查询数据库时的异常问题，高分请教。

Question

>>too many connections to database
写得不是很明显吗? 你程序中取得太多的 connection 了, 一个连接可以做多次操作的.

Answer 1

这段程序有个BUG，就是当程序抛例外时，已建立的连接无法正常释放，造成连接数过多，而无法再连接数据库。在catch后加上：finally{
    rs1.close();
    con.close();
                      
}

Answer 2

我把程序改成：
sqlbean con = new sqlbean();
                            String strSql = "select * from dgkt_user where name='" + uid + "'";
                            try{
                                ResultSet rs1 = con.executeQuery(strSql);
                               
                                //表dgkt_user中没有此用户，则新增一条记录。tie（权限）从dgkt_groupTie中取得。
                                if (!rs1.next())
                                {
                                    String group = "";
                                    //insert code here to use uid get group
                                    group = "用户组一";
                                    strSql = "select tie from dgkt_groupTie where groupName='" + group + "'";
                                    System.out.println("Line192---");
                                    //sqlbean con1 = new sqlbean();
                                    ResultSet rs2 = con.executeQuery(strSql);
                                    System.out.println("Line194---");
                                    String tie = "";
                                    System.out.println("Line196---");
                                    if (rs2.next())
                                    {
                                        tie = rs2.getString("tie");
                                    }else{
                                        System.out.println("表dgkt_groupTie中的数据有误，请检查后更正。");
                                    }
                                    System.out.println("Line203");
                                    rs2.close();
                                    //con1.close();
                                    //向dgkt_user表中插入该记录
                                    strSql = "Insert into dgkt_user(name,tie,pw,nick,privacy)values('" + uid + "','" + tie + "','" + pwd + "','未知','未知')";
                                    System.out.println("Line207");
                                    //sqlbean con2 = new sqlbean();
                                    con.executeInsert(strSql);
                                    //con2.close();
                                    System.out.println("Line209");
                                    //向context中压值
                                    context.setValue("group",group);
                                    context.setValue("tie",tie);
                                }
                            }
                            catch(Exception esql){
                                System.out.println("in LoginComponent.getComponentData(),catch SQLException.");
                                System.out.println(esql);
                            }
                            finally
                            {
                                rs1.close();
                                con.close();
                            }
依然报同样的错误，为什么？

Answer 3

另外，rs1不能在finally中关闭，因为它是在try中定义的，在finally中无法访问。

Answer 4

too many connections to database//连接数太多
java.lang.NullPointerException//有空指针错误读了你的程序，sqlbean的实例有 con、con1、con2而在finally中关闭的仅con也就是说，当空指针例外抛出时，有可能con1、con2的连接并没有正确关闭.