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小編給大家分享一下SpringBoot如何解析配置類以及集成第三方配置，相信大部分人都還不怎么了解，因此分享這篇文章給大家參考一下，希望大家閱讀完這篇文章后大有收獲，下面讓我們一起去了解一下吧！
SpringBoot作為Java領域非常流行的開源框架，集成了大量常用的第三方庫配置，Spring Boot應用中這些第三方庫幾乎可以是零配置的開箱即用，大部分的 Spring Boot 應用都只需要非常少量的配置代碼，開發(fā)者能夠更加專注于業(yè)務邏輯。SpringBoot上手快，但是如果你的項目中業(yè)務場景需要一些特殊定制，甚至對源碼進行定制化，那這時候了解原理就變成必需的了，只有充分了解源碼，知道框架底層的工作原理，才能對源碼中原有的機制進行修改 / 擴展等等。
在SpringBoot中推薦基于Java Config的方式來代替?zhèn)鹘y(tǒng)的XML方式去引入Bean，本文就是分析SpringBoot如何解析這些配置類，為容器中注入我們自定義的以及SpringBoot為我們提供的Bean。SpringBoot版本基于2.1.7.RELEASE。
// 通常一個SpringBoot工程會含有這樣一個主配置類,它位于我們項目的根包下,通過啟動這個main方法就可以啟動我們的項目
// 下面我們先分析@SpringBootApplication注解有哪些作用,在第二節(jié)中分析run方法,在run方法中會進行配置類的解析
@SpringBootApplication
public class SpringbootApplication {
public static void main(String[] args) {
SpringApplication.run(SpringbootApplication.class, args);
}
}// 點擊@SpringBootApplication進去發(fā)現(xiàn)它其實是由三個核心注解構成的,下面分別講解這三個注解
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {// 點進去發(fā)現(xiàn)它其實就是一個@Configuration注解,SpringBoot解析到就會知道這是一個配置類,會給容器中引入一些bean
// 一個被@Configuration標注的類,相當于一個applicationContext.xml文件
// @Configuration點進去發(fā)現(xiàn)其實就是一個@Component注解
@Configuration
public @interface SpringBootConfiguration {
}2、@EnableAutoConfiguration注解
// 結合下面@AutoConfigurationPackage注解,發(fā)現(xiàn)@EnableAutoConfiguration注解就是通過@Import注解給容器中引入了兩個bean,
// 分別是AutoConfigurationImportSelector和AutoConfigurationPackages.Registrar,通過這兩個類可以給容器中引入更多的類
// 下面先介紹下@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;
}
}
第一節(jié)是SpringBoot解析自動配置類會用到的一些知識點，下面我們來看SpringBoot解析配置類的具體過程。上圖是SpringBoot啟動流程圖，其中在refreshContext的第五步會調用容器的BeanFactoryPostProcessor的postProcessBeanDefinitionRegistry方法。其中有一個是ConfigurationClassPostProcessor，它是在創(chuàng)建ConfigurableApplicationContext時設置到容器中的，如下所示。
// 圖中說的創(chuàng)建ConfigurableApplicationContext,默認創(chuàng)建的是普通的Servlet Web容器,就是下面這個
// 通過反射創(chuàng)建會走到其默認的構造函數(shù)
public AnnotationConfigServletWebServerApplicationContext() {
// 這里面進去會走到下面代碼
this.reader = new AnnotatedBeanDefinitionReader(this);
this.scanner = new ClassPathBeanDefinitionScanner(this);
}
// 走到這里
registerAnnotationConfigProcessors(registry, null);
// 走到這里
// 向容器中注入一個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));
}
// 向容器中注入一個AutowiredAnnotationBeanPostProcessor,它是BeanPostProcessor,用于解決依賴注入的
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));
}上面說到在refreshContex中的第五步時，會調用容器中的BeanFactoryPostProcessor
的postProcessBeanDefinitionRegistry方法。其中有一個是ConfigurationClassPostProcessor，這是我們解析自動配置類的入口，下面分析其postProcessBeanDefinitionRegistry方法。
@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
// 刪掉一些非關鍵代碼
processConfigBeanDefinitions(registry);
}public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) { List<beandefinitionholder> configCandidates = new ArrayList<>(); // 獲取容器中已注冊的bean名字,見下圖,注意,這里容器中這些BeanDefinition都是容器初始化過程中容器添加進去的 // 不是我們業(yè)務代碼的beanDefinition,這段代碼其實是連貫的,為了注釋圖片方便才分開 String[] candidateNames = registry.getBeanDefinitionNames(); for (String beanName : candidateNames) { // 獲取BeanDefinition BeanDefinition beanDef = registry.getBeanDefinition(beanName); // 判斷這個BeanDefinition的configurationClass屬性是不是full或者lite,如果是認為已經(jīng)處理過了,第一次時默認為空, // 