亲宝软件园·资讯

展开

我是如何做到springboot自动配置原理解析

知识追寻者 人气:2

一前言

springboot 2.0.0版本分析,整体的自动配置流程如下:

具体配置参考官方文档:springboot-doc

二 @SpringBootApplication

核心注解@SpringBootConfiguration其实就是@Configuration注解,表示是个配置类;@EnableAutoConfiguration表示springboot的自动配置机制;@ComponentScan表示扫描允许注册额外的配置类;

@SpringBootApplication = @Configuration + @EnableAutoConfiguration + @ComponentScan

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) })
public @interface SpringBootApplication {

    // 排除不会被应用的自动配置类,classes形式
    @AliasFor(annotation = EnableAutoConfiguration.class, attribute = "exclude")
    Class<?>[] exclude() default {};

    // 排除不会被应用的自动配置类,字符串数组形式
    @AliasFor(annotation = EnableAutoConfiguration.class, attribute = "excludeName")
    String[] excludeName() default {};

    // 扫描基本包
    @AliasFor(annotation = ComponentScan.class, attribute = "basePackages")
    String[] scanBasePackages() default {};

    // 扫描基本类
    @AliasFor(annotation = ComponentScan.class, attribute = "basePackageClasses")
    Class<?>[] scanBasePackageClasses() default {};

}

三 AutoConfigurationImportSelector

点击@EnableAutoConfiguration 注解进入,看见@Import({AutoConfigurationImportSelector.class})是导入AutoConfigurationImportSelector类;

AutoConfigurationImportSelector 类是自动配置的核心类,其主要进行配置的功能是配置factory.propertiesspring内嵌集成引入的配置;

3.1 具体依赖图如下:

3.2 成员

    // 表示不引入配置
    private static final String[] NO_IMPORTS = new String[0];
    // 配置日志
    private static final Log logger = LogFactory.getLog(AutoConfigurationImportSelector.class);
    // 排除的自动配置
    private static final String PROPERTY_NAME_AUTOCONFIGURE_EXCLUDE = "spring.autoconfigure.exclude";
    // 声明 beanFactory
    private ConfigurableListableBeanFactory beanFactory;
    // 声明 environment (全局环境)
    private Environment environment;
    // 声明 beanClassLoader (bean的类加载器,加载spring-autoconfigure-metadata.properties中集成类)
    private ClassLoader beanClassLoader;
    // 声明 resourceLoader (资源加载器,加载spring的 factory.properties配置类)
    private ResourceLoader resourceLoader;

3.3 selectImports

selectImports 这个方法的主要功能就是导入factory.propertiesspring-autoconfigure-metadata.properties中的配置类;

 public String[] selectImports(AnnotationMetadata annotationMetadata) {
        if (!this.isEnabled(annotationMetadata)) {
            return NO_IMPORTS;
        } else {
            try {
              // 1 加载元数据信息,本质就是加载bean,这里的bean是指我我们spring-autoconfigure-metadata.properties中集成类
                AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader.loadMetadata(this.beanClassLoader);
                // 2 AnnotationAttributes本质是个map
                AnnotationAttributes attributes = this.getAttributes(annotationMetadata);
                // 3  获得 spring.factories 中的配置类
                List<String> configurations = this.getCandidateConfigurations(annotationMetadata, attributes);
                // 4  配置类复制用于排序不需要的配置类
                configurations = this.removeDuplicates(configurations);
                //  优先级排序
                configurations = this.sort(configurations, autoConfigurationMetadata);
                // 需移除配置类
                Set<String> exclusions = this.getExclusions(annotationMetadata, attributes);
                // 校验移除
                this.checkExcludedClasses(configurations, exclusions);
                // 执行移除配置类
                configurations.removeAll(exclusions);
                configurations = this.filter(configurations, autoConfigurationMetadata);
                this.fireAutoConfigurationImportEvents(configurations, exclusions);
                return StringUtils.toStringArray(configurations);
            } catch (IOException var6) {
                throw new IllegalStateException(var6);
            }
        }
    }

1 分析
AutoConfigurationMetadataLoader.loadMetadata(this.beanClassLoader);

