Jackson ObjectMapper: readValue returns null

问题

I need to parse this json:

{
   "id":"cpd4-b39c4b2a-b5cb-4581-b519-6034aaa7fe4e",
   "transactionId":"768a9be4-b5b3-452f-9bd3-9fff2e9ace5c",
   "status":"PUBLIC",
   "confidential":true,
   "expiringAt":1231231,
   "locked":true,
   "metadata":[
      {
         "user":"admin",
         "creationTimestamp":1538578453285,
         "value":"metadata"
      }
   ],
   "security":"read",
   "timestampCreation":1538578453285,
   "userCreation":"admin",
   "appCreation":"app",
   "document":{
      "id":null,
      "transactionId":"768a9be4-b5b3-452f-9bd3-9fff2e9ace5c",
      "docId":"68aab3799a9380fe82ed43ff2d46a5b07da1b270-1282",
      "size":1282,
      "name":"pom.xml",
      "alias":"alias",
      "hash":"68aab3799a9380fe82ed43ff2d46a5b07da1b270",
      "title":"title",
      "encoding":"UTF-8",
      "mimeType":"application/xml"
   }
}

to a object Reference class:

public class Reference {

    private String id;
    private String transactionId;

    private DocumentStatus status;
    private Boolean confidential;
    private Integer expiringAt;
    private Boolean locked;

    private List<Metadata> metadata;
    private String security;

    // IDReferenciaAlta
    private Date timestampCreation;
    private String userCreation;
    private String appCreation;

    private Date timestampModified;
    private String userModified;
    private String appModified;

    private Date timestampDeletion;
    private String userDeletion;
    private String appDeletion;

    //getters and setters...
}

where Metadata is:

public class Metadata {

    private String user;
    private Date creationTimestamp;
    private String value;

    //getters an setters
}

Currently, I'm using this code:

Reference reference = null;
try {
    reference = this.mapper.readValue(jsonDocument, Reference.class);
} catch (IOException e1) {
    // TODO: Throw domain exception...
    e1.printStackTrace();
}

The problem is that this.mapper.readValue(...) returns null.

I know that json schema and Reference class propoerties are not exactly the same, but I expected to get a reference with "common" json properties

回答1:

Without the stack trace, we are almost clueless on what the error is. However, from what can be seen in this question, the document property in not mapped to any field of the Reference class.

So you can either:

Map the document property to a field.
Use @JsonIgnoreProperties("document") in the Reference class to ignore the document property. Alternatively you can use @JsonIgnoreProperties(ignoreUnknown = true) to ignore any unknown properties.

Configure your ObjectMapper to ignore unknown properties by disabling DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES. See below:

ObjectMapper mapper = new ObjectMapper();
mapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);
Reference reference = mapper.readValue(jsonDocument, Reference.class);

来源：https://stackoverflow.com/questions/52643935/jackson-objectmapper-readvalue-returns-null

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java

jackson