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# SpringBoot ConditionalOnBean
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- Author: [HuiFer](https://github.com/huifer)
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- 源码阅读仓库: [SourceHot-spring-boot](https://github.com/SourceHot/spring-boot-read)
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- 在 SpringBoot 中有下列当XXX存在或不存的时候执行初始化
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- ConditionalOnBean
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ConditionalOnClass
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ConditionalOnCloudPlatform
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ConditionalOnExpression
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ConditionalOnJava
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ConditionalOnJndi
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ConditionalOnMissingBean
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ConditionalOnMissingClass
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ConditionalOnNotWebApplication
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ConditionalOnProperty
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ConditionalOnResource
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ConditionalOnSingleCandidate
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ConditionalOnWebApplication
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## ConditionalOnBean
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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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@Conditional(OnBeanCondition.class)
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public @interface ConditionalOnBean {
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/**
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* 需要匹配的 bean 类型
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*/
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Class<?>[] value() default {};
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/**
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* 需要匹配的 bean 类型
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*/
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String[] type() default {};
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/**
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* 匹配的 bean 注解
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*/
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Class<? extends Annotation>[] annotation() default {};
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/**
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* 需要匹配的 beanName
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*/
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String[] name() default {};
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/**
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* 搜索策略
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*/
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SearchStrategy search() default SearchStrategy.ALL;
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/**
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*/
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Class<?>[] parameterizedContainer() default {};
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}
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```
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## SearchStrategy
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```java
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public enum SearchStrategy {
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/**
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* 当前 上下文
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*/
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CURRENT,
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/**
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* 找所有的父容器
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*/
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ANCESTORS,
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/**
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* 当前上下文+父容器
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*/
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ALL
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}
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```
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## OnBeanCondition
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- org.springframework.boot.autoconfigure.condition.OnBeanCondition
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- 这个类是一个条件类,相关的还有
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```properties
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org.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\
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org.springframework.boot.autoconfigure.condition.OnBeanCondition,\
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org.springframework.boot.autoconfigure.condition.OnClassCondition,\
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org.springframework.boot.autoconfigure.condition.OnWebApplicationCondition
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```
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- 类图
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在看这部分源码之前需要先了解 `Conditional`和`Condition`的源码
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- 简单描述
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通过实现`Condition` 来确认是否初始化bean
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- 从类图上我们可以看到 `condition` 的继承关系. 在这里需要去找到`SpringBootCondition`
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- `org.springframework.boot.autoconfigure.condition.SpringBootCondition#matches(org.springframework.context.annotation.ConditionContext, org.springframework.core.type.AnnotatedTypeMetadata)`
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```java
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@Override
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public final boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
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// 类名或者方法名标记
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String classOrMethodName = getClassOrMethodName(metadata);
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try {
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// 比较类,子类实现
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ConditionOutcome outcome = getMatchOutcome(context, metadata);
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// 日志输出
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logOutcome(classOrMethodName, outcome);
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// 报告记录
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recordEvaluation(context, classOrMethodName, outcome);
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// 返回匹配结果
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return outcome.isMatch();
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}
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catch (NoClassDefFoundError ex) {
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throw new IllegalStateException("Could not evaluate condition on " + classOrMethodName + " due to "
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+ ex.getMessage() + " not found. Make sure your own configuration does not rely on "
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+ "that class. This can also happen if you are "
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+ "@ComponentScanning a springframework package (e.g. if you "
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+ "put a @ComponentScan in the default package by mistake)", ex);
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}
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catch (RuntimeException ex) {
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throw new IllegalStateException("Error processing condition on " + getName(metadata), ex);
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}
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}
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```
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- `getOutcomes` 子类实现
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`org.springframework.boot.autoconfigure.condition.OnBeanCondition#getOutcomes`
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```java
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String[] autoConfigurationClasses,
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AutoConfigurationMetadata autoConfigurationMetadata
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```
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- 第一个参数: 需要自动配置的类
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- 配置注解信息
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### ConditionOutcome 和 ConditionMessage
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```java
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public class ConditionOutcome {
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/**
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* 是否匹配
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*/
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private final boolean match;
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/**
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* 条件信息
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*/
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private final ConditionMessage message;
