java session使用问题

package Bean;import java.sql.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;public class UserLogin{
private String username;
private String password;
private String user_username;
private String user_nickname;
        HttpServletRequest request;
public void setUsername(String _username){this.username = _username;}
public String getUsername(){return this.username;}

public void setPassword(String _password){this.password = _password;}
public String getPassword(){return this.password;}

public boolean check_login(){
Connection con = null;
Statement stmt = null;
ResultSet rs = null;
boolean loginflag = false;

try{
Class.forName(DBConfig.getInstance().getProperty("driver"));
con = DriverManager.getConnection(
DBConfig.getInstance().getProperty("url"),
DBConfig.getInstance().getProperty("username"),
DBConfig.getInstance().getProperty("password")
);
String sql = "select * from user_info where username = '"+username+"' ";
stmt = con.createStatement();
rs = stmt.executeQuery(sql);
while(rs.next()){
if(password.equals(rs.getString("password"))){
HttpSession session = request.getSession();
session.setAttribute(user_username,rs.getString("username"));
session.setAttribute(user_nickname,rs.getString("nickname"));
loginflag = true;
}
}
}catch(Exception sqlex1){
sqlex1.printStackTrace();
}finally{
if(con != null){
try{
rs.close();
stmt.close();
con.close();
}catch(Exception sqlex2){sqlex2.printStackTrace();}
}
}
return loginflag;
}

}