springboot自动配置原理

优惠码优惠 2019-08-29

spring 配置 string class list

springboot自动配置原理
从main函数说起

 一切的开始要从SpringbootApplication注解说起。

@SpringBootApplication
public class MyBootApplication {

public static void main(String[] args) {
    SpringApplication.run(MyBootApplication.class);
} 

}

@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan
public @interface SpringBootApplication {

}

   其中最重要的就是EnableAutoConfiguration注解,开启自动配置。

@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 {};

}

   通过Import注解导入AutoConfigurationImportSelector。在这个类中加载/META-INF/spring.factories文件的信息,然后筛选出以EnableAutoConfiguration为key的数据,加载到IOC容器中,实现自动配置功能。

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(AutoConfigurationPackages.Registrar.class)
public @interface AutoConfigurationPackage {

}

   从表面看就是自动配置包,主要使用了Import注解,导入了Registrar类。这里Registrar类的registerBeanDefinitions方法导包,也就是导入当前main函数所在路径的包地址,我这里是com.zhangfei。

QQ截图20190828173328.jpg

怎么自动装配其他N个类
Import({AutoConfigurationImportSelector.class})该注解给当前配置类导入另外N个自动配置类。
这里既然导入N个自动配置类,那么都导入哪些类呢?

//AutoConfigurationImportSelector实现DeferredImportSelector接口,而DeferredImportSelector接口又继承了ImportSelector
public interface ImportSelector {

String[] selectImports(AnnotationMetadata var1);

}
QQ截图20190828174002.jpg
AutoConfigurationImportSelector通过实现接口ImportSelector的selectImports方法返回需要导入的组件,selectImports方法返回一个全类名字符串数组。

主角上场
//AutoConfigurationImportSelector.java
@Override
public String[] selectImports(AnnotationMetadata annotationMetadata) {

if (!isEnabled(annotationMetadata)) {
    return NO_IMPORTS;
}
AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader.loadMetadata(this.beanClassLoader);
AutoConfigurationEntry autoConfigurationEntry = getAutoConfigurationEntry(autoConfigurationMetadata,annotationMetadata);
return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());

}

protected AutoConfigurationEntry getAutoConfigurationEntry(AutoConfigurationMetadata autoConfigurationMetadata,AnnotationMetadata annotationMetadata) {

if (!isEnabled(annotationMetadata)) {
    return EMPTY_ENTRY;
}
AnnotationAttributes attributes = getAttributes(annotationMetadata);
List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);
configurations = removeDuplicates(configurations);
Set<String> exclusions = getExclusions(annotationMetadata, attributes);
checkExcludedClasses(configurations, exclusions);
configurations.removeAll(exclusions);
configurations = filter(configurations, autoConfigurationMetadata);
fireAutoConfigurationImportEvents(configurations, exclusions);
return new AutoConfigurationEntry(configurations, exclusions);

}

protected List getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {

List<String> configurations = SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(),getBeanClassLoader());
return configurations;

}
这里又开始调用SpringFactoriesLoader.loadFactoryNames。
SpringFactoriesLoader.loadFactoryNames方法中关键的三步:
(1)从当前项目的类路径中获取所有 META-INF/spring.factories 这个文件下的信息.
(2)将上面获取到的信息封装成一个 Map 返回,EnableAutoConfiguration为key。
(3)从返回的Map中通过刚才传入的 EnableAutoConfiguration.class参数,获取该 key 下的所有值。

public static List loadFactoryNames(Class<?> factoryClass, @Nullable ClassLoader classLoader) {

String factoryClassName = factoryClass.getName();
return (List)loadSpringFactories(classLoader).getOrDefault(factoryClassName, Collections.emptyList());

}

private static Map> loadSpringFactories(@Nullable ClassLoader classLoader) {

MultiValueMap<String, String> result = (MultiValueMap)cache.get(classLoader);
if (result != null) {
    return result;
} else {
    try {
        Enumeration<URL> urls = classLoader != null ? classLoader.getResources("META-INF/spring.factories") : ClassLoader.getSystemResources("META-INF/spring.factories");
        LinkedMultiValueMap result = new LinkedMultiValueMap();

        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 factoryClassName = ((String)entry.getKey()).trim();
                String[] var9 = StringUtils.commaDelimitedListToStringArray((String)entry.getValue());
                int var10 = var9.length;

                for(int var11 = 0; var11 < var10; ++var11) {
                    String factoryName = var9[var11];
                    result.add(factoryClassName, factoryName.trim());
                }
            }
        }

        cache.put(classLoader, result);
        return result;
    } catch (IOException var13) {
        throw new IllegalArgumentException("Unable to load factories from location [META-INF/spring.factories]", var13);
    }
}

}
自动配置都有哪些内容呢?

Auto Configure

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\
org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\
org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,\
org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration,\
org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration,\
...其他省略
XXXAutoConfiguration和XXProperties
在spring.factories文件中看到的都是自动配置类,那么自动配置用到的属性值在那里呢?我们拿出redis为例

@Configuration
@ConditionalOnClass(RedisOperations.class) //判断当前项目有没有这个类RedisOperations.class
@EnableConfigurationProperties(RedisProperties.class) //启用配置属性,这里看到了熟悉的XXXProperties
@Import({ LettuceConnectionConfiguration.class, JedisConnectionConfiguration.class }) //导入这两个类
public class RedisAutoConfiguration {

@Bean
@ConditionalOnMissingBean(name = "redisTemplate")
public RedisTemplate<Object, Object> redisTemplate(RedisConnectionFactory redisConnectionFactory)
        throws UnknownHostException {
    RedisTemplate<Object, Object> template = new RedisTemplate<>();
    template.setConnectionFactory(redisConnectionFactory);
    return template;
}

@Bean
@ConditionalOnMissingBean
public StringRedisTemplate stringRedisTemplate(RedisConnectionFactory redisConnectionFactory)
        throws UnknownHostException {
    StringRedisTemplate template = new StringRedisTemplate();
    template.setConnectionFactory(redisConnectionFactory);
    return template;
}

}

//这里则保存redis初始化时的属性
@ConfigurationProperties(prefix = "spring.redis")
public class RedisProperties {

private int database = 0;

private String url;

private String host = "localhost";

private String password;

private int port = 6379;

private boolean ssl;

}
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