在循環中自行添加字符串時SQL查詢中的錯誤

Question

我在Servlet中循環查詢時遇到了超時錯誤，因此我決定創建一個只執行一次的長查詢。

下面是代碼：

public void deactivateAccount(String[] userList) { 
    DBConnectionFactory myFactory = DBConnectionFactory.getInstance(); 
    Connection con = myFactory.getConnection(); 

    try { 
     con.setAutoCommit(false); 

     String combinedQueries = ""; 


     for (int i =0; i<userList.length;i++) { 
      String query = "UPDATE users SET active='0' WHERE userID = ? ; "; 
      combinedQueries += query; 
     } 

     System.out.println(combinedQueries); 

     PreparedStatement p = con.prepareStatement(combinedQueries); 

     for (int i =0; i<userList.length;i++) { 
      int currentNum = i+1; 
      p.setInt(currentNum, Integer.parseInt(userList[i])); 

      System.out.println("current num is " + currentNum); 
      System.out.println("userlist value is " + Integer.parseInt(userList[i])); 

     } 


      p.execute(); 



    } catch (SQLException ex) { 
     try { 
      con.rollback(); 
     } catch (SQLException ex1) { 
      Logger.getLogger(UserDAO.class.getName()).log(Level.SEVERE, null, ex1); 
     } 
     Logger.getLogger(UserDAO.class.getName()).log(Level.SEVERE, null, ex); 
    } 
} 

此代碼是在我的DAO - 它的作用是循環需要字符串多次（有多少複選框用戶檢查），然後準備在聲明另一個循環（設置準備語句的參數），然後執行它。

我得到錯誤：

Severe: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'UPDATE users SET active='0' WHERE userID = 1; UPDATE users SET active='0' WHERE ' at line 1 at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)

但是當我在執行前打印查詢中的代碼，這是出現什麼：

Info: UPDATE users SET active='0' WHERE userID = ?; UPDATE users SET active='0' WHERE userID = ?; UPDATE users SET active='0' WHERE userID = ?; UPDATE users SET active='0' WHERE userID = ?; (assuming 4 checkboxes were clicked)

該方法接受的陣列，我從一個請求獲得.getParameterValues來自servlet。

預先感謝您的幫助！

Answer 1

這是不是爲批量更新運行PreparedStatement​​單獨（由於性能原因），最好的做法，相反，你需要使用executeBatch()，如下圖所示：

public void deactivateAccount(String[] userList) { 

    DBConnectionFactory myFactory = DBConnectionFactory.getInstance(); 
    Connection con = myFactory.getConnection(); 
    PreparedStatement p = null; 

    try { 
     con.setAutoCommit(false); 
     String query = "UPDATE users SET active='0' WHERE userID = ?"; 
     p = con.prepareStatement(query); 

     for (int i =0; i<userList.length;i++) { 
      p.setInt(1, Integer.parseInt(userList[i])); 
      p.addBatch(); 
     } 
     int[] affectedRecords = p.executeBatch(); 
     con.commit(); 
     //you can validate rows before commit, upto your requirement 
    } catch (SQLException ex) { 
     try { 
      con.rollback(); 
     } catch (SQLException ex1) { 
      Logger.getLogger(UserDAO.class.getName()).log(Level.SEVERE, null, ex1); 
     } 
     Logger.getLogger(UserDAO.class.getName()).log(Level.SEVERE, null, ex); 
    } finally { 
      if(p != null) 
       p.close(); 
      if(con != null) 
       con.close(); 
    } 
} 

您可以參考here關於更多的細節批量JDBC操作。