fasterxml jackson反序列化时对于非静态内部类报错

朱雀 2024-03-26 08:38 18阅读 0赞

java中通常使用jackson、fastjson两个库来处理json。后者的api使用起来比较方便，但是安全漏洞太多了。

今天在使用jackson反序列化json字符串时，遇到了一个问题：

Exception in thread "main" com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot construct instance of `json.TransferResp$TransforData` (although at least one Creator exists): can only instantiate non-static inner class by using default, no-argument constructor

很多文章没有解释清楚，本文做了一个实验。对于嵌套结构，定义了一个包含内部类的java类来接收，如果这个复杂结构是一个数组形式，那么反序列化时会报上面错误。

#### 实验一 ####

1）java实体类：

@Data
    public class TransforResponse {
        private Integer code;
        
        private Map<String, String> defaultData;
        private TransforData data;
        
        @Data
        public static class TransforData{
            private Long encyId;
            private int score;
            private Map<String, String> other;
        }
    }

2）测试

private static ObjectMapper objectMapper = new ObjectMapper();
    
    public static void main(String[] args) throws Exception {
        String jsonStr = serialization(); //{\"code\":200,\"data\":{\"encyId\":123,\"other\":{\"a\":\"test\"},\"score\":5}}
        deSerialization(jsonStr); //TransferResp(code=200, data=TransferResp.TransforData(encyId=123, score=5, other={a=test}))
        
        System.out.println("----------");
        String jsonStr2 = serialization2(); //{\"code\":200,\"data\":{\"encyId\":123,\"other\":{\"a\":\"test\"},\"score\":5}}
        deSerialization2(jsonStr2); //TransferResp(code=200, data=TransferResp.TransforData(encyId=123, score=5, other={a=test}))
    }
    private static TransferResp createObj() {
        TransferResp tr = new TransferResp();
        
        TransforData transforData = tr.new TransforData();
        transforData.setEncyId(123L);
        transforData.setScore(5);
        Map<String, String> hashMap = new HashMap<>(1);
        hashMap.put("a", "test");
        transforData.setOther(hashMap);
        
        tr.setCode(200);
        tr.setData(transforData);
    
        return tr;
    }
    
    private static String serialization() {
        TransferResp tr = createObj();
        String jsonString = JSONObject.toJSONString(tr);
        System.out.println(jsonString);
        return jsonString;
    }
    private static void deSerialization(String jsonStr) {
        TransferResp parseObject = JSONObject.parseObject(jsonStr, TransferResp.class);
        System.out.println(parseObject.toString());
    }
    
    private static String serialization2() throws JsonProcessingException {
        TransferResp tr = createObj();
        String jsonString = objectMapper.writeValueAsString(tr);
        System.out.println(jsonString);
        return jsonString;
    }
    private static void deSerialization2(String jsonStr) throws JsonParseException, JsonMappingException, IOException {
        TransferResp parseObject = objectMapper.readValue(jsonStr, TransferResp.class);
        System.out.println(parseObject.toString());
    }

运行后正常。

#### 实验二 ####

1）java实体类

@Data
    public class TransferResp {
        private Integer code;
        private List<TransforData> data;
        
        @Data
        public class TransforData{
            private Long encyId;
            private Integer score;
            private Map<String, String> other;
        }
    }

2）测试：

private static ObjectMapper objectMapper = new ObjectMapper();
    
    public static void main(String[] args) throws Exception {
        String jsonStr = serialization(); //{"code":200,"data":[{"encyId":123,"other":{"a":"test"},"score":5}]}
        deSerialization(jsonStr); //TransferResp(code=200, data=[TransferResp.TransforData(encyId=123, score=5, other={a=test})])
        
        System.out.println("----------");
        String jsonStr2 = serialization2(); //{"code":200,"data":[{"encyId":123,"score":5,"other":{"a":"test"}}]}
        deSerialization2(jsonStr2); //error
    }
    private static TransferResp createObj() {
        TransferResp tr = new TransferResp();
        
        TransforData transforData = tr.new TransforData();
        transforData.setEncyId(123L);
        transforData.setScore(5);
        Map<String, String> hashMap = new HashMap<>(1);
        hashMap.put("a", "test");
        transforData.setOther(hashMap);
        
        List<TransforData> list = new ArrayList<>();
        list.add(transforData);
        tr.setCode(200);
        tr.setData(list);
    
        return tr;
    }
    
    private static String serialization() {
        TransferResp tr = createObj();
        String jsonString = JSONObject.toJSONString(tr);
        System.out.println(jsonString);
        return jsonString;
    }
    private static void deSerialization(String jsonStr) {
        TransferResp parseObject = JSONObject.parseObject(jsonStr, TransferResp.class);
        System.out.println(parseObject.toString());
    }
    
    private static String serialization2() throws JsonProcessingException {
        TransferResp tr = createObj();
        String jsonString = objectMapper.writeValueAsString(tr);
        System.out.println(jsonString);
        return jsonString;
    }
    private static void deSerialization2(String jsonStr) throws JsonParseException, JsonMappingException, IOException {
        TransferResp parseObject = objectMapper.readValue(jsonStr, TransferResp.class);
        System.out.println(parseObject.toString());
    }

运行时会报错：Exception in thread "main" com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot construct instance of \`json.TransferResp$TransforData\` (although at least one Creator exists): can only instantiate non-static inner class by using default, no-argument constructor

3）解决方法：

A、使用静态内部类

@Data
    public class TransferResp {
        private Integer code;
        private List<TransforData> data;
        
        @Data
        public static class TransforData{
            private Long encyId;
            private Integer score;
            private Map<String, String> other;
        }
    }

B）将内部类定义在一个单独的类文件中。