MVC三层架构
什么是MVC？
Model View Controller 模型 视图 控制器
模型：可理解为实体类与表中对应的字段
视图：比如jsp页面
控制器：Servlet控制页面跳转与request和response处理
Filter过滤器
Filter：过滤网站数据，如登录验证，中文乱码处理等
Filter开发步骤：1、导包。2、编写过滤器。3、web.xml配置Filter
Filter接口为import javax.servlet.*;包下的。implents接口需要实现三个方法
//初始化
public void init(FilterConfig filterConfig) throws ServletException {
}
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
}
//销毁
public void destroy() {
}
编写Filter
1、过滤器中所有代码在过滤特定请求时都会执行
2、必须要让过滤器filterChain.doFilter()将req和resp转交给后面的过滤器，继续通行
3、filterChain.doFilter(servletRequest,servletResponse); //让我们的请求继续走，如果不写，程序到这里就被拦截停止。后面还有其他过滤器，需要把这次的req和resp传给后面的Filter
public class CharacterEncodingFilter implements Filter {
/*
1、过滤器中所有代码在过滤特定请求时都会执行
2、必须要让过滤器filterChain.doFilter()将req和resp转交给后面的过滤器，继续通行
*/
//初始化:web服务器启动就进行了初始化
public void init(FilterConfig filterConfig) throws ServletException { System.out.println("CharacterEncodingFilter Init..."); }
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
servletRequest.setCharacterEncoding("UTF-8");
servletResponse.setCharacterEncoding("UTF-8");
System.out.println("Filter run start......");
filterChain.doFilter(servletRequest,servletResponse); //让我们的请求继续走，如果不写，程序到这里就被拦截停止。后面还有其他过滤器，需要把这次的req和resp传给后面的Filter
System.out.println("Filter run stop......");
}
//销毁:web服务器关闭时，Filter销毁
public void destroy() { System.out.println("CharacterEncodingFilter Destmroy..."); }
}
注册Filter
<filter>
<filter-name>CharacterEncodingFilter</filter-name>
<filter-class>com.zh1z3ven.filter.CharacterEncodingFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>CharacterEncodingFilter</filter-name>
<!-- 在此设定的路由下的请求都会经过Filter处理-->
<url-pattern>/servlet/*</url-pattern>
</filter-mapping>
下面简单测试下，创建两个路由，一个走过滤器，一个不走过滤器
servlet
public class ShowServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
resp.getWriter().write("你好，世界");
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
Web.xml
<servlet>
<servlet-name>show</servlet-name>
<servlet-class>com.zh1z3ven.servlet.ShowServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>show</servlet-name>
<url-pattern>/show</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>show</servlet-name>
<url-pattern>/servlet/show</url-pattern>
</servlet-mapping>
Filter实现权限拦截
Jsp中实现过滤
<%--在jsp中实现鉴权。如果用户未携带session就跳转到login页面--%>
<%
Object user_session = request.getSession().getAttribute("USER_SESSION");
if (user_session==null){
response.sendRedirect("/login.jsp");
}
%>
但是这样success.jsp和error.jsp都要写一遍，代码写的就很臃肿，不如Filter来实现比较方便和易于管理
主要实现用户登录之后，判断是否存在session，若有才可以进入/sys/success页面。若不存在则跳到error界面。
Login.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>login</title>
</head>
<body>
<h2>登录</h2>
<form action="/servlet/login" method="post" >
<input name="username" type="text">
<input name="submit" type="submit">
</form>
</body>
</html>
error.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>error</title>
</head>
<body>
<h2>error</h2>
<h2><a href="/login.jsp">返回首页</a> </h2>
</body>
</html>
/sys/success.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>success</title>
</head>
<body>
<h2>success</h2>
<p><a href="/servlet/logout" name="logout">logout</a> </p>
</body>
</html>
LoginServlet
public class LoginServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String username = req.getParameter("username");
if ("admin".equals(username)){
req.getSession().setAttribute(Contant.USER_SESSION,req.getSession().getId());
resp.sendRedirect("/sys/success.jsp");
}else {
resp.sendRedirect("/error.jsp");
}
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req,resp);
}
}
LogoutServlet
public class LogoutServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
Object user_session = req.getSession().getAttribute(Contant.USER_SESSION);
if (user_session!=null){
req.getSession().removeAttribute(Contant.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);
}
}
SysFilter
public class SysFilter implements Filter {
public void init(FilterConfig filterConfig) throws ServletException {
}
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
HttpServletRequest Req = (HttpServletRequest) servletRequest;
HttpServletResponse Resp = (HttpServletResponse) servletResponse;
if (Req.getSession().getAttribute(Contant.USER_SESSION)==null){
Resp.sendRedirect("/error.jsp");
}
filterChain.doFilter(Req,Resp);
}
public void destroy() {
}
}
/util/Contant.java 将session处理为常量，便于编写和修改代码
public class Contant {
public final static String USER_SESSION = "USER_SESSION";
}
web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
version="4.0">
<servlet>
<servlet-name>login</servlet-name>
<servlet-class>com.zh1z3ven.servlet.LoginServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>login</servlet-name>
<url-pattern>/servlet/login</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>logout</servlet-name>
<servlet-class>com.zh1z3ven.servlet.LogoutServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>logout</servlet-name>
<url-pattern>/servlet/logout</url-pattern>
</servlet-mapping>
<filter>
<filter-name>SysFilter</filter-name>
<filter-class>com.zh1z3ven.filter.SysFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>SysFilter</filter-name>
<url-pattern>/sys/*</url-pattern>
</filter-mapping>
</web-app>