【jackson】自定义字段注解完成序列化逻辑

背景

Spring默认的JSON序列化工具使用的是jackson，GitHub项目地址: https://github.com/FasterXML/jackson

我们在处理前后端接口交互的时候，可能需要实现各种各样的个性化需求，这篇文章主要介绍自定义注解，然后对特定字段进行业务逻辑处理。

本文开发环境介绍

开发依赖	版本
Spring Boot	3.1.2
JDK	17

新建一个注解

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@JsonSerialize(using = PrintFieldJsonSerializer.class)
public @interface PrintField {Type rule() default Type.TYPE_1;enum Type {TYPE_1, TYPE_2}
}

新建一个JavaBean

在字段上使用自定义注解

import lombok.Builder;
import lombok.Data;/*** @author tangheng*/
@Data
@Builder
public class DemoPerson {@PrintField(rule = PrintField.Type.TYPE_1)private String name;@PrintField(rule = PrintField.Type.TYPE_2)private String email;
}

新建一个JsonSerializer

用来做自定义的业务逻辑

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;
import lombok.RequiredArgsConstructor;
import lombok.extern.slf4j.Slf4j;
import org.apache.commons.lang3.StringUtils;import java.io.IOException;@Slf4j
@RequiredArgsConstructor
public class PrintFieldJsonSerializer extends JsonSerializer<String> {private final PrintField.Type rule;@Overridepublic void serialize(String value, JsonGenerator gen, SerializerProvider serializers) throws IOException {if(StringUtils.isBlank(value)) {return;}switch (rule) {case TYPE_1:log.info("hello, value: {}", value);break;default:log.info("rule: {}, value: {}", rule, value);break;}gen.writeString(value);}
}

新建一个AnnotationIntrospector

import com.fasterxml.jackson.core.Version;
import com.fasterxml.jackson.databind.AnnotationIntrospector;
import com.fasterxml.jackson.databind.introspect.Annotated;import java.lang.annotation.Annotation;public class PrintFieldAnnotationIntrospector extends AnnotationIntrospector {@Overridepublic Version version() {return Version.unknownVersion();}@Overridepublic Object findSerializer(Annotated a) {PrintField ann = _findAnnotation(a, PrintField.class);if (ann != null) {return new PrintFieldJsonSerializer(ann.rule());}return null;}@Overridepublic boolean isAnnotationBundle(Annotation ann) {if (PrintField.class.isAssignableFrom(ann.getClass())) {return true;}return false;}
}

这一步很关键，利用jackson的Introspector机制，起到承上启下的作用
判断字段上有自定义注解，然后使用自定义的JsonSerializer
这样就把整个事情串起来了

单元测试

class PrintFieldJsonSerializerTest extends JsonSpringbootTestBase {private ObjectMapper objectMapper = new ObjectMapper();@SneakyThrows@Testvoid serialize() {objectMapper.setAnnotationIntrospector(new PrintFieldAnnotationIntrospector());DemoPerson demoPerson = DemoPerson.builder().name("zhangsan").email("zhangsan@163.com").build();String testResult = objectMapper.writeValueAsString(demoPerson);log.info("testResult: {}", testResult);assertTrue(StringUtils.isNotBlank(testResult));}
}