servlet的過濾器filter類

• 先上代碼

public class FilterA implements Filter {

    public FilterA() {

        System.out.println("實例化filterA");

    }

    public void destroy() {

        System.out.println("銷燬filterA");

    }

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)

            throws IOException, ServletException {

        System.out.println("經過FilterA的前處理");

        chain.doFilter(request, response);

        System.out.println("到達filterA的後處理");

    }

    public void init(FilterConfig fConfig) throws ServletException {

        System.out.println("初始化FilterA");

    }

}

---

public class FilterB implements Filter {

    public FilterB() {

        System.out.println("實例化filterB");

    }

    public void destroy() {

        System.out.println("銷燬filterB");

    }

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)

            throws IOException, ServletException {

        System.out.println("經過FilterB的前處理");

        chain.doFilter(request, response);

        System.out.println("到達filterB的後處理");

    }

    public void init(FilterConfig fConfig) throws ServletException {

        System.out.println("初始化FilterB");

    }

}

---

public class FilterC implements Filter {

    public FilterC() {

        System.out.println("實例化filterC");

    }

    public void destroy() {

        System.out.println("銷燬filterC");

    }

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)

            throws IOException, ServletException {

        System.out.println("經過FilterC的前處理");

        chain.doFilter(request, response);

        System.out.println("到達filterC的後處理");

    }

    public void init(FilterConfig fConfig) throws ServletException {

        System.out.println("初始化FilterC");

    }

}

• web.xml的配置順序(注意順序)：有先後順序，而且如果同一個攔截器同時使用註解和web.xml配置會在啓動項目時實例化兩次

  <!--配置過濾器A  -->

  <filter>

    <filter-name>FilterA</filter-name>

    <filter-class>com.zhiyou100.crm.filter.FilterA</filter-class>

  </filter>

  <filter-mapping>

    <filter-name>FilterA</filter-name>

    <url-pattern>/test.jsp</url-pattern>

  </filter-mapping>

   <!--配置過濾器B -->

  <filter>

    <filter-name>FilterB</filter-name>

    <filter-class>com.zhiyou100.crm.filter.FilterB</filter-class>

  </filter>

  <filter-mapping>

    <filter-name>FilterB</filter-name>

    <url-pattern>/test.jsp</url-pattern>

  </filter-mapping>

   <!--配置過濾器c  -->

  <filter>

    <filter-name>FilterC</filter-name>

    <filter-class>com.zhiyou100.crm.filter.FilterC</filter-class>

  </filter>

  <filter-mapping>

    <filter-name>FilterC</filter-name>

    <url-pattern>/test.jsp</url-pattern>

  </filter-mapping>

啓動服務器：

實例化FilterA

初始化FilterA

實例化FilterB

初始化FilterB

實例化FilterC

初始化FilterC

瀏覽器訪問web應用的test.jsp

經過FilterA的前處理

經過FilterB的前處理

經過FilterC的前處理

到達filterC的後處理

到達filterB的後處理

到達filterA的後處理