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}
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public final class ConditionMessage {
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private String message;
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}
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```
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- 造一个对象用来进行debug
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```java
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@Component
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public class Beans {
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@Bean
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public A a() {
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return new A();
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}
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@Bean
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@ConditionalOnBean(value = A.class)
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public B b() {
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return new B();
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}
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}
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```
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## getMatchOutcome
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```java
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@Override
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public ConditionOutcome getMatchOutcome(ConditionContext context, AnnotatedTypeMetadata metadata) {
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// 条件信息
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ConditionMessage matchMessage = ConditionMessage.empty();
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// 获取注解求和
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MergedAnnotations annotations = metadata.getAnnotations();
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// 注解是否匹配
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if (annotations.isPresent(ConditionalOnBean.class)) {
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// 搜索 ConditionalOnBean 注解
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Spec<ConditionalOnBean> spec = new Spec<>(context, metadata, annotations,
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ConditionalOnBean.class);
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// 匹配结果
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MatchResult matchResult = getMatchingBeans(context, spec);
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if (!matchResult.isAllMatched()) {
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String reason = createOnBeanNoMatchReason(matchResult);
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return ConditionOutcome.noMatch(spec.message().because(reason));
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}
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// 把注解解析出来获得文本
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matchMessage = spec.message(matchMessage).found("bean", "beans").items(Style.QUOTE,
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matchResult.getNamesOfAllMatches());
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}
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if (metadata.isAnnotated(ConditionalOnSingleCandidate.class.getName())) {
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Spec<ConditionalOnSingleCandidate> spec = new SingleCandidateSpec(context, metadata, annotations);
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MatchResult matchResult = getMatchingBeans(context, spec);
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if (!matchResult.isAllMatched()) {
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return ConditionOutcome.noMatch(spec.message().didNotFind("any beans").atAll());
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}
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else if (!hasSingleAutowireCandidate(context.getBeanFactory(), matchResult.getNamesOfAllMatches(),
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spec.getStrategy() == SearchStrategy.ALL)) {
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return ConditionOutcome.noMatch(spec.message().didNotFind("a primary bean from beans")
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.items(Style.QUOTE, matchResult.getNamesOfAllMatches()));
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}
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matchMessage = spec.message(matchMessage).found("a primary bean from beans").items(Style.QUOTE,
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matchResult.getNamesOfAllMatches());
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}
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if (metadata.isAnnotated(ConditionalOnMissingBean.class.getName())) {
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Spec<ConditionalOnMissingBean> spec = new Spec<>(context, metadata, annotations,
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ConditionalOnMissingBean.class);
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MatchResult matchResult = getMatchingBeans(context, spec);
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if (matchResult.isAnyMatched()) {
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String reason = createOnMissingBeanNoMatchReason(matchResult);
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return ConditionOutcome.noMatch(spec.message().because(reason));
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}
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matchMessage = spec.message(matchMessage).didNotFind("any beans").atAll();
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}
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return ConditionOutcome.match(matchMessage);
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}
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```
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- 开始方法分析
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### getMatchingBeans
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- `org.springframework.boot.autoconfigure.condition.OnBeanCondition#getMatchingBeans`
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```java
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protected final MatchResult getMatchingBeans(ConditionContext context, Spec<?> spec) {
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// 获取上下文
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ClassLoader classLoader = context.getClassLoader();
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// 获取 IOC 容器
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ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
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// 扫描方式比较是否为当前上下文
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boolean considerHierarchy = spec.getStrategy() != SearchStrategy.CURRENT;
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Set<Class<?>> parameterizedContainers = spec.getParameterizedContainers();
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if (spec.getStrategy() == SearchStrategy.ANCESTORS) {
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BeanFactory parent = beanFactory.getParentBeanFactory();
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Assert.isInstanceOf(ConfigurableListableBeanFactory.class, parent,
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"Unable to use SearchStrategy.ANCESTORS");
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beanFactory = (ConfigurableListableBeanFactory) parent;
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}
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// 结果对象初始化
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MatchResult result = new MatchResult();
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Set<String> beansIgnoredByType = getNamesOfBeansIgnoredByType(classLoader, beanFactory, considerHierarchy,
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spec.getIgnoredTypes(), parameterizedContainers);
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for (String type : spec.getTypes()) {
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// 通过类型获取 beanName
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Collection<String> typeMatches = getBeanNamesForType(classLoader, considerHierarchy, beanFactory, type,
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parameterizedContainers);
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typeMatches.removeAll(beansIgnoredByType);
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if (typeMatches.isEmpty()) {
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result.recordUnmatchedType(type);
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}
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else {
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result.recordMatchedType(type, typeMatches);
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}
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}
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for (String annotation : spec.getAnnotations()) {
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Set<String> annotationMatches = getBeanNamesForAnnotation(classLoader, beanFactory, annotation,
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considerHierarchy);
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annotationMatches.removeAll(beansIgnoredByType);
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if (annotationMatches.isEmpty()) {
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result.recordUnmatchedAnnotation(annotation);
