json序列化时忽略值为null的字段的两种方式

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当一个对象里有些属性值为null 的不想参与json序列化时，比如打印日志等场景进行序列化，null字段会占用日志长度。 可以采用如下两种方式：

方法一：JsonInclude.Include.NON_NULL 注解

在类上面增加 @JsonInclude(JsonInclude.Include.NON_NULL)

示例：

//这个是类注解,表示该类实例化的对象里，值为null的字段不参与序列化
@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));
    }

输出：

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

方法2：自定义一个ObjectMapper

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

自定义一个JsonUtils工具类：
可以解析字符串，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);
    }
}

测试

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));
    }

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