filter 简要说明

filter开发步骤

• 导包

• 编写过滤器

  • 包不要导入错误了

    import javax.servlet.Filter;
    

  • 实现Filter接口，重写对应的方法即可

  • web.xml中配置过滤器

  • chain.doFilter将请求转发给过滤器链下一个filter , 如果没有filter那就是你请求的资源

案例演示

public class CharterEncodingFilter implements Filter {
    //过滤器初始化
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("过滤器初始化");
    }

    //chain：链
    /*
    * 1.过滤中的所有代码，再过滤特定请求的时候都会执行
    * 2.必须要让过滤器继续同行
    * 3.filterChain.doFilter(servletRequest, servletResponse);*/
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        servletRequest.setCharacterEncoding("utf-8");
        servletResponse.setCharacterEncoding("utf-8");
        servletResponse.setContentType("text/html;charest=UTF-8");
        System.out.println("CharterEncodingFilter执行前");
        filterChain.doFilter(servletRequest, servletResponse);//让请求继续走，他会去找下一个链，但是它下面已经没有了，所以就会去跳转页面了，根据xml中的配置从过滤器中出来应当进入servlet包下的show
        System.out.println("CharterEncodingFilter执行后.........");
    }
    //过滤器销毁
    //web服务器关闭时会被销毁
    public void destroy() {
        System.out.println("过滤器销毁..........");
    }
}

xml配置

    <servlet>
        <servlet-name>ShowServlet</servlet-name>
        <servlet-class>com.zhang.servlet.ShowServlet</servlet-class>
    </servlet>
    <!--未经过过滤器-->
    <servlet-mapping>
        <servlet-name>ShowServlet</servlet-name>
        <url-pattern>/show</url-pattern>
    </servlet-mapping>
    <!--经过过滤器-->
    <servlet-mapping>
        <servlet-name>ShowServlet</servlet-name>
        <url-pattern>/servlet/show</url-pattern>
    </servlet-mapping>
    <filter>
        <filter-name>CharterEncodingFilter</filter-name>
        <filter-class>com.zhang.filter.CharterEncodingFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>CharterEncodingFilter</filter-name>
        <!--只要是servlet请求都会经过过滤器-->
        <url-pattern>/servlet/*</url-pattern>
    </filter-mapping>

测试servlet

public class ShowServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.getWriter().write("你好世界");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

未过滤结果

过滤后结果