关于Jackson对复杂类型数据反序列化时,泛型对象<T>被转换为 LinkHashMap

代码如下:

先贴一段测试代码

    @Test
    public void json(){
        String jsonStr = "{"code":0,"subcode":0,"message":"ok","data":{"hostuin":914038622,"encrypt_uin":"NKcPoeoF7w-A","hostname":"YAN","totoal":7,"disslist":[{"diss_name":"QZone背景音乐","diss_cover":"http://y.gtimg.cn/mediastyle/y/img/cover_qzone_130.jpg","song_cnt":5,"listen_num":0,"dirid":205,"tid":0,"dir_show":0},{"diss_name":"搞错了，再来","diss_cover":"http://y.gtimg.cn/music/photo_new/T002R300x300M000000wjiaZ0Q68Vt.jpg?n=1","song_cnt":9,"listen_num":87,"dirid":25,"tid":8445417748,"dir_show":1},{"diss_name":"QQ里的网易云","diss_cover":"http://y.gtimg.cn/music/photo_new/T002R300x300M0000044tjcU3HYRUt.jpg?n=1","song_cnt":7,"listen_num":256,"dirid":23,"tid":8445412062,"dir_show":1},{"diss_name":"哦哦哦哦","diss_cover":"http://y.gtimg.cn/music/photo_new/T002R300x300M0000019DOaT2CE0OG.jpg?n=1","song_cnt":10,"listen_num":94,"dirid":22,"tid":8445391399,"dir_show":1},{"diss_name":"睡觉了","diss_cover":"http://y.gtimg.cn/music/photo_new/T002R300x300M000001HM2km2K4GUv.jpg?n=1","song_cnt":9,"listen_num":29,"dirid":1,"tid":8445382323,"dir_show":1},{"diss_name":"惊艳了时光","diss_cover":"http://qpic.y.qq.com/music_cover/T76450IyeJNdibl3a2PvIRDo2zFwbR8L1g2icGu8GfgxKabkyKTVMveg/300?n=1","song_cnt":11,"listen_num":2227,"dirid":17,"tid":8054843490,"dir_show":1},{"diss_name":"1楼选亚索","diss_cover":"http://qpic.y.qq.com/music_cover/T76450IyeJNdibl3a2PvIRAN81k5hQloWCzsnQNE298kGWfqQG7WCmQ/300?n=1","song_cnt":12,"listen_num":550,"dirid":13,"tid":1436210735,"dir_show":1}]}}";
        ApiResp<SongListResp> resp1 = JsonUtil.toResp(jsonStr, new TypeReference<>() {});
        ApiResp<SongListResp> resp2 = JsonUtil.toBean(jsonStr, new TypeReference<>() {});
        ApiResp<SongListResp> resp3 = JsonUtil.toBean(jsonStr, ApiResp.class);
        
        SongListResp data1 = resp1.getData();
        SongListResp data2 = resp2.getData();
        SongListResp data3 = resp3.getData();
    }

运行结果

可以看到 resp3.data的 类型是LinkHashMap 而并非指定的 SongListResp 所以 resp3.getData() 将会报错

而 resp1 resp2 则没有这个问题，因为通过new TypeReference<>() {} 指定了泛型类型

resp1 不同点在于 resp2

resp1是JsonUtil.toResp()的结果,内部指定了返回类型ApiResp<T>

resp2 是JsonUtil.toBean()的结果,放回泛型为T,所以在不做强转的情况下,返回的是Object

Object resp2 = JsonUtil.toBean(jsonStr, new TypeReference<>() {});

以下为此处用到的JAVA类

JsonUtil

@Slf4j
public class JsonUtil {

    private static final ObjectMapper OBJECT_MAPPER;


    static {
        OBJECT_MAPPER = new ObjectMapper();
    }


    /**
     * 装换成一个支持响应的 Resp
     * @param jsonStr json字符串
     * @param type 想要转换的复杂类型
     * @return  ApiResp类型为 泛型为 <T> 的对象
     * @param <T> 指定泛型
     */
    public static <T> ApiResp<T> toResp(String jsonStr,TypeReference<ApiResp<T>> type){
        return toBean(jsonStr, type);
    }

    /**
     * 装换成一个复杂 bean
     * @param jsonStr json字符串
     * @param type 想要转换的复杂类型
     * @return 泛型 T 对象
     * @param <T> 指定泛型
     */
    public static <T> T toBean(String jsonStr,TypeReference<T> type){
        Assert.hasText(jsonStr,"序列化字符串不能为空");
        try {
            return OBJECT_MAPPER.readValue(jsonStr, type);
        } catch (JsonProcessingException e) {
            log.error("JSON字符串反序列化失败",e);
            throw new RuntimeException("JSON字符串反序列化失败");
        }
    }

    /**
     * 装换成一个 简单bean
     * @param jsonStr json字符串
     * @param type 想要转换的Classs
     * @return 泛型 T 对象
     * @param <T> 指定泛型
     */
    public static <T> T toBean(String jsonStr,Class<T> type){
        Assert.hasText(jsonStr,"序列化字符串不能为空");
        try {
            return OBJECT_MAPPER.readValue(jsonStr, type);
        } catch (JsonProcessingException e) {
            log.error("JSON字符串反序列化失败",e);
            throw new RuntimeException("JSON字符串反序列化失败");
        }
    }

}

实体 ApiResp

@Data
@Accessors(chain = true)
@JsonIgnoreProperties(ignoreUnknown = true)
public class ApiResp<T> {

    @JsonProperty("code")
    private String code;

    @JsonProperty("data")
    private T data;

}

实体 SongListResp

@Data
@Accessors(chain = true)
@JsonIgnoreProperties(ignoreUnknown = true)
public class SongListResp {


    @JsonProperty("hostuin")
    private String hostuin;

    @JsonProperty("disslist")
    private List<DisslistDTO> disslist;

    @Data
    @Accessors(chain = true)
    @JsonIgnoreProperties(ignoreUnknown = true)
    public static class DisslistDTO {

        //以下属性省略
    }

}