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尚硅谷最新版JavaWeb全套教程,java web零基础入门完整版（四）

發布時間：2025/3/19 java 20 豆豆

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文件的上傳和下載

文件上傳的介紹

<?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>UploadServlet</servlet-name><servlet-class>com.atguigu.servlet.UploadServlet</servlet-class></servlet><servlet-mapping><servlet-name>UploadServlet</servlet-name><url-pattern>/uploadServlet</url-pattern></servlet-mapping> </web-app> package com.atguigu.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 UploadServlet extends HttpServlet {/*** 用來處理文件生成* @param req* @param resp* @throws ServletException* @throws IOException*/@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {System.out.println("文件上傳過來了");} } <%@ page contentType="text/html;charset=UTF-8" language="java" %> <html> <head><title>Title</title> </head> <body><%-- form:post --%><form action="http://localhost:8080/jstl/uploadServlet" method="post" enctype="multipart/form-data">用戶名：<input type="text" name="username"> <br>頭像：<input type="file" name="photo"> <br><input type="submit" value="上傳"></form> </body> </html>

上傳的http協議介紹

以流的形式上傳和接收
所以如果用getPraramter沒有用

package com.atguigu.servlet;import javax.servlet.ServletException; import javax.servlet.ServletInputStream; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException;public class UploadServlet extends HttpServlet {/*** 用來處理文件生成* @param req* @param resp* @throws ServletException* @throws IOException*/@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {ServletInputStream inputStream = req.getInputStream();byte[] buffer = new byte[1024000];int read = inputStream.read(buffer);System.out.println(new String(buffer, 0, read));} }

上傳合用到的類和方法介紹

使用fileupload解析上傳的數據

選中整行以后 command + option + t 快捷鍵

然后選擇 try catch，然后手動改成Exception

package com.atguigu.servlet;import org.apache.commons.fileupload.FileItem; import org.apache.commons.fileupload.FileItemFactory; import org.apache.commons.fileupload.FileUploadException; import org.apache.commons.fileupload.disk.DiskFileItemFactory; import org.apache.commons.fileupload.servlet.ServletFileUpload;import javax.servlet.ServletException; import javax.servlet.ServletInputStream; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.File; import java.io.IOException; import java.util.List;public class UploadServlet extends HttpServlet {@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// 1、先判斷上傳的數據是否為多段數據（只有是多段數據，才是文件上傳的）if (ServletFileUpload.isMultipartContent((req))) {// 創建FileItemFactory工廠實現類FileItemFactory fileItemFactory = new DiskFileItemFactory();// 創建用于解析上傳數據的工具類 ServletFileUpload類ServletFileUpload servletFileUpload = new ServletFileUpload(fileItemFactory);// 解析上傳的數據，得到每一個表單項FileItemtry {List<FileItem> list = servletFileUpload.parseRequest(req);// 循環判斷，每一個表單項，是普通類型，還是上傳的文件for (FileItem fileItem : list) {if (fileItem.isFormField()) {// 普通表單項System.out.println("表單項的name屬性值：" + fileItem.getFieldName());// 參數UTF-8，解決亂碼問題System.out.println("表單的value屬性值：" + fileItem.getString("UTF-8"));} else {// 上傳的文件System.out.println("表單項的name屬性值：" + fileItem.getFieldName());System.out.println("上傳的文件名：" + fileItem.getName());// fileItem.write((new File(("e:\\" + fileItem.getName()))));}}} catch (Exception e) {e.printStackTrace();}}} }

