springboot自动配置原理,springboot注解大全

首页 > 经验 > 作者:YD1662022-11-01 13:42:12

springboot自动配置原理,springboot注解大全(1)

配置文件能写什么?

相信接触过 SpringBoot 的朋友都知道 SpringBoot 有各种 starter 依赖,想要什么直接勾选加进来就可以了。想要自定义的时候就直接在配置文件写自己的配置就好。但你们有没有困惑,为什么 springBoot 如此智能,到底配置文件里面能写什么呢?

带着这个疑问,我翻了下 SpringBoot 官网看到这么一些配置样例:

springboot自动配置原理,springboot注解大全(2)

SpringBoot 配置样例

发现 SpringBoot 可配置的东西非常多,上图只是节选。有兴趣的查看这个网址:

https://docs.spring.io/spring-boot/docs/2.1.3.RELEASE/reference/htmlsingle/#boot-features-external-config-yaml

自动配置原理

这里我拿之前创建过的 SpringBoot 来举例讲解 SpringBoot 的自动配置原理,首先看这么一段代码:

@SpringBootApplication

public class JpaApplication {

public static void main(String[] args) {

SpringApplication.run(JpaApplication.class, args);

}

}

毫无疑问这里只有 @SpringBootApplication 值得研究,进入 @SpringBootApplication 的源码:

springboot自动配置原理,springboot注解大全(3)

@SpringBootApplication 源码

SpringBoot 启动的时候加载主配置类,开启了自动配置功能 @EnableAutoConfiguration,再进入 @EnableAutoConfiguration 源码:

springboot自动配置原理,springboot注解大全(4)

@EnableAutoConfiguration 源码

发现最重要的就是 @Import(AutoConfigurationImportSelector.class) 这个注解,其中的 AutoConfigurationImportSelector 类的作用就是往 Spring 容器中导入组件,我们再进入这个类的源码,发现有这几个方法:

/**

* 方法用于给容器中导入组件

**/

@Override

public String[] selectImports(AnnotationMetadata annotationMetadata) {

if (!isEnabled(annotationMetadata)) {

return NO_IMPORTS;

}

AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader

.loadMetadata(this.beanClassLoader);

AutoConfigurationEntry autoConfigurationEntry = getAutoConfigurationEntry(

autoConfigurationMetadata, annotationMetadata); // 获取自动配置项

return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());

}

// 获取自动配置项

protected AutoConfigurationEntry getAutoConfigurationEntry(

AutoConfigurationMetadata autoConfigurationMetadata,

AnnotationMetadata annotationMetadata) {

if (!isEnabled(annotationMetadata)) {

return EMPTY_ENTRY;

}

AnnotationAttributes attributes = getAttributes(annotationMetadata);

List < String > configurations = getCandidateConfigurations(annotationMetadata,

attributes); // 获取一个自动配置 List ,这个 List 就包含了所有自动配置的类名

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);

}

// 获取一个自动配置 List ,这个 List 就包含了所有的自动配置的类名

protected List < String > getCandidateConfigurations(AnnotationMetadata metadata,

AnnotationAttributes attributes) {

// 通过 getSpringFactoriesLoaderFactoryClass 获取默认的 EnableAutoConfiguration.class 类名,传入 loadFactoryNames 方法

List < String > configurations = SpringFactoriesLoader.loadFactoryNames(

getSpringFactoriesLoaderFactoryClass(), 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;

}

// 默认的 EnableAutoConfiguration.class 类名

protected Class<?> getSpringFactoriesLoaderFactoryClass() {

return EnableAutoConfiguration.class;

}

代码注释很清楚:

