第三模块:
@Target({ElementType.TYPE}) @Retention(RetentionPolicy.RUNTIME) @Documented @Inherited @SpringBootConfiguration @EnableAutoConfiguration @ComponentScan( excludeFilters = {@Filter( type = FilterType.CUSTOM, classes = {TypeExcludeFilter.class} ), @Filter( type = FilterType.CUSTOM, classes = {AutoConfigurationExcludeFilter.class} )}
进入@EnableAutoConfiguration程序中去
@Target({ElementType.TYPE}) @Retention(RetentionPolicy.RUNTIME) @Documented @Inherited @AutoConfigurationPackage @Import({AutoConfigurationImportSelector.class}) public @interface EnableAutoConfiguration { String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration"; Class<?>[] exclude() default {}; String[] excludeName() default {}; }
然后进入@AutoConfigurationPackage程序中去
// // Source code recreated from a .class file by IntelliJ IDEA // (powered by Fernflower decompiler) // package org.springframework.boot.autoconfigure; import java.lang.annotation.Documented; import java.lang.annotation.ElementType; import java.lang.annotation.Inherited; import java.lang.annotation.Retention; import java.lang.annotation.RetentionPolicy; import java.lang.annotation.Target; import org.springframework.boot.autoconfigure.AutoConfigurationPackages.Registrar; import org.springframework.context.annotation.Import; @Target({ElementType.TYPE}) @Retention(RetentionPolicy.RUNTIME) @Documented @Inherited @Import({Registrar.class}) public @interface AutoConfigurationPackage { String[] basePackages() default {}; Class<?>[] basePackageClasses() default {}; }
然后返回到下面的页面
package org.springframework.boot.autoconfigure; @Target({ElementType.TYPE}) @Retention(RetentionPolicy.RUNTIME) @Documented @Inherited @AutoConfigurationPackage @Import({AutoConfigurationImportSelector.class}) public @interface EnableAutoConfiguration { String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration"; Class<?>[] exclude() default {}; String[] excludeName() default {}; }
在上面的代码中找到:
AutoConfigurationImportSelector.class 点进去
第四模块:
package org.springframework.boot.autoconfigure; public class AutoConfigurationImportSelector implements DeferredImportSelector, BeanClassLoaderAware, ResourceLoaderAware, BeanFactoryAware, EnvironmentAware, Ordered { private static final AutoConfigurationImportSelector.AutoConfigurationEntry EMPTY_ENTRY = new AutoConfigurationImportSelector.AutoConfigurationEntry(); private static final String[] NO_IMPORTS = new String[0]; private static final Log logger = LogFactory.getLog(AutoConfigurationImportSelector.class); private static final String PROPERTY_NAME_AUTOCONFIGURE_EXCLUDE = "spring.autoconfigure.exclude"; private ConfigurableListableBeanFactory beanFactory; private Environment environment; private ClassLoader beanClassLoader; private ResourceLoader resourceLoader; private AutoConfigurationImportSelector.ConfigurationClassFilter configurationClassFilter; public AutoConfigurationImportSelector() { }
在上面的源码的基础上往下翻
在上面的图片中找到
List<String> configurations = this.getCandidateConfigurations(annotationMetadata, attributes);
然后点击getCandidateConfigurations这个单词
protected AutoConfigurationImportSelector.AutoConfigurationEntry getAutoConfigurationEntry(AnnotationMetadata annotationMetadata) { if (!this.isEnabled(annotationMetadata)) { return EMPTY_ENTRY; } else { AnnotationAttributes attributes = this.getAttributes(annotationMetadata); List<String> configurations = this.getCandidateConfigurations(annotationMetadata, attributes); configurations = this.removeDuplicates(configurations); Set<String> exclusions = this.getExclusions(annotationMetadata, attributes); this.checkExcludedClasses(configurations, exclusions); configurations.removeAll(exclusions); configurations = this.getConfigurationClassFilter().filter(configurations); this.fireAutoConfigurationImportEvents(configurations, exclusions); return new AutoConfigurationImportSelector.AutoConfigurationEntry(configurations, exclusions); } }
然后你会发现
protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) { List<String> configurations = new ArrayList(SpringFactoriesLoader.loadFactoryNames(this.getSpringFactoriesLoaderFactoryClass(), this.getBeanClassLoader())); ImportCandidates.load(AutoConfiguration.class, this.getBeanClassLoader()).forEach(configurations::add); Assert.notEmpty(configurations, "No auto configuration classes found in META-INF/spring.factories nor in META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports. If you are using a custom packaging, make sure that file is correct."); return configurations; }
第五模块:下面的单词有三个重点
SpringFactoriesLoader.loadFactoryNames(this.getSpringFactoriesLoaderFactoryClass()
先看第一个getSpringFactoriesLoaderFactoryClass() 单点击是 return EnableAutoConfiguration.class 程序的出口找到
protected Class<?> getSpringFactoriesLoaderFactoryClass() { return EnableAutoConfiguration.class; }
在点击第二个单词:loadFactoryNames 获取所有的配置名 点进去看一下
public static List<String> loadFactoryNames(Class<?> factoryType, @Nullable ClassLoader classLoader) { ClassLoader classLoaderToUse = classLoader; if (classLoader == null) { classLoaderToUse = SpringFactoriesLoader.class.getClassLoader(); } String factoryTypeName = factoryType.getName(); return (List)loadSpringFactories(classLoaderToUse).getOrDefault(factoryTypeName, Collections.emptyList()); }
SpringFactoriesLoader.loadFactoryNames(this.getSpringFactoriesLoaderFactoryClass()
最后一个单词SpringFactoriesLoade 点击进去
第六模块
public final class SpringFactoriesLoader { public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories"; private static final Log logger = LogFactory.getLog(SpringFactoriesLoader.class); static final Map<ClassLoader, Map<String, List<String>>> cache = new ConcurrentReferenceHashMap(); private SpringFactoriesLoader() { }
protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) { List<String> configurations = new ArrayList(SpringFactoriesLoader.loadFactoryNames(this.getSpringFactoriesLoaderFactoryClass(), this.getBeanClassLoader())); ImportCandidates.load(AutoConfiguration.class, this.getBeanClassLoader()).forEach(configurations::add); Assert.notEmpty(configurations, "No auto configuration classes found in META-INF/spring.factories nor in META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports. If you are using a custom packaging, make sure that file is correct."); return configurations; }
private static Map<String, List<String>> loadSpringFactories(ClassLoader classLoader) { Map<String, List<String>> result = (Map)cache.get(classLoader); if (result != null) { return result; } else { HashMap result = new HashMap(); try { Enumeration urls = classLoader.getResources("META-INF/spring.factories"); while(urls.hasMoreElements()) { URL url = (URL)urls.nextElement(); UrlResource resource = new UrlResource(url); Properties properties = PropertiesLoaderUtils.loadProperties(resource); Iterator var6 = properties.entrySet().iterator(); while(var6.hasNext()) { Entry<?, ?> entry = (Entry)var6.next(); String factoryTypeName = ((String)entry.getKey()).trim(); String[] factoryImplementationNames = StringUtils.commaDelimitedListToStringArray((String)entry.getValue()); String[] var10 = factoryImplementationNames; int var11 = factoryImplementationNames.length; for(int var12 = 0; var12 < var11; ++var12) { String factoryImplementationName = var10[var12]; ((List)result.computeIfAbsent(factoryTypeName, (key) -> { return new ArrayList(); })).add(factoryImplementationName.trim()); } } }
结论: springboot所有 自动配置都是在启动的时候扫描并加载: spring . factories所有的自动配置类都在这里面，但是不一-定生效, 要判断条件是否成立,只要导入了对应的start,就有对应的启动器了，有了启动器，我们自动装配就会生效，然后就配置成功!
springboot在启动的时候，从类路径下/META-INF/ spring . factories获取指定的值;
将这些自动配置的类导入容器，自动配置就会生效，帮我进行自动配置!
以前我们需要自动配置的东西，现在springboot帮我们做了
整合javaEE,解决方案和自动配置的东西都在spring-boot-autoconfigure-2.2.0.RELEASE.jar这个包下
它会把所有需要导入的组件,以类名的方式返回，这些
组件就会被添加到容器;
容器中也会存在非常多的xxAutoConfiguration的文件(@Bean),就是这些类给容器中导入了这个场景需要的所有组件;并自动配置，@Configuration ，JavaConfig!
有了自动配置类,免去了我们手动编写配置文件的工作!
核心要义 继承继承在继承 封装封装在封装
实现了SpringBoot自动配置
