抽象类使用Jackson序列化问题

抽象类 Jackson序列化抽象类Jackson序列化 2023-01-01 09:01:23 930人浏览薄情痞子

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摘要

目录抽象类使用Jackson序列化记一次jackson序列化Boolean的坑总结排查思路如下总结抽象类使用Jackson序列化当java对象中含List<Object>

抽象类使用Jackson序列化

当java对象中含List<Object>时，如果Object一个抽象类或接口，这里就会出现java多态的现象，比如List<Animal>, 如果Animal是个抽象类，并且有多个子类时，由于List中保存的Animal没有明确指向具体的子类或实现类，JSON反序列化java对象时就会抛出提示：

Exception in thread "main" com.fasterxml.jackson.databind.jsonMappingException:Can not construct instance of Animal, problem: abstract types either need to be mapped to concrete types, have custom deserializer, or be instantiated with additional type infORMation

可以使用@JsonTypeInfo与@JsonSubTypes来解决此类问题，通过注解，可以在序列化时，保存具体的类型信息到json中，当json反序列到java对象时，就可以根据具体类型信息创建正确的java对象。

@JsonTypeInfo – indicates details of what type information to include in serialization 指出序列化包含的类型信息细节
@JsonSubTypes – indicates sub-types of the annotated type 指出被注解类型的子类
@JsonTypeName – defines a logical type name to use for annotated class 定义被注解类使用的逻辑名称

@JsonTypeInfo(
        use = JsonTypeInfo.Id.NAME,
        include = As.PROPERTY,
        property = "type")
@JsonSubTypes({
        @JsonSubTypes.Type(value = Dog.class, name = "dog"),
        @JsonSubTypes.Type(value = Cat.class, name = "cat")
})
public class Animal {
    public String name;
 
    public Animal(String name) {
    }
}
 
@JsonTypeName("dog")
// 这里在子类中指定的type name必须和抽象类中注解@JsonSubTypes中name属性指定的值保持一致
public class Dog extends Animal {
    public double barkVolume;
 
    public Dog(String name) {
        super(name);
        barkVolume = 0.5;
    }
}
 
@JsonTypeName("cat")
public class Cat extends Animal {
    boolean likesCream;
    public int lives;
 
    public Cat(String name) {
        super(name);
        likesCream = true;
        lives = 10;
    }
}
  
    @Test
    public void whenSerializingPolymorphic_thenCorrect()
            throws JsonProcessingException {
        Zoo.Dog dog = new Zoo.Dog("lacy");
        Zoo zoo = new Zoo(dog);
 
        String result = new ObjectMapper()
                .writeValueAsString(zoo);
 
        assertThat(result, containsString("type"));
        assertThat(result, containsString("dog"));
    }
 
    序列化zoo对象，结果如下:
        {
         "type":"dog",
         "name":"lacy",
         "barkVolume":0
        }
 
    @Test
    public void whenDeserializingPolymorphic_thenCorrect()
            throws IOException {
        String json = "{\"name\":\"lacy\",\"type\":\"cat\"}";
 
        Animal animal =
                new ObjectMapper().readerFor(Animal.class).readValue(json);
 
        assertEquals("lacy", animal.name);
        assertEquals(Cat.class, animal.getClass());
    }

记一次jackson序列化Boolean的坑

@Data
public class CouponTemplateDto {
    
    private Long couponTypeId;
    
    private Long couponTemplateId;
    
    private Long userId;

    
    private String description;
    
    private BigDecimal value;
    
    private Integer delayDays;
    
    private Integer nowDays;
    
    private BigDecimal fullAmount;

    
    private String couponNo;

    
    private Date startTime;

    
    private Date endTime;

    
    private Date createTime;

    
    private Date useTime;

    
    private Integer couponUseStatus;
    
    private Integer overDueRemind;
    
    private String title;

    
//    @JsonProperty("isStart")
    private Boolean start;
    
//    @JsonProperty("isEnd")
    private Boolean end;

    private Boolean getStart() {
        return startTime.before(new Date());
    }

    private Boolean getEnd() {
        return endTime.before(new Date());
    }
}

我定义了一个这样的类，我们项目用的是Spring Boot，默认底层采用的是jackson序列化，但是在使用中出了一个问题private Boolean start跟private Boolean end这两个字段一直无法序列化