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}
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else {
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result.recordMatchedAnnotation(annotation, annotationMatches);
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}
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}
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for (String beanName : spec.getNames()) {
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if (!beansIgnoredByType.contains(beanName) && containsBean(beanFactory, beanName, considerHierarchy)) {
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result.recordMatchedName(beanName);
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}
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else {
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result.recordUnmatchedName(beanName);
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}
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}
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return result;
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}
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```
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- 在`MatchResult result = new MatchResult()` 之前的代码作用是确认ioc容器
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#### getNamesOfBeansIgnoredByType
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```java
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/**
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* 获取忽略的beans(返回对象是 beanName)
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* 循环,忽略的类型, 将类型从 beanFactory 获取,返回
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*/
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private Set<String> getNamesOfBeansIgnoredByType(ClassLoader classLoader, ListableBeanFactory beanFactory,
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boolean considerHierarchy, Set<String> ignoredTypes, Set<Class<?>> parameterizedContainers) {
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Set<String> result = null;
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for (String ignoredType : ignoredTypes) {
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// 从 beanFactory 中获取忽略的beanNames
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Collection<String> ignoredNames = getBeanNamesForType(classLoader, considerHierarchy, beanFactory,
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ignoredType, parameterizedContainers);
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result = addAll(result, ignoredNames);
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}
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return (result != null) ? result : Collections.emptySet();
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}
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```
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#### getBeanNamesForType
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```java
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/**
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* 通过类型获取 beanName
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*/
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private Set<String> getBeanNamesForType(ClassLoader classLoader, boolean considerHierarchy,
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ListableBeanFactory beanFactory, String type, Set<Class<?>> parameterizedContainers) throws LinkageError {
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try {
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// 从beanFactory 中获取忽略的类 返回beanNanme
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return getBeanNamesForType(beanFactory, considerHierarchy, resolve(type, classLoader),
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parameterizedContainers);
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}
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catch (ClassNotFoundException | NoClassDefFoundError ex) {
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return Collections.emptySet();
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}
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}
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```
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#### getBeanNamesForType
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```java
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/**
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* 通过类型获取 beanName
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*/
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private Set<String> getBeanNamesForType(ListableBeanFactory beanFactory, boolean considerHierarchy, Class<?> type,
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Set<Class<?>> parameterizedContainers) {
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// 获取beanName
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Set<String> result = collectBeanNamesForType(beanFactory, considerHierarchy, type, parameterizedContainers,
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null);
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return (result != null) ? result : Collections.emptySet();
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}
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```
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#### collectBeanNamesForType
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- 这里最终回到了spring beanFactory 的方法 getBeanNamesForType
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```java
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private Set<String> collectBeanNamesForType(ListableBeanFactory beanFactory, boolean considerHierarchy,
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Class<?> type, Set<Class<?>> parameterizedContainers, Set<String> result) {
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result = addAll(result, beanFactory.getBeanNamesForType(type, true, false));
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for (Class<?> container : parameterizedContainers) {
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ResolvableType generic = ResolvableType.forClassWithGenerics(container, type);
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result = addAll(result, beanFactory.getBeanNamesForType(generic, true, false));
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}
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if (considerHierarchy && beanFactory instanceof HierarchicalBeanFactory) {
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BeanFactory parent = ((HierarchicalBeanFactory) beanFactory).getParentBeanFactory();
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if (parent instanceof ListableBeanFactory) {
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result = collectBeanNamesForType((ListableBeanFactory) parent, considerHierarchy, type,
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parameterizedContainers, result);
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}
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}
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return result;
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}
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```
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到这里需要忽略的beanName 就全部找出来了
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```java
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// 匹配类型在移除
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for (String type : spec.getTypes()) {
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// 通过类型获取 beanName
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Collection<String> typeMatches = getBeanNamesForType(classLoader, considerHierarchy, beanFactory, type,
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parameterizedContainers);
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typeMatches.removeAll(beansIgnoredByType);
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if (typeMatches.isEmpty()) {
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result.recordUnmatchedType(type);
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}
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else {
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result.recordMatchedType(type, typeMatches);
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}
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}
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// 注解匹配删除忽略的beanname
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for (String annotation : spec.getAnnotations()) {
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Set<String> annotationMatches = getBeanNamesForAnnotation(classLoader, beanFactory, annotation,
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considerHierarchy);
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annotationMatches.removeAll(beansIgnoredByType);
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if (annotationMatches.isEmpty()) {
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result.recordUnmatchedAnnotation(annotation);
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}
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else {
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result.recordMatchedAnnotation(annotation, annotationMatches);
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}
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}
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```
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- 在忽略bean找到之后做一个类型移除的操作.
