springboot的自动配置

Posted 2021-01-09 qunincey

1.spring-boot启动的main入口

SpringBootApplication注解，点击注解，发现这个注解中的@EnableAutoConfiguration 这个注解表示开启自动配置，自动配置一些组件

@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 {};
}

　　这个注解中import这个注解里

AutoConfigurationImportSelector这个类就会扫描所有包，找到所有的配置类，点开这个类

里面最重要的就是这个selectImports方法，我们来分析一下：

public String[] selectImports(AnnotationMetadata annotationMetadata) {
        if (!this.isEnabled(annotationMetadata)) {
            return NO_IMPORTS;
        } else {
            AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader.loadMetadata(this.beanClassLoader);
            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.filter(configurations, autoConfigurationMetadata);
            this.fireAutoConfigurationImportEvents(configurations, exclusions);
            return StringUtils.toStringArray(configurations);
        }
    }　

　

 AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader.loadMetadata(this.beanClassLoader);//会去调用loadMetadata方法，传入的是一个beanClassLoader

查看loadMetadata发现其调用的是重载方法

 public static AutoConfigurationMetadata loadMetadata(ClassLoader classLoader) {
        return loadMetadata(classLoader, "META-INF/spring-autoconfigure-metadata.properties");
    }

    static AutoConfigurationMetadata loadMetadata(ClassLoader classLoader, String path) {
        try {
            Enumeration<URL> urls = classLoader != null ? classLoader.getResources(path) : ClassLoader.getSystemResources(path);
            Properties properties = new Properties();

            while(urls.hasMoreElements()) {
                properties.putAll(PropertiesLoaderUtils.loadProperties(new UrlResource((URL)urls.nextElement())));
            }

            return loadMetadata(properties);
        } catch (IOException var4) {
            throw new IllegalArgumentException("Unable to load @ConditionalOnClass location [" + path + "]", var4);
        }
    }

打断点后发现是把“”META-INF/spring-autoconfigure-metadata.properties“”这个文件变成一个properties返回

然后在org.springframework.boot下随便找一个配置类看一下具体实现，我这里找的是

HttpEncodingAutoConfiguration

这个类上面有个

@EnableConfigurationProperties({HttpEncodingProperties.class})
而点开这个类，里面就见到我熟悉的

ConfigurationProperties
说明我们要找的自动配置的类就在这里，

@ConfigurationProperties(
    prefix = "spring.http.encoding"
)

　　

这个类里面也是我们能够在springboot中能够使用的所有字段，验证一下