Servlet與Jsp進階 · JavaWeb講義新編2020

# Servlet與Jsp進階 [TOC] ## 導學在之前的學習中，我們已經初步認識到什么是Servlet和Jsp。那么今天我們再來重新認識一下Servlet和Jsp，本節課需要掌握Java Web的核心特性（請求與響應的結構）、掌握Servlet的核心對象、Jsp九大內置對象（面試筆試中常遇到）等內容 ## HTTP請求的結構請求是瀏覽器像服務器發送的數據包，那么在請求中其實是包含了三部分的內容的：請求行，請求頭，請求體。 ![](https://img.kancloud.cn/85/30/85300b9dcda73a124752b8d3f151f8a8_625x289.png) 請求行包括請求的方式，請求的地址，以及請求的HTTP版本請求頭中，包括很多輔助的請求信息，能為請求處理提供額外的支持。 **資料（關于請求頭與響應頭)：**[https://www.cnblogs.com/xjcjcsy/p/6135006.html](https://www.cnblogs.com/xjcjcsy/p/6135006.html) 請求體中，描述了請求的參數內容。注意一下，get請求是將參數寫入URL中，所以get請求是沒有請求體的，只有post請求才有請求體。 ~~~java /** * Servlet implementation class MethodServlet */ @WebServlet("/method") public class MethodServlet extends HttpServlet { private static final long serialVersionUID = 1L; /** * @see HttpServlet#HttpServlet() */ public MethodServlet() { super(); // TODO Auto-generated constructor stub } /** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */ protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.getWriter().println("This is Get method"); } /** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */ protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.getWriter().println("This is Post method"); } } ~~~ ~~~html <!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <title>Insert title here</title> </head> <body> <form action="/MyJsp/method" method="get"> <input name="userName"/> <input name="password" type="password"/> <input type="submit"/> </form> </body> </html> ~~~ ![](https://img.kancloud.cn/04/ef/04efb61bebf64abd46f8f1ffb8242ef2_1365x669.png) ![](https://img.kancloud.cn/b6/10/b61058f84cd57fbec97a6f6913b15c27_1363x663.png) ## 利用請求頭開發多端應用早期的程序，基本都是運行的在電腦上的，我們編寫頁面的時候只要考慮電腦端的情況就可以了。但是隨著個人設備越來越多，我們需要考慮的顯示設備也越來越多，那么我們該如何去嘗試著在Java中進行多種設備的考量呢？這個時候我們就可以利用請求頭進行判斷分析 ~~~ /** * Servlet implementation class UserAgentServlet */ @WebServlet("/useragent") public class UserAgentServlet extends HttpServlet { private static final long serialVersionUID = 1L; /** * @see HttpServlet#HttpServlet() */ public UserAgentServlet() { super(); // TODO Auto-generated constructor stub } /** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */ protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String userAgent = request.getHeader("User-Agent");//獲取請求頭信息 response.setContentType("text/html;charset=utf-8");//設置服務器端響應的編碼方式以及內容解析方式 response.getWriter().println(userAgent); String output = ""; if(userAgent.indexOf("Windows NT") != -1) { output = "<h1>這是PC端</h1>"; } else if(userAgent.indexOf("iPhone") != -1 ||userAgent.indexOf("Android") != -1 ){ output = "<h1>這是手機端</h1>"; } response.getWriter().println(output); } /** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */ protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { } } ~~~ ## 響應的結構 HTTP響應包含三部分：響應行、響應頭、響應體 ![](https://img.kancloud.cn/2d/a6/2da6c00a74180e7debfcc301897991f1_668x267.png) HTTP常用狀態碼： ![](https://img.kancloud.cn/f9/a7/f9a70be35916394cdbb3aee1380bc31d_583x330.png) ## ContentType的作用 ContentType決定瀏覽器采用何種的方式對響應體進行處理。 ![](https://img.kancloud.cn/f4/00/f400fdce8c7731104ff7bd6f431a87d6_728x332.png) ~~~java /** * Servlet implementation class ContentTypeServlet */ @WebServlet("/contenttype") public class ContentTypeServlet extends HttpServlet { private static final long serialVersionUID = 1L; /** * @see HttpServlet#HttpServlet() */ public ContentTypeServlet() { super(); // TODO Auto-generated constructor stub } /** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */ protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String output = "<h1><a href='www.baidu.com'><span>百度</span></a></h1>"; /*response.setContentType("text/html;charset=utf-8");*/ /*response.setContentType("text/plain;charset=utf-8");*///輸出純文本 /*response.setContentType("text/xml;charset=utf-8");*/ response.setContentType("application/x-msdownload;charset=utf-8"); response.getWriter().println(output); } /** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */ protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { } } ~~~ ## 請求轉發與重定向在之前的學習中，都是通過一個servlet來完成的程序處理，但在真正的開發中，需要多個servlet進行組合調用。從A servlet到B servlet，完成一場“傳值的游戲”。那么從A到B之間，如何進行通信和跳轉呢？對于多個servlet和jsp之間跳轉有兩鐘方式： 1. 請求轉發:`request.getRequestDispatcher(path).forword(request,response)` 2. 響應重定向：`response.sendRedirect(Contextpath工程名稱/映射地址);` 區別：請求轉發是不會改變一開始訪問的映射地址響應重定向是會改變到最后請求的映射地址 ### 請求轉發與重定向的使用 ~~~ @WebServlet("/direct/index") public class IndexServlet extends HttpServlet { private static final long serialVersionUID = 1L; public IndexServlet() { super(); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.getWriter().println("This is index page"); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { } } ~~~ ~~~ /** * 用戶校驗頁面 * @author LiXinRong * */ @WebServlet("/direct/check") public class CheckLoginServlet extends HttpServlet { private static final long serialVersionUID = 1L; public CheckLoginServlet() { super(); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { System.out.println("用戶登錄成功"); //請求.請求觸發器.轉發->瀏覽器地址欄不會發生改變 request.getRequestDispatcher("/direct/index").forward(request, response); //響應重定向需要增加contextPath->瀏覽器地址欄會發生改變 response.sendRedirect("/sd/direct/index"); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { } } ~~~ 轉發時，是在服務器內部由第一個servlet跳轉到新的servlet。而轉發是在服務器處理完第一個servlet后，通知瀏覽器，由瀏覽器再發送一個請求給服務器的新的servlet。 ### 請求轉發與重定向的原理雖然請求轉發與重定向都是用于地址的跳轉，但是它們兩個在本質上是完全不一樣的。 **請求轉發** 請求轉發是在服務器內部進行跳轉，轉發調用的是HttpServletRequest對象中的方法以及轉發時瀏覽器只請求一次服務器，地址欄的url不會發生變化。 ![](https://img.kancloud.cn/79/e4/79e4ef52edea941e96590d95f986d3a7_677x217.png) 在進行請求轉發時，允許創建自定義屬性。設置請求屬性： `request.setAttribute(屬性名，屬性值)` 獲取請求屬性： `Object attr = request.getAttribute(屬性名)` ~~~ @WebServlet("/direct/check") public class CheckLoginServlet extends HttpServlet { private static final long serialVersionUID = 1L; public CheckLoginServlet() { super(); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { System.out.println("用戶登錄成功"); request.setAttribute("name", "Jack"); //請求.請求觸發器.轉發->瀏覽器地址欄不會發生改變 request.getRequestDispatcher("/direct/index").forward(request, response); //響應重定向需要增加contextPath /*response.sendRedirect("/sd/direct/index");*/ } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { } } ~~~ ~~~ @WebServlet("/direct/index") public class IndexServlet extends HttpServlet { private static final long serialVersionUID = 1L; public IndexServlet() { super(); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String name = (String)request.getAttribute("name"); System.out.println(name); System.out.println("index page"); request.getRequestDispatcher("/direct/index2").forward(request, response); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { } } ~~~ ~~~ @WebServlet("/direct/index2") public class IndexServlet2 extends HttpServlet { private static final long serialVersionUID = 1L; public IndexServlet2() { super(); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String name = (String)request.getAttribute("name"); System.out.println(name); System.out.println("index page2"); request.getRequestDispatcher("/direct/index3").forward(request, response); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { } } ~~~ ~~~ @WebServlet("/direct/index3") public class IndexServlet3 extends HttpServlet { private static final long serialVersionUID = 1L; public IndexServlet3() { super(); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String name = (String)request.getAttribute("name"); System.out.println(name); System.out.println("index page3"); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { } } ~~~ 在servlet中定義的屬性，可以通過請求轉發一直傳遞下去。 **重定向** 重定向則是瀏覽器端跳轉，會產生兩次請求。 ![](https://img.kancloud.cn/94/29/9429b411c154bbfa8e99b8e2f546f41b_662x207.png) 重定向的時候不會去傳遞屬性。 **注意：** 1. 如果需要攜帶數據到要跳轉的界面，建議使用轉發。地址欄不會改變。 2. 如果不需要攜帶數據到要跳轉的界面，建議使用重定向。地址欄會改變 ## Cookie與Session ### Cookie Cookie(小甜餅)是瀏覽器保存在本地的文本內容，cookie常用于保存登錄狀態，用戶資料等小文本。cookie是具有時效性的，有效的cookie內容會伴隨著請求發送給Tomcat。比如我們可以使用cookie保存用戶的登錄信息，這樣在一定時長內，用戶就可以一直保持登錄狀態了。 ![](https://img.kancloud.cn/20/c9/20c9502c5eebab050851bfb8056335ba_1139x600.png) 該文件打開是一堆亂碼，這是因為這個文件往往包含敏感數據，所以瀏覽器對此進行了加密。 ![](https://img.kancloud.cn/77/0f/770f8d9a7c2fa8cb36e0cc5acad9a3a7_1358x514.png) 設置Cookie ~~~ @WebServlet("/cookies/lg") public class LoginServlet extends HttpServlet { private static final long serialVersionUID = 1L; public LoginServlet() { super(); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { System.out.println("用戶登錄成功"); //設置用戶七天內保持登錄 Cookie cookie = new Cookie("user","admin"); cookie.setMaxAge(60*60*24*7); response.addCookie(cookie); response.getWriter().println("login success"); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { } } ~~~ 若不設置有效期，則cookie有效期為當前瀏覽器窗口，若窗口關閉，則cookie清空 ![](https://img.kancloud.cn/90/f1/90f1365c427c48304763a1c41718e351_1365x517.png) 讀取cookie ~~~ @WebServlet("/cookies/is") public class IndexServlet extends HttpServlet { private static final long serialVersionUID = 1L; public IndexServlet() { super(); // TODO Auto-generated constructor stub } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { Cookie[] cs = request.getCookies();//用于獲取所用的用戶信息 String user = null; for(Cookie c :cs) { System.out.println(c.getName() + ":" + c.getValue()); if(c.getName().equals("user")) { user = c.getValue(); break; } } if(user == null) { response.getWriter().println("user not login"); } else { response.getWriter().println("user:" + user); } } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } } ~~~ 注意cookie是作用于本目錄及其子目錄，如果發送cookis那個文件的映射地址是/cookies/login，那么想要獲取的那個也必須是/cookies/xx ~~~ @WebServlet("/cookie/is")//該地址獲取不到對應的cookie public class IndexServlet2 extends HttpServlet { private static final long serialVersionUID = 1L; public