ObjectMapper將json轉對象報錯處理

在使用ObjectMapper將json轉對象，調用mapper.readValue(jsonStr, XwjUser.class)時，報如下錯：

com.fasterxml.jackson.databind.JsonMappingException: Can not construct instance of entity.XwjUser: no suitable constructor found, can not deserialize from Object value (missing default constructor or creator, or perhaps need to add/enable type information?)
 at [Source: {"id":1,"message":"Hello World","sendTime":1525162183195,"intList":null}; line: 1, column: 2]
    at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:261)
    at com.fasterxml.jackson.databind.DeserializationContext.instantiationException(DeserializationContext.java:1456)
    at com.fasterxml.jackson.databind.DeserializationContext.handleMissingInstantiator(DeserializationContext.java:1012)
    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromObjectUsingNonDefault(BeanDeserializerBase.java:1203)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:314)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:148)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:3789)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2833)
    at testJson.TestObjectMapper.testObj(TestObjectMapper.java:47)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

　　....

解決辦法：在XwjUser實體類中，加入無參構造器，即可解決