Filter

过滤器

     1. 过滤中的所有代码，在过滤特定请求的时候都会执行     
     2. 必须要让过滤器继续执行 

public class FilterEncoding  implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("已经初始化了");
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        servletRequest.setCharacterEncoding("utf-8");
        servletResponse.setCharacterEncoding("utf-8");
        servletResponse.setContentType("text/html;charset=utf-8");
        System.out.println("过滤前");
        filterChain.doFilter(servletRequest,servletResponse);
        System.out.println("过滤后");
    }

    @Override
    public void destroy() {
        System.out.println("销毁");
    }
}

映射过滤器：

 <servlet>
        <servlet-name>showFilter</servlet-name>
        <servlet-class>com.xia.Filter.Servlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>showFilter</servlet-name>
        <url-pattern>/show</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>showFilter</servlet-name>
        <url-pattern>/Filter/show</url-pattern>
    </servlet-mapping>
   
    <filter>
        <filter-name>f</filter-name>
        <filter-class>com.xia.Filter.FilterEncoding</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>f</filter-name>
        <url-pattern>/Filter/show</url-pattern>
    </filter-mapping>