走下面分支 if (ConfigurationClassUtils.isFullConfigurationClass(beanDef) || ConfigurationClassUtils.isLiteConfigurationClass(beanDef)) { // 打印日志記錄下 } else if (ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory)) { // 1) 下面先分析下這個checkConfigurationClassCandidate方法,這邊看方法名也可以猜到是檢測該類是不是配置類 // 是配置類的意思就是它會給容器中引入bean,這個方法判斷主要就是看這個類的元信息中有沒有@Configuration注解 // 有沒有@Component注解、有沒有@ComponentScan、@Import、@ImportResource注解,有沒有@Bean方法 // 構造一個BeanDefinitionHolder,放入configCandidates中 configCandidates.add(new BeanDefinitionHolder(beanDef, beanName)); } } // Return immediately if no @Configuration classes were found // 上圖中容易默認已經(jīng)引入了7個BeanDefinition,經(jīng)過上面檢測發(fā)現(xiàn)默認就一個符合條件的配置類,即我們的主配置類 // 這里面configCandidates就一個,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); }); // 刪掉部分代碼 // Parse each @Configuration class // 配置類解析工具 ConfigurationClassParser parser = new ConfigurationClassParser( this.metadataReaderFactory, this.problemReporter, this.environment, this.resourceLoader, this.componentScanBeanNameGenerator, registry); // 待處理集合 Set<beandefinitionholder> candidates = new LinkedHashSet<>(configCandidates); // 已處理集合 Set<configurationclass> alreadyParsed = new HashSet<>(configCandidates.size()); // 循環(huán)處理直到candidates.isEmpty() do { // 這邊開始解析,對應步驟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); // 刪除一部分代碼 // 這邊也會去加載BeanDefinition,對應圖中步驟五 this.reader.loadBeanDefinitions(configClasses); alreadyParsed.addAll(configClasses); } while (!candidates.isEmpty()); }
在配置類解析流程圖中，第二步，會獲取容器中已經(jīng)注冊的BeanDefinition，放入candidateNames中，然后依次遍歷這些BeanDefinition，判斷它有沒有被處理過，如果處理過就不管，否則通過checkConfigurationClassCandidate方法去判斷它是不是配置類，判斷方法如下。通過閱讀這段代碼，發(fā)現(xiàn)如果一個類上面有@Configuration注解、或者有@Component、@ComponentScan、@Import、@ImportResource注解、或者有@Bean標注的方法，則認為它是一個配置類。默認情況下，走到這里時最終只有一個candidateName符合，它是我們的主配置類，也就是SpringbootApplication這個Bean。
ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory);
public static boolean checkConfigurationClassCandidate(BeanDefinition beanDef,
MetadataReaderFactory metadataReaderFactory) {
String className = beanDef.getBeanClassName();
// 獲取下類名,如果類名為空或者該類為工廠類
if (className == null || beanDef.getFactoryMethodName() != null) {
return false;
}
// 獲取類的元數(shù)據(jù)信息
AnnotationMetadata metadata;
// 上圖的7個candidateNames中只有一個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走到這里
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);
// 讀取類的元數(shù)據(jù)信息,這里面包括注解等信息
metadata = metadataReader.getAnnotationMetadata();
}
catch (IOException ex) {
return false;
}
}
// metadata.isAnnotated(Configuration.class.getName()),這個就是判斷類上面有沒有@Configuration注解
if (isFullConfigurationCandidate(metadata)) {
// 如果true的話設置下這個屬性,那么就標記為處理過了
beanDef.setAttribute(CONFIGURATION_CLASS_ATTRIBUTE, CONFIGURATION_CLASS_FULL);
} else if (isLiteConfigurationCandidate(metadata)) {
beanDef.setAttribute(CONFIGURATION_CLASS_ATTRIBUTE, CONFIGURATION_CLASS_LITE);
}
else {
// 其余6個返回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) {
// 獲取下類上的@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) {
// 判斷下類上面有沒有這幾個注解
if (metadata.isAnnotated(indicator)) {
return true;
}
}
// Finally, let's look for @Bean methods...
