(yōu)先級，有Ordered，PriorityOrdered接口，有Order注解，除此之外，spring4.1以后，還可以使用Priority注解。下面我將針對這幾種用法從源碼的角度來進行分析。

Ordered，PriorityOrdered接口

public interface Ordered {
?? ?/**
?? ? * 最高優(yōu)先值
?? ? */
?? ?int HIGHEST_PRECEDENCE = Integer.MIN_VALUE;
?? ?/**
?? ? * 最低優(yōu)先值
?? ? */
?? ?int LOWEST_PRECEDENCE = Integer.MAX_VALUE;
?? ?int getOrder();
}

PriorityOrdered繼承了Ordered，但并未提供任何方法，這是一個標(biāo)記了優(yōu)先級的接口，和Ordered相比，PriorityOrdered就是高人一等，spring中提供了比較器OrderComparator，可以通過構(gòu)建一個OrderComparator，調(diào)用其compare方法，不過OrderComparator提供了一個靜態(tài)sort方法，我們無需自己構(gòu)建OrderComparator了，排序的結(jié)果按照order值從小到大排序。

demo

public class OrderDemo{
?? ?private final OrderComparator comparator = new OrderComparator();
?? ?@Test
? ? void comparePriorityOrderedInstanceToStandardOrderedInstanceWithSamePriority() {
? ? ? ? assertThatPriorityOrderedAlwaysWins(new StubPriorityOrdered(100), new StubOrdered(100));
? ? }
? ? @Test
? ? void comparePriorityOrderedInstanceToStandardOrderedInstanceWithLowerPriority() {
? ? ? ? assertThatPriorityOrderedAlwaysWins(new StubPriorityOrdered(100), new StubOrdered(200));
? ? }
?? ?
?? ?@Test
? ? void compareOrderedInstancesBefore() {
? ? ? ? assertThat(this.comparator.compare(new StubOrdered(100), new StubOrdered(2000))).isEqualTo(-1);
? ? }
? ? @Test
? ? void compareOrderedInstancesNullFirst() {
? ? ? ? assertThat(this.comparator.compare(null, new StubOrdered(100))).isEqualTo(1);
? ? }
? ? @Test
? ? void compareOrderedInstancesNullLast() {
? ? ? ? assertThat(this.comparator.compare(new StubOrdered(100), null)).isEqualTo(-1);
? ? }
?? ?@Test
? ? void test1() {
? ? ? ? assertThat(this.comparator.compare(new Object (), new StubOrdered(2000))).isEqualTo(1);
? ? }
?? ? private static class StubOrdered implements Ordered {
? ? ? ? private final int order;
? ? ? ? StubOrdered(int order) {
? ? ? ? ? ? this.order = order;
? ? ? ? }
? ? ? ? @Override
? ? ? ? public int getOrder() {
? ? ? ? ? ? return this.order;
? ? ? ? }
? ? }
? ? private static class StubPriorityOrdered implements PriorityOrdered {
? ? ? ? private final int order;
? ? ? ? StubPriorityOrdered(int order) {
? ? ? ? ? ? this.order = order;
? ? ? ? }
? ? ? ? @Override
? ? ? ? public int getOrder() {
? ? ? ? ? ? return this.order;
? ? ? ? }
? ? }
}

小結(jié)

PriorityOrdered優(yōu)先級比Ordered高，與設(shè)置的order值無關(guān)。
若兩個對象都實現(xiàn)了Ordered或PriorityOrdered接口，那么設(shè)置的order值越小，優(yōu)先值越高。
若沒有實現(xiàn)Ordered或PriorityOrdered接口，默認是最低的優(yōu)先級。

OrderComparator#compare解讀

在看compare之前，我覺得將OrderSourceProvider這個函數(shù)式接口放在前面講解一下，閱讀源碼時會更清晰一點。

?? ?@FunctionalInterface
?? ?public interface OrderSourceProvider {
?? ??? ?/**
?? ??? ? * 對給定對象校驗并返回一個新的對象
?? ??? ? */
?? ??? ?@Nullable
?? ??? ?Object getOrderSource(Object obj);
?? ?}

