源码学习系列之SpringBoot自动配置源码学习（篇一）
ok，本博客尝试跟一下Springboot的自动配置源码，做一下笔记记录，自动配置是Springboot的一个很关键的特性，也容易被忽略的属性，因为这个属性被包括在@SpringBootApplication注解里，所以不去跟一下源码都不知道还有这个属性，ps：本博客源码基于SpringBoot1.5.7版本
@SpringBootApplication
ok，跟一下@SpringBootApplication，发现@SpringBootApplication其实是一个复合的注解，由很多注解构成，@EnableAutoConfiguration其实只是其一部分，@EnableAutoConfiguration就是开启自动配置的注解
//
// 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.SpringBootConfiguration;
import org.springframework.boot.context.TypeExcludeFilter;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.FilterType;
import org.springframework.context.annotation.ComponentScan.Filter;
import org.springframework.core.annotation.AliasFor;
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration //自动配置注解
@ComponentScan(
excludeFilters = {@Filter(
type = FilterType.CUSTOM,
classes = {TypeExcludeFilter.class}
), @Filter(
type = FilterType.CUSTOM,
classes = {AutoConfigurationExcludeFilter.class}
)}
)
public @interface SpringBootApplication {
....
Class<?>[] scanBasePackageClasses() default {};
}
@EnableAutoConfiguration
点进@EnableAutoConfiguration，比较重要的列出来：
- @AutoConfigurationPackage
- @Import({EnableAutoConfigurationImportSelector.class})
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.context.annotation.Import;
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import({EnableAutoConfigurationImportSelector.class})
public @interface EnableAutoConfiguration {
String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";
Class<?>[] exclude() default {};
String[] excludeName() default {};
}
@AutoConfigurationPackage
先看@AutoConfigurationPackage源码，这个注解是开启自动配置包的，关注点在@Import({Registrar.class})，核心在Registrar类
备注：@import注解是Spring的底层注解，作用是导入一个组件到容器里
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 {
}
Registrar 类是AutoConfigurationPackages类的静态内部类，
static class Registrar implements ImportBeanDefinitionRegistrar, DeterminableImports {
Registrar() {
}
public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {
AutoConfigurationPackages.register(registry, (new AutoConfigurationPackages.PackageImport(metadata)).getPackageName());
}
public Set<Object> determineImports(AnnotationMetadata metadata) {
return Collections.singleton(new AutoConfigurationPackages.PackageImport(metadata));
}
}
看一下(new AutoConfigurationPackages.PackageImport(metadata)).getPackageName()获取的是什么，用idea的工具，计算表达式，可以看到其实获取的是SpringBoot启动类上面的包名
AnnotationMetadata：SpringBoot注解元数据
所以，@AutoConfigurationPackage开启后，就可以将主配置类(@SpringBootApplication)所在包及其子包里面的所有组件都扫描到Spring容器里
public static void register(BeanDefinitionRegistry registry, String... packageNames) {
if (registry.containsBeanDefinition(BEAN)) {
BeanDefinition beanDefinition = registry.getBeanDefinition(BEAN);
ConstructorArgumentValues constructorArguments = beanDefinition.getConstructorArgumentValues();
constructorArguments.addIndexedArgumentValue(0, addBasePackages(constructorArguments, packageNames));
} else {// Spring容器里没有找到对应组件
/* 将组件注册到Spring容器里 */
GenericBeanDefinition beanDefinition = new GenericBeanDefinition(); beanDefinition.setBeanClass(AutoConfigurationPackages.BasePackages.class);
beanDefinition.getConstructorArgumentValues().addIndexedArgumentValue(0, packageNames);
beanDefinition.setRole(2);
registry.registerBeanDefinition(BEAN, beanDefinition);
}
}
ok，跟了源码，当然只是简单跟一下，没有特别细的跟，这个过程可以看出这里的组件扫描只是扫描主配置类(@SpringBootApplication)所在包及其子包里面的所有组件，所以，写了例子验证一下：
在Application类包外写个Controller测试类
@RestController
public class TestController {
@GetMapping("/hello")
public String hello(){
return "hello world!";
}
}
启动项目，进行访问，发现都是404找不到这个接口，再将这个Controller放在包里面，才可以扫描到
@Import({EnableAutoConfigurationImportSelector.class})
package org.springframework.boot.autoconfigure;
import org.springframework.core.type.AnnotationMetadata;