try {
// 判斷有沒有@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) {
// 刪除部分代碼，實際執(zhí)行時這里的configCandidates就一個springBootApplication代表的主配置類
for (BeanDefinitionHolder holder : configCandidates) {
// 獲取BeanDefinition
BeanDefinition bd = holder.getBeanDefinition();
// 我們的SpringBootApplication會走到這邊,下面先分析這邊
parse(((AnnotatedBeanDefinition) bd).getMetadata(), holder.getBeanName());
}
// (**)處這邊也要留意下,這邊會處理DeferredImportSelector,我們前面說的AutoConfigurationImportSelector就是在這邊處理
// 給容器中導入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 {
// 根據(jù)當前類上面的@Conditional注解標注的條件判斷是否要解析這個配置類
if (this.conditionEvaluator.shouldSkip(configClass.getMetadata(), ConfigurationPhase.PARSE_CONFIGURATION)) {
return;
}
// 以configClass作為key去獲取,第一次來肯定是獲取不到的,走下面邏輯
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.
// 這一步其實沒有做啥,重點還是看下一步驟
SourceClass sourceClass = asSourceClass(configClass);
do {
// 這里是重點,里面具體分為8大步驟,單獨拿一小節(jié)分析
// b) doProcessConfigurationClass
sourceClass = doProcessConfigurationClass(configClass, sourceClass);
}
while (sourceClass != null);
// 放入configurationClasses中
this.configurationClasses.put(configClass, configClass);
}// 上面的asSourceClass最終其實就是封裝了一個SourceClass對象
public SourceClass(Object source) {
this.source = source;
if (source instanceof Class) {
this.metadata = new StandardAnnotationMetadata((Class<?>) source, true);
}
else {
this.metadata = ((MetadataReader) source).getAnnotationMetadata();
}
}下面這個doProcessConfigurationClass具體分為8個小步驟去解析，對應步驟四種的A-H步驟
protected final SourceClass doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass)
throws IOException {
// 判斷這個類上面有沒有@Component注解
if (configClass.getMetadata().isAnnotated(Component.class.getName())) {
// Recursively process any member (nested) classes first
// 如果有的話,遍歷其內(nèi)部類,然后也是調用doProcessConfigurationClass遞歸處理
processMemberClasses(configClass, sourceClass);
}
// Process any @PropertySource annotations
// 處理PropertySource注解,之前講解屬性配置也分析過,就是將該注解對應的屬性文件加載到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
// 處理@ComponentScan注解,將其指定的包下的bean注冊到框架中
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
// 處理Import注解
processImports(configClass, sourceClass, getImports(sourceClass), true);
// Process any @ImportResource annotations
// 處理@ImportResource注解,可以通過它來指定xml文件,BeanFactory就會讀取這個xml文件將bean注冊進去
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
// 處理我們的類中使用@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
// 處理接口的默認方法,遍歷這個類的接口,判斷有沒有使用@Bean注解的非抽象方法,添加到configClass的beanMethod中
processInterfaces(configClass, sourceClass);
// Process superclass, if any
// 遞歸處理父類,這邊返回父類上層方法會遞歸處理
if (sourceClass.getMetadata().hasSuperClass()) {
// 判斷父類不為null且不在knownSuperclasses中且不以Java開頭
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();
// 判斷是否有內(nèi)部類,沒有的話直接不處理
if (!memberClasses.isEmpty()) {
List<SourceClass> candidates = new ArrayList<>(memberClasses.size());
for (SourceClass memberClass : memberClasses) {
// 判斷是否是配置類,判斷也很簡單,之前分析過,判斷類上面有沒有@Configuration注解、@Import、@ImportResource
// @Component、@ComponentScan以及@Bean標注的方法
if (ConfigurationClassUtils.isConfigurationCandidate(memberClass.getMetadata()) &&
!memberClass.getMetadata().getClassName().equals(configClass.getMetadata().getClassName())) {
// 加入到candidates中然后排個序
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 {
// 放入棧中并遍歷處理這些配置類,也是遞歸處理,調用之前的doProcessConfigurationClass處理這個配置類
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) {
// 這邊就不進去看了,主要是讀取@PropertySource注解指定的文件,將其封裝成一個屬性集放入到環(huán)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
