springboot启动流程 (3) 自动装配 - IT评测·应用市场-qidao123.com

@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
/**
* Exclude specific auto-configuration classes such that they will never be applied.
*/
Class<?>[] exclude() default {};
/**
* Exclude specific auto-configuration class names such that they will never be
* applied.
* 当类路径下没有指定的类时，可以使用这个属性指定排除的类
*/
String[] excludeName() default {};
}

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private static class AutoConfigurationGroup implements
DeferredImportSelector.Group, BeanClassLoaderAware, BeanFactoryAware, ResourceLoaderAware {
private final Map<String, AnnotationMetadata> entries = new LinkedHashMap<>();
private final List<AutoConfigurationEntry> autoConfigurationEntries = new ArrayList<>();
// ... 略
@Override
public void process(
AnnotationMetadata annotationMetadata,
DeferredImportSelector deferredImportSelector) {
// AutoConfigurationEntry类使用List保存Configuration类
AutoConfigurationEntry autoConfigurationEntry =
((AutoConfigurationImportSelector) deferredImportSelector)
.getAutoConfigurationEntry(annotationMetadata);
this.autoConfigurationEntries.add(autoConfigurationEntry);
for (String importClassName : autoConfigurationEntry.getConfigurations()) {
this.entries.putIfAbsent(importClassName, annotationMetadata);
}
}
@Override
public Iterable<Entry> selectImports() {
// 查找排除的配置类
Set<String> allExclusions = this.autoConfigurationEntries.stream()
.map(AutoConfigurationEntry::getExclusions)
.flatMap(Collection::stream)
.collect(Collectors.toSet());
// 所有配置类
Set<String> processedConfigurations = this.autoConfigurationEntries.stream()
.map(AutoConfigurationEntry::getConfigurations)
.flatMap(Collection::stream)
.collect(Collectors.toCollection(LinkedHashSet::new));
// 将排除的配置类移除掉
processedConfigurations.removeAll(allExclusions);
// 排序
return sortAutoConfigurations(processedConfigurations, getAutoConfigurationMetadata()).stream()
.map((importClassName) -> new Entry(this.entries.get(importClassName), importClassName))
.collect(Collectors.toList());
}
// ... 略
}

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protected AutoConfigurationEntry getAutoConfigurationEntry(AnnotationMetadata annotationMetadata) {
AnnotationAttributes attributes = getAttributes(annotationMetadata);
// 查找自动装配类
List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);
// 以下几行为查找排除类、过滤等操作
configurations = removeDuplicates(configurations);
Set<String> exclusions = getExclusions(annotationMetadata, attributes);
checkExcludedClasses(configurations, exclusions);
configurations.removeAll(exclusions);
// 这里的Filter是从META-INF/spring.factories文件解析出来的
configurations = getConfigurationClassFilter().filter(configurations);
// 触发事件
fireAutoConfigurationImportEvents(configurations, exclusions);
return new AutoConfigurationEntry(configurations, exclusions);
}
protected List<String> getCandidateConfigurations(
AnnotationMetadata metadata, AnnotationAttributes attributes) {
// 从META-INF/spring.factories文件查找EnableAutoConfiguration配置
List<String> configurations = SpringFactoriesLoader.loadFactoryNames(
getSpringFactoriesLoaderFactoryClass(), getBeanClassLoader());
return configurations;
}

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public static List<String> loadFactoryNames(Class<?> factoryType, ClassLoader classLoader) {
String factoryTypeName = factoryType.getName();
return loadSpringFactories(classLoader).getOrDefault(factoryTypeName, Collections.emptyList());
}
private static Map<String, List<String>> loadSpringFactories(ClassLoader classLoader) {
MultiValueMap<String, String> result = cache.get(classLoader);
if (result != null) {
return result;
}
try {
// FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories"
// 从类路径下查找META-INF/spring.factories文件
Enumeration<URL> urls = (classLoader != null ?
classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
result = new LinkedMultiValueMap<>();
while (urls.hasMoreElements()) {
URL url = urls.nextElement();
UrlResource resource = new UrlResource(url);
// 获取properties配置
Properties properties = PropertiesLoaderUtils.loadProperties(resource);
for (Map.Entry<?, ?> entry : properties.entrySet()) {
String factoryTypeName = ((String) entry.getKey()).trim();
for (String factoryImplementationName :
StringUtils.commaDelimitedListToStringArray((String) entry.getValue())) {
result.add(factoryTypeName, factoryImplementationName.trim());
}
}
}
// 把配置添加缓存
cache.put(classLoader, result);
return result;
} catch (IOException ex) {
throw new IllegalArgumentException("Unable to load factories from location [" +
FACTORIES_RESOURCE_LOCATION + "]", ex);
}
}

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