小编给大家分享一下SpringBoot如何解析配置类以及集成第三方配置，相信大部分人都还不怎么了解，因此分享这篇文章给大家参考一下，希望大家阅读完这篇文章后大有收获，下面让我们一起去了解一下吧！
SpringBoot作为Java领域非常流行的开源框架，集成了大量常用的第三方库配置，Spring Boot应用中这些第三方库几乎可以是零配置的开箱即用，大部分的 Spring Boot 应用都只需要非常少量的配置代码，开发者能够更加专注于业务逻辑。SpringBoot上手快，但是如果你的项目中业务场景需要一些特殊定制，甚至对源码进行定制化，那这时候了解原理就变成必需的了，只有充分了解源码，知道框架底层的工作原理，才能对源码中原有的机制进行修改 / 扩展等等。
在SpringBoot中推荐基于Java Config的方式来代替传统的XML方式去引入Bean，本文就是分析SpringBoot如何解析这些配置类，为容器中注入我们自定义的以及SpringBoot为我们提供的Bean。SpringBoot版本基于2.1.7.RELEASE。
// 通常一个SpringBoot工程会含有这样一个主配置类,它位于我们项目的根包下,通过启动这个main方法就可以启动我们的项目
// 下面我们先分析@SpringBootApplication注解有哪些作用,在第二节中分析run方法,在run方法中会进行配置类的解析
@SpringBootApplication
public class SpringbootApplication {
public static void main(String[] args) {
SpringApplication.run(SpringbootApplication.class, args);
}
}// 点击@SpringBootApplication进去发现它其实是由三个核心注解构成的,下面分别讲解这三个注解
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {// 点进去发现它其实就是一个@Configuration注解,SpringBoot解析到就会知道这是一个配置类,会给容器中引入一些bean
// 一个被@Configuration标注的类,相当于一个applicationContext.xml文件
// @Configuration点进去发现其实就是一个@Component注解
@Configuration
public @interface SpringBootConfiguration {
}2、@EnableAutoConfiguration注解
// 结合下面@AutoConfigurationPackage注解,发现@EnableAutoConfiguration注解就是通过@Import注解给容器中引入了两个bean,
// 分别是AutoConfigurationImportSelector和AutoConfigurationPackages.Registrar,通过这两个类可以给容器中引入更多的类
// 下面先介绍下@Import注解的使用
@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
}
@Import(AutoConfigurationPackages.Registrar.class)
public @interface AutoConfigurationPackage {
}@Component public class MyBeanFactoryPostProcessor implements BeanFactoryPostProcessor { @Override public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException { BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory; // 往容器中新增BeanDefinition GenericBeanDefinition beanDefinition = new GenericBeanDefinition(); beanDefinition.setBeanClass(Chicken.class); registry.registerBeanDefinition("beanFactoryPostProcessor-Chicken", beanDefinition); // 修改容器中原有的BeanDefinition BeanDefinition snake = registry.getBeanDefinition("snake"); snake.setLazyInit(true); } }
@Component
public class CatBeanPostProcessor implements BeanPostProcessor {
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
return bean;
}
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
if (bean instanceof Cat){
Cat cat = (Cat) bean;
cat.setName("changeNameCat");
}
return bean;
}
}
第一节是SpringBoot解析自动配置类会用到的一些知识点，下面我们来看SpringBoot解析配置类的具体过程。上图是SpringBoot启动流程图，其中在refreshContext的第五步会调用容器的BeanFactoryPostProcessor的postProcessBeanDefinitionRegistry方法。其中有一个是ConfigurationClassPostProcessor，它是在创建ConfigurableApplicationContext时设置到容器中的，如下所示。
// 图中说的创建ConfigurableApplicationContext,默认创建的是普通的Servlet Web容器,就是下面这个
// 通过反射创建会走到其默认的构造函数
public AnnotationConfigServletWebServerApplicationContext() {
// 这里面进去会走到下面代码
this.reader = new AnnotatedBeanDefinitionReader(this);
this.scanner = new ClassPathBeanDefinitionScanner(this);
}
// 走到这里
registerAnnotationConfigProcessors(registry, null);
// 走到这里
// 向容器中注入一个ConfigurationClassPostProcessor,它是BeanFactoryPostProcessor
if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));
}
// 向容器中注入一个AutowiredAnnotationBeanPostProcessor,它是BeanPostProcessor,用于解决依赖注入的
if (!registry.containsBeanDefinition(AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(AutowiredAnnotationBeanPostProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
}上面说到在refreshContex中的第五步时，会调用容器中的BeanFactoryPostProcessor
的postProcessBeanDefinitionRegistry方法。其中有一个是ConfigurationClassPostProcessor，这是我们解析自动配置类的入口，下面分析其postProcessBeanDefinitionRegistry方法。
@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
// 删掉一些非关键代码
processConfigBeanDefinitions(registry);