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### 返回值
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- 在返回之前做一堆判断条件. 一旦符合条件这个地方会做一个noMatch的一个对象(`ConditionOutcome`) ，通过返回match对象`ConditionOutcome`
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```java
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public static ConditionOutcome noMatch(ConditionMessage message) {
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return new ConditionOutcome(false, message);
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}
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```
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```java
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if (!matchResult.isAllMatched()) {
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String reason = createOnBeanNoMatchReason(matchResult);
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return ConditionOutcome.noMatch(spec.message().because(reason));
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}
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// 把注解解析出来获得文本
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matchMessage = spec.message(matchMessage).found("bean", "beans").items(Style.QUOTE,
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matchResult.getNamesOfAllMatches());
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}
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if (metadata.isAnnotated(ConditionalOnSingleCandidate.class.getName())) {
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Spec<ConditionalOnSingleCandidate> spec = new SingleCandidateSpec(context, metadata, annotations);
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MatchResult matchResult = getMatchingBeans(context, spec);
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if (!matchResult.isAllMatched()) {
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return ConditionOutcome.noMatch(spec.message().didNotFind("any beans").atAll());
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}
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else if (!hasSingleAutowireCandidate(context.getBeanFactory(), matchResult.getNamesOfAllMatches(),
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spec.getStrategy() == SearchStrategy.ALL)) {
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return ConditionOutcome.noMatch(spec.message().didNotFind("a primary bean from beans")
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.items(Style.QUOTE, matchResult.getNamesOfAllMatches()));
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}
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matchMessage = spec.message(matchMessage).found("a primary bean from beans").items(Style.QUOTE,
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matchResult.getNamesOfAllMatches());
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}
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if (metadata.isAnnotated(ConditionalOnMissingBean.class.getName())) {
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Spec<ConditionalOnMissingBean> spec = new Spec<>(context, metadata, annotations,
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ConditionalOnMissingBean.class);
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MatchResult matchResult = getMatchingBeans(context, spec);
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if (matchResult.isAnyMatched()) {
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String reason = createOnMissingBeanNoMatchReason(matchResult);
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return ConditionOutcome.noMatch(spec.message().because(reason));
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}
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matchMessage = spec.message(matchMessage).didNotFind("any beans").atAll();
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}
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return ConditionOutcome.match(matchMessage);
|
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```
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- 到此结果封装完毕.回到方法`org.springframework.boot.autoconfigure.condition.SpringBootCondition#matches(org.springframework.context.annotation.ConditionContext, org.springframework.core.type.AnnotatedTypeMetadata)` 继续进行
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- 再往后就继续执行spring的bean初始化咯
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## MessageSourceAutoConfiguration
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- 启动阶段的一个类运行解读
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|
- `org.springframework.boot.autoconfigure.context.MessageSourceAutoConfiguration`
|
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|
```java
