JavaWeb-MVC、過濾器-有解無憂

一、MVC架構圖

Model

業務處理：業務邏輯(Service)
資料持久層：CRUD(Dao)

View

展示資料
提供連接發起Servlet請求(a,form,img....)

Controller(Servlet)

接收用戶的請求:(req:請求引數，Session資訊)
交給業務層處理對應的代碼
控制視圖的跳轉
比如一個登錄流程

登錄--->接收用戶的登錄請求--->Servlet處理用戶的請求(獲取用戶登錄的引數，username,password)--->交
給業務員層處理登錄業務(判斷用戶名密碼是否正確)--->Dao層查詢用戶名和密碼是否正確-->資料庫

二、過濾器(Filter重點)

Filter:過濾器，用來過濾網站的資料；

處理中文亂碼
登錄驗證.....

1.Filter開發步驟

(1)匯入Maven依賴

<dependency>
          <groupId>javax.servlet</groupId>
          <artifactId>javax.servlet-api</artifactId>
          <version>3.1.0</version>
          <!--            作用域，一般不要-->
          <!--            <scope>provided</scope>-->
      </dependency>
      <!--JSP的依賴-->
      <dependency>
          <groupId>javax.servlet.jsp</groupId>
          <artifactId>javax.servlet.jsp-api</artifactId>
          <version>2.3.3</version>
      </dependency>
      <!--standard標簽庫-->
      <dependency>
          <groupId>taglibs</groupId>
          <artifactId>standard</artifactId>
          <version>1.1.2</version>
      </dependency>
      <!--JSTL運算式的依賴-->
      <dependency>
          <groupId>javax.servlet.jsp.jstl</groupId>
          <artifactId>jstl</artifactId>
          <version>1.2</version>
      </dependency>

(2)撰寫過濾器

* 實作Filter介面 * 重寫方法 ~~~java package com.tang.filter;

import javax.servlet.*;
import java.io.IOException;

public class CharacterEncodingFilter implements Filter {
//初始化：web服務器啟動，就已經初始化了，隨時等待過濾器物件出現
public void init(FilterConfig filterConfig) throws ServletException {
System.out.println("characterEncoding初始化");
}
/*
* chain 鏈
* 1.過濾其中所有代碼，在過濾特定請求
* (特定請求：比如在Servlet中會在web.xml中進行注冊,同理過濾器也一樣需要注冊和添加映射)的時候都會執行
* 2.必須要讓過濾器繼續通行
* chain.doFilter(request,response);*/
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
request.setCharacterEncoding("utf-16");//寫utf-8得寫setContentType為text/html，否則還會亂碼因此我直接寫utf-16
response.setCharacterEncoding("utf-16");
response.setContentType("text/html;charset=UTF-8");

    System.out.println("setCharacterEncoding執行前，，，");
    chain.doFilter(request,response);//對過濾器起一個放行的作用，如果不寫程式到這里就被攔截停止
    System.out.println("setCharacterEncoding執行后，，，");
}
//銷毀：web服務器關閉的時候，過濾器會銷毀
public void destroy() {
    System.out.println("characterEncoding銷毀");
}

}

<h4>(3)在web.xml中配置filter

~~~xml
 <servlet>
      <servlet-name>showservlet</servlet-name>
      <servlet-class>com.tang.servlet.ShowServlet</servlet-class>
  </servlet>
  <servlet-mapping>
      <servlet-name>showservlet</servlet-name>
      <url-pattern>/servlet/show</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
      <servlet-name>showservlet</servlet-name>
      <!--一個請求設定兩個訪問路徑-->
      <url-pattern>/show</url-pattern>
  </servlet-mapping>
  <filter>
      <filter-name>CharacterEncodingFilter</filter-name>
      <filter-class>com.tang.filter.CharacterEncodingFilter</filter-class>
  </filter>
  <filter-mapping>
      <filter-name>CharacterEncodingFilter</filter-name>
      <!--只要是/servlet的任何請求都會經過這個過濾器-->
      <url-pattern>/servlet/*</url-pattern>
  </filter-mapping>

ShowServlet代碼如下

package com.tang.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class ShowServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //resp.setCharacterEncoding("UTF-16");
        resp.getWriter().write("唐三是掛，誰惹誰掛");
    }

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

運行結果圖
同一個請求，以servlet開頭的訪問會被過濾，另一個去訪問則不會被過濾,結果如下

2.常見應用

(1)用戶登錄之后才能進入主頁！用戶注銷后就不能進入主頁了，用過濾器實作
LoginServlet代碼

package com.tang.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class LoginServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
       //獲取前端請求的引數
        System.out.println("進入了登錄");
        //String username = req.getParameter("username");
        if(req.getParameter("username").equals("admin")){//登錄成功
            System.out.println("登錄成功");
            //USER_SESSION為一個常量，通常自己新建util包，并放在新建constant的類中
            req.getSession().setAttribute("USER_SESSION",req.getSession().getId());
            resp.sendRedirect("/Filter_war/sys/success.jsp");

        }else {
            resp.sendRedirect("/Filter_war/error.jsp");
        }
    }

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

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<h1>登錄</h1>
<%--這里如果用post方式提交會出現在前端頁面輸入資訊，但是卻得不到前端請求的引數值--%>
<form action="/Filter_war/servlet/login" method="get">
    <input type="text" name="username">
    <input type="submit">
</form>
</body>
</html>

LogoutServlet代碼

package com.tang.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class LogoutServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String user_session = (String) req.getSession().getAttribute("USER_SESSION");
        if(user_session != null){//說明用戶處于登錄狀態，因為只有登錄狀態USER_SESSION不為空也即user_session不為空
            req.getSession().removeAttribute("USER_SESSION");//將該登錄狀態的用戶移除
            resp.sendRedirect("/Filter_war/login.jsp");//注銷之后進入登錄界面

        }else{
            resp.sendRedirect("/Filter_war/login.jsp");//注銷為空也回到該頁面
        }
    }

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

success.jsp主界面代碼


<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<%
    Object user_session = request.getSession().getAttribute("USER_SESSION");
    if(user_session == null){//用戶沒有登錄就不能進如主界面
        response.sendRedirect("/Filter_war/login.jsp");
    }
%>
<h1>主頁</h1>
<p><a href="https://www.cnblogs.com/Filter_war/servlet/logout">注銷</a></p>
</body>
</html>

error.jsp代碼

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<h1>錯誤</h1>
用戶名或者密碼錯誤
<a href="https://www.cnblogs.com/Filter_war/login.jsp">回傳登錄界面</a>
</body>
</html>

web.xm代碼如下

<servlet>
        <servlet-name>LoginServlet</servlet-name>
        <servlet-class>com.tang.servlet.LoginServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>LoginServlet</servlet-name>
        <url-pattern>/servlet/login</url-pattern>
    </servlet-mapping>

    <servlet>
        <servlet-name>logoutServlet</servlet-name>
        <servlet-class>com.tang.servlet.LogoutServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>logoutServlet</servlet-name>
        <url-pattern>/servlet/logout</url-pattern>
    </servlet-mapping>

運行結果圖

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