demo

public class OrderDemo{
?? ?private final OrderComparator comparator = new OrderComparator();
?? ?private static class TestSourceProvider implements OrderComparator.OrderSourceProvider {
?? ??? ?private final Object target;
?? ??? ?private final Object orderSource;
?? ??? ?TestSourceProvider(Object target, Object orderSource) {
?? ??? ??? ?this.target = target;
?? ??? ??? ?this.orderSource = orderSource;
?? ??? ?}
?? ??? ?@Override
?? ??? ?public Object getOrderSource(Object obj) {
?? ??? ??? ?if (target.equals(obj)) {
?? ??? ??? ??? ?return orderSource;
?? ??? ??? ?}
?? ??? ??? ?return null;
?? ??? ?}
?? ?}
?? ?@Test
?? ?void compareWithSourceProviderArray() {
?? ??? ?Comparator<Object> customComparator = this.comparator.withSourceProvider(
?? ??? ??? ??? ?new TestSourceProvider(5L, new Object[] {new StubOrdered(10), new StubOrdered(-25)}));
?? ??? ?assertThat(customComparator.compare(5L, new Object())).isEqualTo(-1);
?? ?}
?? ?@Test
?? ?void compareWithSourceProviderArrayNoMatch() {
?? ??? ?Comparator<Object> customComparator = this.comparator.withSourceProvider(
?? ??? ??? ??? ?new TestSourceProvider(5L, new Object[] {new Object(), new Object()}));
?? ??? ?assertThat(customComparator.compare(new Object(), 5L)).isEqualTo(0);
?? ?}
?? ?@Test
?? ?void compareWithSourceProviderEmpty() {
?? ??? ?Comparator<Object> customComparator = this.comparator.withSourceProvider(
?? ??? ??? ??? ?new TestSourceProvider(50L, new Object()));
?? ??? ?assertThat(customComparator.compare(new Object(), 5L)).isEqualTo(0);
?? ?}
}

接下來我們來閱讀compare源碼。

?? ?public int compare(@Nullable Object o1, @Nullable Object o2) {
?? ??? ?return doCompare(o1, o2, null);
?? ?}
?? ?private int doCompare(@Nullable Object o1, @Nullable Object o2, @Nullable OrderSourceProvider sourceProvider) {
?? ??? ?// 這里會判斷是否實現(xiàn)了PriorityOrdered接口
?? ??? ?boolean p1 = (o1 instanceof PriorityOrdered);
?? ??? ?boolean p2 = (o2 instanceof PriorityOrdered);
?? ??? ?// 這里會看到根本沒有比較order的值，只要實現(xiàn)PriorityOrdered接口,就會排在前面
?? ??? ?if (p1 && !p2) {
?? ??? ??? ?return -1;
?? ??? ?}else if (p2 && !p1) {
?? ??? ??? ?return 1;
?? ??? ?}
?? ??? ?// 獲取對象設(shè)置的order值
?? ??? ?int i1 = getOrder(o1, sourceProvider);
?? ??? ?int i2 = getOrder(o2, sourceProvider);
?? ??? ?return Integer.compare(i1, i2);
?? ?}
?? ?
?? ?private int getOrder(@Nullable Object obj, @Nullable OrderSourceProvider sourceProvider) {
?? ??? ?Integer order = null;
?? ??? ?if (obj != null && sourceProvider != null) {
?? ??? ??? ?Object orderSource = sourceProvider.getOrderSource(obj);
?? ??? ??? ?if (orderSource != null) {
?? ??? ??? ??? ?// 如果返回的是數(shù)組
?? ??? ??? ??? ?if (orderSource.getClass().isArray()) {
?? ??? ??? ??? ??? ?for (Object source : ObjectUtils.toObjectArray(orderSource)) {
?? ??? ??? ??? ??? ??? ?// 只要找到對象設(shè)置的order值，就跳出
?? ??? ??? ??? ??? ??? ?order = findOrder(source);
?? ??? ??? ??? ??? ??? ?if (order != null) {
?? ??? ??? ??? ??? ??? ??? ?break;
?? ??? ??? ??? ??? ??? ?}
?? ??? ??? ??? ??? ?}
?? ??? ??? ??? ?}else {
?? ??? ??? ??? ??? ?order = findOrder(orderSource);
?? ??? ??? ??? ?}
?? ??? ??? ?}
?? ??? ?}
?? ??? ?// 如果我們沒有提供OrderSourceProvider?
?? ??? ?return (order != null ? order : getOrder(obj));
?? ?}
?? ?protected int getOrder(@Nullable Object obj) {
?? ??? ?if (obj != null) {
?? ??? ??? ?Integer order = findOrder(obj);
?? ??? ??? ?if (order != null) {
?? ??? ??? ??? ?return order;
?? ??? ??? ?}
?? ??? ?}
?? ??? ?// object為null時，返回值最大
?? ??? ?return Ordered.LOWEST_PRECEDENCE;
?? ?}
?? ?protected Integer findOrder(Object obj) {
?? ??? ?// 沒有實現(xiàn)Ordered接口將返回null
?? ??? ?return (obj instanceof Ordered ? ((Ordered) obj).getOrder() : null);
?? ?}

