# SpringBoot ConditionalOnBean
- Author: [HuiFer](https://github.com/huifer)
- 源码阅读仓库: [SourceHot-spring-boot](https://github.com/SourceHot/spring-boot-read)
- 在 SpringBoot 中有下列当XXX存在或不存的时候执行初始化
- ConditionalOnBean
ConditionalOnClass
ConditionalOnCloudPlatform
ConditionalOnExpression
ConditionalOnJava
ConditionalOnJndi
ConditionalOnMissingBean
ConditionalOnMissingClass
ConditionalOnNotWebApplication
ConditionalOnProperty
ConditionalOnResource
ConditionalOnSingleCandidate
ConditionalOnWebApplication
## ConditionalOnBean
```java
@Target({ ElementType.TYPE, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Conditional(OnBeanCondition.class)
public @interface ConditionalOnBean {
/**
* 需要匹配的 bean 类型
*/
Class<?>[] value() default {};
/**
* 需要匹配的 bean 类型
*/
String[] type() default {};
/**
* 匹配的 bean 注解
*/
Class<? extends Annotation>[] annotation() default {};
/**
* 需要匹配的 beanName
*/
String[] name() default {};
/**
* 搜索策略
*/
SearchStrategy search() default SearchStrategy.ALL;
/**
*/
Class<?>[] parameterizedContainer() default {};
}
```
## SearchStrategy
```java
public enum SearchStrategy {
/**
* 当前 上下文
*/
CURRENT,
/**
* 找所有的父容器
*/
ANCESTORS,
/**
* 当前上下文+父容器
*/
ALL
}
```
## OnBeanCondition
- org.springframework.boot.autoconfigure.condition.OnBeanCondition
- 这个类是一个条件类,相关的还有
```properties
org.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\
org.springframework.boot.autoconfigure.condition.OnBeanCondition,\
org.springframework.boot.autoconfigure.condition.OnClassCondition,\
org.springframework.boot.autoconfigure.condition.OnWebApplicationCondition
```
- 类图
在看这部分源码之前需要先了解 `Conditional`和`Condition`的源码
- 简单描述
通过实现`Condition` 来确认是否初始化bean
- 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`
- `org.springframework.boot.autoconfigure.condition.SpringBootCondition#matches(org.springframework.context.annotation.ConditionContext, org.springframework.core.type.AnnotatedTypeMetadata)`
```java
@Override
public final boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
// 类名或者方法名标记
String classOrMethodName = getClassOrMethodName(metadata);
try {
// 比较类,子类实现
ConditionOutcome outcome = getMatchOutcome(context, metadata);
// 日志输出
logOutcome(classOrMethodName, outcome);
// 报告记录
recordEvaluation(context, classOrMethodName, outcome);
// 返回匹配结果
return outcome.isMatch();
}
catch (NoClassDefFoundError ex) {
throw new IllegalStateException("Could not evaluate condition on " + classOrMethodName + " due to "
+ ex.getMessage() + " not found. Make sure your own configuration does not rely on "
+ "that class. This can also happen if you are "
+ "@ComponentScanning a springframework package (e.g. if you "
+ "put a @ComponentScan in the default package by mistake)", ex);
}
catch (RuntimeException ex) {
throw new IllegalStateException("Error processing condition on " + getName(metadata), ex);
}
}
```
- `getOutcomes` 子类实现
`org.springframework.boot.autoconfigure.condition.OnBeanCondition#getOutcomes`
```java
String[] autoConfigurationClasses,
AutoConfigurationMetadata autoConfigurationMetadata
```
- 第一个参数: 需要自动配置的类
- 配置注解信息
### ConditionOutcome 和 ConditionMessage
```java
public class ConditionOutcome {
/**
* 是否匹配
*/
private final boolean match;
/**
* 条件信息
*/
private final ConditionMessage message;
}
public final class ConditionMessage {
private String message;
}
```
- 造一个对象用来进行debug
```java
@Component
public class Beans {
@Bean
public A a() {
return new A();
}
@Bean
@ConditionalOnBean(value = A.class)
public B b() {
return new B();
}
}
```
## getMatchOutcome
```java
@Override
public ConditionOutcome getMatchOutcome(ConditionContext context, AnnotatedTypeMetadata metadata) {
// 条件信息
ConditionMessage matchMessage = ConditionMessage.empty();