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|
@Configuration(proxyBeanMethods = false)
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|
|
@ConditionalOnMissingBean(name = AbstractApplicationContext.MESSAGE_SOURCE_BEAN_NAME, search = SearchStrategy.CURRENT)
|
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|
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
|
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|
@Conditional(ResourceBundleCondition.class)
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|
@EnableConfigurationProperties
|
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|
public class MessageSourceAutoConfiguration {}
|
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|
```
|
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|
|
|
- 根据类的注解信息我们可以找到有`ResourceBundleCondition`
|
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|
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|
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|
|
- 获取类名或者方法名的结果是`MessageSourceAutoConfiguration`全路径
|
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|
|
- 继续往下是一个比较的方法(是否符合match)
|
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|
|
`org.springframework.boot.autoconfigure.condition.SpringBootCondition#getMatchOutcome`这个方法是一个抽象方法子类实现
|
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|
|
|
|
- 上图中红框内标注的类为`org.springframework.boot.autoconfigure.context.MessageSourceAutoConfiguration.ResourceBundleCondition`
|
|
|
|
|
|
同时继承`org.springframework.boot.autoconfigure.condition.SpringBootCondition`
|
|
|
|
|
|
并且重写了方法`getMatchOutcome`
|
|
|
|
|
|
```java
|
|
|
@Override
|
|
|
public ConditionOutcome getMatchOutcome(ConditionContext context, AnnotatedTypeMetadata metadata) {
|
|
|
// 从 容器中获取
|
|
|
String basename = context.getEnvironment().getProperty("spring.messages.basename", "messages");
|
|
|
// 从缓存中获取条件信息
|
|
|
ConditionOutcome outcome = cache.get(basename);
|
|
|
if (outcome == null) {
|
|
|
// 生成条件信息对象
|
|
|
outcome = getMatchOutcomeForBasename(context, basename);
|
|
|
// 放入缓存
|
|
|
cache.put(basename, outcome);
|
|
|
}
|
|
|
return outcome;
|
|
|
}
|
|
|
```
|
|
|
|
|
|
这个方法主要将比较信息放入,
|
|
|
|
|
|
- 后续的行为依然是判断是否匹配,匹配就创建.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
## Spring Boot 启动阶段的自动注入
|
|
|
|
|
|
```java
|
|
|
org.springframework.boot.autoconfigure.AutoConfigurationImportSelector#filter
|
|
|
```
|
|
|
|
|
|
|
|
|
|
|
|
```java
|
|
|
private List<String> filter(List<String> configurations, AutoConfigurationMetadata autoConfigurationMetadata) {
|
|
|
long startTime = System.nanoTime();
|
|
|
String[] candidates = StringUtils.toStringArray(configurations);
|
|
|
boolean[] skip = new boolean[candidates.length];
|
|
|
boolean skipped = false;
|
|
|
// 获取 AutoConfigurationImportFilter 相关配置
|
|
|
for (AutoConfigurationImportFilter filter : getAutoConfigurationImportFilters()) {
|
|
|
// 执行 aware 相关接口
|
|
|
invokeAwareMethods(filter);
|
|
|
// 是否可以初始化的结果
|
|
|
boolean[] match = filter.match(candidates, autoConfigurationMetadata);
|
|
|
for (int i = 0; i < match.length; i++) {
|
|
|
if (!match[i]) {
|
|
|
// 是否跳过
|
|
|
skip[i] = true;
|
|
|
candidates[i] = null;
|
|
|
skipped = true;
|
|
|
}
|
|
|
}
|
|
|
}
|
|
|
if (!skipped) {
|
|
|
return configurations;
|
|
|
}
|
|
|
List<String> result = new ArrayList<>(candidates.length);
|
|
|
// 处理最终需要的类
|
|
|
for (int i = 0; i < candidates.length; i++) {
|
|
|
if (!skip[i]) {
|
|
|
result.add(candidates[i]);
|
|
|
}
|
|
|
}
|
|
|
if (logger.isTraceEnabled()) {
|
|
|
int numberFiltered = configurations.size() - result.size();
|
|
|
logger.trace("Filtered " + numberFiltered + " auto configuration class in "
|
|
|
+ TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - startTime) + " ms");
|
|
|
}
|
|
|
return new ArrayList<>(result);
|
|
|
}
|
|
|
```
|
|
|
|
|
|
|
|
|
|
|
|
- 在这里有一个关注点 循环方法`getAutoConfigurationImportFilters()`
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
```JAVA
|
|
|
protected List<AutoConfigurationImportFilter> getAutoConfigurationImportFilters() {
|
|
|
return SpringFactoriesLoader.loadFactories(AutoConfigurationImportFilter.class, this.beanClassLoader);
|
|
|
}
|
|
|
```
|
|
|
|
|
|
|
|
|
|
|
|
在`spring.factories`文件中找到`AutoConfigurationImportFilter`后面的值
|
|
|
|
|
|
```properties
|
|
|
org.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\
|
|
|
org.springframework.boot.autoconfigure.condition.OnBeanCondition,\
|
|
|
org.springframework.boot.autoconfigure.condition.OnClassCondition,\
|
|
|
org.springframework.boot.autoconfigure.condition.OnWebApplicationCondition
|
|
|
```
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
- 此时我们可以和前文的源码分析连接起来有一个完整的认识了
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
- 最后来看整体类图
|
|
|
|
|
|
|
|
|
|
