代码拉取完成,页面将自动刷新
@Target({ ElementType.TYPE, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Conditional {
/**
* 多个匹配器接口
*/
Class<? extends Condition>[] value();
}
@FunctionalInterface
public interface Condition {
/**
* 匹配,如果匹配返回true进行初始化,返回false跳过初始化
*/
boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata);
}
public interface ConditionContext {
/**
* bean的定义
*/
BeanDefinitionRegistry getRegistry();
/**
* bean 工厂
*/
@Nullable
ConfigurableListableBeanFactory getBeanFactory();
/**
* 环境
*/
Environment getEnvironment();
/**
* 资源加载器
*/
ResourceLoader getResourceLoader();
/**
* 类加载器
*/
@Nullable
ClassLoader getClassLoader();
}
唯一实现 : org.springframework.context.annotation.ConditionEvaluator.ConditionContextImpl
构造方法
public ConditionContextImpl(@Nullable BeanDefinitionRegistry registry,
@Nullable Environment environment, @Nullable ResourceLoader resourceLoader) {
this.registry = registry;
this.beanFactory = deduceBeanFactory(registry);
this.environment = (environment != null ? environment : deduceEnvironment(registry));
this.resourceLoader = (resourceLoader != null ? resourceLoader : deduceResourceLoader(registry));
this.classLoader = deduceClassLoader(resourceLoader, this.beanFactory);
}
public interface AnnotatedTypeMetadata {
/**
* 获取所有注解
*/
MergedAnnotations getAnnotations();
/**
* 是否有注解
*/
default boolean isAnnotated(String annotationName) {
return getAnnotations().isPresent(annotationName);
}
/**
* 获取注解的属性
*/
@Nullable
default Map<String, Object> getAnnotationAttributes(String annotationName) {
return getAnnotationAttributes(annotationName, false);
}
}
org.springframework.context.annotation.ConfigurationClassWithConditionTests
@Test
public void conditionalOnMissingBeanMatch() throws Exception {
AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
ctx.register(BeanOneConfiguration.class, BeanTwoConfiguration.class);
ctx.refresh();
assertThat(ctx.containsBean("bean1")).isTrue();
assertThat(ctx.containsBean("bean2")).isFalse();
assertThat(ctx.containsBean("configurationClassWithConditionTests.BeanTwoConfiguration")).isFalse();
}
@Configuration
static class BeanOneConfiguration {
@Bean
public ExampleBean bean1() {
return new ExampleBean();
}
}
@Configuration
@Conditional(NoBeanOneCondition.class)
static class BeanTwoConfiguration {
@Bean
public ExampleBean bean2() {
return new ExampleBean();
}
}
static class NoBeanOneCondition implements Condition {
@Override
public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
return !context.getBeanFactory().containsBeanDefinition("bean1");
}
}
org.springframework.context.annotation.AnnotatedBeanDefinitionReader#doRegisterBean
public boolean shouldSkip(@Nullable AnnotatedTypeMetadata metadata, @Nullable ConfigurationPhase phase) {
if (metadata == null || !metadata.isAnnotated(Conditional.class.getName())) {
return false;
}
if (phase == null) {
if (metadata instanceof AnnotationMetadata &&
ConfigurationClassUtils.isConfigurationCandidate((AnnotationMetadata) metadata)) {
return shouldSkip(metadata, ConfigurationPhase.PARSE_CONFIGURATION);
}
return shouldSkip(metadata, ConfigurationPhase.REGISTER_BEAN);
}
List<Condition> conditions = new ArrayList<>();
// 获取注解 Conditional 的属性值
for (String[] conditionClasses : getConditionClasses(metadata)) {
for (String conditionClass : conditionClasses) {
// 序列化成注解
Condition condition = getCondition(conditionClass, this.context.getClassLoader());
// 插入注解列表
conditions.add(condition);
}
}
AnnotationAwareOrderComparator.sort(conditions);
for (Condition condition : conditions) {
ConfigurationPhase requiredPhase = null;
if (condition instanceof ConfigurationCondition) {
requiredPhase = ((ConfigurationCondition) condition).getConfigurationPhase();
}
// matches 进行验证
if ((requiredPhase == null || requiredPhase == phase) && !condition.matches(this.context, metadata)) {
return true;
}
}
return false;
}
读取注解信息, 并且执行注解对应的类的方法
用例如下. 实例化BeanTwoConfiguration
对象的时候会去执行NoBeanOneCondition
方法
@Configuration
@Conditional(NoBeanOneCondition.class)
static class BeanTwoConfiguration {
@Bean
public ExampleBean bean2() {
return new ExampleBean();
}
}
static class NoBeanOneCondition implements Condition {
@Override
public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
return !context.getBeanFactory().containsBeanDefinition("bean1");
}
}
在开发中可以自定义 matches 规则
这也是在注册的时候第一个方法
private <T> void doRegisterBean(Class<T> beanClass, @Nullable String name,
@Nullable Class<? extends Annotation>[] qualifiers, @Nullable Supplier<T> supplier,
@Nullable BeanDefinitionCustomizer[] customizers) {
AnnotatedGenericBeanDefinition abd = new AnnotatedGenericBeanDefinition(beanClass);
// 和条件注解相关的函数
if (this.conditionEvaluator.shouldSkip(abd.getMetadata())) {
return;
}
// 省略其他
}
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