自动配置原理
1.加载主配置类,开启了自动配置注解@EnableAutoConfiguration
@EnableAutoConfiguration作用
按住Ctrl+鼠标左键发现有这个注解,导入了这个组件
@Import({EnableAutoConfigurationImportSelector.class})
它的父类 AutoConfigurationImportSelector
public class EnableAutoConfigurationImportSelector extends AutoConfigurationImportSelector {
AutoConfigurationImportSelector的方法selectImports中放入了组件,获取候选配置
List<String> configurations = this.getCandidateConfigurations(annotationMetadata, attributes);
如何获取呢?
1.使用SpringFactoriesLoader.loadFactoryNames()的方法
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;
}
2.扫描所有jar包类路径下 META‐INF/spring.factories
public abstract class SpringFactoriesLoader {
private static final Log logger = LogFactory.getLog(SpringFactoriesLoader.class);
public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";
3.从properties中获取到EnableAutoConfiguration.class类(类名)对应的值,
获取EnableAutoConfiguration.class类
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;
}
protected Class<?> getSpringFactoriesLoaderFactoryClass() {
return EnableAutoConfiguration.class;
}
4.把扫描到的这些文件的内容包装成properties对象,并添加到容器中
public static List<String> loadFactoryNames(Class<?> factoryClass, ClassLoader classLoader) {
String factoryClassName = factoryClass.getName();
try {
Enumeration<URL> urls = classLoader != null ? classLoader.getResources("META-INF/spring.factories") : ClassLoader.getSystemResources("META-INF/spring.factories");
ArrayList result = new ArrayList();
while(urls.hasMoreElements()) {
URL url = (URL)urls.nextElement();
Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url));
String factoryClassNames = properties.getProperty(factoryClassName);
result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassNames)));
}
return result;
} catch (IOException var8) {
throw new IllegalArgumentException("Unable to load [" + factoryClass.getName() + "] factories from location [" + "META-INF/spring.factories" + "]", var8);
}
}
这些代码的意思就是从类路径下META-INF/spring.factories里面的配置的所有EnableAutoConfiguration的值读取并添加到容器中,这就是自动配置的原理
META-INF/spring.factories里面的配置类都是容器中的组件,每个自动配置类将提供自动配置功能
解释自动配置原理
以HttpEncodingAutoConfiguration(Http编码自动配置)为例
源代码
@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(Spring注解版),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pring.http.encoding.enabled=true,也是默认生效的*/
public class HttpEncodingAutoConfiguration {
//与SpringBoot的配置文件映射
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})//判断容器没有这个组件?
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;
}
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;
有自动配置的属性都是在xxxxProperties封装
能配什么属性,去看某个模块对应的属性类
HttpEncodingAutoConfiguration的第二个注解中的HttpEncodingProperties.class
@ConfigurationProperties(
prefix = "spring.http.encoding"
)
public class HttpEncodingProperties {
public static final Charset DEFAULT_CHARSET = Charset.forName("UTF-8");
private Charset charset;
private Boolean force;
private Boolean forceRequest;
private Boolean forceResponse;
private Map<Locale, Charset> mapping;
精髓
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;
参考资料:尚硅谷springboot课程
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