文件下載的實現

package com.atguigu.servlet;import org.apache.commons.io.IOUtils;import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.ServletOutputStream; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException; import java.io.InputStream;public class Download extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// 1、獲取要下載的文件名String downloadFileName = "1.png";// 2、讀取要下載的文件內容（通過ServletContext對象可以讀取）ServletContext servletContext = getServletContext();// 獲取要下載的文件類型String mimeType = servletContext.getMimeType("/file/" + downloadFileName);System.out.println("下載的文件類型：" + mimeType);// 4、在回傳前，通過響應頭告訴客戶端返回的數據類型resp.setContentType(mimeType);// 5、還要告訴客戶端收到的數據是用于下載使用（還是使用響應頭）// Content-Disposition響應頭，表示收到的數據怎么處理// attacjment表示附件，表示下載使用// filename= 表示指定下載的文件名resp.setHeader("Content-Disposition", "attachment;filename=" + downloadFileName);/*** /斜杠被服務器解析表示地址為http://ip:port/工程名/ 映射到代碼的web目錄*/InputStream resourceAsStream = servletContext.getResourceAsStream("/file/" + downloadFileName);// 獲取響應的輸出流ServletOutputStream outputStream = resp.getOutputStream();// 3、把下載的文件內容回傳給客戶端// 讀取輸入流中全部的數據，復制給輸出流，輸出給客戶端IOUtils.copy(resourceAsStream, outputStream);} }

輸入后敲回車，直接就下載文件了

使用URLEncoder解決谷歌和IE瀏覽器中文下載名亂碼問題

可以和原文件名不同，下載下來顯示的名稱就是filename
如果filename=中國.jpg，文件名會無法識別
因此，要對中文進行URL編碼

Base64編解碼操作

如果是火狐瀏覽器不支持上面這種方式

發現這個類和URLEncode類不同，不是靜態方法，因此要先new

Base64編解碼操作解決火狐瀏覽器的附近中文名問題

將原先那個setHeader換成resp.setHeader("Content-Disposition", "attachment; filename==?UTF-8?B?" + new BASE64Encoder().encode("中國.jpg".getBytes("UTF-8")) + "?=");

使用User-Agent請求頭判斷，動態切換不同的方案解決所有瀏覽器附件中文亂碼問題

書城項目

command + shift + R 可以查找替換（可以先選中目錄）

動態的base標簽值

表單提交失敗的錯誤回顯

合并LoginServlet和RegistServlet程序為UserServlet程序

使用反射優化大量else if代碼

protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { String action = req.getParameter("action"); try {// 獲取 action 業務鑒別字符串，獲取相應的業務方法反射對象 Method method = this.getClass().getDeclaredMethod(action, HttpServletRequest.class, HttpServletResponse.class); // System.out.println(method); // 調用目標業務方法 method.invoke(this, req, resp); } catch (Exception e) {e.printStackTrace(); } }

抽取 BaseServlet 程序

public abstract class BaseServlet extends HttpServlet { protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { String action = req.getParameter("action"); try {// 獲取 action 業務鑒別字符串，獲取相應的業務方法反射對象 Method method = this.getClass().getDeclaredMethod(action, HttpServletRequest.class, HttpServletResponse.class); // System.out.println(method); // 調用目標業務方法 method.invoke(this, req, resp); } catch (Exception e) { e.printStackTrace(); } } }