}public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) { List<beandefinitionholder> configCandidates = new ArrayList<>(); // 获取容器中已注册的bean名字,见下图,注意,这里容器中这些BeanDefinition都是容器初始化过程中容器添加进去的 // 不是我们业务代码的beanDefinition,这段代码其实是连贯的,为了注释图片方便才分开 String[] candidateNames = registry.getBeanDefinitionNames(); for (String beanName : candidateNames) { // 获取BeanDefinition BeanDefinition beanDef = registry.getBeanDefinition(beanName); // 判断这个BeanDefinition的configurationClass属性是不是full或者lite,如果是认为已经处理过了,第一次时默认为空, // 走下面分支 if (ConfigurationClassUtils.isFullConfigurationClass(beanDef) || ConfigurationClassUtils.isLiteConfigurationClass(beanDef)) { // 打印日志记录下 } else if (ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory)) { // 1) 下面先分析下这个checkConfigurationClassCandidate方法,这边看方法名也可以猜到是检测该类是不是配置类 // 是配置类的意思就是它会给容器中引入bean,这个方法判断主要就是看这个类的元信息中有没有@Configuration注解 // 有没有@Component注解、有没有@ComponentScan、@Import、@ImportResource注解,有没有@Bean方法 // 构造一个BeanDefinitionHolder,放入configCandidates中 configCandidates.add(new BeanDefinitionHolder(beanDef, beanName)); } } // Return immediately if no @Configuration classes were found // 上图中容易默认已经引入了7个BeanDefinition,经过上面检测发现默认就一个符合条件的配置类,即我们的主配置类 // 这里面configCandidates就一个,就是SpringBootApplication if (configCandidates.isEmpty()) { return; } // Sort by previously determined @Order value, if applicable // 排序 configCandidates.sort((bd1, bd2) -> { int i1 = ConfigurationClassUtils.getOrder(bd1.getBeanDefinition()); int i2 = ConfigurationClassUtils.getOrder(bd2.getBeanDefinition()); return Integer.compare(i1, i2); }); // 删掉部分代码 // Parse each @Configuration class // 配置类解析工具 ConfigurationClassParser parser = new ConfigurationClassParser( this.metadataReaderFactory, this.problemReporter, this.environment, this.resourceLoader, this.componentScanBeanNameGenerator, registry); // 待处理集合 Set<beandefinitionholder> candidates = new LinkedHashSet<>(configCandidates); // 已处理集合 Set<configurationclass> alreadyParsed = new HashSet<>(configCandidates.size()); // 循环处理直到candidates.isEmpty() do { // 这边开始解析,对应步骤4 parser.parse(candidates); parser.validate(); // 取出第四步解析得到的一些configurationClasses集合 Set<configurationclass> configClasses = new LinkedHashSet<>(parser.getConfigurationClasses()); configClasses.removeAll(alreadyParsed); // 删除一部分代码 // 这边也会去加载BeanDefinition,对应图中步骤五 this.reader.loadBeanDefinitions(configClasses); alreadyParsed.addAll(configClasses); } while (!candidates.isEmpty()); }
在配置类解析流程图中，第二步，会获取容器中已经注册的BeanDefinition，放入candidateNames中，然后依次遍历这些BeanDefinition，判断它有没有被处理过，如果处理过就不管，否则通过checkConfigurationClassCandidate方法去判断它是不是配置类，判断方法如下。通过阅读这段代码，发现如果一个类上面有@Configuration注解、或者有@Component、@ComponentScan、@Import、@ImportResource注解、或者有@Bean标注的方法，则认为它是一个配置类。默认情况下，走到这里时最终只有一个candidateName符合，它是我们的主配置类，也就是SpringbootApplication这个Bean。
ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory);
public static boolean checkConfigurationClassCandidate(BeanDefinition beanDef,
MetadataReaderFactory metadataReaderFactory) {
String className = beanDef.getBeanClassName();
// 获取下类名,如果类名为空或者该类为工厂类
if (className == null || beanDef.getFactoryMethodName() != null) {
return false;
}
// 获取类的元数据信息
AnnotationMetadata metadata;
// 上图的7个candidateNames中只有一个springbootApplication是AnnotatedBeanDefinition,其余全返回false
if (beanDef instanceof AnnotatedBeanDefinition &&
className.equals(((AnnotatedBeanDefinition) beanDef).getMetadata().getClassName())) {
// Can reuse the pre-parsed metadata from the given BeanDefinition...
// springbootApplication走到这里
metadata = ((AnnotatedBeanDefinition) beanDef).getMetadata();
}
else if (beanDef instanceof AbstractBeanDefinition && ((AbstractBeanDefinition) beanDef).hasBeanClass()) {
// Check already loaded Class if present...
// since we possibly can't even load the class file for this Class.
Class<?> beanClass = ((AbstractBeanDefinition) beanDef).getBeanClass();
metadata = new StandardAnnotationMetadata(beanClass, true);
}
else {
try {
MetadataReader metadataReader = metadataReaderFactory.getMetadataReader(className);
// 读取类的元数据信息,这里面包括注解等信息
metadata = metadataReader.getAnnotationMetadata();
}
catch (IOException ex) {
return false;
}
}
// metadata.isAnnotated(Configuration.class.getName()),这个就是判断类上面有没有@Configuration注解
if (isFullConfigurationCandidate(metadata)) {
// 如果true的话设置下这个属性,那么就标记为处理过了
beanDef.setAttribute(CONFIGURATION_CLASS_ATTRIBUTE, CONFIGURATION_CLASS_FULL);
} else if (isLiteConfigurationCandidate(metadata)) {
beanDef.setAttribute(CONFIGURATION_CLASS_ATTRIBUTE, CONFIGURATION_CLASS_LITE);
}
else {
// 其余6个返回false
return false;
}
// It's a full or lite configuration candidate... Let's determine the order value, if any.
