java - 过滤器 - Servlets 和 Spring beans 集成 NullPointerException

Question

我在 servlet 之前执行过滤器:

    public class UserFilter implements Filter {


    List<String> sessionIdsList;

    WebContentDAOIF webContentDAOIF;

        public void setWebContentDAOIF(WebContentDAOIF webContentDAOIF) {
            this.webContentDAOIF = webContentDAOIF;
        }


        @Override
        public void init(FilterConfig arg0) throws ServletException {

                    sessionIdsList = new ArrayList<String>();
                    sessionIdsList = webContentDAOIF.fetchAllSessionIds();

            }


        @Override
        public void doFilter(ServletRequest request, ServletResponse response,
                                                     FilterChain filterChain) throws IOException, ServletException {

            System.out.println("List size: " + sessionIdsList.size());

                HttpServletRequest httpRequest = (HttpServletRequest)request;

                HttpSession session = httpRequest.getSession();
                String userSessionId = session.getId();
                System.out.println("Filter: " + userSessionId);

                if(sessionIdsList.size() !=0 && sessionIdsList.contains(userSessionId)) {

                        System.out.println("There is same sessionID");

                } else {

                    System.out.println("Hello anonim");

                }

                RequestDispatcher dispatcher = request.getRequestDispatcher("main");
                dispatcher.forward(request, response);


        }


        @Override
        public void destroy() {


            }


}

我有 spring 上下文 xml 文件，我在其中声明了我的所有 bean:

<bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"> 
            <property name="driverClassName"><value>com.mysql.jdbc.Driver</value></property>
            <property name="url"><value>jdbc:mysql://localhost:3306/contentDB</value></property> 
            <property name="username"><value>root</value></property>
            <property name="password" ><value>25051988</value></property>

        </bean>


        <bean id="sessionFactory" class="org.springframework.orm.hibernate4.LocalSessionFactoryBean">

            <property name="dataSource" ref="dataSource"></property>
            <property name="mappingResources">
                <list>
                    <value>user.hbm.xml</value>
                    <value>userEvents.hbm.xml</value>
                </list>
            </property>
            <property name="hibernateProperties">
                <props>

                    <prop key="hibernate.hbm2ddl.auto">update</prop>

                    <prop key="hibernate.dialect">org.hibernate.dialect.MySQLDialect</prop>
                    <prop key="hibernate.show_sql">true</prop>
                    <prop key="hibernate.max_fetch_depth">3</prop>
                    <prop key="hibernate.jdbc.fetch_size">50</prop>
                    <prop key="hibernate.jdbc.batch_size">15</prop>
                </props> 

            </property>

        </bean>


        <bean id="webContentDAOImpl" class="demidov.pkg.persistence.WebContentDAOImpl">
            <property name="sessionFactory" ref="sessionFactory"/>
        </bean>


        <tx:annotation-driven/>

        <bean id="transactionManager" class="org.springframework.orm.hibernate4.HibernateTransactionManager">
            <property name="sessionFactory" ref="sessionFactory"/>
        </bean>


        <bean id="userFilter" class="demidov.pkg.web.UserFilter">
            <property name="webContentDAOIF" ref="webContentDAOImpl"/>
        </bean>

我还在我的 web.xml 中声明了过滤器:

 <context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>/WEB-INF/*-context.xml</param-value>
      </context-param>

      <listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
      </listener>

      <filter>
        <filter-name>userFilter</filter-name>
        <filter-class>demidov.pkg.web.UserFilter</filter-class>
      </filter>

      <filter-mapping>
        <filter-name>userFilter</filter-name>
        <url-pattern>/*</url-pattern>
      </filter-mapping>

      <servlet>
        <servlet-name>initialContentRendering</servlet-name>
        <servlet-class>demidov.pkg.web.InitialContentRendering</servlet-class>
      </servlet>

      <servlet-mapping>
        <servlet-name>initialContentRendering</servlet-name>
        <url-pattern>/main</url-pattern>
      </servlet-mapping>

      <servlet>
        <servlet-name>orderEventServlet</servlet-name>
        <servlet-class>demidov.pkg.web.OrderEventServlet</servlet-class>
      </servlet>

      <servlet-mapping>
        <servlet-name>orderEventServlet</servlet-name>
        <url-pattern>/event</url-pattern>
      </servlet-mapping>

但是当我加载应用程序时它说:

   SEVERE: Exception starting filter userFilter
    java.lang.NullPointerException
        at demidov.pkg.web.UserFilter.init(UserFilter.java:35)
        at org.apache.catalina.core.ApplicationFilterConfig.initFilter(ApplicationFilterConfig.java:273)
        at org.apache.catalina.core.ApplicationFilterConfig.getFilter(ApplicationFilterConfig.java:254)
        at org.apache.catalina.core.ApplicationFilterConfig.setFilterDef(ApplicationFilterConfig.java:372)
        at org.apache.catalina.core.ApplicationFilterConfig.<init>(ApplicationFilterConfig.java:98)
        at org.apache.catalina.core.StandardContext.filterStart(StandardContext.java:4562)
        at org.apache.catalina.core.StandardContext$2.call(StandardContext.java:5240)
        at org.apache.catalina.core.StandardContext$2.call(StandardContext.java:5235)
        at java.util.concurrent.FutureTask.run(FutureTask.java:262)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
        at java.lang.Thread.run(Thread.java:724)

请帮我看看我做错了什么。谢谢大家。

Answer 1

您将获得 UserFilter 的 2 个不同实例，一个由 Servlet 容器管理，另一个由 Spring 管理 - 由 Servlet 容器创建的 UserFilter 当然会有一个空的 WebContentDAOIF。

解决方案是让 Spring 管理您的 UserFilter(并正确注入(inject) WebContentDAOIF)。然后使用Spring的DelegatingFilterProxy , 来处理最终委托(delegate)给您的 UserFilter 的过滤。

在您的 web.xml 中，删除您的 UserFilter 声明并改为声明 DelegatingFilterProxy。

<filter>
  <filter-name>userFilter</filter-name>
  <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
  <init-param>
    <param-name>targetBeanName</param-name>
    <param-value>userFilter</param-value>
  </init-param> 
</filter>