  1. 首先注意到 selectImports 方法,其实从方法名就能看出,这个方法用于给容器中导入组件,然后跳到 getAutoConfigurationEntry 方法就是用于获取自动配置项的。
  2. 再来进入 getCandidateConfigurations 方法就是 获取一个自动配置 List ,这个 List 就包含了所有的自动配置的类名 。
  3. 再进入 SpringFactoriesLoader 类的 loadFactoryNames 方法,跳转到 loadSpringFactories 方法发现 ClassLoader 类加载器指定了一个 FACTORIES_RESOURCE_LOCATION 常量。
  4. 然后利用 PropertiesLoaderUtils 把 ClassLoader 扫描到的这些文件的内容包装成 properties 对象,从 properties 中获取到 EnableAutoConfiguration.class 类(类名)对应的值,然后把他们添加在容器中。

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

String factoryClassName = factoryClass.getName();

return loadSpringFactories(classLoader).getOrDefault(factoryClassName, Collections.emptyList());

}

private static Map < String, List < String >> loadSpringFactories(@Nullable ClassLoader classLoader) {

MultiValueMap < String, String > result = cache.get(classLoader);

if (result != null) {

return result;

}

try {

// 扫描所有 jar 包类路径下 META-INF/spring.factories

Enumeration < URL > urls = (classLoader != null ?

classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :

ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));

result = new LinkedMultiValueMap < > ();

while (urls.hasMoreElements()) {

URL url = urls.nextElement();

UrlResource resource = new UrlResource(url);

// 把扫描到的这些文件的内容包装成 properties 对象

Properties properties = PropertiesLoaderUtils.loadProperties(resource);

for (Map.Entry < ? , ? > entry : properties.entrySet()) {

String factoryClassName = ((String) entry.getKey()).trim();

for (String factoryName: StringUtils.commaDelimitedListToStringArray((String) entry.getValue())) {

// 从 properties 中获取到 EnableAutoConfiguration.class 类(类名)对应的值,然后把他们添加在容器中

result.add(factoryClassName, factoryName.trim());

}

}

}

cache.put(classLoader, result);

return result;

} catch (IOException ex) {

throw new IllegalArgumentException("Unable to load factories from location ["

FACTORIES_RESOURCE_LOCATION "]", ex);

}

}

点击 FACTORIES_RESOURCE_LOCATION 常量,我发现它指定的是 jar 包类路径下 META-INF/spring.factories 文件:

public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";

将类路径下 META-INF/spring.factories 里面配置的所有 EnableAutoConfiguration 的值加入到了容器中,所有的 EnableAutoConfiguration 如下所示:注意到 EnableAutoConfiguration 有一个 = 号,= 号后面那一串就是这个项目需要用到的自动配置类。

# 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,\

org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration,\

org.springframework.boot.autoconfigure.cloud.CloudServiceConnectorsAutoConfiguration,\

org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration,\

org.springframework.boot.autoconfigure.context.MessageSourceAutoConfiguration,\

org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration,\

org.springframework.boot.autoconfigure.couchbase.CouchbaseAutoConfiguration,\

org.springframework.boot.autoconfigure.dao.PersistenceExceptionTranslationAutoConfiguration,\

org.springframework.boot.autoconfigure.data.cassandra.CassandraDataAutoConfiguration,\

org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveDataAutoConfiguration,\

org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveRepositoriesAutoConfiguration,\

org.springframework.boot.autoconfigure.data.cassandra.CassandraRepositoriesAutoConfiguration,\

org.springframework.boot.autoconfigure.data.couchbase.CouchbaseDataAutoConfiguration,\

org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveDataAutoConfiguration,\

org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveRepositoriesAutoConfiguration,\

org.springframework.boot.autoconfigure.data.couchbase.CouchbaseRepositoriesAutoConfiguration,\

org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchAutoConfiguration,\

org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchDataAutoConfiguration,\

org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchRepositoriesAutoConfiguration,\

org.springframework.boot.autoconfigure.data.jdbc.JdbcRepositoriesAutoConfiguration,\

org.springframework.boot.autoconfigure.data.jpa.JpaRepositoriesAutoConfiguration,\

org.springframework.boot.autoconfigure.data.ldap.LdapRepositoriesAutoConfiguration,\

org.springframework.boot.autoconfigure.data.mongo.MongoDataAutoConfiguration,\

org.springframework.boot.autoconfigure.data.mongo.MongoReactiveDataAutoConfiguration,\