// 获取注解求和
MergedAnnotations annotations = metadata.getAnnotations();
// 注解是否匹配
if (annotations.isPresent(ConditionalOnBean.class)) {
// 搜索 ConditionalOnBean 注解
Spec<ConditionalOnBean> spec = new Spec<>(context, metadata, annotations,
ConditionalOnBean.class);
// 匹配结果
MatchResult matchResult = getMatchingBeans(context, spec);
if (!matchResult.isAllMatched()) {
String reason = createOnBeanNoMatchReason(matchResult);
return ConditionOutcome.noMatch(spec.message().because(reason));
}
// 把注解解析出来获得文本
matchMessage = spec.message(matchMessage).found("bean", "beans").items(Style.QUOTE,
matchResult.getNamesOfAllMatches());
}
if (metadata.isAnnotated(ConditionalOnSingleCandidate.class.getName())) {
Spec<ConditionalOnSingleCandidate> spec = new SingleCandidateSpec(context, metadata, annotations);
MatchResult matchResult = getMatchingBeans(context, spec);
if (!matchResult.isAllMatched()) {
return ConditionOutcome.noMatch(spec.message().didNotFind("any beans").atAll());
}
else if (!hasSingleAutowireCandidate(context.getBeanFactory(), matchResult.getNamesOfAllMatches(),
spec.getStrategy() == SearchStrategy.ALL)) {
return ConditionOutcome.noMatch(spec.message().didNotFind("a primary bean from beans")
.items(Style.QUOTE, matchResult.getNamesOfAllMatches()));
}
matchMessage = spec.message(matchMessage).found("a primary bean from beans").items(Style.QUOTE,
matchResult.getNamesOfAllMatches());
}
if (metadata.isAnnotated(ConditionalOnMissingBean.class.getName())) {
Spec<ConditionalOnMissingBean> spec = new Spec<>(context, metadata, annotations,
ConditionalOnMissingBean.class);
MatchResult matchResult = getMatchingBeans(context, spec);
if (matchResult.isAnyMatched()) {
String reason = createOnMissingBeanNoMatchReason(matchResult);
return ConditionOutcome.noMatch(spec.message().because(reason));
}
matchMessage = spec.message(matchMessage).didNotFind("any beans").atAll();
}
return ConditionOutcome.match(matchMessage);
}
```
- 开始方法分析
### getMatchingBeans
- `org.springframework.boot.autoconfigure.condition.OnBeanCondition#getMatchingBeans`
```java
protected final MatchResult getMatchingBeans(ConditionContext context, Spec<?> spec) {
// 获取上下文
ClassLoader classLoader = context.getClassLoader();
// 获取 IOC 容器
ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
// 扫描方式比较是否为当前上下文
boolean considerHierarchy = spec.getStrategy() != SearchStrategy.CURRENT;
Set<Class<?>> parameterizedContainers = spec.getParameterizedContainers();
if (spec.getStrategy() == SearchStrategy.ANCESTORS) {
BeanFactory parent = beanFactory.getParentBeanFactory();
Assert.isInstanceOf(ConfigurableListableBeanFactory.class, parent,
"Unable to use SearchStrategy.ANCESTORS");
beanFactory = (ConfigurableListableBeanFactory) parent;
}
// 结果对象初始化
MatchResult result = new MatchResult();
Set<String> beansIgnoredByType = getNamesOfBeansIgnoredByType(classLoader, beanFactory, considerHierarchy,
spec.getIgnoredTypes(), parameterizedContainers);
for (String type : spec.getTypes()) {
// 通过类型获取 beanName
Collection<String> typeMatches = getBeanNamesForType(classLoader, considerHierarchy, beanFactory, type,
parameterizedContainers);
typeMatches.removeAll(beansIgnoredByType);
if (typeMatches.isEmpty()) {
result.recordUnmatchedType(type);
}
else {
result.recordMatchedType(type, typeMatches);
}
}
for (String annotation : spec.getAnnotations()) {
Set<String> annotationMatches = getBeanNamesForAnnotation(classLoader, beanFactory, annotation,
considerHierarchy);
annotationMatches.removeAll(beansIgnoredByType);
if (annotationMatches.isEmpty()) {
result.recordUnmatchedAnnotation(annotation);
}
else {
result.recordMatchedAnnotation(annotation, annotationMatches);