數據的封裝和抽取 BeanUtils 的使用

command + option + t 選擇代碼的環繞方式

MVC概念

Cookie

什么是Cookie

Cookie的創建

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <head> <meta http-equiv="pragma" content="no-cache" /> <meta http-equiv="cache-control" content="no-cache" /> <meta http-equiv="Expires" content="0" /> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>Cookie</title><base href="http://localhost:8080/cookie/"> <style type="text/css">ul li {list-style: none;}</style> </head> <body><iframe name="target" width="500" height="500" style="float: left;"></iframe><div style="float: left;"><ul><li><a href="cookieServlet?action=createCookie" target="target">Cookie的創建</a></li><li><a href="cookieServlet?action=getCookie" target="target">Cookie的獲取</a></li><li><a href="cookieServlet?action=updateCookie" target="target">Cookie值的修改</a></li><li>Cookie的存活周期</li><li><ul><li><a href="cookieServlet?action=defaultLife" target="target">Cookie的默認存活時間（會話）</a></li><li><a href="cookieServlet?action=deleteNow" target="target">Cookie立即刪除</a></li><li><a href="cookieServlet?action=life3600" target="target">Cookie存活3600秒（1小時）</a></li></ul></li><li><a href="cookieServlet?action=testPath" target="target">Cookie的路徑設置</a></li><li><a href="" target="target">Cookie的用戶免登錄練習</a></li></ul></div> </body> </html> package com.atguigu.servlet;import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException; import java.lang.reflect.Method;public abstract class BaseServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doPost(req, resp);}protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// 解決post請求中文亂碼問題// 一定要在獲取請求參數之前調用才有效req.setCharacterEncoding("UTF-8");// 解決響應中文亂碼問題resp.setContentType("text/html; charset=UTF-8");String action = req.getParameter("action");try {// 獲取action業務鑒別字符串，獲取相應的業務方法反射對象Method method = this.getClass().getDeclaredMethod(action, HttpServletRequest.class, HttpServletResponse.class); // System.out.println(method);// 調用目標業務方法method.invoke(this, req, resp);} catch (Exception e) {e.printStackTrace();}}} package com.atguigu.servlet;import javax.servlet.ServletException; import javax.servlet.http.Cookie; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException;public class CookieServlet extends BaseServlet{protected void createCookie(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// 1、創建Cookie對象Cookie cookie = new Cookie("key1", "value1");// 2、通知客戶端保存Cookieresp.addCookie(cookie);resp.getWriter().write("Cookie創建成功");} }

Cookie的獲取

package com.atguigu.servlet;import com.example.Cookie.CookieUtils;import javax.servlet.ServletException; import javax.servlet.http.Cookie; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException;public class CookieServlet extends BaseServlet{protected void createCookie(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// 1、創建Cookie對象Cookie cookie = new Cookie("key1", "value1");// 2、通知客戶端保存Cookieresp.addCookie(cookie);resp.getWriter().write("Cookie創建成功");}protected void getCookie(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {Cookie[] cookies = req.getCookies();// getName方法// getValue方法for (Cookie cookie : cookies) {resp.getWriter().write("Cookie[" + cookie.getName() + " = " + cookie.getValue() + "] <br>");}Cookie iWantCookie = CookieUtils.findCookie("key1", cookies);if (iWantCookie != null) {resp.getWriter().write("找到了需要的Cookie");}} }

package com.atguigu.util;import javax.servlet.http.Cookie;public class CookieUtils {/*** 查找指定名稱的cookie對象* @param name* @param cookies* @return*/public static Cookie findCookie(String name, Cookie[] cookies) {if (name == null || cookies == null || cookies.length == 0) {return null;}for (Cookie cookie : cookies) {if (name.equals(cookie.getName())) {return cookie;}}return null;} } <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <head> <meta http-equiv="pragma" content="no-cache" /> <meta http-equiv="cache-control" content="no-cache" /> <meta http-equiv="Expires" content="0" /> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>Cookie</title><base href="http://localhost:8080/cookie/"> <style type="text/css">ul li {list-style: none;}</style> </head> <body><iframe name="target" width="500" height="500" style="float: left;"></iframe><div style="float: left;"><ul><li><a href="cookieServlet?action=createCookie" target="target">Cookie的創建</a></li><li><a href="cookieServlet?action=getCookie" target="target">Cookie的獲取</a></li><li><a href="cookieServlet?action=updateCookie" target="target">Cookie值的修改</a></li><li>Cookie的存活周期</li><li><ul><li><a href="cookieServlet?action=defaultLife" target="target">Cookie的默認存活時間（會話）</a></li><li><a href="cookieServlet?action=deleteNow" target="target">Cookie立即刪除</a></li><li><a href="cookieServlet?action=life3600" target="target">Cookie存活3600秒（1小時）</a></li></ul></li><li><a href="cookieServlet?action=testPath" target="target">Cookie的路徑設置</a></li><li><a href="" target="target">Cookie的用戶免登錄練習</a></li></ul></div> </body> </html><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <head> <meta http-equiv="pragma" content="no-cache" /> <meta http-equiv="cache-control" content="no-cache" /> <meta http-equiv="Expires" content="0" /> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>Cookie</title><base href="http://localhost:8080/cookie/"> <style type="text/css">ul li {list-style: none;}</style> </head> <body><iframe name="target" width="500" height="500" style="float: left;"></iframe><div style="float: left;"><ul><li><a href="cookieServlet?action=createCookie" target="target">Cookie的創建</a></li><li><a href="cookieServlet?action=getCookie" target="target">Cookie的獲取</a></li><li><a href="cookieServlet?action=updateCookie" target="target">Cookie值的修改</a></li><li>Cookie的存活周期</li><li><ul><li><a href="cookieServlet?action=defaultLife" target="target">Cookie的默認存活時間（會話）</a></li><li><a href="cookieServlet?action=deleteNow" target="target">Cookie立即刪除</a></li><li><a href="cookieServlet?action=life3600" target="target">Cookie存活3600秒（1小時）</a></li></ul></li><li><a href="cookieServlet?action=testPath" target="target">Cookie的路徑設置</a></li><li><a href="" target="target">Cookie的用戶免登錄練習</a></li></ul></div> </body> </html>

