Filter

java类
主要重写dofilter方法，这里用来处理字符乱码问题

public class CharacterEncodingFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("开始执行CharacterEncodingFilter");
    }

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

    }

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

注意Chain:需要继续传递参数到其他的过滤器，过滤器像一条链

filter启动：web服务器启动时filter启动
filter销毁：服务器关闭时销毁

filter在xml中的配置：

   <filter>
        <filter-name>filter1</filter-name>
        <filter-class>com.liu.filter.CharacterEncodingFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>filter1</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

和servlet相同的配置