Why does Jackson display these values ​​twice, otherwise?

Question

I map the Java object to JSON using Jackson, this object is a pretty simple pojo class that looks like this:

import com.fasterxml.jackson.annotation.JsonAutoDetect; import com.fasterxml.jackson.annotation.JsonProperty; @JsonAutoDetect public class Area { @JsonProperty("Id") public int Id; @JsonProperty("Name") public String Name; public Area() { Name = ""; } public int getId() { return Id; } public void setId(int id) { Id = id; } public String getName() { return Name; } public void setName(String Name) { this.Name = Name; } } 

Then the display code is as follows:

 ObjectMapper mapper = new ObjectMapper(); mapper.setVisibilityChecker(mapper.getSerializationConfig().getDefaultVisibilityChecker() .withFieldVisibility(JsonAutoDetect.Visibility.ANY) .withGetterVisibility(JsonAutoDetect.Visibility.NONE) .withSetterVisibility(JsonAutoDetect.Visibility.NONE) .withCreatorVisibility(JsonAutoDetect.Visibility.NONE)); areaJSON = mapper.writeValueAsString(area); 

But the areaJSON value at this point will be as follows:

 {"id":0,"name":"","Name":"","Id":0} 

Pay attention to several values ​​with a different case.

What am I doing wrong?

Answer 1

Jackson believes that the Id and Name fields are different from the properties returned by the getters because the case is different. Using standard JavaBeans naming conventions, Jackson introduces getter-specific fields called Id and Name , not Id and Name .

tl; dr matters.

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There are two easy ways to solve this problem:

• Remove the @JsonAutoDetect annotation of this class. I am sure that annotation defaults take precedence over ObjectMapper configuration. As an alternative:

• Do not guess with ObjectMapper at all. Change @JsonAutoDetect on class to

   @JsonAutoDetect( fieldVisibility = Visibility.ANY, getterVisibility = Visibility.NONE, setterVisibility = Visibility.NONE, creatorVisibility = Visibility.NONE ) 

Answer 2

You need to annotate the getId method with @JsonProperty ("Id"), otherwise getId will also be added with a lowercase id.

Answer 3

I know this is an old post, but there is a simpler solution: use only annotation in the fields:

 @XmlRootElement @XmlAccessorType(XmlAccessType.FIELD) public class Area { public int id; public String name; public Area() { name = ""; } public int getId() { return id; } public void setId(int id) { id = id; } public String getName() { return name; } public void setName(String Name) { this.name = Name; } } 

You can choose how to serialize the object: using a field or using properties. If you use fields, the getter and setter are ignored.

The problem in the code is created with the first letter in upper case : access to the field, property json - Id; access to getter, getId became id (the first letter after get is encoded in lower case).