Integer order = getOrder(metadata);
if (order != null) {
// 获取下类上的@Order信息
beanDef.setAttribute(ORDER_ATTRIBUTE, order);
}
return true;
}public static boolean isLiteConfigurationCandidate(AnnotationMetadata metadata) {
// Do not consider an interface or an annotation...
if (metadata.isInterface()) {
return false;
}
// Any of the typical annotations found?
for (String indicator : candidateIndicators) {
// 判断下类上面有没有这几个注解
if (metadata.isAnnotated(indicator)) {
return true;
}
}
// Finally, let's look for @Bean methods...
try {
// 判断有没有@Bean的方法
return metadata.hasAnnotatedMethods(Bean.class.getName());
}
return false;
}
}
private static final Set<string> candidateIndicators = new HashSet<>();
static {
candidateIndicators.add(Component.class.getName());
candidateIndicators.add(ComponentScan.class.getName());
candidateIndicators.add(Import.class.getName());
candidateIndicators.add(ImportResource.class.getName());
}public void parse(Set<beandefinitionholder> configCandidates) {
// 删除部分代码，实际执行时这里的configCandidates就一个springBootApplication代表的主配置类
for (BeanDefinitionHolder holder : configCandidates) {
// 获取BeanDefinition
BeanDefinition bd = holder.getBeanDefinition();
// 我们的SpringBootApplication会走到这边,下面先分析这边
parse(((AnnotatedBeanDefinition) bd).getMetadata(), holder.getBeanName());
}
// (**)处这边也要留意下,这边会处理DeferredImportSelector,我们前面说的AutoConfigurationImportSelector就是在这边处理
// 给容器中导入xxxAutoConfiguration
this.deferredImportSelectorHandler.process();
}
protected final void parse(AnnotationMetadata metadata, String beanName) throws IOException {
processConfigurationClass(new ConfigurationClass(metadata, beanName));
}
protected void processConfigurationClass(ConfigurationClass configClass) throws IOException {
// 根据当前类上面的@Conditional注解标注的条件判断是否要解析这个配置类
if (this.conditionEvaluator.shouldSkip(configClass.getMetadata(), ConfigurationPhase.PARSE_CONFIGURATION)) {
return;
}
// 以configClass作为key去获取,第一次来肯定是获取不到的,走下面逻辑
ConfigurationClass existingClass = this.configurationClasses.get(configClass);
if (existingClass != null) {
if (configClass.isImported()) {
if (existingClass.isImported()) {
existingClass.mergeImportedBy(configClass);
}
// Otherwise ignore new imported config class; existing non-imported class overrides it.
return;
}
else {
// Explicit bean definition found, probably replacing an import.
// Let's remove the old one and go with the new one. this.configurationClasses.remove(configClass);
this.knownSuperclasses.values().removeIf(configClass::equals);
}
}
// Recursively process the configuration class and its superclass hierarchy.
// 这一步其实没有做啥,重点还是看下一步骤
SourceClass sourceClass = asSourceClass(configClass);
do {
// 这里是重点,里面具体分为8大步骤,单独拿一小节分析
// b) doProcessConfigurationClass
sourceClass = doProcessConfigurationClass(configClass, sourceClass);
}
while (sourceClass != null);
// 放入configurationClasses中
this.configurationClasses.put(configClass, configClass);
}// 上面的asSourceClass最终其实就是封装了一个SourceClass对象
public SourceClass(Object source) {
this.source = source;
if (source instanceof Class) {
this.metadata = new StandardAnnotationMetadata((Class<?>) source, true);
}
else {
this.metadata = ((MetadataReader) source).getAnnotationMetadata();
}
}下面这个doProcessConfigurationClass具体分为8个小步骤去解析，对应步骤四种的A-H步骤
protected final SourceClass doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass)
throws IOException {
// 判断这个类上面有没有@Component注解
if (configClass.getMetadata().isAnnotated(Component.class.getName())) {
// Recursively process any member (nested) classes first
// 如果有的话,遍历其内部类,然后也是调用doProcessConfigurationClass递归处理
processMemberClasses(configClass, sourceClass);
}
// Process any @PropertySource annotations
// 处理PropertySource注解,之前讲解属性配置也分析过,就是将该注解对应的属性文件加载到Environment中
for (AnnotationAttributes propertySource : AnnotationConfigUtils.attributesForRepeatable(
sourceClass.getMetadata(), PropertySources.class,
org.springframework.context.annotation.PropertySource.class)) {
if (this.environment instanceof ConfigurableEnvironment) {
processPropertySource(propertySource);
}
}
// Process any @ComponentScan annotations
// 处理@ComponentScan注解,将其指定的包下的bean注册到框架中
Set<annotationattributes> componentScans = AnnotationConfigUtils.attributesForRepeatable(
sourceClass.getMetadata(), ComponentScans.class, ComponentScan.class);
if (!componentScans.isEmpty() &&
!this.conditionEvaluator.shouldSkip(sourceClass.getMetadata(), ConfigurationPhase.REGISTER_BEAN)) {
for (AnnotationAttributes componentScan : componentScans) {
// The config class is annotated with @ComponentScan -> perform the scan immediately
Set<beandefinitionholder> scannedBeanDefinitions =
this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName());
// Check the set of scanned definitions for any further config classes and parse recursively if needed
for (BeanDefinitionHolder holder : scannedBeanDefinitions) {
BeanDefinition bdCand = holder.getBeanDefinition().getOriginatingBeanDefinition();
