使用多个参数构造函数进行Jackson JSON反序列化

I've been using FasterXML/Jackson-Databind in my project for a while now, and all was working great, until I've discovered this post and started to use this approach to desserialize objects without the @JsonProperty annotations.

我在我的项目中使用FasterXML/Jackson-Databind已经有一段时间了，一切都运行得很好，直到我发现了这篇文章并开始使用这种方法来在没有@JsonProperty注释的情况下反序列化对象。

The problem is that when I have a constructor which take multiple parameters and decorate this constructor with the @JsonCreator annotation Jackson throw the following error:

问题是，当我有一个构造函数接受多个参数并使用@JsonCreator注释Jackson来修饰这个构造函数时，会抛出以下错误:

Exception in thread "main" com.fasterxml.jackson.databind.JsonMappingException: 
Argument #0 of constructor [constructor for com.eliti.model.Cruiser, annotations: {interface com.fasterxml.jackson.annotation.JsonCreator=@com.fasterxml.jackson.annotation.JsonCreator(mode=DEFAULT)}] has no property name annotation; must have name when multiple-parameter constructor annotated as Creator
 at [Source: {
  "class" : "com.eliti.model.Cruiser",
  "inventor" : "afoaisf",
  "type" : "MeansTransport",
  "capacity" : 123,
  "maxSpeed" : 100
}; line: 1, column: 1]

I've created a little project to illustrate the problem, the class I'm trying to desserialize is this one:

我创建了一个小项目来说明这个问题，我试图去序列化的类是这个:

public class Cruise extends WaterVehicle {

 private Integer maxSpeed;

  @JsonCreator
  public Cruise(String name, Integer maxSpeed) {
    super(name);
    System.out.println("Cruise.Cruise");
    this.maxSpeed = maxSpeed;
  }

  public Integer getMaxSpeed() {
    return maxSpeed;
  }

  public void setMaxSpeed(Integer maxSpeed) {
    this.maxSpeed = maxSpeed;
  }

}

And the code to desserialize is like this:

反序列化的代码是这样的:

public class Test {
  public static void main(String[] args) throws IOException {
    Cruise cruise = new Cruise("asd", 100);
    cruise.setMaxSpeed(100);
    cruise.setCapacity(123);
    cruise.setInventor("afoaisf");

    ObjectMapper mapper = new ObjectMapper().enable(SerializationFeature.INDENT_OUTPUT);
    mapper.registerModule(new ParameterNamesModule(JsonCreator.Mode.PROPERTIES));

    String cruiseJson = mapper.writeValueAsString(cruise);

    System.out.println(cruiseJson);

    System.out.println(mapper.readValue(cruiseJson, Cruise.class));

}

I already tried to remove the @JsonCreator, but if I do so, the throws the following exception:

我已经尝试删除@JsonCreator，但是如果这样做，会抛出以下异常:

Exception in thread "main" com.fasterxml.jackson.databind.JsonMappingException: Can not construct instance of com.eliti.model.Cruise: no suitable constructor found, can not deserialize from Object value (missing default constructor or creator, or perhaps need to add/enable type information?)
 at [Source: {
  "class" : "com.eliti.model.Cruise",
  "inventor" : "afoaisf",
  "type" : "MeansTransport",
  "capacity" : 123,
  "maxSpeed" : 100
}; line: 3, column: 3]

I have tried to issue a "mvn clean install", but the problem persists.

我已经尝试发出“mvn清洁安装”，但问题仍然存在。

Just to include some extra information, I've researched thoroughly about this problem (GitHub issues, Blog posts, * Q&A). Here are some debbuging/investigation that I have been doing on my end:

为了包含一些额外的信息，我对这个问题进行了深入的研究(GitHub问题、博客文章、*问答)。以下是我一直在做的一些拆穿/调查:

Investigation 1

javap -v on the generated bytecode give me this:

在生成的字节码上的javap -v给我这个:

 MethodParameters:
      Name                           Flags
      name
      maxSpeed

When talking about the constructor, so I guess that the -parameters flag is really being set for javac compiler.

当谈到构造函数时，我猜想-parameters标志实际上是为javac编译器设置的。

Investigation 2

If I create a constructor with a single parameter the object gets initialized, but I want/need to use the multiple parameter constructor.

