過濾器filter（重點）

1、簡介

應用場景

• 自動登入；
• 統一設定編碼格式；
• 通路權限控制；
• 敏感字元過濾等。

2、編寫過濾器

1. test

public class FilterTest01 implements Filter {
    //初始化：web伺服器啟動的時候就會初始化，随時等待過濾對象出現
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("初始化");
    }

    /*
    FilterChain:鍊；
    1.過濾中的所有代碼，在過濾特定請求的時候都會執行；
    2.必須要讓過濾器繼續通行
     */
    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("執行FilterTest01前");
        filterChain.doFilter(request,response);//讓我們的請求繼續走，如果不寫，程式就會被攔截停止在這裡
        System.out.println("執行FilterTest01後");
    }
    //銷毀：web伺服器關閉的時候，過濾器才會銷毀
    public void destroy() {
        System.out.println("銷毀");
    }
}
           

<filter>
    <filter-name>Demo01</filter-name>
    <filter-class>com.beyond.filter.FilterTest01</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>Demo01</filter-name>
    <!--隻要是 /servlet的任何請求都會經過這個過濾器-->
    <url-pattern>/servlet/*</url-pattern>
  </filter-mapping>
           

2.判斷使用者賬号、權限登入（使用者登陸之後才能進入首頁，使用者登出後就不能進入首頁了）

//登陸驗證
public class LoginTest01 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //擷取前端請求的參數
        String username = req.getParameter("username");

        if(username.equals("admin")){//登陸成功
            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);
    }
}

=================================================
//登陸成功後，登出，過濾
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() {

    }
}

=================================================
//登陸失敗
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>登入</h2>
<form action="login" method="post">
    <input type="text" name="username">
    <input type="submit">
</form>
        
================================================= 
<h1>首頁</h1>

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

=================================================         
<h1>自定義500的錯誤頁面</h1>
<h3>賬号錯誤，沒有權限</h3>
<a href="../login.jsp">傳回登陸頁面</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>