@Order與@Priority

spring中提供了對@Order與@Priority支持的比較器AnnotationAwareOrderComparator，該類繼承OrderComparator，并覆蓋了findOrder方法，我們來一起看下源碼。

?? ?protected Integer findOrder(Object obj) {
?? ??? ?Integer order = super.findOrder(obj);
?? ??? ?if (order != null) {
?? ??? ??? ?return order;
?? ??? ?}
?? ??? ?// 調(diào)用父類的findOrder方法無法找到設(shè)定的order值時
?? ??? ?return findOrderFromAnnotation(obj);
?? ?}
?? ?
?? ?private Integer findOrderFromAnnotation(Object obj) {
?? ??? ?AnnotatedElement element = (obj instanceof AnnotatedElement ? (AnnotatedElement) obj : obj.getClass());
?? ??? ?// 對整個類型層次結(jié)構(gòu)執(zhí)行完整搜索,包括父類和接口
?? ??? ?MergedAnnotations annotations = MergedAnnotations.from(element, SearchStrategy.TYPE_HIERARCHY);
?? ??? ?// 獲取注解中設(shè)置的order值
?? ??? ?Integer order = OrderUtils.getOrderFromAnnotations(element, annotations);
?? ??? ?if (order == null && obj instanceof DecoratingProxy) {
?? ??? ??? ?return findOrderFromAnnotation(((DecoratingProxy) obj).getDecoratedClass());
?? ??? ?}
?? ??? ?return order;
?? ?}
?? ?
?? ?static Integer getOrderFromAnnotations(AnnotatedElement element, MergedAnnotations annotations) {
?? ??? ?if (!(element instanceof Class)) {
?? ??? ??? ?return findOrder(annotations);
?? ??? ?}
?? ??? ?// 加入緩存中
?? ??? ?Object cached = orderCache.get(element);
?? ??? ?if (cached != null) {
?? ??? ??? ?return (cached instanceof Integer ? (Integer) cached : null);
?? ??? ?}
?? ??? ?Integer result = findOrder(annotations);
?? ??? ?orderCache.put(element, result != null ? result : NOT_ANNOTATED);
?? ??? ?return result;
?? ?}
?? ?
?? ?// 沒有找到Order注解后才去尋找@Priority注解
?? ?private static Integer findOrder(MergedAnnotations annotations) {
?? ??? ?MergedAnnotation<Order> orderAnnotation = annotations.get(Order.class);
?? ??? ?if (orderAnnotation.isPresent()) {
?? ??? ??? ?return orderAnnotation.getInt(MergedAnnotation.VALUE);
?? ??? ?}
?? ??? ?MergedAnnotation<?> priorityAnnotation = annotations.get(JAVAX_PRIORITY_ANNOTATION);
?? ??? ?if (priorityAnnotation.isPresent()) {
?? ??? ??? ?return priorityAnnotation.getInt(MergedAnnotation.VALUE);
?? ??? ?}
?? ??? ?return null;
?? ?}

demo

public class AnnotationAwareOrderComparatorTests {
?? ?@Test
?? ?void sortInstancesWithSubclass() {
?? ??? ?List<Object> list = new ArrayList<>();
?? ??? ?list.add(new B());
?? ??? ?list.add(new C());
?? ??? ?AnnotationAwareOrderComparator.sort(list);
?? ??? ?assertThat(list.get(0) instanceof C).isTrue();
?? ??? ?assertThat(list.get(1) instanceof B).isTrue();
?? ?}
?? ?@Test
?? ?void sortInstancesWithOrderAndPriority() {
?? ??? ?List<Object> list = new ArrayList<>();
?? ??? ?list.add(new B());
?? ??? ?list.add(new A2());
?? ??? ?AnnotationAwareOrderComparator.sort(list);
?? ??? ?assertThat(list.get(0) instanceof A2).isTrue();
?? ??? ?assertThat(list.get(1) instanceof B).isTrue();
?? ?}
?? ?
?? ?@Order(1)
?? ?private static class A {
?? ?}
?? ?@Order(2)
?? ?private static class B {
?? ?}
?? ?
?? ?private static class C extends A {
?? ?}
?? ?@Priority(1)
?? ?private static class A2 {
?? ?}
}