if (bdCand == null) {
bdCand = holder.getBeanDefinition();
}
if (ConfigurationClassUtils.checkConfigurationClassCandidate(bdCand, this.metadataReaderFactory)) {
parse(bdCand.getBeanClassName(), holder.getBeanName());
}
}
}
}
// Process any @Import annotations
// 处理Import注解
processImports(configClass, sourceClass, getImports(sourceClass), true);
// Process any @ImportResource annotations
// 处理@ImportResource注解,可以通过它来指定xml文件,BeanFactory就会读取这个xml文件将bean注册进去
AnnotationAttributes importResource =
AnnotationConfigUtils.attributesFor(sourceClass.getMetadata(), ImportResource.class);
if (importResource != null) {
String[] resources = importResource.getStringArray("locations");
Class<? extends BeanDefinitionReader> readerClass = importResource.getClass("reader");
for (String resource : resources) {
String resolvedResource = this.environment.resolveRequiredPlaceholders(resource);
configClass.addImportedResource(resolvedResource, readerClass);
}
}
// Process individual @Bean methods
// 处理我们的类中使用@Bean注解的方法,添加到configClass的beanMethod中
Set<methodmetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);
for (MethodMetadata methodMetadata : beanMethods) {
configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
}
// Process default methods on interfaces
// 处理接口的默认方法,遍历这个类的接口,判断有没有使用@Bean注解的非抽象方法,添加到configClass的beanMethod中
processInterfaces(configClass, sourceClass);
// Process superclass, if any
// 递归处理父类,这边返回父类上层方法会递归处理
if (sourceClass.getMetadata().hasSuperClass()) {
// 判断父类不为null且不在knownSuperclasses中且不以Java开头
String superclass = sourceClass.getMetadata().getSuperClassName();
if (superclass != null && !superclass.startsWith("java") &&
!this.knownSuperclasses.containsKey(superclass)) {
this.knownSuperclasses.put(superclass, configClass);
// Superclass found, return its annotation metadata and recurse
return sourceClass.getSuperClass();
}
}
// No superclass -> processing is complete
return null;
}[object Object]if (configClass.getMetadata().isAnnotated(Component.class.getName())) {
// Recursively process any member (nested) classes first
processMemberClasses(configClass, sourceClass);
}
// Register member (nested) classes that happen to be configuration classes themselves.
private void processMemberClasses(ConfigurationClass configClass, SourceClass sourceClass) throws IOException {
Collection<SourceClass> memberClasses = sourceClass.getMemberClasses();
// 判断是否有内部类,没有的话直接不处理
if (!memberClasses.isEmpty()) {
List<SourceClass> candidates = new ArrayList<>(memberClasses.size());
for (SourceClass memberClass : memberClasses) {
// 判断是否是配置类,判断也很简单,之前分析过,判断类上面有没有@Configuration注解、@Import、@ImportResource
// @Component、@ComponentScan以及@Bean标注的方法
if (ConfigurationClassUtils.isConfigurationCandidate(memberClass.getMetadata()) &&
!memberClass.getMetadata().getClassName().equals(configClass.getMetadata().getClassName())) {
// 加入到candidates中然后排个序
candidates.add(memberClass);
}
}
OrderComparator.sort(candidates);
for (SourceClass candidate : candidates) {
// 防止A引入防止A引入B,B引入A
if (this.importStack.contains(configClass)) {
this.problemReporter.error(new CircularImportProblem(configClass, this.importStack));
}
else {
this.importStack.push(configClass);
try {
// 放入栈中并遍历处理这些配置类,也是递归处理,调用之前的doProcessConfigurationClass处理这个配置类
processConfigurationClass(candidate.asConfigClass(configClass));
}
finally {
this.importStack.pop();
}
}
}
}
}@SpringBootApplication
@PropertySource({"demo.properties"})
public class Springboot2Application {for (AnnotationAttributes propertySource : AnnotationConfigUtils.attributesForRepeatable(
sourceClass.getMetadata(), PropertySources.class,
org.springframework.context.annotation.PropertySource.class)) {
if (this.environment instanceof ConfigurableEnvironment) {
// 这边就不进去看了,主要是读取@PropertySource注解指定的文件,将其封装成一个属性集放入到环境中
processPropertySource(propertySource);
}
}Set<AnnotationAttributes> componentScans = AnnotationConfigUtils.attributesForRepeatable(
sourceClass.getMetadata(), ComponentScans.class, ComponentScan.class);
if (!componentScans.isEmpty() &&
!this.conditionEvaluator.shouldSkip(sourceClass.getMetadata(), ConfigurationPhase.REGISTER_BEAN)) {
for (AnnotationAttributes componentScan : componentScans) {
// The config class is annotated with @ComponentScan -> perform the scan immediately
// 下面先分析这个parse方法
Set<BeanDefinitionHolder> scannedBeanDefinitions =
this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName());
// Check the set of scanned definitions for any further config classes and parse recursively if needed
for (BeanDefinitionHolder holder : scannedBeanDefinitions) {
BeanDefinition bdCand = holder.getBeanDefinition().getOriginatingBeanDefinition();
if (bdCand == null) {
bdCand = holder.getBeanDefinition();
}
// 如果是配置类,再递归处理
if (ConfigurationClassUtils.checkConfigurationClassCandidate(bdCand, this.metadataReaderFactory)) {
parse(bdCand.getBeanClassName(), holder.getBeanName());
