撰写邮件错误。 ＆＃34;在启动ResultSet之前。＆＃34;

Question

我正在尝试创建一个电子邮件管理系统。以下是撰写电子邮件的代码，但是它会在启动ResultSet之前抛出错误。＆＃34;你能帮我吗？

String To = to.getText();
String Cc = cc.getText();
String Bcc = bcc.getText();
String Sub  = sub.getText();
String Msg = text.getText();
if(To.equals("") || Sub.equals("") || Msg.equals(""))
{
 JOptionPane.showMessageDialog(null, "Please Fill All Appropiate Details");
}
else   
{
 try {

     Class.forName("com.mysql.jdbc.Driver");
     Connection con = DriverManager.getConnection( "jdbc:mysql://localhost:3306/email management system","root", "ok" );
     Statement stmt = con.createStatement();
     ResultSet rs = stmt.executeQuery("select first,email,mail,name from login,curlogin;");
     String from =rs.getString("mail");
         String frmname =rs.getString("name");
     String recipent = "";
     String rname = "";
     Boolean tof;
     loop1: while(rs.next())
     {
         recipent = rs.getString("email");
          rname = rs.getString("first");
        if(recipent.equals(To))
          {
              tof = true;
              break loop1;

         }
          else 
          {
              tof= false;
          }
     }
    if(tof=true)
    {
        stmt.executeUpdate("Insert into inbox Values('"+frmname+"','"+Sub+"','"+Msg+"',curDate(), curTime(),'"+rname+"','"+from+"');");
                new inbox().setVisible(true);
        this.dispose();
    }  
    else
    {
        JOptionPane.showMessageDialog(null,"Sorry the 'To' Email you entered does not exist.");
    }
     ResultSet rs1 = stmt.executeQuery("select first,email,mail,name from login,curlogin;");
    Boolean taf = false;
    Boolean entered = false;
   loop2: while(rs1.next())
     {
         recipent = rs1.getString("email");
          rname = rs1.getString("first");
       if(Cc.equals(""))
               {

               }
       else
       {
           entered= true;
          if(recipent.equals(Cc))
          {
              taf = true;
              break loop2;

         }
          else 
          {
              taf= false;
          }
       }
     }
   if(entered=true)
   {
    if(taf=true)
    {
        stmt.executeUpdate("Insert into inbox Values('"+frmname+"','"+Sub+"','"+Msg+"',curDate(), curTime(),'"+rname+"','"+from+"');");
                new inbox().setVisible(true);
        this.dispose();
    }  
    else
    {
        JOptionPane.showMessageDialog(null,"Sorry the 'CC' Email you entered does not exist.");
    }
   }
    ResultSet rs2 = stmt.executeQuery("select first,email,mail,name from login,curlogin;");
    Boolean fot=false;
    Boolean entered2 =false;
    loop3: while(rs2.next())
     {
         recipent = rs2.getString("email");
          rname = rs2.getString("first");
       if(Bcc.equals(""))
       {

       }
       else
       {


          if(recipent.equals(Bcc))
          {
              fot = true;
              break loop3;

         }
          else 
          {
              fot= false;
          }
       }
     }
   if(entered2=true)
   {
    if(fot=true)
    {
        stmt.executeUpdate("Insert into inbox Values('"+frmname+"','"+Sub+"','"+Msg+"',curDate(), curTime(),'"+rname+"','"+from+"');");
        new inbox().setVisible(true);
        this.dispose();
    }  
    else
    {
        JOptionPane.showMessageDialog(null,"Sorry the 'CC' Email you entered does not exist.");
    }

   }

 }

是否可以因为创建了多个结果集？还是因为创建了多个while语句？

Answer 1

以下内容无效：

ResultSet rs = stmt.executeQuery("select first,email,mail,name from login,curlogin;");
String from =rs.getString("mail");
String frmname =rs.getString("name");

执行查询在位置-1返回ResultSet。您需要通过迭代器或首先调用rs.next();来访问它（假设您有任何结果）。

Answer 2

首先访问之前，您需要致电rs.next() ：

 ResultSet rs = stmt.executeQuery("select first,email,mail,name from login,curlogin;");
 if(rs.next()) { //Advances cursor to first/next row
   String from =rs.getString("mail");
   String frmname =rs.getString("name");

然后再次 - 使用标签循环有点GOTO - 您可能也想重新考虑while(rs.next())循环。

Answer 3

您需要移动ResultSet的光标才能从中获取值。在致电rs.first()之前，请先使用rs.next()或rs.getString("mail")。

例如：

ResultSet rs = stmt.executeQuery("select first,email,mail,`name from login`,curlogin;");
String from;
if(rs.first()){
   from =rs.getString("mail");
}