// 下面先分析這個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();
}
// 如果是配置類,再遞歸處理
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);
// 設置一個bean名字生成器,默認就是使用org.springframework.beans.factory.support.BeanNameGenerator
scanner.setBeanNameGenerator(useInheritedGenerator ? this.beanNameGenerator :
BeanUtils.instantiateClass(generatorClass));
// 就是默認的
ScopedProxyMode scopedProxyMode = componentScan.getEnum("scopedProxy");
if (scopedProxyMode != ScopedProxyMode.DEFAULT) {
scanner.setScopedProxyMode(scopedProxyMode);
}
else {
Class<? extends ScopeMetadataResolver> resolverClass = componentScan.getClass("scopeResolver");
// 理解是元數(shù)據(jù)解析器
scanner.setScopeMetadataResolver(BeanUtils.instantiateClass(resolverClass));
}
// 設置下掃描的資源模式,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);
}
}
// 設置是否懶加載
boolean lazyInit = componentScan.getBoolean("lazyInit");
if (lazyInit) {
scanner.getBeanDefinitionDefaults().setLazyInit(true);
}
// 解析掃描的包路徑加入到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,將聲明該注解所在的類的包加入到basePackages
if (basePackages.isEmpty()) {
// 通常我們的主配置類是沒有聲明包掃描的路徑的,所以這里會將主配置類所在的包加到這里面
basePackages.add(ClassUtils.getPackageName(declaringClass));
}
// 添加一個ExcludeFilter,跳過聲明該注解的類
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<>();
// 遍歷所有的包路徑
for (String basePackage : basePackages) {
// 獲取該包下面所有符合條件的BeanDefinition,然后遍歷處理,下面會分析
Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
for (BeanDefinition candidate : candidates) {
ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
candidate.setScope(scopeMetadata.getScopeName());
// 通過beanNameGenerator生成beanName
String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
// 這兩個if判斷邏輯比較簡單,就是設置一些Lazy、DependsOn屬性
if (candidate instanceof AbstractBeanDefinition) {
postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);
}
if (candidate instanceof AnnotatedBeanDefinition) {
AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);
}
// 這邊是檢查下有沒有之前定義過這個BeanDefinition
if (checkCandidate(beanName, candidate)) {
BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata,
definitionHolder, this.registry);
// 將該beanDefinition加入到集合中,并注冊到容器中
beanDefinitions.add(definitionHolder);
registerBeanDefinition(definitionHolder, this.registry);
}
}
}
return beanDefinitions;
}private Set<BeanDefinition> scanCandidateComponents(String basePackage) {
Set<BeanDefinition> candidates = new LinkedHashSet<>();
try {
// 掃描指定包路徑及其子包下面的class文件,將其封裝成Resource對象
// 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;
}// 通過之前設置的幾個filter進行過濾
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方法就是去遞歸掃描configClass上面所有的注解,將@Import注解標注的值放入importCandidates中,見下圖 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) {
// 依次遍歷判斷類型
// 其中有一個是這個類型,@Import(AutoConfigurationImportSelector.class)
// 這個就是自動配置原理,導入xxxAutoConfiguration這些類
if (candidate.isAssignable(ImportSelector.class)) {
// Candidate class is an ImportSelector -> delegate to it to determine imports
Class<?> candidateClass = candidate.loadClass();
// 實例化并調用xxxAware的方法并注入相關屬性
ImportSelector selector = BeanUtils.instantiateClass(candidateClass, ImportSelector.class);
ParserStrategyUtils.invokeAwareMethods(
selector, this.environment, this.resourceLoader, this.registry);
// 它是DeferredImportSelector類型的
if (selector instanceof DeferredImportSelector) {
// deferredImportSelectors = new ArrayList<>()
// 這邊會將兩個參數(shù)封裝下加入到deferredImportSelectors中,后面處理