}
}
}
}public Set<BeanDefinitionHolder> parse(AnnotationAttributes componentScan, final String declaringClass) {
ClassPathBeanDefinitionScanner scanner = new ClassPathBeanDefinitionScanner(this.registry,
componentScan.getBoolean("useDefaultFilters"), this.environment, this.resourceLoader);
Class<? extends BeanNameGenerator> generatorClass = componentScan.getClass("nameGenerator");
boolean useInheritedGenerator = (BeanNameGenerator.class == generatorClass);
// 设置一个bean名字生成器,默认就是使用org.springframework.beans.factory.support.BeanNameGenerator
scanner.setBeanNameGenerator(useInheritedGenerator ? this.beanNameGenerator :
BeanUtils.instantiateClass(generatorClass));
// 就是默认的
ScopedProxyMode scopedProxyMode = componentScan.getEnum("scopedProxy");
if (scopedProxyMode != ScopedProxyMode.DEFAULT) {
scanner.setScopedProxyMode(scopedProxyMode);
}
else {
Class<? extends ScopeMetadataResolver> resolverClass = componentScan.getClass("scopeResolver");
// 理解是元数据解析器
scanner.setScopeMetadataResolver(BeanUtils.instantiateClass(resolverClass));
}
// 设置下扫描的资源模式,是**/*.class
scanner.setResourcePattern(componentScan.getString("resourcePattern"));
// 添加IncludeFilter和ExcludeFilter
for (AnnotationAttributes filter : componentScan.getAnnotationArray("includeFilters")) {
for (TypeFilter typeFilter : typeFiltersFor(filter)) {
scanner.addIncludeFilter(typeFilter);
}
}
for (AnnotationAttributes filter : componentScan.getAnnotationArray("excludeFilters")) {
for (TypeFilter typeFilter : typeFiltersFor(filter)) {
scanner.addExcludeFilter(typeFilter);
}
}
// 设置是否懒加载
boolean lazyInit = componentScan.getBoolean("lazyInit");
if (lazyInit) {
scanner.getBeanDefinitionDefaults().setLazyInit(true);
}
// 解析扫描的包路径加入到basePackages中
Set<String> basePackages = new LinkedHashSet<>();
String[] basePackagesArray = componentScan.getStringArray("basePackages");
for (String pkg : basePackagesArray) {
String[] tokenized = StringUtils.tokenizeToStringArray(this.environment.resolvePlaceholders(pkg),
ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
Collections.addAll(basePackages, tokenized);
}
for (Class<?> clazz : componentScan.getClassArray("basePackageClasses")) {
// 解析basePackageClasses所在的包并加入到basePackages
basePackages.add(ClassUtils.getPackageName(clazz));
}
// 如果是空的,将声明该注解所在的类的包加入到basePackages
if (basePackages.isEmpty()) {
// 通常我们的主配置类是没有声明包扫描的路径的,所以这里会将主配置类所在的包加到这里面
basePackages.add(ClassUtils.getPackageName(declaringClass));
}
// 添加一个ExcludeFilter,跳过声明该注解的类
scanner.addExcludeFilter(new AbstractTypeHierarchyTraversingFilter(false, false) {
@Override
protected boolean matchClassName(String className) {
return declaringClass.equals(className);
}
});
return scanner.doScan(StringUtils.toStringArray(basePackages));
}protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
Assert.notEmpty(basePackages, "At least one base package must be specified");
Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<>();
// 遍历所有的包路径
for (String basePackage : basePackages) {
// 获取该包下面所有符合条件的BeanDefinition,然后遍历处理,下面会分析
Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
for (BeanDefinition candidate : candidates) {
ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
candidate.setScope(scopeMetadata.getScopeName());
// 通过beanNameGenerator生成beanName
String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
// 这两个if判断逻辑比较简单,就是设置一些Lazy、DependsOn属性
if (candidate instanceof AbstractBeanDefinition) {
postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);
}
if (candidate instanceof AnnotatedBeanDefinition) {
AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);
}
// 这边是检查下有没有之前定义过这个BeanDefinition
if (checkCandidate(beanName, candidate)) {
BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata,
definitionHolder, this.registry);
// 将该beanDefinition加入到集合中,并注册到容器中
beanDefinitions.add(definitionHolder);
registerBeanDefinition(definitionHolder, this.registry);
}
}
}
return beanDefinitions;
}private Set<BeanDefinition> scanCandidateComponents(String basePackage) {
Set<BeanDefinition> candidates = new LinkedHashSet<>();
try {
// 扫描指定包路径及其子包下面的class文件,将其封装成Resource对象
// classpath*:com/lwh/springboot/**/*.class
String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX +
resolveBasePackage(basePackage) + '/' + this.resourcePattern;
Resource[] resources = getResourcePatternResolver().getResources(packageSearchPath);
for (Resource resource : resources) {
if (resource.isReadable()) {
try {
MetadataReader metadataReader = getMetadataReaderFactory().getMetadataReader(resource);
if (isCandidateComponent(metadataReader)) {
ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader);
sbd.setResource(resource);
sbd.setSource(resource);
if (isCandidateComponent(sbd)) {
candidates.add(sbd);
}
}
}
}
}
}
return candidates;
}// 通过之前设置的几个filter进行过滤
protected boolean isCandidateComponent(MetadataReader metadataReader) throws IOException {
for (TypeFilter tf : this.excludeFilters) {
