我创建了一个Java Web应用程序,并使用过滤器来防止未经授权的访问,但它无法正常工作。成功登录后,它应该进入home.jsp,但不能继续。当我运行应用程序时,它从AuthFilter.java中的init方法开始执行,在init方法之后,控件转到了Method.java netbeans预定义方法。
在浏览器中显示以下错误:
HTTP Status 500 -
type Exception report
message
description The server encountered an internal error that prevented it from fulfilling this request.
exception
java.lang.NullPointerException
Filters.AuthFilter.doFilter(AuthFilter.java:47)
note注意在Apache Tomcat / 8.0.3日志中可以找到根本原因的完整堆栈跟踪。这是代码。
LoginServlet.java
package Servlets;
//all important files are imported
public class LoginServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
}
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String user = "king";
String pass = "king";
String uname = request.getParameter("user");
String upass = request.getParameter("pwd");
if(uname.equals(user) && upass.equals(pass))
{
HttpSession session = request.getSession(true);
session.setAttribute("username", uname);
// Cookie userName = new Cookie("user", user);
// userName.setMaxAge(10*60);
// response.addCookie(userName);
response.sendRedirect("home.jsp");
}
else
{
RequestDispatcher rd = getServletContext().getRequestDispatcher("index.jsp");
PrintWriter out = response.getWriter();
out.println("<font color=red>Either user name or password is wrong.</font>");
rd.include(request, response);
}
}
}
AuthFilter.java
package Filters;
public class AuthFilter implements Filter {
ArrayList<String> array = new ArrayList<>();
private ServletContext context;
@Override
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain)
throws IOException, ServletException {
System.out.println("2");
HttpServletRequest req = (HttpServletRequest) request;
HttpServletResponse res = (HttpServletResponse) response;
String uri = req.getRequestURI();
HttpSession session = req.getSession(false);
boolean r = false;
if(array.contains(uri))
{
r = true;
}
System.out.println(" r result my = " + r);
Object o = session.getAttribute("username");
System.out.println("abcde = " + o);
if(o == null)
System.out.println("null session my = " + session);
else
System.out.println(" not null session my = " + session);
// System.out.println("session getAttribute = " + session.getAttribute("username"));
if(o == null && r == true)
{
System.out.println("unauthorized");
r = false;
res.sendRedirect("index.jsp");
}
else
{
System.out.println("auth");
chain.doFilter(request, response);
}
}
@Override
public void destroy() {
System.out.println("3");
}
@Override
public void init(FilterConfig filterConfig) {
System.out.println("1");
this.context = filterConfig.getServletContext();
array.add("/MyFilter/demo.jsp");
array.add("/MyFilter/more.jsp");
array.add("/MyFilter/home.jsp");
System.out.println("show array list:-\n");
for (String array1 : array) {
System.out.print(array1 + "\n");
}
this.context.log("AuthenticationFilter initialized");
}
}
Web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.1" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd">
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
<filter>
<filter-name>AuthFilter</filter-name>
<filter-class>Filters.AuthFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>AuthFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<servlet>
<servlet-name>LoginServlet</servlet-name>
<servlet-class>Servlets.LoginServlet</servlet-class>
</servlet>
<servlet>
<servlet-name>LogoutServlet</servlet-name>
<servlet-class>Servlets.LogoutServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>LoginServlet</servlet-name>
<url-pattern>/LoginServlet</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>LogoutServlet</servlet-name>
<url-pattern>/LogoutServlet</url-pattern>
</servlet-mapping>
<session-config>
<session-timeout>
30
</session-timeout>
</session-config>
</web-app>
最佳答案
在您的servlet中,您尝试使用request.getSession(false)
访问当前会话。那不会创建任何会话,因此,在第一次访问时,您只会得到一个null
,表示未初始化任何会话。但是您不对其进行测试并立即使用它,因此会出现错误。相反,您应该使用request.getSession(true)
来确保在不存在会话的情况下正确地使用现有会话来创建会话。
关于java - Servlet筛选器提供NullPointerException,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/25621501/