filter过滤器的初步使用，以及他的基本应用

本文链接：https://blog.youkuaiyun.com/sinstar1/article/details/50936872

本文介绍如何通过myfilter类设置项目的字符编码为UTF-8，并实现对非法登录的拦截。isloginFilter类用于检查用户的登录状态，如果未登录则重定向到特定页面。

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一，设置项目的字符
myfilter.java

public class myfilter implements Filter {
    private String ecodingString="";

    public void destroy() {
        // TODO Auto-generated method stub

    }

    public void doFilter(ServletRequest req, ServletResponse resp,
            FilterChain chain) throws IOException, ServletException {
            req.setCharacterEncoding(ecodingString);
            resp.setCharacterEncoding(ecodingString);
            resp.setContentType("text/html");

            chain.doFilter(req, resp);

    }

    public void init(FilterConfig arg0) throws ServletException {
        this.ecodingString=arg0.getInitParameter("ecoding");


    }

}

web.xml

<filter>
    <filter-name>myfilter</filter-name>
    <filter-class>com.bright.filter.myfilter</filter-class>
        <init-param>
            <param-name>ecoding</param-name>
            <param-value>utf-8</param-value>
        </init-param>   

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

  </filter-mapping>

(2)拦截非法登录
isLoginfilter.java

public class isloginFilter implements Filter {

    public void destroy() {
        // TODO Auto-generated method stub

    }

    public void doFilter(ServletRequest req, ServletResponse resp,
            FilterChain chain) throws IOException, ServletException {
        HttpSession session=((HttpServletRequest)req).getSession();
        String islogin=(String)session.getAttribute("uname");
        if("ok".equals(islogin)){
            chain.doFilter(req, resp);
        }else{
            //在filter中一定要用绝对路径！一定，一定，一定！以‘/’开头的就是绝对路径
            ((HttpServletResponse)resp).sendRedirect("/day08/please");
        }

    }

    public void init(FilterConfig arg0) throws ServletException {
        // TODO Auto-generated method stub

    }

}

web.xml

<filter>
    <filter-name>isf</filter-name>
    <filter-class>com.bright.filter.isloginFilter</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>isf</filter-name>
    <url-pattern>/show</url-pattern>
  </filter-mapping>