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自动配置原理

自动配置原理

作者: 杨健kimyeung | 来源:发表于2020-08-06 11:50 被阅读0次

概要

  1. SpringBoot启动的时候加载主配置类，开启了自动配置功能 @EnableAutoConfiguration

  2. 利用EnableAutoConfigurationImportSelector给容器中导入一些组件可以查看selectImports()方法的内容

    • List configurations = getCandidateConfigurations(annotationMetadata, attributes);获取候选的配置

    • SpringFactoriesLoader.loadFactoryNames()扫描所有jar包类路径下META‐INF/spring.factories

  3. 把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

@EnableAutoConfiguration

作用

@EnableAutoConfiguration这个类很重要,主要的作用是自动载入应用程序所需要的所有默认配置,达到智能的自动配置作用

主要是通过他来实现约定大于配置

源码

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" cid="n19" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; margin-top: 0px; margin-bottom: 20px; font-size: 0.9rem; display: block; break-inside: avoid; text-align: left; white-space: normal; background: rgb(51, 51, 51); position: relative !important; padding: 10px 10px 10px 30px; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
// 自动配置包
@AutoConfigurationPackage
// 给IOC容器导入组件
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";
Class<?>[] exclude() default {};
​
String[] excludeName() default {};
}
​</pre>

说明

@Import(AutoConfigurationImportSelector.class) 这个注解里的AutoConfigurationImportSelector最为重要

利用AutoConfigurationImportSelector，@EnableAutoConfiguration可以帮助SpringBoot应用将所有符合条件的@Configuration配置都加载到当前SpringBoot创建并使用的IoC容器。

AutoConfigurationImportSelector

selectImports()方法

首先执行selectImports()方法 中调用 getAutoConfigurationEntry()

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" cid="n26" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; margin-top: 0px; margin-bottom: 20px; font-size: 0.9rem; display: block; break-inside: avoid; text-align: left; white-space: normal; background: rgb(51, 51, 51); position: relative !important; padding: 10px 10px 10px 30px; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">public String[] selectImports(AnnotationMetadata annotationMetadata) {
...
AutoConfigurationEntry autoConfigurationEntry = getAutoConfigurationEntry(autoConfigurationMetadata,
annotationMetadata);
return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());
}</pre>

getAutoConfigurationEntry

该方法主要作用获取EnableAutoConfiguration中的属性,调用getCandidateConfigurations()方法

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" cid="n29" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; margin-top: 0px; margin-bottom: 20px; font-size: 0.9rem; display: block; break-inside: avoid; text-align: left; white-space: normal; background: rgb(51, 51, 51); position: relative !important; padding: 10px 10px 10px 30px; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;"> protected AutoConfigurationEntry getAutoConfigurationEntry(AutoConfigurationMetadata autoConfigurationMetadata,
AnnotationMetadata annotationMetadata) {
...
List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);
..
}</pre>

getCandidateConfigurations

获取候选的配置信息,在候选信息的中使用SpringFactoriesLoader.loadFactoryNames()

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" cid="n32" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; margin-top: 0px; margin-bottom: 20px; font-size: 0.9rem; display: block; break-inside: avoid; text-align: left; white-space: normal; background: rgb(51, 51, 51); position: relative !important; padding: 10px 10px 10px 30px; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
//加载所有的配置类信息
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;
    }
    ​</pre>

SpringFactoriesLoader

这个类中有一个比较重要的工具类SpringFactoriesLoader主要功能就是从指定的配置文件META-INF/spring-factories加载配置，spring-factories是一个典型的java properties文件，只不过Key和Value都是Java类型的完整类名，

主要的作用:

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

  2. 把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，

  3. 然后把他们添加在容器中 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

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" cid="n43" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; margin-top: 0px; margin-bottom: 20px; font-size: 0.9rem; display: block; break-inside: avoid; text-align: left; white-space: normal; background: rgb(51, 51, 51); position: relative !important; padding: 10px 10px 10px 30px; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">/**

  • 使用内部工具 SpringFactoriesLoader，查找classpath上所有jar包中的META-INF\spring.factories
  • 找出其中key为org.springframework.boot.autoconfigure.AutoConfigurationImportFilter的属性定义的过滤器类并实例化。
  • AutoConfigurationImportFilter过滤器可以被注册到 spring.factories用于对自动配置类做一些限制，在这些自动配置类的字节码被读取之前做快速排除处理。
  • spring boot autoconfigure 缺省注册了一个 AutoConfigurationImportFilter :
    **/
    public static List<String> loadFactoryNames(Class<?> factoryClass, @Nullable ClassLoader classLoader) {
    String factoryClassName = factoryClass.getName();
    return (List)loadSpringFactories(classLoader).getOrDefault(factoryClassName, Collections.emptyList());
    }</pre>
image

