java - MySQL 中的异常

Question

我用 Java 编写了一段代码，它必须填充一个点文件。我收到错误，但我不明白为什么。所有路径均已设置。

Class.forName("com.mysql.jdbc.Driver");                     
Connection connects = DriverManager.getConnection("jdbc:mysql://localhost:3306/userlogin", "root","12345");
Statement stm = connects.createStatement();
ResultSet rs=stm.executeQuery("SELECT * FROM authors_4 WHERE self_authors='"+getTxt+"'");

                         int l=0;
                         /*if(rsx.next())
                         {
                             div = Double.parseDouble(rsx.getString("divs"));


                         }*/


                       do
                         {
                             if(l==0)
                             {

                                 diva = Integer.parseInt(rs.getString("tot_pub"));

                                 //fout.write("a [label=" + "\"" + rsx.getString(2) + "\\n" + rsx.getString(4) + "\"" + "color=blue,fontsize=24,fontcolor=red,style=filled];\r\n");
                                 fout.write("\"" + rs.getString("self_authors") + "\"" + "[fixedsize=true, width="+diva+",height="+diva+", label=" + "\"" + rs.getString("self_authors") + "\\n" + rs.getString("tot_pub") + "\"" + "color=blue,fontsize=24,fontcolor=red,style=filled];\r\n");
                               l++;
                             }


                             divb = Integer.parseInt(rs.getString("tot_pub")) ;

                             fout.write("\"" + rs.getString("co_auths") + "\"" + "[fixedsize=true, width="+divb+",height="+divb+",label=" + "\"" + rs.getString("co_auths") + "\\n" + rs.getString("tot_pub") + "\"];" +"\r\n");    


                             //fout.write("a ->" + "\"" + rsx.getString(6) + "\"" + "[penwidth=" +  rsx.getString(8)  +", label =" + rsx.getString(8) +" ];" + "\r\n");
                               fout.write("\"" + rs.getString("self_authors") + "\" ->" + "\"" + rs.getString("co_auths") + "\"" + "[penwidth=" +  rs.getString("1")  +", label =" + 1 +" ];" + "\r\n");

                             //System.out.println(rsx.getString(1));

                         }while(rs.next());

                         fout.write("}");
                         fout.close();
                     }

我编写的代码很长，无法解释，所以我只发布出现异常的部分。

异常(exception)情况是:

java.sql.SQLException: Before start of result set
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1078)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:989)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:975)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:920)
at com.mysql.jdbc.ResultSetImpl.checkRowPos(ResultSetImpl.java:855)
at com.mysql.jdbc.ResultSetImpl.getStringInternal(ResultSetImpl.java:5773)
at com.mysql.jdbc.ResultSetImpl.getString(ResultSetImpl.java:5693)
at com.mysql.jdbc.ResultSetImpl.getString(ResultSetImpl.java:5733) 

Answer 1

我相信您发布的代码不会引发任何错误。当您尝试访问结果集数据而不将光标移动到第一条记录时，会返回此错误。

ResultSet rs = stm.executeQuery("SELECT * FROM authors_4 WHERE self_authors='"+getTxt+"'");

// Did you use rs.next() ???
while (rs.next())
{
   // You need rs.next() before trying to access 
   // Without rs.next(), you'll see the "Before start of result set" exception
   int myInt = rs.getInt(1);   
   ...
   ...
}