// 加入到deferredImportSelectors中后,具體的處理是this.deferredImportSelectorHandler.process();
this.deferredImportSelectorHandler.handle(configClass, (DeferredImportSelector) selector);
}
else {
// 不是的話獲取@Import導入的類名數(shù)組
String[] importClassNames = selector.selectImports(currentSourceClass.getMetadata());
Collection<SourceClass> importSourceClasses = asSourceClasses(importClassNames);
// 然后再遞歸處理
processImports(configClass, currentSourceClass, importSourceClasses, false);
}
}
// @Import(AutoConfigurationPackages.Registrar.class),我們的主配置類上面的注解就是這個類型
// 這個是用于導入主配置類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);
// 這邊就是將這兩個參數(shù)作為key,value放入了一個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());
// 當做一個普通類處理,判斷是不是配置類,遞歸處理
processConfigurationClass(candidate.asConfigClass(configClass));
}
}
}
finally {
this.importStack.pop();
}
}
}// 這種就是Spring中常用的通過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,導入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) {
// 這邊就是放入到了map中,這邊是先統(tǒng)一存放起來,在步驟五的4)在真正進行導入BeanDefinition
this.importedResources.put(importedResource, readerClass);
}
private final Map<String, Class<? extends BeanDefinitionReader>> importedResources = new LinkedHashMap<>();// Process individual @Bean methods
// 獲取當前類中的Bean方法
Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);
for (MethodMetadata methodMetadata : beanMethods) {
// 這邊也是加入到set中,見下面代碼,也是在步驟五的3)中進行處理
configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
}
private final Set<BeanMethod> beanMethods = new LinkedHashSet<>();// 默認方法舉例,主配置類實現(xiàn)這個接口就可以
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.
// 這邊也是遞歸處理其父接口,判斷父接口中默認方法是不是@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()) {
// 也是在步驟五的3)中進行處理
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();
}
}講到這邊步驟四中的大部分方法已經(jīng)分析完了，但是還有一個重要步驟沒有分析，就是導入xxxAutoConfiguration這些自動配置類部分。下面分析：
// 在解析@Import注解時，我們的AutoConfigurationImportSelector就是DeferredImportSelector類型的，它的意思是延遲導
// 入. 為啥要延遲導入? 因為AutoConfigurationImportSelector是給容器中導入一些默認的組件，如果容器中已經(jīng)有這種類型
// 的組件了，那么就不再導入. 因此，它是故意先等SpringBoot容器去解析那些用戶自定義的Bean,最后發(fā)現(xiàn)沒有才來導入這
// 些默認的組件
if (selector instanceof DeferredImportSelector) {
// deferredImportSelectors = new ArrayList<>()
// 這邊會將兩個參數(shù)封裝下加入到deferredImportSelectors中,后面處理
// 加入到deferredImportSelectors中后,具體的處理是this.deferredImportSelectorHandler.process();
this.deferredImportSelectorHandler.handle(configClass, (DeferredImportSelector) selector);
}// 步驟四就是從這里開始分析的
public void parse(Set<beandefinitionholder> configCandidates) {
// 刪除部分代碼，實際執(zhí)行時這里的configCandidates就一個springBootApplication代表的主配置類
for (BeanDefinitionHolder holder : configCandidates) {
// 獲取BeanDefinition
BeanDefinition bd = holder.getBeanDefinition();
// 我們的SpringBootApplication會走到這邊,下面先分析這邊
parse(((AnnotatedBeanDefinition) bd).getMetadata(), holder.getBeanName());
}
// 給容器中導入xxxAutoConfiguration,我們現(xiàn)在分析這邊
this.deferredImportSelectorHandler.process();
}// 上面方法會走到這里
public void processGroupImports() {
for (DeferredImportSelectorGrouping grouping : this.groupings.values()) {
// 下面先分析這個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() {
// 這邊的deferredImports是通過grouping.add(deferredImport)添加進去的
for (DeferredImportSelectorHolder deferredImport : this.deferredImports) {
this.group.process(deferredImport.getConfigurationClass().getMetadata(),
deferredImport.getImportSelector());
}
return this.group.selectImports();
}
public void process(AnnotationMetadata annotationMetadata, DeferredImportSelector deferredImportSelector) {