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="properties" cid="n45" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; margin-top: 0px; margin-bottom: 20px; font-size: 0.9rem; display: block; break-inside: avoid; text-align: left; white-space: normal; background: rgb(51, 51, 51); position: relative !important; padding: 10px 10px 10px 30px; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;"># 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,</pre>

以MultipartAutoConfiguration(文件上传)为例

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="javascript" cid="n47" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; margin-top: 0px; margin-bottom: 20px; font-size: 0.9rem; display: block; break-inside: avoid; text-align: left; white-space: normal; background: rgb(51, 51, 51); position: relative !important; padding: 10px 10px 10px 30px; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">// 表示这是一个配置类
@Configuration
// 判断当前项目有没有这些类 有这些类则配置生效
@ConditionalOnClass({ Servlet.class, StandardServletMultipartResolver.class, MultipartConfigElement.class })
// 判断配置文件中是否存在某个配置spring.servlet.multipart.enabled；
@ConditionalOnProperty(prefix = "spring.servlet.multipart", name = "enabled", matchIfMissing = true)
// 判断当前应用是否是web应用，如果是，当前配置类生效
@ConditionalOnWebApplication(type = Type.SERVLET)
@EnableConfigurationProperties(MultipartProperties.class)
public class MultipartAutoConfiguration {
// 配置文件中对应的JavaBean
private final MultipartProperties multipartProperties;

public MultipartAutoConfiguration(MultipartProperties multipartProperties) {
this.multipartProperties = multipartProperties;
}
}</pre>

根据当前不同的条件判断，决定这个配置类是否生效？一但这个配置类生效；这个配置类就会给容器中添加各种组件；这些组件的属性是从对应的properties类中获取的，这些类中每一个属性又是和配置文件绑定；

MultipartProperties

所有在配置文件中能配置的属性都是在xxxxProperties类中封装者‘；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

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" cid="n51" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; margin-top: 0px; margin-bottom: 20px; font-size: 0.9rem; display: block; break-inside: avoid; text-align: left; white-space: normal; background: rgb(51, 51, 51); position: relative !important; padding: 10px 10px 10px 30px; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">@ConfigurationProperties(prefix = "spring.servlet.multipart", ignoreUnknownFields = false)
public class MultipartProperties {
//是否开启文件上传功能 默认开启
private boolean enabled = true;
// 上传的路径
private String location;

public void setMaxFileSize(DataSize maxFileSize) {
this.maxFileSize = maxFileSize;
}
​
public void setMaxRequestSize(DataSize maxRequestSize) {
this.maxRequestSize = maxRequestSize;
}

public void setResolveLazily(boolean resolveLazily) {
this.resolveLazily = resolveLazily;
}
public void setFileSizeThreshold(DataSize fileSizeThreshold) {
this.fileSizeThreshold = fileSizeThreshold;
}
}</pre>

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="yaml" cid="n52" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; margin-top: 0px; margin-bottom: 20px; font-size: 0.9rem; display: block; break-inside: avoid; text-align: left; white-space: normal; background: rgb(51, 51, 51); position: relative !important; padding: 10px 10px 10px 30px; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">spring:
servlet:
multipart:
enabled: true
location: /upload/files

支持文件写入磁盘

file-size-threshold: 0

上传文件总的最大值

max-request-size: 50MB

单个文件上传的大小

max-file-size: 5MB

上传时是否支持懒加载

resolve-lazily: false</pre>

小结

  1. SpringBoot启动会加载大量的自动配置类

  2. 自动配置类添加组件的时候，会从properties类中获取某些属性。我们可以在配置文件中指定这些属性的值

    xxxxAutoConfigurartion：自动配置类给容器中添加组件

    xxxxProperties：对应配置文件中相关属性,在配置对象可以是setter方法 也有可以是属性

根据当前不同的条件判断，决定这个配置类是否生效。

一但这个配置类生效，这个配置类就会给容器中添加各种组件，这些组件的属性是从对应的properties类中获取的，这些类里面的每一个属性又是和配置文件绑定的。

5.所有在配置文件中能配置的属性都是在xxxxProperties类中封装者，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

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="javascript" cid="n65" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; margin-top: 0px; margin-bottom: 20px; font-size: 0.9rem; display: block; break-inside: avoid; text-align: left; white-space: normal; background: rgb(51, 51, 51); position: relative !important; padding: 10px 10px 10px 30px; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">@ConfigurationProperties(prefix = "spring.http.encoding") //从配置文件中获取指定的值和bean的属性进行绑定
public class HttpEncodingProperties {
​
public static final Charset DEFAULT_CHARSET = Charset.forName("UTF-8");</pre>

精髓：

1）、SpringBoot启动会加载大量的自动配置类

2）、先看我们需要的功能有没有SpringBoot默认写好的自动配置类

3）、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；给容器中添加组件；

xxxxProperties:封装配置文件中相关属性；

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