Gson反序列化生成NULL值

如何解决Gson反序列化生成NULL值

您的Gson映射与给定的JSON不匹配。默认情况下，Gson通过 确切 名称将JSON属性映射到目标映射中的相应字段。看一眼：

"idmessage":"27301"

和

private String IdMessage

属性名称大小写和字段名称大小写不匹配。您需要的是正确映射JSON。要么：

private String idmessage

或通过覆盖名称匹配（这更适合Java命名约定）：

@Serializedname("idmessage")
private String idMessage;

注意每行一个字段。为了分别注释每个字段，这是必需的。或者，如果可能，在Java和JSON中同时使用camelCase。

解决方法

我试图读取JSON文件并将其转换为数组，但是在读取JSON文件后从数组获取空值。我正在为我的ShipDetail班级使用默认构造函数。

  BufferedReader detailReader = new BufferedReader( new  FileReader(shipDetails));
  // Buffered passed to convert json array to java array
  ShipDetail[] shipDetail  = gson.fromJson(detailReader,ShipDetail[].class );

  System.out.println( shipDetail[0].toString());

  // Convert  array to arrayList
  ArrayList<ShipDetail> detailArray = new ArrayList<ShipDetail>(Arrays.asList(shipDetail));

JSON文件：

[  
   {  
      "idmessage":"27301","idsession":"362","time_stamp_system":"2017-01-20 14:51:14","NMEA_string":"xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx","processed":"1","MMSI":"0000000001","AIS_version":"0","IMO_number":"xxxxxxxxxx","callSign":"ODLK1","name":"ODLXJ KWW","type_of_ship_and_cargo":"0","bow_to_possition_unit":"212","stern_to_possition_unit":"71","port_to_possition_unit":"22","starboard_to_possitio_unit":"22","type_of_position_fixing_divice":"1","ETA":null,"destination":"","last_static_draught":"0","DTE":"127"
   }
]

本ShipDetail类：

public class ShipDetail {

    private String IdMessage,IdSession,Time_Stamp_System,Nmea_String,Processed;
    private String Mmsi,Ais_Version,Imo_Number,Callsign,Name,Type_Of_Ship_And_Cargo;
    private String Bow_To_Position_Unit,Stern_To_Position_Unit,Port_To_Position_Unit,Starboard_To_Position_Unit,Type_Of_Position_Fixing_Device;
    private String Eta,Destination,Last_Ship_Draught,Dte;

    public String getMmsi() {
        return Mmsi;
    }

    public String toString() {
        return "\n Id Message : " + IdMessage + "\n Id Session : " + IdSession + "\n Time Stam System : "
                + Time_Stamp_System + "\n NMEA String : " + Nmea_String + "\n Processed : " + Processed + "\n MMSI : "
                + Mmsi + "\n AIS Version : " + Ais_Version + "\n IMO Number : " + Imo_Number + "\n Call Sign : "
                + Callsign + "\n Name : " + Name + "\n Type Of Ship And Cargo : " + Type_Of_Ship_And_Cargo
                + "\n Bow To Position Unit : " + Bow_To_Position_Unit + "\n Stern To Position Unit : "
                + Stern_To_Position_Unit + "\n Port To Position Unit : " + Port_To_Position_Unit
                + "\n Starboard To Position Fixing Device : " + Starboard_To_Position_Unit
                + "\n Type Of Position Fixing Device : " + Type_Of_Position_Fixing_Device + "\n ETA : " + Eta
                + "\n Destination : " + Destination + "\n Last Ship Draught : " + Last_Ship_Draught + "\n DTE : " + Dte;
    }
}