Jackson JSON使用多个参数构造函数进行反序列化

我已经在我的项目中使用了FasterXML / Jackson-Databind一段时间了，一切都很好，直到我发现这篇文章并开始使用这种方法来反序列化没有@JsonProperty注释的对象。

问题是，当我有一个带有多个参数的构造函数并使用@JsonCreator注释修饰此构造函数时，Jackson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] 

我已经创建了一个小项目来说明问题，我正在尝试反序列化的类是这样的：

 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; } } 

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)); } 

我已经尝试删除@JsonCreator，但如果我这样做，则抛出以下exception：

 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] 

我试图发出“mvn clean install”，但问题仍然存在。

为了包含一些额外的信息，我已经彻底研究了这个问题（GitHub问题，博客文章，StackOverflow问答）。 以下是我一直在做的一些调整/调查：

调查1

生成的字节码上的javap -v给我这个：

  MethodParameters: Name Flags name maxSpeed 

在谈论构造函数时，我猜-parameters标志实际上是为javac编译器设置的。

调查2

如果我使用单个参数创建构造函数，则对象将被初始化，但我希望/需要使用多参数构造函数。

调查3

如果我在每个字段上使用注释@JsonProperty它也可以工作，但是对于我的原始项目来说，由于我在构造函数中有很多字段（而且很难用注释重构代码），所以开销太大了。

剩下的问题是： 如何在没有注释的情况下让Jackson使用多个参数构造函数？

Answer 1

您需要添加注释@JsonProperty，指定在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; } } 

编辑

我刚刚使用下面的代码进行了测试，它对我有用

 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); } } 

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 } 

确保pom文件中有compilerArgs。

  -parameters  

Answer 2

简短回答：使用Java 8， javac -parameters和jackson-module-parameter-names

答案很简单： 为什么当构造函数用@JsonCreator注释时，它的参数必须用@JsonProperty注释？