JDBC：java.sql.SQLException: Before start of result set怎么办

这是由于Statement执行了之后，得到ResultSet，直接rs.getString，而没有运行.next()的关系

运行一下.next()即可

Connection conn = DriverManager.getConnection(url_2, tar_username, tar_password);
Statement stmt = conn.createStatement();



ResultSet rs2=stmt2.executeQuery(tmp);
int col2 = rs2.getMetaData().getColumnCount();
rs2.next();

int t_num=Integer.parseInt(rs2.getString(1));