fasterxml jackson反序列化时对于非静态内部类报错问题及解决
作者：赶路人儿
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fasterxml jackson反序列化时对于非静态内部类报错
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。
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。
总结
以上为个人经验，希望能给大家一个参考，也希望大家多多支持脚本之家。