前言

用springboot开发的过程中，我们会用到@ConfigurationProperties注解，主要是用来把properties或者yml配置文件转化为bean来使用的，而@EnableConfigurationProperties注解的作用是@ConfigurationProperties注解生效。 如果只配置@ConfigurationProperties注解，在IOC容器中是获取不到properties配置文件转化的bean的，当然在@ConfigurationProperties加入注解的类上加@Component也可以使交于springboot管理。

举个栗子

第一步:创建一个类TestConfigurationProperties

@ConfigurationProperties(prefix = "properties")
public class TestConfigurationProperties {private String name;public String getName() {return name;}public void setName(String name) {this.name = name;}
}
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注意:得加上set和get方法
第二步:创建TestAutoConfiguration类

@Configuration
@EnableConfigurationProperties(TestConfigurationProperties.class)
public class TestAutoConfiguration {private TestConfigurationProperties testConfigurationProperties;public TestAutoConfiguration(TestConfigurationProperties testConfigurationProperties) {this.testConfigurationProperties = testConfigurationProperties;}@Beanpublic User user(){User user = new User();user.setName(testConfigurationProperties.getName());return user;}
}
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注意:得创建一个有参构造方法
第三步:配置文件加入属性

properties.name=test
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第四步:跑一下，打印出User这个类

@RestController
@RequestMapping("/api/test")
@Slf4j
public class TestController {@AutowiredTestConfigurationProperties testConfigurationProperties;@AutowiredUser user;@RequestMapping(value = "/testConfigurationProperties")public String testConfigurationProperties() {log.info("test testConfigurationProperties.............{}", testConfigurationProperties.getName());log.info("user:{}", user);return "SUCCESS";}
}
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控制台输出：

2019-04-21/16:11:36.638||||||||^_^|[http-nio-8088-exec-1] INFO  com.stone.zplxjj.controller.TestController 37 - test testConfigurationProperties.............test
2019-04-21/16:11:36.639||||||||^_^|[http-nio-8088-exec-1] INFO  com.stone.zplxjj.controller.TestController 38 - user:User(id=null, name=test)
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@EnableConfigurationProperties是怎么加载的

通过查看@EnableConfigurationProperties的注解：

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(EnableConfigurationPropertiesImportSelector.class)
public @interface EnableConfigurationProperties {/*** Convenient way to quickly register {@link ConfigurationProperties} annotated beans* with Spring. Standard Spring Beans will also be scanned regardless of this value.* @return {@link ConfigurationProperties} annotated beans to register*/Class<?>[] value() default {};}
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通过分析自动配置可以知道，肯定是这个类EnableConfigurationPropertiesImportSelector起的作用：

private static final String[] IMPORTS = {ConfigurationPropertiesBeanRegistrar.class.getName(),ConfigurationPropertiesBindingPostProcessorRegistrar.class.getName() };@Overridepublic String[] selectImports(AnnotationMetadata metadata) {return IMPORTS;}
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selectImports方法返回了这两个类：ConfigurationPropertiesBeanRegistrar和ConfigurationPropertiesBindingPostProcessorRegistrar，是何时加载的，我们只需要看这个类ConfigurationPropertiesBeanRegistrar即可：

public static class ConfigurationPropertiesBeanRegistrarimplements ImportBeanDefinitionRegistrar {@Overridepublic void registerBeanDefinitions(AnnotationMetadata metadata,BeanDefinitionRegistry registry) {getTypes(metadata).forEach((type) -> register(registry,(ConfigurableListableBeanFactory) registry, type));}//找到加入这个注解@EnableConfigurationProperties里面的value值，其实就是类classprivate List<Class<?>> getTypes(AnnotationMetadata metadata) {MultiValueMap<String, Object> attributes = metadata.getAllAnnotationAttributes(EnableConfigurationProperties.class.getName(), false);return collectClasses((attributes != null) ? attributes.get("value"): Collections.emptyList());}private List<Class<?>> collectClasses(List<?> values) {return values.stream().flatMap((value) -> Arrays.stream((Object[]) value)).map((o) -> (Class<?>) o).filter((type) -> void.class != type).collect(Collectors.toList());}//注册方法：根据找到的类名name和type，将加入注解@ConfigurationProperties的类加入spring容器里面private void register(BeanDefinitionRegistry registry,ConfigurableListableBeanFactory beanFactory, Class<?> type) {String name = getName(type);if (!containsBeanDefinition(beanFactory, name)) {registerBeanDefinition(registry, name, type);}}//找到加入注解@ConfigurationProperties的类的名称，加入一定格式的拼接private String getName(Class<?> type) {ConfigurationProperties annotation = AnnotationUtils.findAnnotation(type,ConfigurationProperties.class);String prefix = (annotation != null) ? annotation.prefix() : "";return (StringUtils.hasText(prefix) ? prefix + "-" + type.getName(): type.getName());}private boolean containsBeanDefinition(ConfigurableListableBeanFactory beanFactory, String name) {if (beanFactory.containsBeanDefinition(name)) {return true;}BeanFactory parent = beanFactory.getParentBeanFactory();if (parent instanceof ConfigurableListableBeanFactory) {return containsBeanDefinition((ConfigurableListableBeanFactory) parent,name);}return false;}private void registerBeanDefinition(BeanDefinitionRegistry registry, String name,Class<?> type) {assertHasAnnotation(type);GenericBeanDefinition definition = new GenericBeanDefinition();definition.setBeanClass(type);registry.registerBeanDefinition(name, definition);}private void assertHasAnnotation(Class<?> type) {Assert.notNull(AnnotationUtils.findAnnotation(type, ConfigurationProperties.class),() -> "No " + ConfigurationProperties.class.getSimpleName()+ " annotation found on  '" + type.getName() + "'.");}}
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结语

另外还有这个类：ConfigurationPropertiesBindingPostProcessorRegistrar，刚刚没有分析，看了下源码，其实他做的事情就是将配置文件当中的属性值赋予到加了@ConfigurationProperties的注解的类的属性上，具体就不分析了，有兴趣自己可以阅读，入口知道了，就简单了

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