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前言
这个月过去两天了,这篇文章才跟大家见面,最近比较累,大家见谅下。下班后闲着无聊看了下 SpringBoot 中的自动配置,把我的理解跟大家说下。
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:
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 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:
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:
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。
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。
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。
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。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:
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。
后语
如果本文对你哪怕有一丁点帮助,请帮忙点好看。你的好看是我坚持写作的动力。
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