public class ResultEntity implements Serializable {
    @SerializedName("IsError")//设置这个 是因为服务器返回的字段叫这个名字，但是这样写违反我们自己的命名规则，所以加上这个注解
    private int code;
    @SerializedName("InfoMessage")
    private String message;

 
    public int getCode() {
        return code;
    }

    public void setCode(int code) {
        this.code = code;
    }

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }


}

//T泛型，任意对象
public class ResultDataEntity<T> extends ResultEntity implements Serializable {

    @SerializedName("ReturnData")
    private T data;

    public T getData() {
        return data;
    }

    public void setData(T data) {
        this.data = data;
    }
  
//以下方法是专门用来转换json to bean  or bean to json 
   public static ResultDataEntity fromJson(String json, Class clazz) {
        Gson gson = new Gson();
        Type objectType = type(ResultDataEntity.class, clazz);
        return gson.fromJson(json, objectType);
    }

    public String toJson(Class<T> clazz) {
        Gson gson = new Gson();
        Type objectType = type(ResultDataEntity.class, clazz);
        return gson.toJson(this, objectType);
    }

    static ParameterizedType type(final Class raw, final Type... args) {
        return new ParameterizedType() {
            public Type getRawType() {
                return raw;
            }

            public Type[] getActualTypeArguments() {
                return args;
            }

            public Type getOwnerType() {
                return null;
            }
        };
    }
}

例子

{
    "Code": 200,
    "Message": "登录成功！",
    "Data": {
            "IDCardNum": "32098122226112495",
            "MemberMobile": "123123444",
            "MemberName": "杨x",
            "Balance": 460,
            "IsEnabled": 1,
            "CreatedDate": "2016-12-09 19:43:22.187",
            "LastLoginTime": "2016-12-09 19:43:22.187",
            "LastLoginIP": "192.168.199.153",
           }
}

如何进行解析呢？Data 里面放的是一个用户对象。那么首先我们要创建一个用户类。

public class UserEntity implements Serializable {

    /**
     * IDCardNum : 32098122226112495
     * MemberMobile : 123123444
     * MemberName : 杨x
     * Balance : 460
     * IsEnabled : 1
     * CreatedDate : 2016-12-09 19:43:22.187
     * LastLoginTime : 2016-12-09 19:43:22.187
     * LastLoginIP : 192.168.199.153
     */

      @SerializedName("IDCardNum")//可使用该注解 重命名
    private String cardNum;
    private String MemberMobile;
    private String MemberName;
    private int Balance;
    private int IsEnabled;
    private String CreatedDate;
    private String LastLoginTime;
    private String LastLoginIP;

  //各种set get

如何解析呢？

String json ="";//就是服务器返回的数据
  ResultDataEntity<UserEntity> userResult =ResultDataEntity.fromJson(json ,UserEntity.class);

UserEntity userEntity =userResult .getData();//取得用户对象，然后进行各种操作

小记

如有更好的方式，请给出建议，如有错误请指出，谢谢