求教：关于JSP修改数据库信息的问题？

public boolean mm(String user,String oldpsw,String newpsw){
String dlsql = "SELECT * from person WHERE user=? and psw=?";
String xgsql = "UPDATE person SET psw=? WHERE user=?";
boolean flag = false;
try{
  stmt = conn.prepareStatement(dlsql);
  stmt.setString(1, user);
  stmt.setString(2,oldpsw);
  rs = stmt.executeQuery();
  if(rs.next()){ 
 
  stmt = conn.prepareStatement(xgsql);
  stmt.setString(1,newpsw);
  stmt.setString(2,user);
  rs1 = stmt.executeQuery();
  if(rs1.next()){flag = true;}else{flag=false;}
  }else{flag = false;}
}catch(Exception e){
  System.out.println("修改异常");
  System.err.println(e.getMessage());
}
return flag;
}
上面是我写的关于密码修改的代码。连的是ACCESS，库是连上了，只是修改不成功，帮看看哪有错误。是程序错？还是SQL语句错？

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Java code:

public boolean mm(String user,String oldpsw,String newpsw){
String dlsql = "SELECT * from person WHERE user=? and psw=?";
String xgsql = "UPDATE person SET psw=? WHERE user=?";
boolean flag = false;
try{
stmt = conn.prepareStatement(dlsql);