如何编写处理字段的自定义注释 [英] How to write custom annotation that processes a field

问题描述

我正在研究注解，希望有人指出我正确的方向.

i am delving into annotations and would like someone to point me in the right direction.

我想创建一个注释，当将其从JSON映射到POJO时，它能够修剪String值.

I want to create an annotation that will be able to trim the String value when it is being mapped from a JSON into a POJO.

不确定如何做到.

即

@trim
private String referenceField;

推荐答案

@JacksonAnnotationsInside
@Retention(RUNTIME)
@Target(FIELD)
@JsonDeserialize(using = StringStripDeserializer.class)
public @interface @Strip {}

class StringStripDeserializer extends StdDeserializer<String> {

   @Override 
   public Date deserialize(JsonParser parser, DeserializationContext context) 
      throws IOException, JsonProcessingException { 
      String text = parser.getText();
      return text != null ? text.strip : null;
   }
   ...
}

或者，如果要修剪所有所有字符串:

Or, if you want to trim all the strings:

    @Bean
    public Module stringStripModule() {
        SimpleModule module = new SimpleModule();
        module.addDeserializer(String.class, (JsonParser jsonParser, DeserializationContext deserializationContext) => {
            String string = super.deserialize(jsonParser, deserializationContext);
            return Objects.nonNull(string) ? string.strip() : null;
        });
        return module;
    }

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