Question

为啥我的jsp页面验证用户名和密码的时候会报空指针错误？代码如下

jsp页面代码：（其中username和password是已经获取到的，抛出的两个异常也是我定义好的）
try
{
User u=User.userCheck(username,password);
session.setAttribute("user",u);
}catch(UserNotFoundException e)
{
out.println(e.getMessage());
return;
}catch(PasswordNotCorrectException e)
{
out.println(e.getMessage());
return;
}
javabean代码如下：
public static User check(String username, String password)
throws UserNotFoundException, PasswordNotCorrectException {
User u = null;
Connection conn = DB.getConn();
String sql = "select * from user where username = '" + username + "'";
Statement stmt = DB.getStatement(conn);
ResultSet rs = DB.getResultSet(stmt, sql);
try {
if(!rs.next()) {
throw new UserNotFoundException("用户不存在:" + username);
} else {
if(!password.equals(rs.getString("password"))) {
throw new PasswordNotCorrectException("密码不正确哦!");
}
u = new User();
u.setId(rs.getInt("id"));
u.setUsername(rs.getString("username"));
u.setPassword(rs.getString("password"));
u.setPhone(rs.getString("phone"));
u.setAddr(rs.getString("addr"));
u.setRdate(rs.getTimestamp("rdate"));
}

} catch (SQLException e) {
e.printStackTrace();
} finally {
DB.close(rs);
DB.close(stmt);
DB.close(conn);
}
return u;
}
报错：java.lang.NullPointerException
at com.shop.user.User.userCheck(User.java:84) （就是if(!rs.next())那一行）
at org.apache.jsp.LoginDeal_jsp._jspService(LoginDeal_jsp.java:64)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)

Answer 1

你加个断点，看看那个rs的值是空的吗？如果rs的值是空的，只要出现rs.next()，就会报空指针异常。

Answer 2

你确定username和password已经从表单获取到了吗？你直接在jsp页面上打印username和password能显示出来吗？测试一下

Answer 3

if(!rs.next())你这是判断rs是否有数据集，这样判断不好，我建议你这样判断就可以if(rs == null)

Answer 4

你直接判断结果集是否为空不就行了