使用 Jackson 往返 JSON，其中每个 class 实现相同的接口

Question

我正在尝试使用 Jackson 反序列化一个相当复杂的 JSON 结构。

序列化工作正常：

参数接口：

public interface Param<T> {
}

Not.java:

public class Not implements Param<Param<?>> {

    private Param not;

    public Not(){

    }

    public Not(Param not) {
        this.not = not;
    }

    public Param getNot() {
        return not;
    }

}

And.java:

public class And implements Param<List<?>> {

    private List<Param> and;

    public List<Param> getAnd() {
        return and;
    }

    public List<Param> add(Param ... params){
        for (Param param : params){
            this.and.add(param);
        }
        return this.and;
    }

    public And() {
        this.and = new ArrayList<>();
    }

    public And(Param ... params){
        this.and = new ArrayList<>();
        for (Param param : params){
            this.and.add(param);
        }
    }

}

Company.java:

public class CompanyName implements Param<String> {

    private String companyName;

    public CompanyName(String value) {
        this.companyName = value;
    }

    public String getCompanyName() {
        return companyName;
    }
}

序列化：

ObjectMapper mapper = new ObjectMapper();
System.out.println(mapper.writeValueAsString(new And(new Or(new CompanyName("ABC"), new CompanyName("DEF")), new Not(new CompanyName("GHI")))));

打印：

{"and":[{"or":[{"companyName":"ABC"},{"companyName":"DEF"}]},{"not":{"companyName":"GHI"}}]}

现在反序列化，Jackson 怎么知道如何映射和/或/companyName/不返回他们的对象？

And and = mapper.readValue(json, And.class);

Exception in thread "main" com.fasterxml.jackson.databind.JsonMappingException: Can not construct instance of com.ahp.messaging.param.Param, problem: abstract types either need to be mapped to concrete types, have custom deserializer, or be instantiated with additional type information at [Source: {"and":[{"or":[{"companyName":"ABC"},{"companyName":"DEF"}]},{"not":{"companyName":"GHI"}}]}; line: 1, column: 9] (through reference chain: com.ahp.messaging.param.And["and"]->java.util.ArrayList[0])

为了消除异常，我修改了Param接口如下：

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "T", visible = false)
@JsonSubTypes({
    @JsonSubTypes.Type(value = Not.class, name = "not"),
    @JsonSubTypes.Type(value = And.class, name = "and"),
    @JsonSubTypes.Type(value = Or.class, name = "or"),
    @JsonSubTypes.Type(value = CompanyName.class, name = "companyName")

})
public interface Param<T> {

}

现在序列化为：

{"T":"and","and":[{"T":"or","or":[{"T":"companyName","companyName":"ABC"},{"T":"companyName","companyName":"DEF"}]},{"T":"not","not":{"T":"companyName","companyName":"GHI"}}]}

反序列化完美，但所有内容都有类型信息，有没有办法摆脱类型信息，只在真正需要的地方使用它？

Answer 1

简答，需要类型信息。

使用 XML 可以获取每个元素的类型信息，使用 JSON 可以为更小的表示牺牲类型信息，但在这种情况下，废弃类型信息意味着没有办法推断 class 它应该映射到什么。

使用 Jackson 往返 JSON，其中每个 class 实现相同的接口

Using Jackson to / from JSON where each class implements the same interface

java

serialization

json

jackson

deserialization