huifer
4 years ago
parent
7dbed255f6
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# Spring Conditional
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- Author: [HuiFer](https://github.com/huifer)
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- 源码阅读仓库: [SourceHot-spring](https://github.com/SourceHot/spring-framework-read)
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## Conditional
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```java
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@Target({ ElementType.TYPE, ElementType.METHOD })
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@Retention(RetentionPolicy.RUNTIME)
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@Documented
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public @interface Conditional {
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/**
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* 多个匹配器接口
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*/
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Class<? extends Condition>[] value();
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}
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```
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## Condition
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```
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@FunctionalInterface
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public interface Condition {
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/**
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* 匹配,如果匹配返回true进行初始化,返回false跳过初始化
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*/
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boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata);
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}
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```
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- ConditionContext 上下文
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- AnnotatedTypeMetadata 注解信息
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### ConditionContext
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```
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public interface ConditionContext {
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/**
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* bean的定义
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*/
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BeanDefinitionRegistry getRegistry();
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/**
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* bean 工厂
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*/
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@Nullable
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ConfigurableListableBeanFactory getBeanFactory();
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/**
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* 环境
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*/
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Environment getEnvironment();
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/**
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* 资源加载器
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*/
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ResourceLoader getResourceLoader();
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/**
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* 类加载器
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*/
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@Nullable
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ClassLoader getClassLoader();
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}
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```
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- 唯一实现 : `org.springframework.context.annotation.ConditionEvaluator.ConditionContextImpl`
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- 构造方法
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```java
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public ConditionContextImpl(@Nullable BeanDefinitionRegistry registry,
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@Nullable Environment environment, @Nullable ResourceLoader resourceLoader) {
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this.registry = registry;
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this.beanFactory = deduceBeanFactory(registry);
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this.environment = (environment != null ? environment : deduceEnvironment(registry));
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this.resourceLoader = (resourceLoader != null ? resourceLoader : deduceResourceLoader(registry));
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this.classLoader = deduceClassLoader(resourceLoader, this.beanFactory);
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}
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```
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- 在构造方法中加载了一些变量, 这些变量是根据一定规则转换后得到. 具体规则不展开.
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### AnnotatedTypeMetadata
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- 元数据接口
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```java
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public interface AnnotatedTypeMetadata {
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/**
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* 获取所有注解
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*/
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MergedAnnotations getAnnotations();
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/**
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* 是否有注解
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*/
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default boolean isAnnotated(String annotationName) {
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return getAnnotations().isPresent(annotationName);
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}
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/**
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* 获取注解的属性
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*/
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@Nullable
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default Map<String, Object> getAnnotationAttributes(String annotationName) {
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return getAnnotationAttributes(annotationName, false);
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}
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}
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```
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## 源码分析
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- 对应测试类`org.springframework.context.annotation.ConfigurationClassWithConditionTests`
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```java
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@Test
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public void conditionalOnMissingBeanMatch() throws Exception {
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AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
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ctx.register(BeanOneConfiguration.class, BeanTwoConfiguration.class);
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ctx.refresh();
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assertThat(ctx.containsBean("bean1")).isTrue();
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assertThat(ctx.containsBean("bean2")).isFalse();
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assertThat(ctx.containsBean("configurationClassWithConditionTests.BeanTwoConfiguration")).isFalse();
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}
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@Configuration
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static class BeanOneConfiguration {
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@Bean
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public ExampleBean bean1() {
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return new ExampleBean();
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}
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}
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@Configuration
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@Conditional(NoBeanOneCondition.class)
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static class BeanTwoConfiguration {
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@Bean
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public ExampleBean bean2() {
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return new ExampleBean();
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}
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}
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static class NoBeanOneCondition implements Condition {
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@Override
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public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
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return !context.getBeanFactory().containsBeanDefinition("bean1");
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}
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}
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```
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- `org.springframework.context.annotation.AnnotatedBeanDefinitionReader#doRegisterBean`
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### shouldSkip
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```java
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public boolean shouldSkip(@Nullable AnnotatedTypeMetadata metadata, @Nullable ConfigurationPhase phase) {
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if (metadata == null || !metadata.isAnnotated(Conditional.class.getName())) {
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return false;
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}
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if (phase == null) {
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if (metadata instanceof AnnotationMetadata &&
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ConfigurationClassUtils.isConfigurationCandidate((AnnotationMetadata) metadata)) {
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return shouldSkip(metadata, ConfigurationPhase.PARSE_CONFIGURATION);
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}
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return shouldSkip(metadata, ConfigurationPhase.REGISTER_BEAN);
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}
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List<Condition> conditions = new ArrayList<>();
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// 获取注解 Conditional 的属性值
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for (String[] conditionClasses : getConditionClasses(metadata)) {
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for (String conditionClass : conditionClasses) {
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// 序列化成注解
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Condition condition = getCondition(conditionClass, this.context.getClassLoader());
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// 插入注解列表
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conditions.add(condition);
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}
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}
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AnnotationAwareOrderComparator.sort(conditions);
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for (Condition condition : conditions) {
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ConfigurationPhase requiredPhase = null;
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if (condition instanceof ConfigurationCondition) {
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requiredPhase = ((ConfigurationCondition) condition).getConfigurationPhase();
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}
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// matches 进行验证
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if ((requiredPhase == null || requiredPhase == phase) && !condition.matches(this.context, metadata)) {
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return true;
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}
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}
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return false;
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}
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```
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- 读取注解信息, 并且执行注解对应的类的方法
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用例如下. 实例化`BeanTwoConfiguration`对象的时候会去执行`NoBeanOneCondition`方法
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```java
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@Configuration
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@Conditional(NoBeanOneCondition.class)
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static class BeanTwoConfiguration {
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@Bean
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public ExampleBean bean2() {
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return new ExampleBean();
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}
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}
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static class NoBeanOneCondition implements Condition {
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@Override
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public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
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return !context.getBeanFactory().containsBeanDefinition("bean1");
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}
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}
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```
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在开发中可以自定义matches规则
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这也是在注册的时候第一个方法
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```java
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private <T> void doRegisterBean(Class<T> beanClass, @Nullable String name,
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@Nullable Class<? extends Annotation>[] qualifiers, @Nullable Supplier<T> supplier,
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@Nullable BeanDefinitionCustomizer[] customizers) {
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AnnotatedGenericBeanDefinition abd = new AnnotatedGenericBeanDefinition(beanClass);
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// 和条件注解相关的函数
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if (this.conditionEvaluator.shouldSkip(abd.getMetadata())) {
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return;
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}
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// 省略其他
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}
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```
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