org.springframework.boot.autoconfigure.data.mongo.MongoReactiveRepositoriesAutoConfiguration,\

org.springframework.boot.autoconfigure.data.mongo.MongoRepositoriesAutoConfiguration,\

org.springframework.boot.autoconfigure.data.neo4j.Neo4jDataAutoConfiguration,\

org.springframework.boot.autoconfigure.data.neo4j.Neo4jRepositoriesAutoConfiguration,\

org.springframework.boot.autoconfigure.data.solr.SolrRepositoriesAutoConfiguration,\

org.springframework.boot.autoconfigure.data.redis.RedisAutoConfiguration,\

org.springframework.boot.autoconfigure.data.redis.RedisReactiveAutoConfiguration,\

org.springframework.boot.autoconfigure.data.redis.RedisRepositoriesAutoConfiguration,\

org.springframework.boot.autoconfigure.data.rest.RepositoryRestMvcAutoConfiguration,\

org.springframework.boot.autoconfigure.data.web.SpringDataWebAutoConfiguration,\

org.springframework.boot.autoconfigure.elasticsearch.jest.JestAutoConfiguration,\

org.springframework.boot.autoconfigure.elasticsearch.rest.RestClientAutoConfiguration,\

org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration,\

org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration,\

org.springframework.boot.autoconfigure.gson.GsonAutoConfiguration,\

org.springframework.boot.autoconfigure.h2.H2ConsoleAutoConfiguration,\

org.springframework.boot.autoconfigure.hateoas.HypermediaAutoConfiguration,\

org.springframework.boot.autoconfigure.hazelcast.HazelcastAutoConfiguration,\

org.springframework.boot.autoconfigure.hazelcast.HazelcastJpaDependencyAutoConfiguration,\

org.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration,\

org.springframework.boot.autoconfigure.http.codec.CodecsAutoConfiguration,\

org.springframework.boot.autoconfigure.influx.InfluxDbAutoConfiguration,\

org.springframework.boot.autoconfigure.info.ProjectInfoAutoConfiguration,\

org.springframework.boot.autoconfigure.integration.IntegrationAutoConfiguration,\

org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration,\

org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration,\

org.springframework.boot.autoconfigure.jdbc.JdbcTemplateAutoConfiguration,\

org.springframework.boot.autoconfigure.jdbc.JndiDataSourceAutoConfiguration,\

org.springframework.boot.autoconfigure.jdbc.XADataSourceAutoConfiguration,\

org.springframework.boot.autoconfigure.jdbc.DataSourceTransactionManagerAutoConfiguration,\

org.springframework.boot.autoconfigure.jms.JmsAutoConfiguration,\

org.springframework.boot.autoconfigure.jmx.JmxAutoConfiguration,\

org.springframework.boot.autoconfigure.jms.JndiConnectionFactoryAutoConfiguration,\

org.springframework.boot.autoconfigure.jms.activemq.ActiveMQAutoConfiguration,\

org.springframework.boot.autoconfigure.jms.artemis.ArtemisAutoConfiguration,\

org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAutoConfiguration,\

org.springframework.boot.autoconfigure.jersey.JerseyAutoConfiguration,\

org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,\

org.springframework.boot.autoconfigure.jsonb.JsonbAutoConfiguration,\

org.springframework.boot.autoconfigure.kafka.KafkaAutoConfiguration,\

org.springframework.boot.autoconfigure.ldap.embedded.EmbeddedLdapAutoConfiguration,\

org.springframework.boot.autoconfigure.ldap.LdapAutoConfiguration,\

org.springframework.boot.autoconfigure.liquibase.LiquibaseAutoConfiguration,\

org.springframework.boot.autoconfigure.mail.MailSenderAutoConfiguration,\

org.springframework.boot.autoconfigure.mail.MailSenderValidatorAutoConfiguration,\

