@Configuration

表示这是一个配置类，是@Component的派生类，扫描到这个类时会它加入到IOC容器中

@ConfigurationProperties

将配置文件中对应的值和加了这个注解的类绑定起来
比如下面的HelloProperties类，初始化时会读取配置文件的spring.hello为前缀的属性与自己定义的字段关联

@ConfigurationProperties(prefix = "spring.hello")
//@Component
public class HelloProperties {
    private String name;
    private Integer age;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Integer getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
}

spring.hello.name=b
spring.hello.age=1

@EnableConfigurationProperties

比如上面HelloProperties类，只加了@ConfigurationProperties注解，是不会被扫描加载到IOC容器中的，只有在HelloProperties类上加上@Component注解，或者使用@EnableConfigurationProperties(HelloProperties.class)注解HelloProperties类才会被IOC容器加载
@EnableConfigurationProperties(HelloProperties.class)作用
启动指定类的@ConfigurationProperties功能,将配置文件中对应的值和HelloProperties类绑定起来,并把HelloProperties加入到ioc容器中
@EnableConfigurationProperties需要加在配置类上(加了@Configuration的类,或@Component和其派生类上)
当HelloConfig类被容器扫描时，就会将HelloProperties加载到IOC容器中

@Configuration
@EnableConfigurationProperties(HelloProperties.class)
public class HelloConfig{
}

@Conditional注解的派生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
拿springboot中自动配置类，HttpEncodingAutoConfiguration做例子

@Configuration(proxyBeanMethods = false)
@EnableConfigurationProperties(HttpProperties.class)
@ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.SERVLET)
@ConditionalOnClass(CharacterEncodingFilter.class)
@ConditionalOnProperty(prefix = "spring.http.encoding", value = "enabled", matchIfMissing = true)
public class HttpEncodingAutoConfiguration {

    private final HttpProperties.Encoding properties;

    public HttpEncodingAutoConfiguration(HttpProperties properties) {
        this.properties = properties.getEncoding();
    }

    @Bean
    @ConditionalOnMissingBean
    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;
    }
...
}

@ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.SERVLET)

判断当前应用是否是web应用，如果是，当前配置类生效(加载到IOC容器中)，如果不是web应用，HttpEncodingAutoConfiguration类就不会被加载到IOC容器中

@ConditionalOnClass(CharacterEncodingFilter.class)

判断当前项目有没有CharacterEncodingFilter这个类(存不存在CharacterEncodingFilter.class文件)，如果有，则Conditional条件判断为true(成立),当前HttpEncodingAutoConfiguration配置类生效

@ConditionalOnProperty(prefix = "spring.http.encoding", value = "enabled", matchIfMissing = true)

//判断配置文件中是否存在spring.http.encoding.enabled配置，matchIfMissing = true表示如果没有配置spring.http.encoding.enabled，也是满足Conditional的条件，HttpEncodingAutoConfiguration配置类生效也生效

@ConditionalOnMissingBean

上面的HttpEncodingAutoConfiguration把@ConditionalOnMissingBean用在加上@Bean的characterEncodingFilter方法上表示：如果当前项目中没有CharacterEncodingFilter这个bean(CharacterEncodingFilter类没有被初始化、未被加入到IOC容器中)，则执行characterEncodingFilter方法初始化characterEncodingFilter，将其加入到IOC容器中

@ConditionalOnClass(CharacterEncodingFilter.class)和@ConditionalOnMissingBean的区别是
@ConditionalOnClass(CharacterEncodingFilter.class)是判断项目中是否存在CharacterEncodingFilter的类路径(是否存在CharacterEncodingFilter.class这个文件)
@ConditionalOnMissingBean是判断CharacterEncodingFilter这个类是否已经初始化了(是否已经加入到IOC容器中)

这里记录一些@Conditional派生的注解

@Conditional派生注解（Spring注解版原生的@Conditional作用）

作用：必须是@Conditional指定的条件成立，才给容器中添加组件，配置配里面的所有内容才生效；