浅谈springboot自动配置原理

浅谈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。

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);

}

tQcipzq

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;

}

AnnotQcipzqtationAttributes attributes = getAttributes(annotationMetadata);

List configurations = getCandidateConfigurations(annotationMetadata, attributes);

configurations = removeDuplicates(configurations);

Set 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 configurations = SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(),getBeanClassLoader());

return configurations;

}

这里又开始调用SpringFactoriesLoader.loadFactoryNhttp://ames。

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 result = (MultiValueMap)cache.get(classLoader);

if (result != null) {

return result;

} else {

try {

Enumeration 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

throws UnknownHostException {

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;

}

版权声明：本文内容由网络用户投稿，版权归原作者所有，本站不拥有其著作权，亦不承担相应法律责任。如果您发现本站中有涉嫌抄袭或描述失实的内容，请联系我们jiasou666@gmail.com 处理，核实后本网站将在24小时内删除侵权内容。