org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration,\

org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration,\

org.springframework.boot.autoconfigure.mongo.MongoReactiveAutoConfiguration,\

org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration,\

org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration,\

org.springframework.boot.autoconfigure.quartz.QuartzAutoConfiguration,\

org.springframework.boot.autoconfigure.reactor.core.ReactorCoreAutoConfiguration,\

org.springframework.boot.autoconfigure.security.servlet.SecurityAutoConfiguration,\

org.springframework.boot.autoconfigure.security.servlet.SecurityRequestMatcherProviderAutoConfiguration,\

org.springframework.boot.autoconfigure.security.servlet.UserDetailsServiceAutoConfiguration,\

org.springframework.boot.autoconfigure.security.servlet.SecurityFilterAutoConfiguration,\

org.springframework.boot.autoconfigure.security.reactive.ReactiveSecurityAutoConfiguration,\

org.springframework.boot.autoconfigure.security.reactive.ReactiveUserDetailsServiceAutoConfiguration,\

org.springframework.boot.autoconfigure.sendgrid.SendGridAutoConfiguration,\

org.springframework.boot.autoconfigure.session.SessionAutoConfiguration,\

org.springframework.boot.autoconfigure.security.oauth2.client.servlet.OAuth2ClientAutoConfiguration,\

org.springframework.boot.autoconfigure.security.oauth2.client.reactive.ReactiveOAuth2ClientAutoConfiguration,\

org.springframework.boot.autoconfigure.security.oauth2.resource.servlet.OAuth2ResourceServerAutoConfiguration,\

org.springframework.boot.autoconfigure.security.oauth2.resource.reactive.ReactiveOAuth2ResourceServerAutoConfiguration,\

org.springframework.boot.autoconfigure.solr.SolrAutoConfiguration,\

org.springframework.boot.autoconfigure.task.TaskExecutionAutoConfiguration,\

org.springframework.boot.autoconfigure.task.TaskSchedulingAutoConfiguration,\

org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration,\

org.springframework.boot.autoconfigure.transaction.TransactionAutoConfiguration,\

org.springframework.boot.autoconfigure.transaction.jta.JtaAutoConfiguration,\

org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration,\

org.springframework.boot.autoconfigure.web.client.RestTemplateAutoConfiguration,\

org.springframework.boot.autoconfigure.web.embedded.EmbeddedWebServerFactoryCustomizerAutoConfiguration,\

org.springframework.boot.autoconfigure.web.reactive.HttpHandlerAutoConfiguration,\

org.springframework.boot.autoconfigure.web.reactive.ReactiveWebServerFactoryAutoConfiguration,\

org.springframework.boot.autoconfigure.web.reactive.WebFluxAutoConfiguration,\

org.springframework.boot.autoconfigure.web.reactive.error.ErrorWebFluxAutoConfiguration,\

org.springframework.boot.autoconfigure.web.reactive.function.client.ClientHttpConnectorAutoConfiguration,\

org.springframework.boot.autoconfigure.web.reactive.function.client.WebClientAutoConfiguration,\

org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration,\

org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration,\

org.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration,\

org.springframework.boot.autoconfigure.web.servlet.HttpEncodingAutoConfiguration,\

org.springframework.boot.autoconfigure.web.servlet.MultipartAutoConfiguration,\

org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration,\

org.springframework.boot.autoconfigure.websocket.reactive.WebSocketReactiveAutoConfiguration,\

org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration,\

org.springframework.boot.autoconfigure.websocket.servlet.WebSocketMessagingAutoConfiguration,\

org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration,\

org.springframework.boot.autoconfigure.webservices.client.WebServiceTemplateAutoConfiguration

每一个这样的 xxxAutoConfiguration 类都是容器中的一个组件,都加入到容器中,用他们来做自动配置。上述的每一个自动配置类都有自动配置功能,也可在配置文件中自定义配置。

举例说明 Http 编码自动配置原理

@Configuration

// 表示这是一个配置类,以前编写的配置文件一样,也可以给容器中添加组件

@EnableConfigurationProperties(HttpEncodingProperties.class)

