public?static?void?main(String[]?args)?throws?SQLException?{
UserDao?dao?=?new?UserDao()?;
List<User>?ls?=?new?ArrayList<User>();
ls?=?dao.query();
for(int?i=0?;?i<ls.size()?;?i++){
System.out.print("賬號："+ls.get(i).getUsername()+"?,?");
System.out.println("密碼："+ls.get(i).getPassword());
}
}以上代碼我用JAVA運行能在控制臺輸出我數據庫中的幾個數據public?void?doGet(HttpServletRequest?request,?HttpServletResponse?response)
throws?ServletException,?IOException?{
request.setCharacterEncoding("utf-8");
UserDao?dao?=?new?UserDao()?;
List<User>?ls?=?new?ArrayList<User>();
try?{
ls=dao.query();
}?catch?(SQLException?e)?{
//?TODO?Auto-generated?catch?block
e.printStackTrace();
}
String?name?=?request.getParameter("name");
String?password?=?request.getParameter("password");
for(int?i=0?;?i<ls.size()?;?i++){
if(ls.get(i).getUsername().equals(name)?&&?ls.get(i).getPassword().equals(password)){
request.getRequestDispatcher("/Success.jsp").forward(request,response);
}
else{
request.getRequestDispatcher("/Fail.jsp").forward(request,response);
}
}
}然后運行這個就報錯了我沒用數據庫的時候用if判斷就能跳轉頁面所以我感覺其他的代碼應該沒錯 就把這部分粘出來了 String?name?=?request.getParameter("name");
String?password?=?request.getParameter("password");
if("a".equals(name)?&&?"a".equals(password)){
request.getRequestDispatcher("/Success.jsp").forward(request,response);
}
else{
request.getRequestDispatcher("/Fail.jsp").forward(request,response);
}
}上面代碼是不用數據庫就可以正常跳轉 所以其他的代碼應該沒問題
5 回答
慕粉4208695
TA貢獻3條經驗 獲得超2個贊
public?class?UserDao?{
public?List<User>?query()?throws?SQLException{
Connection?conn?=?DBUtil.getConnection();
PreparedStatement?ptmt?=?null?;
ResultSet?rs?=?null?;
String?sql?=?"select?*?from?user?";
ptmt?=?conn.prepareStatement(sql);
rs?=?ptmt.executeQuery()?;
User?user?=?null?;
List<User>?list?=?new?ArrayList<User>()?;
while(rs.next()){
user?=?new?User()?;
user.setUsername(rs.getString("username"));
user.setPassword(rs.getString("password"));
list.add(user);
}
rs.close();
ptmt.close();
conn.close();
return?list;
}
}這是報錯的那個代碼 19行是ptmt = conn.prepareStatement(sql);
你好小Song
TA貢獻29條經驗 獲得超10個贊
目測是因為DBUtil里的getConnection()方法返回的connection是空.
將try{}catch(){}代碼放到getConnection()中試下,別用static{}代碼塊了.
慕粉4208695
TA貢獻3條經驗 獲得超2個贊
public?class?DBUtil?{
private?static?final?String?USER?=?"root"?;
private?static?final?String?PASSWORD?=?"mj199609"?;
private?static?final?String?URL?=?"jdbc:mysql://localhost:3306/reg"?;
private?static?Connection?conn?=?null?;
static{
try?{
Class.forName("com.mysql.jdbc.Driver");
conn?=?DriverManager.getConnection(URL,USER,PASSWORD);
}catch?(ClassNotFoundException?e)?{
//?TODO?Auto-generated?catch?block
e.printStackTrace();
}catch?(SQLException?e)?{
//?TODO?Auto-generated?catch?block
e.printStackTrace();
}
}
public?static?Connection?getConnection(){
return?conn?;
}
}
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