从属性获取Null值 [英] Getting Null value from attribute
问题描述
在动态网络应用程序中,我遇到了一些问题,所以我发布了我的代码:
In the Dynamic web application I facing some issues,so I'm posting my code:
这是我的控制器(servlet):
Here is my controller(servlet):
String select = request.getParameter("select"); // getting proper value
String search = request.getParameter("search"); // getting proper value
request.setAttribute("select", select);
request.setAttribute("search", search);
System.out.println("Select : "+select+" Search : "+search);
int page = 1;
int recordsPerPage = 20;
if(request.getParameter("page") != null)
page = Integer.parseInt(request.getParameter("page"));
SearchDAO searchDAO=new SearchDAO();
List<User> list=searchDAO.searchAllUsers((page-1)*recordsPerPage,recordsPerPage,select,search);
int noOfRecords = searchDAO.getNoOfRecords();
System.out.println("4> NoOfRecords : "+noOfRecords);
int noOfPages = (int) Math.ceil(noOfRecords * 1.0 / recordsPerPage);
System.out.println("5> NoOfPages : "+noOfPages);
request.setAttribute("searchList", list);
System.out.println("6> List : "+list);
request.setAttribute("noOfPages", noOfPages); // Getting null value, 0
request.setAttribute("currentPage", page); // Getting null value, 0
RequestDispatcher view = request.getRequestDispatcher("/jsp/Securex_Anti_Theft_SearchUserList.jsp");
view.forward(request, response);
这是我的DAO(简单java类):
And here is my DAO (simple java class):
public class SearchDAO {
private int noOfRecords;
Connection connection;
Statement stmt;
public List<User> searchAllUsers(int offset ,int noOfRecords,String select,String search){
private static Connection getConnection() throws SQLException,ClassNotFoundException{
Connection con = ConnectionFactory.getInstance().getConnection();
return con; //ConnectionFactory is class for making the connection to DB.
}
String query="select SQL_CALC_FOUND_ROWS * from info where '"+select+
"' like '%"+search+"%' order by serialNo asc limit
" + offset + " , " + noOfRecords;
List<User> list1 = new ArrayList<User>();
User user1=null;
try {
connection = getConnection();
stmt = connection.createStatement();
ResultSet rs=stmt.executeQuery(query);
System.out.println("1> :"+rs);
while(rs.next()){
user1=new User();
user1.setSerial(rs.getInt(1));
System.out.println("I'm inside a loop");
user1.setName(rs.getString(2));
user1.setEmail(rs.getString(3));
list1.add(user1);
}
rs.close();
rs = stmt.executeQuery("SELECT FOUND_ROWS()");
System.out.println("2> :" +rs);
if(rs.next())
this.noOfRecords = rs.getInt(1);
System.out.println("3> :" +this.noOfRecords);
} catch (SQLException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}finally
{
try {
if(stmt != null)
stmt.close();
if(connection != null)
connection.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
return list1;
}
public int getNoOfRecords() {
return noOfRecords;
}
}
输出为:
1> :com.mysql.jdbc.JDBC4ResultSet@1af8502
2> :com.mysql.jdbc.JDBC4ResultSet@455aa8
3> :0
4> NoOfRecords : 0
5> NoOfPages : 0
6> List : []
对于所有用户,我有相同的servlet和类,并且工作正常, bbut从此处获取空值.En ResultSet返回值即com.mysql.jdbc.JDBC4ResultSet @ 88d319,但无法从DAO获取值到servlet。
I have same same servlet and class for select all users,and that's working properly,bbut getting null value from here.Even ResultSet returns value i.e. com.mysql.jdbc.JDBC4ResultSet@88d319,but unable fetch the value from DAO to servlet.
获取空值来自 //
属性,对我来说一切都应该没问题,但仍然得到空值,随时指出我的错误,如果我做了什么
Getting null value from //
attributes,To me everything should be going fine but still getting null value,feel free to point out my mistake,If I have done anything
推荐答案
很可能你的DAO返回空列表。所有其他代码看起来很好。所以,首先我会检查这个电话
Most likely your DAO returns empty list. All other code looks fine. So, first of all I would check this call
searchDAO.searchAllUsers((page-1)*recordsPerPage,recordsPerPage,select,search);
page
变量的值是多少?其他参数?请在以下后面记录查询:
What is the value for page
variable? Other parameters? Please log the query after:
String query="select SQL_CALC_FOUND_ROWS * from info where '"+select+
"' like '%"+search+"%' order by serialNo asc limit
" + offset + " , " + noOfRecords;
并单独针对DB运行,它应该给你答案。
and run it separately against DB, it should give you an answer.
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