if (tf.match(metadataReader, getMetadataReaderFactory())) {
return false;
}
}
for (TypeFilter tf : this.includeFilters) {
if (tf.match(metadataReader, getMetadataReaderFactory())) {
return isConditionMatch(metadataReader);
}
}
return false;
}// Process any @Import annotations // getImports方法就是去递归扫描configClass上面所有的注解,将@Import注解标注的值放入importCandidates中,见下图 processImports(configClass, sourceClass, getImports(sourceClass), true);
private void processImports(ConfigurationClass configClass, SourceClass currentSourceClass,
Collection<SourceClass> importCandidates, boolean checkForCircularImports) {
if (importCandidates.isEmpty()) {
return;
}
if (checkForCircularImports && isChainedImportOnStack(configClass)) {
this.problemReporter.error(new CircularImportProblem(configClass, this.importStack));
}
else {
this.importStack.push(configClass);
try {
for (SourceClass candidate : importCandidates) {
// 依次遍历判断类型
// 其中有一个是这个类型,@Import(AutoConfigurationImportSelector.class)
// 这个就是自动配置原理,导入xxxAutoConfiguration这些类
if (candidate.isAssignable(ImportSelector.class)) {
// Candidate class is an ImportSelector -> delegate to it to determine imports
Class<?> candidateClass = candidate.loadClass();
// 实例化并调用xxxAware的方法并注入相关属性
ImportSelector selector = BeanUtils.instantiateClass(candidateClass, ImportSelector.class);
ParserStrategyUtils.invokeAwareMethods(
selector, this.environment, this.resourceLoader, this.registry);
// 它是DeferredImportSelector类型的
if (selector instanceof DeferredImportSelector) {
// deferredImportSelectors = new ArrayList<>()
// 这边会将两个参数封装下加入到deferredImportSelectors中,后面处理
// 加入到deferredImportSelectors中后,具体的处理是this.deferredImportSelectorHandler.process();
this.deferredImportSelectorHandler.handle(configClass, (DeferredImportSelector) selector);
}
else {
// 不是的话获取@Import导入的类名数组
String[] importClassNames = selector.selectImports(currentSourceClass.getMetadata());
Collection<SourceClass> importSourceClasses = asSourceClasses(importClassNames);
// 然后再递归处理
processImports(configClass, currentSourceClass, importSourceClasses, false);
}
}
// @Import(AutoConfigurationPackages.Registrar.class),我们的主配置类上面的注解就是这个类型
// 这个是用于导入主配置类所在包及其子包下的BeanDefinition
else if (candidate.isAssignable(ImportBeanDefinitionRegistrar.class)) {
// Candidate class is an ImportBeanDefinitionRegistrar ->
// delegate to it to register additional bean definitions
Class<?> candidateClass = candidate.loadClass();
ImportBeanDefinitionRegistrar registrar =
BeanUtils.instantiateClass(candidateClass, ImportBeanDefinitionRegistrar.class);
ParserStrategyUtils.invokeAwareMethods(
registrar, this.environment, this.resourceLoader, this.registry);
// 这边就是将这两个参数作为key,value放入了一个map中
// this.importBeanDefinitionRegistrars.put(registrar, importingClassMetadata);
configClass.addImportBeanDefinitionRegistrar(registrar, currentSourceClass.getMetadata());
}
else {
// Candidate class not an ImportSelector or ImportBeanDefinitionRegistrar ->
// process it as an @Configuration class
this.importStack.registerImport(
currentSourceClass.getMetadata(), candidate.getMetadata().getClassName());
// 当做一个普通类处理,判断是不是配置类,递归处理
processConfigurationClass(candidate.asConfigClass(configClass));
}
}
}
finally {
this.importStack.pop();
}
}
}// 这种就是Spring中常用的通过XML形式注入的方式
@SpringBootApplication
@ImportResource("test.xml")
public class Springboot2Application {// Process any @ImportResource annotations
// 可以使用@ImportResource注解指定xml文件,导入BeanDefinition
AnnotationAttributes importResource =
AnnotationConfigUtils.attributesFor(sourceClass.getMetadata(), ImportResource.class);
if (importResource != null) {
String[] resources = importResource.getStringArray("locations");
Class<? extends BeanDefinitionReader> readerClass = importResource.getClass("reader");
for (String resource : resources) {
// 就是test.xml
String resolvedResource = this.environment.resolveRequiredPlaceholders(resource);
configClass.addImportedResource(resolvedResource, readerClass);
}
}
public void addImportedResource(String importedResource, Class<? extends BeanDefinitionReader> readerClass) {
// 这边就是放入到了map中,这边是先统一存放起来,在步骤五的4)在真正进行导入BeanDefinition
this.importedResources.put(importedResource, readerClass);
}
private final Map<String, Class<? extends BeanDefinitionReader>> importedResources = new LinkedHashMap<>();// Process individual @Bean methods
// 获取当前类中的Bean方法
Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);
for (MethodMetadata methodMetadata : beanMethods) {
// 这边也是加入到set中,见下面代码,也是在步骤五的3)中进行处理
configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
}
private final Set<BeanMethod> beanMethods = new LinkedHashSet<>();// 默认方法举例,主配置类实现这个接口就可以
public interface ConfigurationInterface {
@Bean
default Pig pig(){
return new Pig();
}
}// Process default methods on interfaces
processInterfaces(configClass, sourceClass);
// Register default methods on interfaces implemented by the configuration class.