Cookie值的修改

protected void updateCookie(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { // 方案一： // 1、先創建一個要修改的同名的Cookie對象 // 2、在構造器，同時賦于新的cookie值Cookie cookie = new Cookie("key1", "newValue1"); // 3、調用resp.addCookie(cookie); ；通知客戶端保存修改resp.addCookie(cookie);resp.getWriter().write("key1的cookie已經修改好了");}

protected void updateCookie(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {Cookie cookie = CookieUtils.findCookie("key1", req.getCookies());if (cookie != null) {cookie.setValue("newValue1");resp.addCookie(cookie);}}

中文也是

谷歌和火狐瀏覽器如何查看Cookie

Cookie的生命設置

protected void defaultLife(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {Cookie cookie = new Cookie("defaultLife", "defaultLife");cookie.setMaxAge(-1); // 設置存活時間resp.addCookie(cookie);} protected void deleteNow(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// 先找到要刪除的cookie對象Cookie cookie = CookieUtils.findCookie(("key1"), req.getCookies());if (cookie != null) {// 調用setMaxAge（0）；cookie.setMaxAge(0); // 表示馬上刪除，都不需要等待瀏覽器關閉// 調用addCookieresp.addCookie(cookie);resp.getWriter().write("key1的cookie已經被刪除");}}

Cookie 有效路徑 Path 的設置

protected void testPath(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {Cookie cookie = new Cookie("path1", "path1");// getContextPath 得到工程路徑cookie.setPath( req.getContextPath() + "/abc" ); // 工程路徑/abcresp.addCookie(cookie);resp.getWriter().write("創建了一個帶有Path路徑的Cookie");}

Cookie 練習—免輸入用戶名登錄

<%@ page contentType="text/html;charset=UTF-8" language="java" %> <html> <head><title>login.jsp</title> </head> <body><form action="http://localhost:8080/cookie/loginServlet" method="get">用戶名：<input type="text" name="username" value="${ cookie.username.value }"> <br>密碼：<input type="password" name="password"> <br><input type="submit" value="登陸"></form> </body> </html> package com.atguigu.servlet;import javax.servlet.ServletException; import javax.servlet.http.Cookie; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException;public class LoginServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {String username = req.getParameter("username");String password = req.getParameter("password");if ("wzg168".equals(username) && "123456".equals(password)) {Cookie cookie = new Cookie("username", username);cookie.setMaxAge(60 * 60 * 24 * 7); // 當前Cookie一周內有效resp.addCookie(cookie);System.out.println("登陸成功");} else {System.out.println("登陸失敗");}} }

在登陸成功一次，且在cookie消亡時間之前，再次訪問login.jsp用戶名會自動顯示

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