The use and introduction of SpringBoot annotations

Introduction of some annotations in SpringBoot

1.ConfigurationProperties：

Function: Tell SpringBoot to bind all the attributes in this class to the configuration related to the configuration file.

2.PropertySource：

Function: Load the configuration file at the specified location, but if there is the same matching data elsewhere, other data may be bound first

3.Conditional derived annotation

Function: The derived annotation of the native annotation Conditional in the Spring annotation is used to determine the condition to determine whether the annotation is valid

//这是HttpEncodingAutoConfiguration 类上的部分注解，全部都是用于判断，判断为true的情况才会使HttpEncodingAutoConfiguration 生效
@ConditionalOnWebApplication(
    type = Type.SERVLET
)
@ConditionalOnClass({
    
    CharacterEncodingFilter.class})
@ConditionalOnProperty(
    prefix = "server.servlet.encoding",
    value = {
    
    "enabled"},
    matchIfMissing = true
)
public class HttpEncodingAutoConfiguration {
    
    }

//这是HttpEncodingAutoConfiguration上的ConditionalOnProperty注解底层，可以看到产生作用的是Conditional注解。
@Retention(RetentionPolicy.RUNTIME)
@Target({
    
    ElementType.TYPE, ElementType.METHOD})
@Documented
@Conditional({
    
    OnPropertyCondition.class})
public @interface ConditionalOnProperty {
    
    }