java - 在 doFilter 方法中获取 IllegalStateException

Question

当我在 Spring MVC 中创建 servlet 过滤器时，出现以下异常。

 [javax.servlet.ServletException: java.lang.IllegalStateException: Cannot create a session after the response has been committed] with root cause

当我输入系统输出时，我可以理解异常发生在重定向行，但不明白为什么

谁能告诉我一些解决方案

SessionFilter.java

public class SessionFilter implements Filter {

    private ArrayList<String> urlList;

    @Override
    public void destroy() {
    }

    @Override
    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) res;
        String url = request.getServletPath();
        boolean allowedRequest = false;

        if(urlList.contains(url)) {
            allowedRequest = true;
        }

        if (!allowedRequest) {
            HttpSession session = request.getSession(false);
            if (null == session) {
                System.out.println("preparing for redirect");
                response.sendRedirect("index.jsp");
            }
        }

        chain.doFilter(req, res);
    }

    @Override
    public void init(FilterConfig config) throws ServletException {
        System.out.println("entered init");
        String urls = config.getInitParameter("avoid-urls");
        StringTokenizer token = new StringTokenizer(urls, ",");

        urlList = new ArrayList<String>();

        while (token.hasMoreTokens()) {
            urlList.add(token.nextToken());

        }
    }

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>SpringMVCHibernate</display-name>

  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>

  <servlet>
        <servlet-name>dispatcher</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <load-on-startup>1</load-on-startup>
    </servlet>

    <servlet-mapping>
        <servlet-name>dispatcher</servlet-name>
        <url-pattern>*.do</url-pattern>
    </servlet-mapping>

    <session-config>
        <session-timeout>1</session-timeout>
    </session-config>


    <filter>
        <filter-name>SessionFilter</filter-name>
        <filter-class>com.common.dao.SessionFilter</filter-class>
        <init-param>
            <param-name>avoid-urls</param-name>
            <param-value>index.jsp</param-value>
        </init-param>
    </filter>

    <filter-mapping>
        <filter-name>SessionFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
:
:
:

Answer 1

简单简短地回答您的问题:

为了避免这种情况，你应该有一个返回语句，或者避免重定向或转发请求，或者这些事情应该由过滤器链中的最后一个过滤器来完成。

有关更多详细信息，您可以阅读以下内容:

当响应已经提交并刷新给用户时，当您尝试再次发送响应时，会发生此异常。例如:

在下面的示例代码中，首先请求将被转发到index_test.jsp，响应将刷新到用户，然后控件将再次返回过滤器并尝试向用户发送另一个响应(重定向)，并且它将会失败。

通常我们会检查过滤器中的多个条件，并相应地进行转发和重定向，如果满足两个条件，那么就会产生问题。

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { 

  request.getRequestDispatcher("index_test.jsp").forward(request, response);
  ((HttpServletResponse)response).sendRedirect("new.jsp");
  chain.doFilter(request, response);
 }

您的案例的解决方案:

为了避免这种情况，你应该有一个返回语句，或者避免重定向或转发请求，或者这些事情应该由过滤器链中的最后一个过滤器来完成。

所以你可以将代码更改为:

public class SessionFilter implements Filter {

    private ArrayList<String> urlList;

    @Override
    public void destroy() {
    }

    @Override
    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) res;
        String url = request.getServletPath();
        boolean allowedRequest = false;

        if(urlList.contains(url)) {
            allowedRequest = true;
        }

        if (!allowedRequest) {
            HttpSession session = request.getSession(false);
            if (null == session) {
                System.out.println("preparing for redirect");
                response.sendRedirect("index.jsp");
                return;
            }
        }

        chain.doFilter(req, res);
    }

    @Override
    public void init(FilterConfig config) throws ServletException {
        System.out.println("entered init");
        String urls = config.getInitParameter("avoid-urls");
        StringTokenizer token = new StringTokenizer(urls, ",");

        urlList = new ArrayList<String>();

        while (token.hasMoreTokens()) {
            urlList.add(token.nextToken());

        }
    }