java.lang.IllegalStateException: 这不是一个 JSON 数组

Question

我有两个问题：

1) java.lang.IllegalStateException: 这不是一个 JSON 数组

这是我在尝试将 List 转换为 JSON 时得到的。另外请告诉我如何将空数组处理为 json。

2) 当我运行查询数据库时，它为我获取了 5 个结果。当我调试 OperatorDetailsDao.java 时，我只得到 rs.next() 到运行一次。另一个问题是，尽管它是运算符数组，但我在 operatorList 中得到的结果为空。

麻烦帮我解决一下，卡了两天。

控制器Class

public class SearchController extends HttpServlet {
  private static final long serialVersionUID = 1L;

  protected void doPost(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException {

            response.setContentType("application/json");
            try {
                String term = request.getParameter("terms");
                System.out.println("Data from ajax call " + term);

                OperatorDetialsDao details = new OperatorDetialsDao();
                List<OperatorDetailsBean> operatorList = details.getOperators(term);
                            System.out.println("Operator List " + operatorList); 
                JsonElement element = new Gson().toJsonTree(operatorList);
                            System.out.println(element);
                            JsonArray jsonArray = element.getAsJsonArray();
                            response.getWriter().print(jsonArray);
                            response.getWriter().flush();

            } catch (Exception e) {
                e.printStackTrace();
            }
}

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

             doPost(request, response);
    }

}

OperatorDetailsDao -> getOperators()

public List<OperatorDetailsBean> getOperators(String name) {
          PreparedStatement ps = null;
          List<OperatorDetailsBean> operatorList = new ArrayList();
          operatorList = null;
          name = name.toUpperCase();
          String data;
          try {
              ps = connection.prepareStatement("SELECT * FROM operator_details_m  WHERE upper(name) LIKE ?");
              ps.setString(1, name + '%');
              ResultSet rs = ps.executeQuery();

              while (rs.next()) {
                  uname = rs.getString("NAME");
                  token = rs.getString("TOKEN_NO");
                  OperatorDetailsBean op = new OperatorDetailsBean();
                  op.setName(uname);
                  op.setTokenNo(token);
                  operatorList.add(op);
              }

          } catch (Exception e) {
              //System.out.println(e.getMessage());
          }
          return operatorList;
}

OperatorDetailsBean 是一个具有 getter 和设置器的 bean class。

Answer 1

这两个问题似乎都与 OperatorDetailsDao.getOperators() 方法中 operatorList 的错误初始化有关。下面是问题的注释解释：

public List<OperatorDetailsBean> getOperators(String name) {
          PreparedStatement ps = null;
          List<OperatorDetailsBean> operatorList = new ArrayList();
          //Prahaladd - Setting this to null will cause operatorList to be null.
         // This is not being re-initalized anywhere else
          operatorList = null; 
          name = name.toUpperCase();
          String data;
          try {
              ps = connection.prepareStatement("SELECT * FROM operator_details_m  WHERE upper(name) LIKE ?");
              ps.setString(1, name + '%');
              ResultSet rs = ps.executeQuery();

              while (rs.next()) {
                  uname = rs.getString("NAME");
                  token = rs.getString("TOKEN_NO");
                  OperatorDetailsBean op = new OperatorDetailsBean();
                  op.setName(uname);
                  op.setTokenNo(token);
                  operatorList.add(op); //Prahaladd - definitely a NullPointerException
              }

          } catch (Exception e) {
              //Prahaladd - Oops!! NPE thrown above was gulped.
              //System.out.println(e.getMessage());
          }
          return operatorList; //returned operatorList is null. Will impact gson library processing
}

现在在控制器中调用此方法时：

 //Prahaladd - operatorList returned would be null
 List<OperatorDetailsBean> operatorList = details.getOperators(term);
                                System.out.println("Operator List " + operatorList); 
//Prahaladd - GSON processes this null value.
JsonElement element = new Gson().toJsonTree(operatorList);

 System.out.println(element);
 //Prahaladd - this will fail since we are trying to process a non-array
 // as a JSON array.
 JsonArray jsonArray = element.getAsJsonArray();

删除有问题的行 operatorList = null 将确保有效的 empty 数组列表和 not a null 值将被返回并被 GSON 正确处理。

附带说明 - GSON 库中有一个 issue logged 无法处理 NULL 数组，根据评论，这已得到修复。

java.lang.IllegalStateException: 这不是一个 JSON 数组

java.lang.IllegalStateException: This is not a JSON Array

java

arrays

json

prepared-statement