// 启动指定类的 ConfigurationProperties 功能;将配置文件中对应的值和 HttpEncodingProperties 绑定起来;并把 HttpEncodingProperties 加入到 ioc 容器中

@ConditionalOnWebApplication

// Spring 底层 @Conditional 注解,根据不同的条件,如果满足指定的条件,整个配置类里面的配置就会生效;判断当前应用是否是 web 应用,如果是,当前配置类生效

@ConditionalOnClass(CharacterEncodingFilter.class)

// 判断当前项目有没有这个类 CharacterEncodingFilter;SpringMVC 中进行乱码解决的过滤器;

@ConditionalOnProperty(prefix = "spring.http.encoding", value = "enabled", matchIfMissing = true)

// 判断配置文件中是否存在某个配置 spring.http.encoding.enabled;如果不存在,判断也是成立的

// 即使我们配置文件中不配置 pring.http.encoding.enabled=true,也是默认生效的;

public class HttpEncodingAutoConfiguration {

// 已经和 SpringBoot 的配置文件建立映射关系了

private final HttpEncodingProperties properties;

//只有一个有参构造器的情况下,参数的值就会从容器中拿

public HttpEncodingAutoConfiguration(HttpEncodingProperties properties) {

this.properties = properties;

}

@Bean

// 给容器中添加一个组件,这个组件的某些值需要从 properties 中获取

@ConditionalOnMissingBean(CharacterEncodingFilter.class)

public CharacterEncodingFilter characterEncodingFilter() {

CharacterEncodingFilter filter = new OrderedCharacterEncodingFilter();

filter.setEncoding(this.properties.getCharset().name());

filter.setForceRequestEncoding(this.properties.shouldForce(Type.REQUEST));

filter.setForceResponseEncoding(this.properties.shouldForce(Type.RESPONSE));

return filter;

}

自动配置类做了什么不在这里赘述,请见上面代码注释。所有在配置文件中能配置的属性都是在 xxxxProperties 类中封装的;配置文件能配置什么就可以参照某个功能对应的这个属性类,例如上述提到的 @EnableConfigurationProperties(HttpProperties.class) ,我们打开 HttpProperties 文件源码节选:

@ConfigurationProperties(prefix = "spring.http")

public class HttpProperties {

public static class Encoding {

public static final Charset DEFAULT_CHARSET = StandardCharsets.UTF_8;

/**

* Charset of HTTP requests and responses. Added to the "Content-Type" header if

* not set explicitly.

*/

private Charset charset = DEFAULT_CHARSET;

/**

* Whether to force the encoding to the configured charset on HTTP requests and

* responses.

*/

private Boolean force;

}

在上面可以发现里面的属性 charset 、force 等,都是我们可以在配置文件中指定的,它的前缀就是 spring.http.encoding 如:

springboot自动配置原理,springboot注解大全(5)

spring.http.encoding 属性

另外,如果配置文件中有配该属性就取配置文件的,若无就使用 XxxxProperties.class 文件的默认值,比如上述代码的 Charset 属性,如果不配那就使用 UTF-8 默认值。

总结
  1. SpringBoot 启动会加载大量的自动配置类
  2. 我们看我们需要的功能有没有 SpringBoot 默认写好的自动配置类;
  3. 我们再来看这个自动配置类中到底配置了哪些组件 ( 只要我们要用的组件有,我们就不需要再来配置,若没有,我们可能就要考虑自己写一个配置类让 SpringBoot 扫描了)
  4. 给容器中自动配置类添加组件的时候,会从 properties 类中获取某些属性。我们就可以在配置文件中指定这些属性的值;

xxxxAutoConfigurartion 自动配置类的作用就是给容器中添加组件

xxxxProperties 的作用就是封装配置文件中相关属性

至此,总算弄明白了 SpringBoot 的自动配置原理。我水平优先,如有不当之处,敬请指出,相互交流学习,希望对你们有帮助。

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