进入方法发现加载的元数据信息的路径是 META-INF/spring-autoconfigure-metadata.properties

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

在自动配置包底下找到spring-autoconfigure-metadata.properties


点进属性文件发现都spring自动配置类名的配置信息,部分如下:

#Thu Mar 01 04:46:13 UTC 2018
org.springframework.boot.autoconfigure.data.jpa.JpaRepositoriesAutoConfiguration=
org.springframework.boot.autoconfigure.web.client.RestTemplateAutoConfiguration.AutoConfigureAfter=org.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveDataAutoConfiguration.Configuration=
org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveDataAutoConfiguration.ConditionalOnClass=com.datastax.driver.core.Cluster,org.springframework.data.cassandra.core.ReactiveCassandraTemplate,reactor.core.publisher.Flux
org.springframework.boot.autoconfigure.data.solr.SolrRepositoriesAutoConfiguration.ConditionalOnClass=org.apache.solr.client.solrj.SolrClient,org.springframework.data.solr.repository.SolrRepository
org.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration=
............................

我们随意点开其中的一个配置类,比如第一个HttpMessageConvertersAutoConfiguration,其中的class注解如下,可以发现其自动配置类都是通过注解配置;

// 表示配置类相当于xml中的 bean标签
@Configuration
// 判定是否存在HttpMessageConverter.class类,如果不存在则引入
@ConditionalOnClass({HttpMessageConverter.class})
// 在这三个配置类配置之后再进行配置
@AutoConfigureAfter({GsonAutoConfiguration.class, JacksonAutoConfiguration.class, JsonbAutoConfiguration.class})
// 导入配置类相当于xml中的 import标签
@Import({JacksonHttpMessageConvertersConfiguration.class, GsonHttpMessageConvertersConfiguration.class, JsonbHttpMessageConvertersConfiguration.class})
public class HttpMessageConvertersAutoConfiguration {

3 分析

this.getCandidateConfigurations(annotationMetadata, attributes);方法的主要功能是获取候选配置;

进入getCandidateConfigurations方法发现里面的主要方法是loadFactoryNames;

// 获得factory配置信息类名
 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;
    }

进入 loadFactoryNames 方法 主要是2部分;第一个是loadSpringFactories(classLoader),第二个是getOrDefault

// 加载factory类名
 public static List<String> loadFactoryNames(Class<?> factoryClass, @Nullable ClassLoader classLoader) {
        String factoryClassName = factoryClass.getName();
        //  返回类名的list
        return (List)loadSpringFactories(classLoader).getOrDefault(factoryClassName, Collections.emptyList());
    }

第一部分:
loadSpringFactories本质就是使用spring的Resource资源调用获得 spring.factories 中的配置类;

// 加载spring.factories中的配置类信息
private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
        MultiValueMap<String, String> result = (MultiValueMap)cache.get(classLoader);
        if (result != null) {
            return result;
        } else {
            try {
                // 获得 `spring.factories` 配置类的URL
                Enumeration<URL> urls = classLoader != null ? classLoader.getResources("META-INF/spring.factories") : ClassLoader.getSystemResources("META-INF/spring.factories");
                LinkedMultiValueMap result = new LinkedMultiValueMap();
                // 将 `spring.factories`  每个配置类的key 和 val 存储进 map
                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();
                        List<String> factoryClassNames = Arrays.asList(StringUtils.commaDelimitedListToStringArray((String)entry.getValue()));
                        result.addAll((String)entry.getKey(), factoryClassNames);
                    }
                }

                cache.put(classLoader, result);
                return result;
            } catch (IOException var9) {
                throw new IllegalArgumentException("Unable to load factories from location [META-INF/spring.factories]", var9);
            }
        }
    }

classLoader.getResources("META-INF/spring.factories") ;中找到自动配置包中的配置如下图:

spring.factories装载配置类部分信息如下,没错这些配置都是sping启动需要的配置类信息,监听器,过滤器,自动配置的start配置类,以及启动的失败的错误分析还有模板引擎的支持,详细大家翻下配置包即可;

# Initializers
org.springframework.context.ApplicationContextInitializer=\
org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,\
org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener
....................................

第二部分:
getOrDefault是个Map集合,map中有这个key时,就使用这个key值,如果没有就使用默认值defaultValue,返回也就是类名的list;

加载全部内容

相关教程
猜你喜欢
用户评论