// 这边也是递归处理其父接口,判断父接口中默认方法是不是@Bean方法
private void processInterfaces(ConfigurationClass configClass, SourceClass sourceClass) throws IOException {
for (SourceClass ifc : sourceClass.getInterfaces()) {
Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(ifc);
for (MethodMetadata methodMetadata : beanMethods) {
if (!methodMetadata.isAbstract()) {
// 也是在步骤五的3)中进行处理
configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
}
}
processInterfaces(configClass, ifc);
}
}// Process superclass, if any
if (sourceClass.getMetadata().hasSuperClass()) {
String superclass = sourceClass.getMetadata().getSuperClassName();
if (superclass != null && !superclass.startsWith("java") &&
!this.knownSuperclasses.containsKey(superclass)) {
this.knownSuperclasses.put(superclass, configClass);
// Superclass found, return its annotation metadata and recurse
return sourceClass.getSuperClass();
}
}讲到这边步骤四中的大部分方法已经分析完了，但是还有一个重要步骤没有分析，就是导入xxxAutoConfiguration这些自动配置类部分。下面分析：
// 在解析@Import注解时，我们的AutoConfigurationImportSelector就是DeferredImportSelector类型的，它的意思是延迟导
// 入. 为啥要延迟导入? 因为AutoConfigurationImportSelector是给容器中导入一些默认的组件，如果容器中已经有这种类型
// 的组件了，那么就不再导入. 因此，它是故意先等SpringBoot容器去解析那些用户自定义的Bean,最后发现没有才来导入这
// 些默认的组件
if (selector instanceof DeferredImportSelector) {
// deferredImportSelectors = new ArrayList<>()
// 这边会将两个参数封装下加入到deferredImportSelectors中,后面处理
// 加入到deferredImportSelectors中后,具体的处理是this.deferredImportSelectorHandler.process();
this.deferredImportSelectorHandler.handle(configClass, (DeferredImportSelector) selector);
}// 步骤四就是从这里开始分析的
public void parse(Set<beandefinitionholder> configCandidates) {
// 删除部分代码，实际执行时这里的configCandidates就一个springBootApplication代表的主配置类
for (BeanDefinitionHolder holder : configCandidates) {
// 获取BeanDefinition
BeanDefinition bd = holder.getBeanDefinition();
// 我们的SpringBootApplication会走到这边,下面先分析这边
parse(((AnnotatedBeanDefinition) bd).getMetadata(), holder.getBeanName());
}
// 给容器中导入xxxAutoConfiguration,我们现在分析这边
this.deferredImportSelectorHandler.process();
}// 上面方法会走到这里
public void processGroupImports() {
for (DeferredImportSelectorGrouping grouping : this.groupings.values()) {
// 下面先分析这个getImports方法
grouping.getImports().forEach(entry -> {
ConfigurationClass configurationClass = this.configurationClasses.get(entry.getMetadata());
try {
processImports(configurationClass, asSourceClass(configurationClass),
asSourceClasses(entry.getImportClassName()), false);
}
});
}
}
public Iterable<group.entry> getImports() {
// 这边的deferredImports是通过grouping.add(deferredImport)添加进去的
for (DeferredImportSelectorHolder deferredImport : this.deferredImports) {
this.group.process(deferredImport.getConfigurationClass().getMetadata(),
deferredImport.getImportSelector());
}
return this.group.selectImports();
}
public void process(AnnotationMetadata annotationMetadata, DeferredImportSelector deferredImportSelector) {
// 下面先分析下这个getAutoConfigurationEntry方法
AutoConfigurationEntry autoConfigurationEntry = ((AutoConfigurationImportSelector) deferredImportSelector)
.getAutoConfigurationEntry(getAutoConfigurationMetadata(), annotationMetadata);
// 加入到这个autoConfigurationEntries中
this.autoConfigurationEntries.add(autoConfigurationEntry);
for (String importClassName : autoConfigurationEntry.getConfigurations()) {
// 接着依次遍历放入到这个map中,Map<string, annotationmetadata> entries = new LinkedHashMap<>()
this.entries.putIfAbsent(importClassName, annotationMetadata);
}
}// 这边就到了AutoConfigurationImportSelector类的方法中
protected AutoConfigurationEntry getAutoConfigurationEntry(AutoConfigurationMetadata autoConfigurationMetadata,
AnnotationMetadata annotationMetadata) {
