[英]java.lang.NumberFormatException: null at java.lang.Integer.parseInt
[英]java.lang.NumberFormatException: null java.lang.Integer.parseInt(Unknown Source)
我正在嘗試從 jsp 頁面獲取值並希望使用 java 將這些值存儲在 mysql(xampp) 數據庫中。 建立連接並成功登錄,但是當我試圖讓值出現空指針異常
MainController.java
是
package classes;
import java.io.IOException;
import java.sql.Connection;
import java.sql.Date;
import java.sql.DriverManager;
//import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.sql.Time;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
/**
* Servlet implementation class MainController
*/
@WebServlet("/MainController")
public class MainController extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public MainController() {
super();
// TODO Auto-generated constructor stub
}
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
* response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
* response)
*/
}
//@SuppressWarnings("null")
protected void doPost(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
String url= "jdbc:mysql://localhost/meeting_planner";
System.out.println("start");
// boolean stfound = false;
try {
System.out.println("reached controller");
Class.forName("com.mysql.jdbc.Driver");
Connection con = DriverManager.getConnection(url, "admin", "admin");
Statement stmt = con.createStatement();
//System.out.println("connection");
String button=request.getParameter("button");
System.out.println(button + request.getParameter("AId"));
if(button.equals("login"))
{
System.out.println("inside if");
String AdminId= request.getParameter("AId");
String password= request.getParameter("Password");
System.out.println(AdminId+" sadia "+password);
if(!(AdminId=="" || password==""))
{
boolean stfound = false;
System.out.println(AdminId+" sadia "+password);
String query = "SELECT AId,Password FROM administrator";
ResultSet rs = stmt.executeQuery(query);
System.out.println(query);
while(rs.next())
{
String dbadminid = rs.getString(1);
String dbadminpwd = rs.getString(2);
if(AdminId.equals(dbadminid) && password.equals(dbadminpwd))
{
HttpSession session = request.getSession(true);
session.setAttribute("userid",dbadminid);
stfound = true;
break;
}
}
if(stfound){
RequestDispatcher dispatcher = getServletContext().getRequestDispatcher ( "/meeting_Id.jsp" ) ;
dispatcher.forward ( request, response ) ;
}
}
else{
RequestDispatcher dispatcher = getServletContext().getRequestDispatcher ( "/index.jsp" ) ;
dispatcher.forward ( request, response ) ;
}
}
if(button.equals("Next"))
{
HttpSession session = request.getSession(true);
String AID =(String) session.getAttribute("aid");
int meetingid = Integer.parseInt(request.getParameter("meeting_id"));
/*String CNM= request.getParameter("CNM");
int CCD = Integer.parseInt(request.getParameter("CCD"));
int CCDD= Integer.parseInt(request.getParameter("CCDD"));
int PID= Integer.parseInt(request.getParameter("PID"));
int STFID=Integer.parseInt(AID);*/
meeting obj=new meeting();
obj.addmeeting(meetingid);
System.out.print("Sadia");
RequestDispatcher dispatcher = getServletContext().getRequestDispatcher ( "/creat_date.jsp" ) ;
dispatcher.forward ( request, response ) ;
}
}catch (ClassNotFoundException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
} catch (SQLException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
}
}
和 Meeting.java 是
package classes;
import java.sql.Connection;
import java.sql.Date;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Time;
import java.sql.Statement;
public class meeting {
private int meeting_id;
Connection con=null;
Statement smt = null;
public static void main(String[] args) {
// TODO Auto-generated method stub
}
public meeting()throws ClassNotFoundException//construtor
, SQLException{
// try{
String url = "jdbc:mysql://localhost/meeting_planner";
