启用Object Mapper writeValueAsString方法以包含空值

Question

我有一个JSON对象,可能包含一些空值.我使用com.fasterxml.jackson.databind中的ObjectMapper将我的JSON对象转换为String.

private ObjectMapper mapper = new ObjectMapper();
String json = mapper.writeValueAsString(object);

如果我的对象包含任何包含值为null的字段,则该字段不包含在来自writeValueAsString的String中.我希望我的ObjectMapper给我字符串中的所有字段,即使它们的值为null.

例:

object = {"name": "John", "id": 10}
json   = {"name": "John", "id": 10}

object = {"name": "John", "id": null}
json   = {"name": "John"}

Answer 1

杰克逊应默认将null字段序列化null.请参阅以下示例

public class Example {

    public static void main(String... args) throws Exception {
        ObjectMapper mapper = new ObjectMapper();
        mapper.configure(SerializationFeature.INDENT_OUTPUT, true);
        String json = mapper.writeValueAsString(new Test());
        System.out.println(json);
    }

    static class Test {
        private String help = "something";
        private String nope = null;

        public String getHelp() {
            return help;
        }

        public void setHelp(String help) {
            this.help = help;
        }

        public String getNope() {
            return nope;
        }

        public void setNope(String nope) {
            this.nope = nope;
        }
    }
}

版画

{
  "help" : "something",
  "nope" : null
}

你不需要做任何特别的事情.