1.使用GSON時，預設不對null欄位進行轉換，而ObjectMapper和JSONObject預設對null欄位進行轉換

（1）使用GSON時，對null欄位進行轉換的設定

 Gson gsonSerializeNull = new GsonBuilder().serializeNulls().create();

ObjectMapper objectMapper= new ObjectMapper();
objectMapper.setSerializationInclusion(Include.NON_NULL);

 PropertyFilter filter = new PropertyFilter() {
            public boolean apply(Object object, String fieldName,
                    Object fieldValue) {
                return null == fieldValue;
            }
        };
        jsonConfig.setJsonPropertyFilter(filter);
        System.out.println(JSONObject.fromObject(s, jsonConfig).toString());
 

Student類

package com.beanjson.test;


public class Student {
    private String name;

    private int id;

    private Integer age = null;

    public Student() {
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

}
 

package com.beanjson.test;

import net.sf.json.JSONObject;
import net.sf.json.JsonConfig;
import net.sf.json.util.PropertyFilter;

import com.fasterxml.jackson.annotation.JsonInclude.Include;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;

public class Test {

    private static ObjectMapper objectMapper;

    public static void main(String[] args) throws JsonProcessingException {
        Student s = new Student();
        s.setName("abc");
        s.setId(1);
        s.setAge(null);

        System.out.println("----------gson(預設對null不轉換)---------");
        Gson gson = new Gson();
        System.out.println(gson.toJson(s));
        System.out.println("----------gson(對null欄位轉換)---------");
        Gson gsonSerializeNull = new GsonBuilder().serializeNulls().create();
        System.out.println(gsonSerializeNull.toJson(s));

        System.out.println("----------objectMapper對null欄位不轉換的設定---------");
        objectMapper = new ObjectMapper();
        objectMapper.setSerializationInclusion(Include.NON_NULL);
        System.out.println(objectMapper.writeValueAsString(s));

        System.out.println("----------json-lib對null欄位不轉換的設定---------");
        JsonConfig jsonConfig = new JsonConfig();
        PropertyFilter filter = new PropertyFilter() {
            public boolean apply(Object object, String fieldName,
                    Object fieldValue) {
                return null == fieldValue;
            }
        };
        jsonConfig.setJsonPropertyFilter(filter);
        System.out.println(JSONObject.fromObject(s, jsonConfig).toString());
    }

}