// 判断是否支持自动配置
if (!isEnabled(annotationMetadata)) {
return EMPTY_ENTRY;
}
// 这个attributes属性就是上图中显示的,用来过滤自动配置类的
AnnotationAttributes attributes = getAttributes(annotationMetadata);
// 下面分析这个方法,这个就是加载容器中的自动配置类
List<string> configurations = getCandidateConfigurations(annotationMetadata, attributes);
// 去除重复的,方法就是放入set再放入list中
configurations = removeDuplicates(configurations);
// 去除掉应该被排除的
Set<string> exclusions = getExclusions(annotationMetadata, attributes);
checkExcludedClasses(configurations, exclusions);
configurations.removeAll(exclusions);
// 通过filter过滤,下面分析,过滤完发现只有22个了
configurations = filter(configurations, autoConfigurationMetadata);
// 发布一个事件,好像没有做啥关键的
fireAutoConfigurationImportEvents(configurations, exclusions);
// 将configurations封装成AutoConfigurationEntry返回
return new AutoConfigurationEntry(configurations, exclusions);
}
protected boolean isEnabled(AnnotationMetadata metadata) {
if (getClass() == AutoConfigurationImportSelector.class) {
// 判断有没有配置这个属性,没有的话默认为true,
// String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";
return getEnvironment().getProperty(EnableAutoConfiguration.ENABLED_OVERRIDE_PROPERTY, Boolean.class, true);
}
return true;
}protected List<string> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
// getSpringFactoriesLoaderFactoryClass()返回EnableAutoConfiguration.class,那么这边就是获取容器中所有的字段配置类
List<string> configurations = SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(),
getBeanClassLoader());
return configurations;
}protected List<autoconfigurationimportfilter> getAutoConfigurationImportFilters() {
return SpringFactoriesLoader.loadFactories(AutoConfigurationImportFilter.class, this.beanClassLoader);
}// 上面分析的是配置类解析的步骤四 parser.parse(candidates); // 下面来看第五步,步骤四中解析得到的配置类会放在configurationClasses中 Set<ConfigurationClass> configClasses = new LinkedHashSet<>(parser.getConfigurationClasses()); configClasses.removeAll(alreadyParsed); this.reader.loadBeanDefinitions(configClasses);
public void loadBeanDefinitions(Set<ConfigurationClass> configurationModel) {
TrackedConditionEvaluator trackedConditionEvaluator = new TrackedConditionEvaluator();
for (ConfigurationClass configClass : configurationModel) {
loadBeanDefinitionsForConfigurationClass(configClass, trackedConditionEvaluator);
}
}private void loadBeanDefinitionsForConfigurationClass(
ConfigurationClass configClass, TrackedConditionEvaluator trackedConditionEvaluator) {
// 判断是否应该跳过
if (trackedConditionEvaluator.shouldSkip(configClass)) {
return;
}
// 向容器中注入这个配置类所代表的的BeanDefinition
if (configClass.isImported()) {
registerBeanDefinitionForImportedConfigurationClass(configClass);
}
// 遍历这个配置类的所有的Bean方法,注入这些@Bean标注的方法要引入的BeanDefinition
for (BeanMethod beanMethod : configClass.getBeanMethods()) {
loadBeanDefinitionsForBeanMethod(beanMethod);
}
// 处理该配置类上的@ImportResource指定的配置文件,就是Spring中常用的XML配置方式
// 这边会通过解析该XML文件给容器中注入BeanDefinition,SpringBoot中不推荐这种方式,具体就不往下分析了
loadBeanDefinitionsFromImportedResources(configClass.getImportedResources());
// 处理步骤四中D解析@Import注解时获得的importBeanDefinitionRegistrars,调用其registerBeanDefinitions
// 方法给容器中注入BeanDefinition,这在前面讲解@Import方式时已经讲过了
loadBeanDefinitionsFromRegistrars(configClass.getImportBeanDefinitionRegistrars());
}private void loadBeanDefinitionsFromRegistrars(Map<ImportBeanDefinitionRegistrar, AnnotationMetadata> registrars) {
registrars.forEach((registrar, metadata) -> registrar.registerBeanDefinitions(metadata, this.registry));
}以上是“SpringBoot如何解析配置类以及集成第三方配置”这篇文章的所有内容，感谢各位的阅读！相信大家都有了一定的了解，希望分享的内容对大家有所帮助，如果还想学习更多知识，欢迎关注亿速云行业资讯频道！
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