}
}
for (String beanName : spec.getNames()) {
if (!beansIgnoredByType.contains(beanName) && containsBean(beanFactory, beanName, considerHierarchy)) {
result.recordMatchedName(beanName);
}
else {
result.recordUnmatchedName(beanName);
}
}
return result;
}
```
- 在`MatchResult result = new MatchResult()` 之前的代码作用是确认ioc容器
#### getNamesOfBeansIgnoredByType
```java
/**
* 获取忽略的beans(返回对象是 beanName)
* 循环,忽略的类型, 将类型从 beanFactory 获取,返回
*/
private Set<String> getNamesOfBeansIgnoredByType(ClassLoader classLoader, ListableBeanFactory beanFactory,
boolean considerHierarchy, Set<String> ignoredTypes, Set<Class<?>> parameterizedContainers) {
Set<String> result = null;
for (String ignoredType : ignoredTypes) {
// 从 beanFactory 中获取忽略的beanNames
Collection<String> ignoredNames = getBeanNamesForType(classLoader, considerHierarchy, beanFactory,
ignoredType, parameterizedContainers);
result = addAll(result, ignoredNames);
}
return (result != null) ? result : Collections.emptySet();
}
```
#### getBeanNamesForType
```java
/**
* 通过类型获取 beanName
*/
private Set<String> getBeanNamesForType(ClassLoader classLoader, boolean considerHierarchy,
ListableBeanFactory beanFactory, String type, Set<Class<?>> parameterizedContainers) throws LinkageError {
try {
// 从beanFactory 中获取忽略的类 返回beanNanme
return getBeanNamesForType(beanFactory, considerHierarchy, resolve(type, classLoader),
parameterizedContainers);
}
catch (ClassNotFoundException | NoClassDefFoundError ex) {
return Collections.emptySet();
}
}
```
#### getBeanNamesForType
```java
/**
* 通过类型获取 beanName
*/
private Set<String> getBeanNamesForType(ListableBeanFactory beanFactory, boolean considerHierarchy, Class<?> type,
Set<Class<?>> parameterizedContainers) {
// 获取beanName
Set<String> result = collectBeanNamesForType(beanFactory, considerHierarchy, type, parameterizedContainers,
null);
return (result != null) ? result : Collections.emptySet();
}
```
#### collectBeanNamesForType
- 这里最终回到了spring beanFactory 的方法 getBeanNamesForType
```java
private Set<String> collectBeanNamesForType(ListableBeanFactory beanFactory, boolean considerHierarchy,
Class<?> type, Set<Class<?>> parameterizedContainers, Set<String> result) {
result = addAll(result, beanFactory.getBeanNamesForType(type, true, false));
for (Class<?> container : parameterizedContainers) {
ResolvableType generic = ResolvableType.forClassWithGenerics(container, type);
result = addAll(result, beanFactory.getBeanNamesForType(generic, true, false));
}
if (considerHierarchy && beanFactory instanceof HierarchicalBeanFactory) {
BeanFactory parent = ((HierarchicalBeanFactory) beanFactory).getParentBeanFactory();
if (parent instanceof ListableBeanFactory) {
result = collectBeanNamesForType((ListableBeanFactory) parent, considerHierarchy, type,
parameterizedContainers, result);
}
}
return result;
}
```
到这里需要忽略的beanName 就全部找出来了
```java
// 匹配类型在移除
for (String type : spec.getTypes()) {
// 通过类型获取 beanName
Collection<String> typeMatches = getBeanNamesForType(classLoader, considerHierarchy, beanFactory, type,
parameterizedContainers);
typeMatches.removeAll(beansIgnoredByType);
if (typeMatches.isEmpty()) {
result.recordUnmatchedType(type);
}
else {
result.recordMatchedType(type, typeMatches);
}
}
// 注解匹配删除忽略的beanname
for (String annotation : spec.getAnnotations()) {
Set<String> annotationMatches = getBeanNamesForAnnotation(classLoader, beanFactory, annotation,
considerHierarchy);
annotationMatches.removeAll(beansIgnoredByType);
if (annotationMatches.isEmpty()) {
result.recordUnmatchedAnnotation(annotation);
}
else {
result.recordMatchedAnnotation(annotation, annotationMatches);
}
}
```
- 在忽略bean找到之后做一个类型移除的操作.
