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java：jackson 五：Custom Jackson Annotation

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java：jackson 五：Custom Jackson Annotation

1 前言

参考文档地址：

https://www.baeldung.com/jackson

https://www.baeldung.com/jackson-annotations

SpringBoot自带的jackson版本如下：

<parent>
    <artifactId>spring-boot-starter-parent</artifactId>
    <groupId>org.springframework.boot</groupId>
    <version>2.5.4</version>
</parent>

在这里插入图片描述

或者不使用SpringBoot情况下，单独配置jackson-databind版本：

<properties>
    <maven.compiler.source>8</maven.compiler.source>
    <maven.compiler.target>8</maven.compiler.target>
    <jackson-databind.version>2.14.1</jackson-databind.version>
</properties>
    
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>${jackson-databind.version}</version>
</dependency>

同时使用SpringBoot和自定义的jackson版本时，注意避免依赖冲突。

2 使用

@JacksonAnnotationsInside

Next let’s see how to create a custom Jackson annotation. We can make use of the @JacksonAnnotationsInside annotation

自定义jackson的注解时，如果使用了@JsonSerialize，相应的，@JsonPropertyOrder、@JsonInclude将失效，依赖自定义的序列化器等实现即可：

package com.xiaoxu.test.jackson;

import com.fasterxml.jackson.annotation.JacksonAnnotationsInside;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.*;
import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
import com.fasterxml.jackson.databind.annotation.JsonSerialize;
import com.fasterxml.jackson.databind.deser.ContextualDeserializer;
import com.fasterxml.jackson.databind.module.SimpleModule;
import com.fasterxml.jackson.databind.ser.ContextualSerializer;
import lombok.Data;
import lombok.ToString;

import java.io.IOException;
import java.lang.annotation.*;
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.util.Date;
import java.util.Optional;

/**
 * @author xiaoxu
 * @date 2022-12-30
 * java_demo:com.xiaoxu.test.jackson.CustomJackSonAnnotationTest
 */
public class CustomJackSonAnnotationTest {
    private static final ObjectMapper objectMapper;
    static {
        objectMapper = new ObjectMapper();
        objectMapper.configure(SerializationFeature.INDENT_OUTPUT,true);

        /* 单独使用了@JsonSerialize(using = CusAnnoSerializer.class)，可省略全局的配置 */
        SimpleModule simpleModule = new SimpleModule();
        simpleModule.addSerializer(CusAnno.class, new CusAnnoSerializer());
        simpleModule.addDeserializer(CusAnno.class, new CusAnnoDeSerializer());
        objectMapper.registerModule(simpleModule);
    }

    public static void demo() throws Exception{
        CusAnno cusAnno = new CusAnno();
        cusAnno.setToday(new Date());
        cusAnno.setTodayNew(LocalDateTime.now());

        Optional.ofNullable(CusAnno.class.getAnnotation(CusJack.class)).ifPresent(annotation -> {
            if(annotation.isEffect()){
                System.out.println("CusJack注解生效:");
                try {
                    System.out.println(objectMapper.writeValueAsString(cusAnno));
                } catch (JsonProcessingException e) {
                    throw new RuntimeException(e);
                }
            }else{
                System.out.println("CusJack注解未生效.");
            }
        });
        System.out.print("\n\n");
        WrapCusAnno wrapCusAnno = new WrapCusAnno();
        wrapCusAnno.setMid(999);
        wrapCusAnno.setCusAnno(cusAnno);
        System.out.println(objectMapper.writeValueAsString(wrapCusAnno));

        System.out.print("\n\n");
        System.out.println(objectMapper.readValue(objectMapper.writeValueAsString(cusAnno), CusAnno.class));
        System.out.print("\n\n");
        System.out.println(objectMapper.readValue(objectMapper.writeValueAsString(wrapCusAnno), WrapCusAnno.class));
    }

    public static void main(String[] args) throws Exception{
        demo();
    }
}

class CusAnnoSerializer extends JsonSerializer<CusAnno> implements ContextualSerializer{

    @Override
    public void serialize(CusAnno cusAnno, JsonGenerator jsonGenerator, 
                          SerializerProvider serializerProvider) throws IOException {
        /* 注意：若使用writeObject()方法，不要直接把参数 cusAnno 再次写入，会造成StackOverflowError 错误*/
        jsonGenerator.writeStartObject();
        /* 改变自定义的顺序即可实现类似 @JsonPropertyOrder(value = {"today","todayNew","name","id"}) 的效果 */
        jsonGenerator.writeStringField("name",cusAnno.getName());
        jsonGenerator.writeNumberField("id",cusAnno.id+1);

