Amazon Web Services，在Android程序中读取存储DynamoDB Json数据

Question

I store Json Data into a DynamoDB table, the data looks like this:

"payload": {
"M": {
  "state": {
    "M": {
      "reported": {
        "M": {
          "alive": {
            "BOOL": true
          },
          "reg": {
            "N": "0"
          },
          "timestamp": {
            "N": "1520357203.4857106"
          }
        }
      }
    }
  }
}

I need to retrieve this data to an android program, using the scan command to read all the data in the table:

DynamoDBScanExpression scanExpression = new DynamoDBScanExpression();
      List<PcObject2DO> result = dynamoDBMapper.scan(PcObject2DO.class, scanExpression);

Where

PcObject2DO

is the class with the accesors methods that Amazon provide for the DynamoDB table, all fields in the table are strings, simply. I receive this error in the scan command:

com.amazonaws.mobileconnectors.dynamodbv2.dynamodbmapper.DynamoDBMappingException: Expected S in value {M:......

and mentioned the use of custom marshaler, the problem is retrieve the data of the field "payload" that is in DynamoDB Json format. The documentation about read Json and the use of marshalers are vague and not cover all needs. After Investigate in forums and get sample code, I tested using marshalers of many types, create a class for the payload, and also change the type of the table accesors, but the problem is still there, the data of the payload field cannot be retrieved.

I Include the payload class, the custom marshaller, and the changes made in the table accesors, the changes are commented. Sorry, Im new in android and AWS, I understand the concept of the marshaler and the seriealized data, but I really dont know how do this or if is possible.

PcObject2DO.java

@DynamoDBTable(tableName = "xxxxxxxxxxxx-thing")

public class PcObject2DO {
    private String _reg;
    private String _timestamp;
    private String _payload;

    //private Map<String, Payload> _payload;

    //private static final JsonMarshaller<Payload>PAYLOAD_JSON_MARSHALLER    = new JsonMarshaller<Payload>();

    @DynamoDBHashKey(attributeName = "reg")
    @DynamoDBAttribute(attributeName = "reg")
    public String getReg() {
        return _reg;
    }

    public void setReg(final String _reg) {
        this._reg = _reg;
    }
    @DynamoDBRangeKey(attributeName = "timestamp")
    @DynamoDBAttribute(attributeName = "timestamp")
    public String getTimestamp() {
        return _timestamp;
    }

    public void setTimestamp(final String _timestamp) {
        this._timestamp = _timestamp;
    }
    @DynamoDBAttribute(attributeName = "payload")
    public String getPayload() {
        return _payload;
   }
    public void setPayload(final String  _payload) {
        this._payload = _payload;
    }
    /*public Set<String> getPayload() {
        if(_payload !=null){
            Set<String> jsonSet = new HashSet<String>(_payload.size());
            for(Payload data : _payload){
                String json = PAYLOAD_JSON_MARSHALLER.marshall(data);
                jsonSet.add(json);
            }
            return jsonSet;
        }else {
            return null;
        }
    }
    public void setPayload(Set<String> jsonSet) {
        if(jsonSet != null){
            _payload = new HashSet<Payload>(jsonSet.size());
            for(String json : jsonSet){
                Payload data =    PAYLOAD_JSON_MARSHALLER.unmarshall(Payload.class, json);
                _payload.add(data);
            }
        }
    }*/
    //-----
}

Payload.Java

public class Payload {
    private Boolean alive;
    private int reg;
    private String timestamp;

    public Boolean getAlive() {return alive;}
    public void setAlive(Boolean alive) {this.alive = alive;}

    public int getReg() {return  reg;}
    public void setReg(int reg){this.reg = reg;}

    public String getTimestamp() {return  timestamp;}
    public void  setTimestamp(String timestamp) {this.timestamp = timestamp;}
}

PayloadMarshaller.java

public class PayloadMarshaller implements    DynamoDBMarshaller<List<Payload>> {

    private static final ObjectMapper mapper = new ObjectMapper();
    private static final ObjectWriter writer = mapper.writer();

    @Override
    public String marshall(List<Payload> obj ) {
        try {
            return writer.writeValueAsString(obj);
        }catch (JsonProcessingException e){
            e.printStackTrace();
            return "";
        }
     }

    @Override
    public List<Payload> unmarshall (Class<List<Payload>> clazz, String json){
        final CollectionType type =    mapper.getTypeFactory().constructCollectionType(List.class, Payload.class);
        try{
            return mapper.readValue(json, type);
        }catch (Exception e){
            e.printStackTrace();
            return null;
        }
    }
}

Answer 1

It looks like you have a boolean instead of a String

 "alive": {
        "BOOL": true
      },