### 返回值
- 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`
```java
public static ConditionOutcome noMatch(ConditionMessage message) {
return new ConditionOutcome(false, message);
}
```
```java
if (!matchResult.isAllMatched()) {
String reason = createOnBeanNoMatchReason(matchResult);
return ConditionOutcome.noMatch(spec.message().because(reason));
}
// 把注解解析出来获得文本
matchMessage = spec.message(matchMessage).found("bean", "beans").items(Style.QUOTE,
matchResult.getNamesOfAllMatches());
}
if (metadata.isAnnotated(ConditionalOnSingleCandidate.class.getName())) {
Spec<ConditionalOnSingleCandidate> spec = new SingleCandidateSpec(context, metadata, annotations);
MatchResult matchResult = getMatchingBeans(context, spec);
if (!matchResult.isAllMatched()) {
return ConditionOutcome.noMatch(spec.message().didNotFind("any beans").atAll());
}
else if (!hasSingleAutowireCandidate(context.getBeanFactory(), matchResult.getNamesOfAllMatches(),
spec.getStrategy() == SearchStrategy.ALL)) {
return ConditionOutcome.noMatch(spec.message().didNotFind("a primary bean from beans")
.items(Style.QUOTE, matchResult.getNamesOfAllMatches()));
}
matchMessage = spec.message(matchMessage).found("a primary bean from beans").items(Style.QUOTE,
matchResult.getNamesOfAllMatches());
}
if (metadata.isAnnotated(ConditionalOnMissingBean.class.getName())) {
Spec<ConditionalOnMissingBean> spec = new Spec<>(context, metadata, annotations,
ConditionalOnMissingBean.class);
MatchResult matchResult = getMatchingBeans(context, spec);
if (matchResult.isAnyMatched()) {
String reason = createOnMissingBeanNoMatchReason(matchResult);
return ConditionOutcome.noMatch(spec.message().because(reason));
}
matchMessage = spec.message(matchMessage).didNotFind("any beans").atAll();
}
return ConditionOutcome.match(matchMessage);
```
- 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
- 再往后就继续执行spring的bean初始化咯
## MessageSourceAutoConfiguration
- 启动阶段的一个类运行解读
- `org.springframework.boot.autoconfigure.context.MessageSourceAutoConfiguration`
```java
@Configuration(proxyBeanMethods = false)
@ConditionalOnMissingBean(name = AbstractApplicationContext.MESSAGE_SOURCE_BEAN_NAME, search = SearchStrategy.CURRENT)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Conditional(ResourceBundleCondition.class)
@EnableConfigurationProperties
public class MessageSourceAutoConfiguration {}
```
- 根据类的注解信息我们可以找到有`ResourceBundleCondition`
- 获取类名或者方法名的结果是`MessageSourceAutoConfiguration`全路径
- 继续往下是一个比较的方法(是否符合match)
`org.springframework.boot.autoconfigure.condition.SpringBootCondition#getMatchOutcome`这个方法是一个抽象方法子类实现
- 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