小結(jié)

@Order與@Priority注解放置在類，接口或參數(shù)上，可以被繼承；它們之間是可以互相替換的關(guān)系。

應(yīng)用

spring源碼中有很多地方都顯式的調(diào)用AnnotationAwareOrderComparator的sort方法，也有一些地方調(diào)用的OrderComparator的sort方法，大家自己可以找找看。

我這里發(fā)現(xiàn)了一點有意思的地方，我們?nèi)绻x多個ControllerAdvice的bean，分別通過實現(xiàn)Ordered，PriorityOrdered接口來定義執(zhí)行時的順序，會發(fā)現(xiàn)上面我們總結(jié)的 PriorityOrdered優(yōu)先級就是比Ordered高這一點不成立，其實只是spring將ControllerAdvice相關(guān)信息封裝了一下欺騙了我們。我看的源碼的版本是5.3.1，低于5.2版本的不會發(fā)生這樣的事情。這里我們就來看看5.2版本前后源碼有哪些變化，導(dǎo)致了這個現(xiàn)象的發(fā)生。

這里就拿RequestMappingHandlerAdapter初始化去尋找ControllerAdvice注解的代碼來舉例

?? ?private void initControllerAdviceCache() {
?? ??? ?if (getApplicationContext() == null) {
?? ??? ??? ?return;
?? ??? ?}
?? ??? ?List<ControllerAdviceBean> adviceBeans = ControllerAdviceBean.findAnnotatedBeans(getApplicationContext());
?? ??? ?// 5.2版本前使用下面注釋的這行代碼，5.2之后這行代碼就去掉了，而是在上面findAnnotatedBeans
?? ??? ?// 方法中使用OrderComparator.sort(adviceBeans)
?? ??? ?//AnnotationAwareOrderComparator.sort(adviceBeans);
?? ??? ?...
?? ?}

我們知道OrderComparator適用范圍是比AnnotationAwareOrderComparator要窄一點的，它不支持注解，那么上面這樣的改動是不是就意味著我們定義ControllerAdvice時，就不能使用@Order與@Pri-ority呢？

其實它是支持的，ControllerAdviceBean#findAnnotatedBeans方法中會將我們定義的Con-trollerAdvice類包裝成ControllerAdviceBean,而ControllerAdviceBean是實現(xiàn)了Ordered接口的，那么OrderComparator#sort方法要想支持使用注解，ControllerAdviceBean的getOrder方法中就必須干點啥，分析了挺多，我們還是看源碼實現(xiàn)吧。

