JavaWeb--Filter

程序员文章站 2022-05-23 08:36:35

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什么是Filter？

Filter是一种过滤器，根据需求来过滤数据

Filter的使用步骤

导入javax.servlet包中的Filter接口
重写Filter接口下的方法
三个方法的介绍
在web.xml中配置filter信息，整体逻辑和配置servlet一致

 <filter>
        <filter-name>test</filter-name>
        <filter-class>org.westos.demo03.FilterTest</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>test</filter-name>
        <url-pattern>/filter</url-pattern>
    </filter-mapping>

Filter过滤器的应用

需求:输入正确的用户名才能访问登录成功的页面，注销之后就不能访问
存储attribute的常量

public class Constant {
	public final static String USER_SESSION="USER_SESSION";
}

登陆的类

public class Login extends HttpServlet {
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		String username = req.getParameter("username");
		//如果用户名正确，则跳转到登录成功页面，不正确，则跳转到错误页面
		if (username.equals("admin")){
			//在session添加信息，即不注销就可以访问成功页面
			req.getSession().setAttribute(Constant.USER_SESSION,req.getSession().getId());
			//页面跳转
			resp.sendRedirect("/sys/success.jsp");
		}else {
			resp.sendRedirect("/error.jsp");
		}
	}

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

注销的类

public class Logout extends HttpServlet {
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		Object attribute = req.getSession().getAttribute(Constant.USER_SESSION);
		//如果arrribute不为空，则证明已经登陆了
		if (attribute!=null){
			req.getSession().removeAttribute(Constant.USER_SESSION);
			resp.sendRedirect("/login.jsp");
		}
		else {
			resp.sendRedirect("/login.jsp");
		}
	}

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

过滤信息的类

public class LoginFilter implements Filter {
	@Override
	public void init(FilterConfig filterConfig) throws ServletException {

	}

	@Override
	public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
		HttpServletRequest request = (HttpServletRequest) servletRequest;
		HttpServletResponse response = (HttpServletResponse) servletResponse;
		//过滤信息：如果session的信息为空，则不能登陆
		if (request.getSession().getAttribute(Constant.USER_SESSION)==null) {
			response.sendRedirect("/error.jsp");
		}
		filterChain.doFilter(request, response);
	}

	@Override
	public void destroy() {

	}
}

web.xml信息

<!--登陆-->
    <servlet>
        <servlet-name>login</servlet-name>
        <servlet-class>org.westos.demo01.Login</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>login</servlet-name>
        <url-pattern>/servlet/login</url-pattern>
    </servlet-mapping>

    <!--注销-->
    <servlet>
        <servlet-name>logout</servlet-name>
        <servlet-class>org.westos.demo01.Logout</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>logout</servlet-name>
        <url-pattern>/servlet/logout</url-pattern>
    </servlet-mapping>

    <!--过滤-->
    <filter>
        <filter-name>loginfilter</filter-name>
        <filter-class>org.westos.demo01.LoginFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>loginfilter</filter-name>
        <url-pattern>/sys/*</url-pattern>
    </filter-mapping>

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<h1>登陆</h1>
<form action="servlet/login"method="get">
    用户名: <input type="text" name="username"><br>
    <input type="submit">
</form>

</body>
</html>

error.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<h1>登陆失败</h1>
<a href="/login.jsp">重新登陆</a>
</body>
</html>

success.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<h1>登陆成功</h1>
<a href="/servlet/logout">注销</a>
</body>
</html>