如果我用一个参数创建一个构造函数，对象将被初始化，但是我想/需要使用多个参数构造函数。

Investigation 3

If I use the annotation @JsonProperty on each field it works as well, but for my original project it is too much overhead since I have a lot of fields in the constructor (and also it gets very hard to refactor code with annotations).

如果我在每个字段上使用annotation @JsonProperty，那么它也可以工作，但是对于我的原始项目来说，由于在构造函数中有很多字段，所以它的开销太大了(而且使用注释重构代码也非常困难)。

The question that remain is: How can I make Jackson work with multiple parameter constructor without annotations?

剩下的问题是:如何让Jackson使用没有注解的多参数构造函数?

2 个解决方案

#1

You need to add the annotation @JsonProperty specifying the name of the json property that needs to be passed to the constructor when creating the object.

您需要添加注释@JsonProperty来指定创建对象时需要传递给构造函数的json属性的名称。

public class Cruise extends WaterVehicle {

 private Integer maxSpeed;

  @JsonCreator
  public Cruise(@JsonProperty("name") String name, @JsonProperty("maxSpeed")Integer maxSpeed) {
    super(name);
    System.out.println("Cruise.Cruise");
    this.maxSpeed = maxSpeed;
  }

  public Integer getMaxSpeed() {
    return maxSpeed;
  }

  public void setMaxSpeed(Integer maxSpeed) {
    this.maxSpeed = maxSpeed;
  }

}

EDIT

编辑

I just tested using the below code and it works for me

我刚刚用下面的代码进行了测试，它对我很有用

import java.io.IOException;

import com.fasterxml.jackson.annotation.JsonCreator.Mode;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import com.fasterxml.jackson.module.paramnames.ParameterNamesModule;

class WaterVehicle {

    private String name;
    private int capacity;
    private String inventor;
    public WaterVehicle(String name) {
        this.name=name;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getCapacity() {
        return capacity;
    }
    public void setCapacity(int capacity) {
        this.capacity = capacity;
    }
    public String getInventor() {
        return inventor;
    }
    public void setInventor(String inventor) {
        this.inventor = inventor;
    }


}

 class Cruise  extends WaterVehicle{

        private Integer maxSpeed;

        public Cruise(String name, Integer maxSpeed) {
            super(name);
            this.maxSpeed = maxSpeed;
        }

        public Integer getMaxSpeed() {
            return maxSpeed;
        }

        public void setMaxSpeed(Integer maxSpeed) {
            this.maxSpeed = maxSpeed;
        }


    }

public class Test {
      public static void main(String[] args) throws IOException {
        Cruise cruise = new Cruise("asd", 100);
        cruise.setMaxSpeed(100);
        cruise.setCapacity(123);
        cruise.setInventor("afoaisf");

        ObjectMapper mapper = new ObjectMapper().enable(SerializationFeature.INDENT_OUTPUT);
        mapper.registerModule(new ParameterNamesModule(Mode.PROPERTIES));

        String jsonString = mapper.writeValueAsString( cruise);
        System.out.println(jsonString);

        Cruise anotherCruise = mapper.readValue(jsonString, Cruise.class);
         System.out.println(anotherCruise );
         jsonString = mapper.writeValueAsString( anotherCruise );
         System.out.println(jsonString);

    }

}

It produces the following output

它产生以下输出。

{
  "name" : "asd",
  "capacity" : 123,
  "inventor" : "afoaisf",
  "maxSpeed" : 100
}
Cruise@56f4468b
{
  "name" : "asd",
  "capacity" : 123,
  "inventor" : "afoaisf",
  "maxSpeed" : 100
}

Make sure you have the compilerArgs in the pom file.

确保在pom文件中有编译器。

<compilerArgs>
     <arg>-parameters</arg>
</compilerArgs>

#2

Short answer: use Java 8, javac -parameters, and jackson-module-parameter-names

简短的回答:使用Java 8、javac参数和jackson-module参数名

Long answer: Why when a constructor is annotated with @JsonCreator, its arguments must be annotated with @JsonProperty?

长答案:为什么当一个构造函数被@JsonCreator注释时，它的参数必须被@JsonProperty注释?

#1