过滤器filter（重点）

1、简介

应用场景

• 自动登录；
• 统一设置编码格式；
• 访问权限控制；
• 敏感字符过滤等。

2、编写过滤器

1. test

public class FilterTest01 implements Filter {
    //初始化：web服务器启动的时候就会初始化，随时等待过滤对象出现
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("初始化");
    }

    /*
    FilterChain:链；
    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通行
     */
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws IOException, ServletException {
        request.setCharacterEncoding("utf-8");
        response.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=utf-8");

        System.out.println("执行FilterTest01前");
        filterChain.doFilter(request,response);//让我们的请求继续走，如果不写，程序就会被拦截停止在这里
        System.out.println("执行FilterTest01后");
    }
    //销毁：web服务器关闭的时候，过滤器才会销毁
    public void destroy() {
        System.out.println("销毁");
    }
}
           

<filter>
    <filter-name>Demo01</filter-name>
    <filter-class>com.beyond.filter.FilterTest01</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>Demo01</filter-name>
    <!--只要是 /servlet的任何请求都会经过这个过滤器-->
    <url-pattern>/servlet/*</url-pattern>
  </filter-mapping>
           

2.判断用户账号、权限登录（用户登陆之后才能进入主页，用户注销后就不能进入主页了）

//登陆验证
public class LoginTest01 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取前端请求的参数
        String username = req.getParameter("username");

        if(username.equals("admin")){//登陆成功
            req.getSession().setAttribute("USER_SESSION",req.getSession().getId());
            resp.sendRedirect("sys/success.jsp");
        }else {
            resp.sendRedirect("error/500.jsp");
        }
    }

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

=================================================
//登陆成功后，注销，过滤
public class LoginFilter implements Filter {

    public void init(FilterConfig filterConfig) throws ServletException {

    }

    public void doFilter(ServletRequest sreq, ServletResponse sresp, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) sreq;
        HttpServletResponse response = (HttpServletResponse) sresp;

        if(request.getSession().getAttribute("USER_SESSION")==null){
            response.sendRedirect("error/500.jsp");
        }

        filterChain.doFilter(request,response);
    }

    public void destroy() {

    }
}

=================================================
//登陆失败
public class LogoutTest01 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        Object user_session = req.getSession().getAttribute("USER_SESSION");
        if(user_session!=null){
            req.getSession().removeAttribute("USER_SESSION");
            resp.sendRedirect("login.jsp");
        }else {
            resp.sendRedirect("login.jsp");
        }
    }

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

<h2>登录</h2>
<form action="login" method="post">
    <input type="text" name="username">
    <input type="submit">
</form>
        
================================================= 
<h1>主页</h1>

<p><a href="/jsp_01/logout">注销</a></p>

=================================================         
<h1>自定义500的错误页面</h1>
<h3>账号错误，没有权限</h3>
<a href="../login.jsp">返回登陆页面</a>
        
=================================================  
  <servlet>
    <servlet-name>LoginTest01</servlet-name>
    <servlet-class>com.beyond.filter.LoginTest01</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>LoginTest01</servlet-name>
    <url-pattern>/login</url-pattern>
  </servlet-mapping>
  
  <servlet>
    <servlet-name>LogoutTest01</servlet-name>
    <servlet-class>com.beyond.filter.LogoutTest01</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>LogoutTest01</servlet-name>
    <url-pattern>/logout</url-pattern>
  </servlet-mapping>
  
  <filter>
    <filter-name>LoginFilter</filter-name>
    <filter-class>com.beyond.filter.LoginFilter</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>LoginFilter</filter-name>
    <url-pattern>/sys/*</url-pattern>
  </filter-mapping>