Class.forName("com.mysql.jdbc.Driver");
con = DriverManager.getConnection(url, "admin", "admin");
smt = con.createStatement();
//}catch(ClassNotFoundException e1){
//e1.printStackTrace();
}
public void addmeeting(int meeting_id1)throws ClassNotFoundException // from attribute web.xml
, SQLException{
System.out.println("------TRY INSERTION------");
String query = "SELECT meeting_Id FROM meeting";
ResultSet rs = smt.executeQuery(query);
int numCols = rs.getMetaData().getColumnCount()+1;
// STAFF_ID=numCols+1;
String query1 = "INSERT INTO Meeting VALUE ( "+meeting_id+")";
System.out.println(query1);
smt.executeUpdate(query1);
}
}
當我在這一行中打印next
的值時,Next 按鈕的名稱是“next” System.out.println("next"+next);
它為下一個參數打印 null
** 編輯:NullPointerException 的問題已解決,但現在拋出 NumberFormatException **
控制台是這樣的
start
reached controller
inside if
111 sadia sadia
111 sadia sadia
SELECT AId,Password FROM administrator
start
reached controller
Oct 29, 2014 6:44:57 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [classes.MainController] in context with path [/Meeting1] threw
exception
java.lang.NumberFormatException: null
at java.lang.Integer.parseInt(Unknown Source)
at java.lang.Integer.parseInt(Unknown Source)
at classes.MainController.doPost(MainController.java:141)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
at
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1023)
at
org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
index.jsp 是
<form method = "post" name="create" action="MainController">
<label for="author">Enter id: </label> <input type="text"
id="AId" name="AId" required="required" />
<div class="cleaner_h10"></div>
<label for="author">Enter_password: </label><input
type="password" name="Password" required="required" />
<div class="cleaner_h10"></div>
<br> <input type="submit"
name="button" " value="login"
style="height: 30px; width: 70px"></a>
</input>
</form>
meeting_Id.jsp 是
<form method="post" name="create" action="MainController">
<label for="author">Enter Meeting Id:</label> <input type="text" id="meeting_id" name="mid" required="required" />
<div class="cleaner_h10"></div>
<div class="cleaner_h10"></div><br>
<input type="submit" name="cancelbutton" value="Cancel" style="height:30px; width:70px">
</input>
<input type="submit" name="button" value="Next" style="height:30px; width:70px">
</input>
</form>
問題出在這里:
//System.out.println("connection");
String button=request.getParameter("button");
System.out.println(button + request.getParameter("AId"));
if(button.equals("login"))
從您自己的調試打印中可以看出,您打印的button
和參數AId
均為空。
因此,當您嘗試調用button.equals("login")
您會收到 NullPointerException。 那是因為您不能在 null 上調用方法。
在使用它們之前,您應該始終檢查您的參數是否為null
。 即使您認為它們永遠不應該為null
- 因為黑客可以嘗試在不控制您的表單的情況下將內容發送到您的 servlet。
這是發生的事情,一步一步。
index.jsp
。 你點擊按鈕。index.jsp
的button
參數,所以一切正常,它到達最后的代碼,將其轉發到現在顯示在瀏覽器上的meeting_Id.jsp
。meeting_Id.jsp
的表單發送回MainController
。button
。 因此,您會收到 NullPointerException。 您正在 MVC 環境中工作。 每個表單都被發送到同一個控制器MainContoller
,並且MainController
應該足夠聰明,知道哪個表單向它發送了請求,並相應地處理它。 但是你的假設只有index.jsp
正在調用它。 但它不是這樣工作的。 當您單擊meeting_Id.jspa
上的next
按鈕時,您正在創建一個新的 request ,它轉到同一個MainController
servlet,並導致錯誤。
你應該確保你的表單發送某種 ID 來告訴MainController
哪個表單正在使用它,然后控制器可以發送請求以由適當的模型處理。 您使用它的輸入應該具有相同的名稱,並且應該存在於您發送的所有表單中。
現在由於不同的原因您遇到了類似的問題。 在這一行:
int meetingid = Integer.parseInt(request.getParameter("meeting_id"));
您正在嘗試解析名為meeting_id
的參數。 問題是,同樣,您沒有檢查空值。 您實際上沒有這樣的參數。
為什么? 因為這是您的 HTML(在meeting_Id.jsp
)所說的:
<input type="text" id="meeting_id" name="mid" required="required" />
如您所見,“meeting_id”是它的id ,而不是它的name ,並且getParameter()
始終與輸入的name
。
除此之外,在解決此問題后,您必須確保(使用正則表達式)參數中只有數字,或者您必須使用parseInt
行周圍的 try-catch 塊捕獲NumberFormatException
。
始終,始終,檢查您從用戶那里獲得的參數。 永遠不要假設它們存在,它們不為空,或者它們具有您期望它們具有的值。
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