// 下面先分析下這個getAutoConfigurationEntry方法
AutoConfigurationEntry autoConfigurationEntry = ((AutoConfigurationImportSelector) deferredImportSelector)
.getAutoConfigurationEntry(getAutoConfigurationMetadata(), annotationMetadata);
// 加入到這個autoConfigurationEntries中
this.autoConfigurationEntries.add(autoConfigurationEntry);
for (String importClassName : autoConfigurationEntry.getConfigurations()) {
// 接著依次遍歷放入到這個map中,Map<string, annotationmetadata> entries = new LinkedHashMap<>()
this.entries.putIfAbsent(importClassName, annotationMetadata);
}
}// 這邊就到了AutoConfigurationImportSelector類的方法中
protected AutoConfigurationEntry getAutoConfigurationEntry(AutoConfigurationMetadata autoConfigurationMetadata,
AnnotationMetadata annotationMetadata) {
// 判斷是否支持自動配置
if (!isEnabled(annotationMetadata)) {
return EMPTY_ENTRY;
}
// 這個attributes屬性就是上圖中顯示的,用來過濾自動配置類的
AnnotationAttributes attributes = getAttributes(annotationMetadata);
// 下面分析這個方法,這個就是加載容器中的自動配置類
List<string> configurations = getCandidateConfigurations(annotationMetadata, attributes);
// 去除重復的,方法就是放入set再放入list中
configurations = removeDuplicates(configurations);
// 去除掉應該被排除的
Set<string> exclusions = getExclusions(annotationMetadata, attributes);
checkExcludedClasses(configurations, exclusions);
configurations.removeAll(exclusions);
// 通過filter過濾,下面分析,過濾完發(fā)現(xiàn)只有22個了
configurations = filter(configurations, autoConfigurationMetadata);
// 發(fā)布一個事件,好像沒有做啥關鍵的
fireAutoConfigurationImportEvents(configurations, exclusions);
// 將configurations封裝成AutoConfigurationEntry返回
return new AutoConfigurationEntry(configurations, exclusions);
}
protected boolean isEnabled(AnnotationMetadata metadata) {
if (getClass() == AutoConfigurationImportSelector.class) {
// 判斷有沒有配置這個屬性,沒有的話默認為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,那么這邊就是獲取容器中所有的字段配置類
List<string> configurations = SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(),
getBeanClassLoader());
return configurations;
}protected List<autoconfigurationimportfilter> getAutoConfigurationImportFilters() {
return SpringFactoriesLoader.loadFactories(AutoConfigurationImportFilter.class, this.beanClassLoader);
}// 上面分析的是配置類解析的步驟四 parser.parse(candidates); // 下面來看第五步,步驟四中解析得到的配置類會放在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) {
// 判斷是否應該跳過
if (trackedConditionEvaluator.shouldSkip(configClass)) {
return;
}
// 向容器中注入這個配置類所代表的的BeanDefinition
if (configClass.isImported()) {
registerBeanDefinitionForImportedConfigurationClass(configClass);
}
// 遍歷這個配置類的所有的Bean方法,注入這些@Bean標注的方法要引入的BeanDefinition
for (BeanMethod beanMethod : configClass.getBeanMethods()) {
loadBeanDefinitionsForBeanMethod(beanMethod);
}
// 處理該配置類上的@ImportResource指定的配置文件,就是Spring中常用的XML配置方式
// 這邊會通過解析該XML文件給容器中注入BeanDefinition,SpringBoot中不推薦這種方式,具體就不往下分析了
loadBeanDefinitionsFromImportedResources(configClass.getImportedResources());
// 處理步驟四中D解析@Import注解時獲得的importBeanDefinitionRegistrars,調用其registerBeanDefinitions
// 方法給容器中注入BeanDefinition,這在前面講解@Import方式時已經(jīng)講過了
loadBeanDefinitionsFromRegistrars(configClass.getImportBeanDefinitionRegistrars());
}private void loadBeanDefinitionsFromRegistrars(Map<ImportBeanDefinitionRegistrar, AnnotationMetadata> registrars) {
registrars.forEach((registrar, metadata) -> registrar.registerBeanDefinitions(metadata, this.registry));
}以上是“SpringBoot如何解析配置類以及集成第三方配置”這篇文章的所有內(nèi)容，感謝各位的閱讀！相信大家都有了一定的了解，希望分享的內(nèi)容對大家有所幫助，如果還想學習更多知識，歡迎關注億速云行業(yè)資訊頻道！
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