/** @deprecated */
@Deprecated
public class EnableAutoConfigurationImportSelector extends AutoConfigurationImportSelector {
public EnableAutoConfigurationImportSelector() {
}
protected boolean isEnabled(AnnotationMetadata metadata) {
return this.getClass().equals(EnableAutoConfigurationImportSelector.class) ? (Boolean)this.getEnvironment().getProperty("spring.boot.enableautoconfiguration", Boolean.class, true) : true;
}
}
主要看一下其基类AutoConfigurationImportSelector代码，看一下selectImport方法：
/**装载很多自动配置类，以全类名的方式返回一个字符数组**/
public String[] selectImports(AnnotationMetadata annotationMetadata) {
if (!this.isEnabled(annotationMetadata)) {
return NO_IMPORTS;
} else {
try {
//获取自动配置的元数据
AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader.loadMetadata(this.beanClassLoader);
//装载配置属性
AnnotationAttributes attributes = this.getAttributes(annotationMetadata);
//通过类加载器读取所有的配置类全类名
List<String> configurations = this.getCandidateConfigurations(annotationMetadata, attributes);
configurations = this.removeDuplicates(configurations);
configurations = this.sort(configurations, autoConfigurationMetadata);
Set<String> exclusions = this.getExclusions(annotationMetadata, attributes);
this.checkExcludedClasses(configurations, exclusions);
configurations.removeAll(exclusions);
configurations = this.filter(configurations, autoConfigurationMetadata);
this.fireAutoConfigurationImportEvents(configurations, exclusions);
return (String[])configurations.toArray(new String[configurations.size()]);
} catch (IOException var6) {
throw new IllegalStateException(var6);
}
}
}
- AutoConfigurationMetadata信息，获取整个JavaEE体系的一些配置类，当然是Springboot集成的，比如有WebMvcAutoConfiguration自动配置类
跟一下getCandidateConfigurations方法，SpringFactoriesLoader是Spring-code工程的工厂加载类，使用SpringFactoriesLoader，需要在模块的META-INF/spring.factories文件自己配置属性，这个Properties格式的文件中的key是接口、注解、或抽象类的全名，value是以逗号 “ , “ 分隔的实现类，使用SpringFactoriesLoader可以实现将相应的实现类注入Spirng容器
protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
List<String> configurations = SpringFactoriesLoader.loadFactoryNames(this.getSpringFactoriesLoaderFactoryClass(), this.getBeanClassLoader());
Assert.notEmpty(configurations, "No auto configuration classes found in META-INF/spring.factories. If you are using a custom packaging, make sure that file is correct.");
return configurations;
}
loadFactoryNames方法代码，
public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";
/* 将spring.factories的类都装载到Spring容器*/
public static List<String> loadFactoryNames(Class<?> factoryClass, ClassLoader classLoader) {
String factoryClassName = factoryClass.getName();
try {
//将META-INF/spring.factories文件里配置的属性都装载到Enumeration数据结构里
Enumeration<URL> urls = classLoader != null ? classLoader.getResources("META-INF/spring.factories") : ClassLoader.getSystemResources("META-INF/spring.factories");
ArrayList result = new ArrayList();
//遍历获取属性，然后再获取对应的配置类全类名
while(urls.hasMoreElements()) {
URL url = (URL)urls.nextElement();
Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url));
String factoryClassNames = properties.getProperty(factoryClassName);
result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassNames)));
}
return result;
} catch (IOException var8) {
throw new IllegalArgumentException("Unable to load [" + factoryClass.getName() + "] factories from location [" + "META-INF/spring.factories" + "]", var8);
}
}
然后META-INF/spring.factories文件放在哪？很显然是放在Springboot的自动配置模块里，如图：
所以，@Import({EnableAutoConfigurationImportSelector.class})开启之后，主要是EnableAutoConfigurationImportSelector这个类的作用就是在SpringBoot启动时候将从SpringBoot自动配置工程的META-INF/spring.factories文件中获取指定的值，经过SpringFactoriesLoader加载之后将很多自动配置类加载到Spring容器，所以我们不需要配置，mvc等等默认配置就已经随着SpringBoot启动而自动生效
ok，Springboot的自动配置类都在这个包里，源码很多，所以本博客只是简单跟一下源码
