java.lang.IllegalStateException：這不是一個JSON陣列

Question

我有兩個問題：

1）java.lang.IllegalStateException：這不是一個JSON陣列

這種努力的時候我得到將List轉換爲JSON。也PLZ告訴我如何處理空數組到JSON。

2）當我在數據庫運行查詢它取了我5個結果。當我調試OperatorDetailsDao.java時，我得到rs.next（）只運行一次。另一個問題是我在operatorList中得到null結果，雖然它是運算符數組。

請幫我理清問題，堅持兩天。

控制器類

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是一個bean類吸氣劑和setter。

Answer 1

看來，這兩個問題都涉及到operatorList的OperatorDetailsDao.getOperators()方法中的不正確初始化。下面是問題的一個註釋說明：

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 
} 

當這個方法現在在控制器內調用：

//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(); 

刪除違規線operatorList = null將確保有效空數組列表和不一個空值將被返回，並將由GSON正確處理。

在旁註中 - 在GSON庫中存在一個issue logged，它無法處理NULL數組，並按照已修復的註釋操作。