json序列化時忽略值為null的字段的兩種方式

#暑期創作大賽#

當一個對象裡有些屬性值為null 的不想參與json序列化時，比如列印日志等場景進行序列化，null字段會占用日志長度。 可以采用如下兩種方式：

方法一：JsonInclude.Include.NON_NULL 注解

在類上面增加 @JsonInclude(JsonInclude.Include.NON_NULL)

示例：

//這個是類注解,表示該類執行個體化的對象裡，值為null的字段不參與序列化
@JsonInclude(JsonInclude.Include.NON_NULL)
@Data
public class Person {
    private Long id;
    private String name;  
}

 public static void main(String[] args) {
        Person p1 = new Person();
        p1.setId(1L);
        p1.setName("test1");
        System.out.println("p1: " +JSONObject.toJSON(p1));

        Person p2 = new Person();
        p2.setId(1L);
        System.out.println("p2: " +JSONObject.toJSON(p2));
    }

           

輸出：

p1: {"name":"test1","id":1}
p2: {"id":1}
           

方法2：自定義一個ObjectMapper

ObjectMapper objectMapper = new ObjectMapper();

objectMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);

自定義一個JsonUtils工具類：

可以解析字元串，array, map等

@Slf4j
public class JsonUtils {
    private static final String EMPTY_JSON = "{}";
    private static final String EMPTY_ARRAY_JSON = "[]";

    private static final ObjectMapper MAPPER = new ObjectMapper();

    static {
        MAPPER.setSerializationInclusion(JsonInclude.Include.NON_EMPTY);
    }


    public static String toJSON(@Nullable Object obj) {
        if (obj == null) {
            return null;
        }
        try {
            return MAPPER.writeValueAsString(obj);
        } catch (JsonProcessingException e) {
            log.error("toJson error, ", e);
            throw new BusinessException(e.getMessage());
        }
    }

    public static <T> T parseObject(@Nullable String json, Class<T> valueType) {
        if (json == null) {
            return null;
        }
        try {
            return MAPPER.readValue(json, valueType);
        } catch (IOException e) {
            log.error("parse object error, ", e);
            throw new BusinessException(e.getMessage());
        }
    }

    public static <E, T extends Collection<E>> T parseArray(String json,
                                                            Class<? extends Collection> collectionType, Class<E> valueType) {
        if (StringUtils.isEmpty(json)) {
            json = EMPTY_ARRAY_JSON;
        }
        try {
            return MAPPER.readValue(json,
                    defaultInstance().constructCollectionType(collectionType, valueType));
        } catch (IOException e) {
            log.error("parseArray error, ", e);
            throw new BusinessException(e.getMessage());
        }
    }

    public static <T> List<T> parseArray(String json, Class<T> valueType) {
        return parseArray(json, List.class, valueType);
    }

    /**
     *
     */
    public static <K, V, T extends Map<K, V>> T parseMap(String json, Class<? extends Map> mapType,
                                                         Class<K> keyType, Class<V> valueType) {
        if (StringUtils.isEmpty(json)) {
            json = EMPTY_JSON;
        }
        try {
            return MAPPER.readValue(json,
                    defaultInstance().constructMapType(mapType, keyType, valueType));
        } catch (IOException e) {
            log.error("parseMap error, ", e);
            throw new BusinessException(e.getMessage());
        }
    }

    public static Map<String, Object> parseMap(String string) {
        return parseMap(string, Map.class, String.class, Object.class);
    }
}

           

測試

public static void main(String[] args) {
        Person p1 = new Person();
        p1.setId(1L);
        p1.setName("test1");
        System.out.println("p1: " +JsonUtils.toJSON(p1));

        Person p2 = new Person();
        p2.setId(1L);
        System.out.println("p2: " +JsonUtils.toJSON(p2));
    }

//輸出:
// p1: {"id":1,"name":"test1"}
// p2: {"id":1}