自动配置原理
- SpringBoot启动的时候,开启了自动配置功能@EnableAutoConfiguration,会加载大量的自动配置类
- @EnableAutoConfiguration 详情:
2.1 利用 @Import(AutoConfigurationImportSelector.class) 给容器中导入一些组件,如下方法用于获取 候选的配置
List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
List<String> configurations = SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(),
getBeanClassLoader());
return configurations;
}
protected Class<?> getSpringFactoriesLoaderFactoryClass() {
return EnableAutoConfiguration.class;
}
2.2 SpringFactoriesLoader.loadFactoryNames()扫描所有jar包类路径下: META-INF/spring.factories,把扫描到的文件内容包装成properties对象,从properties中获取到EnableAutoConfiguration.class类名对应的值,然后把他们添加到容器,具体源代码如下:
private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
MultiValueMap<String, String> result = cache.get(classLoader);
if (result != null) {
return result;
}
try {
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);
Properties properties = PropertiesLoaderUtils.loadProperties(resource);
for (Map.Entry<?, ?> entry : properties.entrySet()) {
String factoryTypeName = ((String) entry.getKey()).trim();
for (String factoryImplementationName : StringUtils.commaDelimitedListToStringArray((String) entry.getValue())) {
result.add(factoryTypeName, factoryImplementationName.trim());
}
}
}
cache.put(classLoader, result);
return result;
}
catch (IOException ex) {
throw new IllegalArgumentException("Unable to load factories from location [" +
FACTORIES_RESOURCE_LOCATION + "]", ex);
}
}
2.3 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(截取部分),每一个这样的 xxxAutoConfiguration类都是容器中的一个组件,用他们来做自动配置;
# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\
org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\
org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration,\
org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration,\
org.springframework.boot.autoconfigure.cloud.CloudAutoConfiguration,\
org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration,\
org.springframework.boot.autoconfigure.context.MessageSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchDataAutoConfiguration,\
org.springframework.boot.autoconfigure.web.HttpEncodingAutoConfiguration,\
org.springframework.boot.autoconfigure.web.HttpMessageConvertersAutoConfiguration,\
org.springframework.boot.autoconfigure.web.MultipartAutoConfiguration,\
org.springframework.boot.autoconfigure.web.ServerPropertiesAutoConfiguration,\
org.springframework.boot.autoconfigure.web.WebClientAutoConfiguration,\
org.springframework.boot.autoconfigure.web.WebMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.WebSocketAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.WebSocketMessagingAutoConfiguration,\
org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration
- 以HttpEncodingAutoConfiguration(Http编码自动配置)为例解释自动配置原理
@Configuration(proxyBeanMethods = false)
// 启动指定类的ConfigurationProperties功能,将yml配置文件中对应的值和ServerProperties绑定起来
@EnableConfigurationProperties(ServerProperties.class)
// 判断当前web应用是否基于Servlet,如果是,则生效
@ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.SERVLET)
// 判断项目中是否有CharacterEncodingFilter类
@ConditionalOnClass(CharacterEncodingFilter.class)
// 判断配置文件中是否存在配置server.servlet.encoding,不存在默认生效
@ConditionalOnProperty(prefix = "server.servlet.encoding", value = "enabled", matchIfMissing = true)
public class HttpEncodingAutoConfiguration {
private final Encoding properties;
public HttpEncodingAutoConfiguration(ServerProperties properties) {
this.properties = properties.getServlet().getEncoding();
}
@Bean // 给容器中添加组件,这个组件的某些值需要从properties中获取
@ConditionalOnMissingBean
public CharacterEncodingFilter characterEncodingFilter() {
CharacterEncodingFilter filter = new OrderedCharacterEncodingFilter();
filter.setEncoding(this.properties.getCharset().name());
filter.setForceRequestEncoding(this.properties.shouldForce(Encoding.Type.REQUEST));
filter.setForceResponseEncoding(this.properties.shouldForce(Encoding.Type.RESPONSE));
return filter;
}
- 所有在配置文件中能配置的属性都是在xxxxProperties类中封装着;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
@ConfigurationProperties(prefix = "server", ignoreUnknownFields = true)
public class ServerProperties {
.......
}
细节
- @Conditional 派生注解,必须是@Conditional指定的条件成立,才给容器中添加组件,配置类里面的所有内容才生效;
@Conditional 扩展注解 | 作用(判断是否满足当前指定条件) |
---|---|
@ConditionalOnJava | 系统的java版本是否符合要求 |
@ConditionalOnBean | 容器中存在指定Bean; |
@ConditionalOnMissingBean | 容器中不存在指定Bean; |
@ConditionalOnExpression | 满足SpEL表达式指定 |
@ConditionalOnClass | 系统中有指定的类 |
@ConditionalOnMissingClass | 系统中没有指定的类 |
@ConditionalOnSingleCandidate | 容器中只有一个指定的Bean,或者这个Bean是首选Bean |
@ConditionalOnProperty | 系统中指定的属性是否有指定的值 |
@ConditionalOnResource | 类路径下是否存在指定资源文件 |
@ConditionalOnWebApplication | 当前是web环境 |
@ConditionalOnNotWebApplication | 当前不是web环境 |
@ConditionalOnJndi | JNDI存在指定项 |
- 自动配置类必须在一定的条件下才能生效
可以通过启用 debug=true属性;来让控制台打印自动配置报告,这样我们就可以很方便的知道哪些自动配置类生效;
============================
CONDITIONS EVALUATION REPORT
============================
Positive matches:(生效的自动配置类,截取部分)
-----------------
AopAutoConfiguration matched:
- @ConditionalOnProperty (spring.aop.auto=true) matched (OnPropertyCondition)
AopAutoConfiguration.ClassProxyingConfiguration matched:
- @ConditionalOnMissingClass did not find unwanted class 'org.aspectj.weaver.Advice' (OnClassCondition)
- @ConditionalOnProperty (spring.aop.proxy-target-class=true) matched (OnPropertyCondition)
DispatcherServletAutoConfiguration matched:
- @ConditionalOnClass found required class 'org.springframework.web.servlet.DispatcherServlet' (OnClassCondition)
- found 'session' scope (OnWebApplicationCondition)
Negative matches:(没有启动,没有匹配成功的自动配置类,截取部分)
-----------------
ActiveMQAutoConfiguration:
Did not match:
- @ConditionalOnClass did not find required class 'javax.jms.ConnectionFactory' (OnClassCondition)
AopAutoConfiguration.AspectJAutoProxyingConfiguration:
Did not match:
- @ConditionalOnClass did not find required class 'org.aspectj.weaver.Advice' (OnClassCondition)
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