（已解決）獲取只有一個隨機行的值，並將這些值設置爲一個類

Question

我一直在嘗試從我的表中設置一個隨機行的值，但它在嘗試檢索時一直給我一個空值它來自我的servlet。

這是我的代碼來檢索隨機行並將值設置爲我的課程。 sq是表格的名稱。

public Question getQuestion() throws Exception{ 
    System.out.println("Getting the questions"); 

    Question question = null; 
    try{ 
     String selectStatement = "select * from sq order by rand() limit 1"; 
     PreparedStatement prepStmt = con.prepareStatement(selectStatement); 
     ResultSet rs = prepStmt.executeQuery(); 

     if(rs.next()){ 
      Question myquestion = new Question(); 
      myquestion.setQid(rs.getInt("QID")); 
      myquestion.setQuestion(rs.getString("question")); 
      //System.out.println(rs.getString("question")); 
      System.out.println(myquestion.getQuestion()); 
     } 

    }catch(Exception ex){ 
     throw new Exception("Error:" + ex.getMessage()); 
    } 
    return question; 
} 

它打印出這裏的問題，但它給我一個空值在我的servlet。

try{ 
      Database myDatabase = new Database(); 
      Question question = myDatabase.getQuestion(); 
      if(question != null){ 
       HttpSession session = request.getSession(true); 
       session.setAttribute("secquestion", question); 
       request.getRequestDispatcher("SecQn.jsp").forward(request, response); 
      }else{ 
       System.out.println("ERROR"); 
      } 
      //request.getRequestDispatcher("Home.jsp").forward(request, response); 
     }catch(Exception ex){ 
      System.out.println(ex.getMessage()); 
     } 
    } 

它打印出錯誤，這意味着當我已經設置了以前的值時，問題的值爲空。如何正確設置值？或者我的代碼有什麼問題？

解決了錯誤。這是最新的更新代碼。

public Question getQuestion() throws Exception{ 
    System.out.println("Getting the questions"); 

    Question question = null; 
    try{ 
     String selectStatement = "select * from sq order by rand() limit 1"; 
     PreparedStatement prepStmt = con.prepareStatement(selectStatement); 
     ResultSet rs = prepStmt.executeQuery(); 
     if(rs.next()){ 
      question = new Question(); 
      question.setQid(rs.getInt("QID")); 
      question.setQuestion(rs.getString("question")); 
      System.out.println(question.getQuestion()); 
     }  
    }catch(Exception ex){ 
     throw new Exception("Error:" + ex.getMessage()); 
    } 
    return question; 
} 

Answer 1

在getQuestion()方法中，您正在返回問題，但您從未爲其指定任何值。 您應該返回myquestion，或者在返回之前分配。

question = myquestion ;