        Optional.ofNullable(cusAnno.getToday()).ifPresent(date -> {
            try {
                jsonGenerator.writeStringField("nowDay",cusAnno.getToday().toString());
            } catch (IOException e) {
                throw new RuntimeException("today转换异常:"+e.getMessage(),e.getCause());
            }
        });
        Optional.ofNullable(cusAnno.getTodayNew()).ifPresent(localDate -> {
            try {
                jsonGenerator.writeStringField("localDate",
                        cusAnno.getTodayNew().format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm")));
            } catch (IOException e) {
                throw new RuntimeException("todayNew转换异常:"+e.getMessage(),e.getCause());
            }
        });
        jsonGenerator.writeEndObject();
    }

    @Override
    public JsonSerializer<CusAnno> createContextual(SerializerProvider serializerProvider, 
                                                    BeanProperty beanProperty) throws JsonMappingException {
        System.out.println("序列化BeanProperty:"+beanProperty);
        Optional.ofNullable(beanProperty).ifPresent(beanProperty1 -> {
            System.out.println("序列化BeanProperty不为null:"+beanProperty1.getAnnotation(CusJack.class));
        });
        return this;
    }

}

class CusAnnoDeSerializer extends JsonDeserializer<CusAnno> implements ContextualDeserializer{

    @Override
    public CusAnno deserialize(JsonParser jsonParser, 
                               DeserializationContext deserializationContext) 
            throws IOException, JsonProcessingException {
        JsonNode node = jsonParser.getCodec().readTree(jsonParser);
        int id = node.get("id").intValue();
        String name = node.get("name").asText();
        /* 注意：node.get("name")，若name不存在，则该值为null，可能导致NPE */
        if(node.get("name").isNull()){
            name = "defualt-xiaoxu";
        }

        String localDate = node.get("localDate").asText();
        LocalDateTime dtime = LocalDateTime.parse(localDate, 
                DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm"));

        CusAnno cusAnnoDe = new CusAnno();
        cusAnnoDe.setId(id);
        cusAnnoDe.setName(name);
        cusAnnoDe.setToday(new Date());
        cusAnnoDe.setTodayNew(dtime);
        return cusAnnoDe;
    }

    @Override
    public JsonDeserializer<?> createContextual(DeserializationContext deserializationContext, 
                                                BeanProperty beanProperty) throws JsonMappingException {
        System.out.println("反序列化BeanProperty:"+beanProperty);
        Optional.ofNullable(beanProperty).ifPresent(beanProperty1 -> {
            System.out.println("反序列化BeanProperty不为null:"+beanProperty1.getAnnotation(CusJack.class));
        });
        return this;
    }
}

//@CusJack  类上一定不能有该注解
@ToString
@Data
class WrapCusAnno{
    int mid;
    //字段上可有可无该@CusJack注解，但是类上不能有,直接带上即可
    @CusJack
    CusAnno cusAnno;
}

@CusJack(isEffect = true)
@Data
class CusAnno{
    int id;
    String name;
    Date today;
    LocalDateTime todayNew;
}

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE, ElementType.FIELD})
@JacksonAnnotationsInside
/* 使用 JsonSerialize自定义的序列化器时，序列化注解@JsonPropertyOrder、
@JsonInclude将不会生效，需要自定义展示效果 */
@JsonPropertyOrder(value = {"today","todayNew","name","id"})
@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonSerialize(using = CusAnnoSerializer.class)
@JsonDeserialize(using = CusAnnoDeSerializer.class)
@interface CusJack{
    boolean isEffect() default false;
}

执行结果如下：

CusJack注解生效:
序列化BeanProperty:null
{
  "name" : null,
  "id" : 1,
  "nowDay" : "Fri Dec 30 16:33:18 CST 2022",
  "localDate" : "2022-12-30 16:33"
}


序列化BeanProperty:com.fasterxml.jackson.databind.BeanProperty$Std@67205a84
序列化BeanProperty不为null:@com.xiaoxu.test.jackson.CusJack(isEffect=false)
{
  "mid" : 999,
  "cusAnno" : {
    "name" : null,
    "id" : 1,
    "nowDay" : "Fri Dec 30 16:33:18 CST 2022",
    "localDate" : "2022-12-30 16:33"
  }
}


反序列化BeanProperty:null
CusAnno(id=1, name=defualt-xiaoxu, today=Fri Dec 30 16:33:18 CST 2022, todayNew=2022-12-30T16:33)


反序列化BeanProperty:[property 'cusAnno']
反序列化BeanProperty不为null:@com.xiaoxu.test.jackson.CusJack(isEffect=false)
反序列化BeanProperty:[property 'cusAnno']
反序列化BeanProperty不为null:@com.xiaoxu.test.jackson.CusJack(isEffect=false)
WrapCusAnno(mid=999, cusAnno=CusAnno(id=1, name=defualt-xiaoxu, today=Fri Dec 30 16:33:18 CST 2022, todayNew=2022-12-30T16:33))

可见，自定义jackson注解，可以整合多个注解，使用自定义的1个注解，可达到相同效果。

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