如何将 MySQL 表中的行存储到 Java 中的数组中

Question

我正在尝试将数据库表中的行存储到数组中。我总是在我的 NetBeans IDE 7.1.1 中收到此错误“类或接口，预期枚举”

这是我写的代码

<table border="2">
   <tr>
      <th>Coop No</th>
      <th>Salutation</th>
      <th>First Name</th>
      <th>Middle Name</th>
      <th>Last Name</th>
      <th>Form Type</th>
   </tr>
   <%! double[][] g_testdata;
      ResultSet rs = null;
      %>           
   <% 
      //ResultSet rs = null;

      try
      {     
           Class.forName("com.mysql.jdbc.Driver"); //Load the driver– Not required in Java SE 6.0 and later (JDBC 4.0 and later), the driver is loaded automatically.
           String host = "jdbc:mysql://localhost/cooperative";
           String uName = "root";
           String uPass = "Hecares4me";

           //Connection con = DriverManager.getConnection( host, username, password );
           Connection con = DriverManager.getConnection(host, uName, uPass );

           Statement st = con.createStatement( );
           String SQL = "SELECT transfacdept.transfacdept_id, transfacdept.faculty_id, transfacdept.department_id, transfaculties.faculty_id, transfaculties.facultyname FROM transfacdept, transfaculties WHERE transfacdept.transfacdept_id = transfaculties.faculty_id ";
           rs = st.executeQuery( SQL );
           //ResultSet rs=st.executeQuery("SELECT transfacdept.transfacdept_id, transfacdept.faculty_id, transfacdept.department_id, transfaculties.faculty_id, transfaculties.facultyname FROM transfacdept, transfaculties WHERE transfacdept.transfacdept_id = transfaculties.faculty_id"); 

           g_testdata = new double[5][6]; 

           int numRows, numCols;

           if(!rs.next()){
               return;
           }
           rs.last();
           numRows = rs.getRow();
           numCols = rs.getMetaData().getColumnCount();
           out.println(numRows + " " + numCols);
           //rs.first();
           while(rs.next()){

                   for (int i=1; i <= numRows; i++)
                   {
                           for (int j=1; j <= numCols; j++) // populate the test data array
                           {
                                   g_testdata[i][j] = rs.getDouble(j);
                                   out.println(g_testdata[i][j]);

                           }
                   }

           }
       }
       catch(ClassNotFoundException xcp)
       {
           out.println("The SQLException exception has occurred:");
       }
       catch( SQLException err )
       {
           out.println( err.getMessage() );
       }                                                                                                                                                                                      }     
      %>
</table>

知道我哪里出错了吗？

Answer 1

1. Netbeans 7.1 已经很老了。考虑升级。
2. 不要在 JSP 中编写 Java 代码。用 servlet 编写，通过 Bean 发送到 JSP，使用 JSTL 从 JSP 中读取。

3. 您阅读 ResultSet 的方式很弱。试试下面的方法。

   public List findMyRecord(int 参数) { PreparedStatement ps = null; 结果集 rs=null; 连接 con = null; Listlist = new ArrayList();

            try
            {
                con = DBMaster.getInstance().getConnection(); //bcs I am using connection pooling. You can use `DriverManager.getConnection`.....
                String cmd="select * from table where parameter=? ORDER BY columnName DESC";
                ps=con.prepareStatement(cmd.toLowerCase());
   
                ps.setInt(1, parameter);
   
                rs=ps.executeQuery();
   
                if(rs.isBeforeFirst())
                {
                    while(rs.next())
                    {
                        YourBean pb = new YourBean ();
                        pb.setMyData(pb.getInt("columnName"));
   
                        list.add(pb);
                    }
                }
   
   
            }
            catch (Exception e)
            {
                e.printStackTrace();
            }
            finally
            {
                try
                {
                    if(rs!=null){rs.close();}
                    if(ps!=null){ps.close();}
                    if(con!=null){con.close();}
                }
                catch(Exception e)
                {
                    e.printStackTrace();
                }
            }
   
            return list;
     }
   

4. 在您的情况下，您应该认真尝试阅读如下结果集，这可能会解决您的问题...

if(rs.isBeforeFirst())
                {
                    while(rs.next())
                    {//read data}
    })

5. 使用连接池确保 MySQL 不会为 1000 个请求使用 1000 个连接。 C3P0 是一个简单的库。