How an optional property can be ignored when using jackson to convert Java object

问题

I'm using Jackson 1.9.2(org.codehaus.jackson) to convent from Java object to matching JSON construct. Here is my java object:

Class ColorLight {
    String type;
    boolean isOn;
    String value;

    public String getType(){
        return type;
    }

    public setType(String type) {
        this.type = type;
    }

    public boolean getIsOn(){
        return isOn;
    }

    public setIsOn(boolean isOn) {
        this.isOn = isOn;
    }

    public String getValue(){
        return value;
    }

    public setValue(String value) {
        this.value = value;
    }
}

If I did the following conversion, I'd get the result I want.

ColorLight light = new ColorLight();
light.setType("red");
light.setIsOn("true");
light.setValue("255");
objectMapper mapper = new ObjectMapper();
jsonString = mapper.writeValueAsString();

jsonString would be like:

{"type":"red","isOn":"true", "value":"255"}

But sometimes I don't have the value of isOn property

ColorLight light = new ColorLight();
light.setType("red");
light.setValue("255");

But the jsonString is still like:

{"type":"red","isOn":"false", "value":"255"}

Where "isOn:false" is default value of Java boolean type which I don't want it be there. How can I remove the isOn property in the final json construct like this?

{"type":"red","value":"255"}

回答1:

To skip the value if it's not present:

Use Boolean instead of the boolean primitive (boolean values are always set to true or false).
Configure Jackson not to serialize nulls by using @JsonInclude(Include.NON_NULL) or @JsonSerialize(include=JsonSerialize.Inclusion.NON_NULL), depending on the version.

回答2:

You can mark your class with the @JsonSerialize(include = JsonSerialize.Inclusion.NON_DEFAULT) in 1.x annotation that indicates that only properties that have values that differ from default settings (meaning values they have when Bean is constructed with its no-arguments constructor) are to be included.

The @JsonInclude(JsonInclude.Include.NON_DEFAULT) annotation is used for version 2.x.

Here is an example:

public class JacksonInclusion {

    @JsonSerialize(include = JsonSerialize.Inclusion.NON_DEFAULT)
    public static class ColorLight {
        public String type;
        public boolean isOn;

        public ColorLight() {
        }

        public ColorLight(String type, boolean isOn) {
            this.type = type;
            this.isOn = isOn;
        }
    }

    public static void main(String[] args) throws IOException {
        ColorLight light = new ColorLight("value", false);
        ObjectMapper mapper = new ObjectMapper();
        System.out.println(mapper.writeValueAsString(light));
    }
}

Output:

{"type":"value"}

来源：https://stackoverflow.com/questions/24622635/how-an-optional-property-can-be-ignored-when-using-jackson-to-convert-java-objec

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jackson