?? ?// 5.2版本后
?? ?public int getOrder() {
?? ??? ?if (this.order == null) {
?? ??? ??? ?String beanName = null;
?? ??? ??? ?Object resolvedBean = null;
?? ??? ??? ?// 這里根據(jù)beanName獲取bean
?? ??? ??? ?if (this.beanFactory != null && this.beanOrName instanceof String) {
?? ??? ??? ??? ?beanName = (String) this.beanOrName;
?? ??? ??? ??? ?String targetBeanName = ScopedProxyUtils.getTargetBeanName(beanName);
?? ??? ??? ??? ?boolean isScopedProxy = this.beanFactory.containsBean(targetBeanName);
?? ??? ??? ??? ?if (!isScopedProxy && !ScopedProxyUtils.isScopedTarget(beanName)) {
?? ??? ??? ??? ??? ?resolvedBean = resolveBean();
?? ??? ??? ??? ?}
?? ??? ??? ?}else {
?? ??? ??? ??? ?resolvedBean = resolveBean();
?? ??? ??? ?}
?? ??? ??? ?// 這里只判斷了是否實現(xiàn)了Ordered接口，并沒有對實現(xiàn)PriorityOrdered作特殊處理
?? ??? ??? ?// 這里優(yōu)先判斷是否實現(xiàn)了Ordered接口，如果同時使用注解的話將被忽略
?? ??? ??? ?if (resolvedBean instanceof Ordered) {
?? ??? ??? ??? ?this.order = ((Ordered) resolvedBean).getOrder();
?? ??? ??? ?}else {
?? ??? ??? ??? ?if (beanName != null && this.beanFactory instanceof ConfigurableBeanFactory) {
?? ??? ??? ??? ??? ?ConfigurableBeanFactory cbf = (ConfigurableBeanFactory) this.beanFactory;
?? ??? ??? ??? ??? ?try {
?? ??? ??? ??? ??? ??? ?BeanDefinition bd = cbf.getMergedBeanDefinition(beanName);
?? ??? ??? ??? ??? ??? ?if (bd instanceof RootBeanDefinition) {
?? ??? ??? ??? ??? ??? ??? ?Method factoryMethod = ((RootBeanDefinition) bd).getResolvedFactoryMethod();
?? ??? ??? ??? ??? ??? ??? ?if (factoryMethod != null) {
?? ??? ??? ??? ??? ??? ??? ??? ?// 這里將會從注解@Order與@Priority中獲取order值
?? ??? ??? ??? ??? ??? ??? ??? ?this.order = OrderUtils.getOrder(factoryMethod);
?? ??? ??? ??? ??? ??? ??? ?}
?? ??? ??? ??? ??? ??? ?}
?? ??? ??? ??? ??? ?}catch (NoSuchBeanDefinitionException ex) {
?? ??? ??? ??? ??? ??? ?// ignore -> probably a manually registered singleton
?? ??? ??? ??? ??? ?}
?? ??? ??? ??? ?}
?? ??? ??? ??? ?if (this.order == null) {
?? ??? ??? ??? ??? ?if (this.beanType != null) {
?? ??? ??? ??? ??? ??? ?this.order = OrderUtils.getOrder(this.beanType, Ordered.LOWEST_PRECEDENCE);
?? ??? ??? ??? ??? ?}
?? ??? ??? ??? ??? ?else {
?? ??? ??? ??? ??? ??? ?this.order = Ordered.LOWEST_PRECEDENCE;
?? ??? ??? ??? ??? ?}
?? ??? ??? ??? ?}
?? ??? ??? ?}
?? ??? ?}
?? ??? ?return this.order;
?? ?}

源碼分析后，我們來看一段測試demo

public class ControllerAdviceBeanTests {
?? ?@ControllerAdvice
?? ?@Order(100)
?? ?@Priority(200)
?? ?static class OrderedControllerAdvice implements Ordered {
?? ??? ?@Override
?? ??? ?public int getOrder() {
?? ??? ??? ?return 42;
?? ??? ?}
?? ?}
?? ?@ControllerAdvice
?? ?// Order和@Priority由于Order的實現(xiàn)應(yīng)該被忽略
?? ?@Order(100)
?? ?@Priority(200)
?? ?static class PriorityOrderedControllerAdvice implements PriorityOrdered {
?? ??? ?@Override
?? ??? ?public int getOrder() {
?? ??? ??? ?return 55;
?? ??? ?}
?? ?}
?? ?@Configuration(proxyBeanMethods = false)
?? ?static class Config {
?? ??? ?@Bean
?? ??? ?OrderedControllerAdvice orderedControllerAdvice() {
?? ??? ??? ?return new OrderedControllerAdvice();
?? ??? ?}
?? ??? ?@Bean
?? ??? ?PriorityOrderedControllerAdvice priorityOrderedControllerAdvice() {
?? ??? ??? ?return new PriorityOrderedControllerAdvice();
?? ??? ?}
?? ?}
?? ?@Test
?? ?@SuppressWarnings({"rawtypes", "unchecked"})
?? ?public void findAnnotatedBeansSortsBeans() {
?? ??? ?AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(Config.class);
?? ??? ?List<ControllerAdviceBean> adviceBeans = ControllerAdviceBean.findAnnotatedBeans(context);
?? ??? ?// 輸出順序并不是 55 42，而是42，55
?? ??? ?for (ControllerAdviceBean adviceBean : adviceBeans) {
?? ??? ??? ?System.out.println (adviceBean.getOrder ());
?? ??? ?}
?? ?}
}

以上為個人經(jīng)驗，希望能給大家一個參考，也希望大家多多支持腳本之家。

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