IndexServlet2() { super(); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { Cookie[] cs = request.getCookies();//用于獲取所用的用戶信息 String user = null; for(Cookie c :cs) { System.out.println(c.getName() + ":" + c.getValue()); if(c.getName().equals("user")) { user = c.getValue(); break; } } if(user == null) { response.getWriter().println("user not login"); } else { response.getWriter().println("user:" + user); } } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } } ~~~ ### session cookie是保存在我們本地的數據，但是這個數據不一定可靠，保存在本地遲早會被破解，而且設置cookie之后，每次發送請求都會攜帶cookie，增加了瀏覽器的帶寬負擔。于是，我們有了一個新的解決方案session，用于將數據保存在服務器上。 **session特點：** 1. Sesstion(用戶會話)用于保存"瀏覽器窗口"對應的數據 2. Session的數據存儲在Tomcat服務器的內存中，具有時效性（無人訪問時長為30分鐘） 3. Session通過瀏覽器Cookie的SessionId（瀏覽器的session識別碼）值提取用戶數據，每個瀏覽器的SessionId都不一樣。 ~~~ @WebServlet("/session/sl") public class SessionLoginServlet extends HttpServlet { private static final long serialVersionUID = 1L; public SessionLoginServlet() { super(); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { System.out.println("用戶登錄成功"); //獲取用戶會話session HttpSession session = request.getSession(); session.setAttribute("name", "張三"); String sessionId = session.getId(); System.out.println(sessionId); request.getRequestDispatcher("/session/id").forward(request,response); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } } ~~~ ~~~ @WebServlet("/session/sil") public class SessionIndexServlet extends HttpServlet { private static final long serialVersionUID = 1L; public SessionIndexServlet() { super(); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { HttpSession session = request.getSession(); String sessionId = session.getId(); System.out.println(sessionId); String name = (String)session.getAttribute("name"); response.setContentType("text/html;charset=utf-8");//設置返回內容解碼方式 response.getWriter().println("這是首頁，當前用戶為：" + name); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } } ~~~ #### session使用的原理 session 對象是由服務器自動創建的與用戶請求相關的對象。服務器為每個用戶都生成一個session對象，用于保存該用戶的信息，跟蹤用戶的操作狀態，服務器創建的每個session對象互不干涉。session是會話級別的變量，我們一般使用 session 處理用戶的登陸信息。簡單的理解，打開一個瀏覽器，無論你打開多少標簽頁，用 session 存儲的變量都會存在，除非使用 session.removeAttribute() 將其顯式銷毀。其實可以將session看做在Tomcat中存儲的與客戶端瀏覽器窗口綁定的數據存儲空間。在使用的時候只需要使用`setAttribute`和`getAttribute`進行存值和取值即可。但是在底層卻不是簡單，是如何實現的呢？當瀏覽器第一次創建session對象的時候會tomcat會在內存空間中開辟一個空間存放session數據，并且給session空間一個sessionid，tomcat在返回響應數據的時候會把sessionid一起返回給瀏覽器，瀏覽器把sessionid保存在cookie中，之后從瀏覽器傳送過來的數據都通過sessionid來查找session的位置來保存數據。 ![](https://img.kancloud.cn/cb/7f/cb7fcfbb692c794da4d98da4cda513bf_974x506.png) session在工程的使用是非常廣泛的，最常用的就是根據session可以與瀏覽器對應的原理，用于保存每個用戶的登錄信息。 ## ServletContext ServletContext（Servlet上下文對象），是web應用的上下文對象。在一個Web應用程序中只會存在一個ServletContext對象，該對象在Tomcat啟動的時候創建，在Tomcat關閉的時候銷毀。 ![](https://img.kancloud.cn/b4/f3/b4f326a183af0c3ca131ef855ca2a415_1357x424.png) 類似于這種網站備案信息和版權信息，會顯示于整個網站全局，這個時候我們就可以使用ServletContext這種全局對象來進行設置。 ~~~ @WebServlet("/servletcontext/init") public class ServletContextInitServlet extends HttpServlet { private static final long serialVersionUID = 1L; public ServletContextInitServlet() { super(); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //獲取應用程序上下文對象，其實也就是應用程序對象 ServletContext sc = request.getServletContext(); //利用該對象的特性，設置作用范圍為全局的自定義屬性 sc.setAttribute("copyright", "Powered by EduSoho v8.6.4 ?2014-2020 課程存檔 \n課程內容版權均歸南通在渡教育咨詢有限公司所有蘇ICP備18015371號"); //sc.setAttribute("copyright","");如果設置了相同的屬性名，則新的屬性值會覆蓋舊的屬性值，其他設置request自定義屬性和session自定義屬性也是相同的道理 sc.setAttribute("title", "渡課IT教育"); response.getWriter().println("init success"); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { } } ~~~ ~~~ @WebServlet("/servletcontext/defualt") public class ServletContextDefaultServlet extends HttpServlet { private static final long serialVersionUID = 1L; public ServletContextDefaultServlet() { super(); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { ServletContext sc = request.getServletContext(); String copyright = (String)sc.getAttribute("copyright"); String title = (String)sc.getAttribute("title"); response.setContentType("text/html;charset=utf-8"); response.getWriter().println("<h1>" + title + "</h1>" + copyright); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { } } ~~~ ## Java Web三大作用域 * HttpServletRequest -請求對象 * HttpSession - 用戶會話對象 * ServletContext - web應用全局對象這三個對象的作用域，從上到下是依次遞增的。請求對象，它的生命周期最短，當瀏覽器發送請求到Tomcat，則請求對象就被創建，當servlet處理完成并返回響應到瀏覽器時，當前的請求對象就會被銷毀。用戶會話對象用于保存與瀏覽器窗口對應的數據，該對象是在用戶第一次向瀏覽器發送請求的時候被創建，默認情況下，這個對象如果在三十分鐘后沒有訪問就會被銷毀。注意一下，關閉瀏覽器該對象不會被銷毀，銷毀的是保存在瀏覽器cookie中的sessionId。就好像銀行卡與存在銀行中的錢一樣，丟失了銀行卡，但是銀行中的錢還在，只是取不出來這筆錢而已。全局對象在web應用啟動的時候就被創建了，只有在web應用程序關閉或重啟的時候才會被銷毀。有個注意點，為了程序維護的需要和資源避免浪費的情況，如果能用小作用域完成的任務就不用大作用域完成，所以request請求對象是以后使用的最多的對象 ## 中文亂碼中文亂碼的核心就是解析字符集不支持中文，所以解決中文亂碼的關鍵就是將默認字符集變成UTF-8，servlet中的請求與響應都需要設置為UTF-8。 ### Post請求中文亂碼 ~~~HTML <!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <title>Insert title here</title> </head> <body> <form action="/servlet_advanced/charset/process" method="post"> 姓名：<input name="ename"> 地址：<input name="address"> <input type="submit" value="提交"> </form> </body> </html> ~~~ ~~~ @WebServlet("/charset/process") public class CharsetServlet extends HttpServlet { private static final long serialVersionUID = 1L; public CharsetServlet() { super(); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //request.setCharacterEncoding方法用于將請求體中的字符集轉換為UTF-8，對于get請求，沒有請求體，所以該方法只對post請求生效。 request.setCharacterEncoding("UTF-8"); String ename = request.getParameter("ename"); String address = request.getParameter("address"); System.out.println(ename + ":" + address); //通過字符串構造器將字符串的解析字符集轉換為utf-8，但是不怎么方便，所以使用setCharacterEncoding方法 //String utf8Ename = new String(ename.getBytes("iso-8859-1") , "utf-8"); //String utf8Address = new String(address.getBytes("iso-8859-1") , "utf-8"); //System.out.println(utf8Ename + ":" + utf8Address); } } ~~~ ### Get請求與響應中文亂碼 ~~~ @WebServlet("/charset/process") public class CharsetServlet extends HttpServlet { private static final long serialVersionUID = 1L; public CharsetServlet() { super(); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //對于Tomcat8.x的版本，默認get請求發送中文就是UTF-8的格式，因此無需轉換 String ename = request.getParameter("ename"); String address = request.getParameter("address"); System.out.println(ename + ":" + address); response.setContentType("text/html;charset=utf-8"); response.getWriter().println(ename + ":" + address); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { } } ~~~ ## web.xml的常用配置在本章節中，我們將做到以下功能： * 修改web應用默認首頁 * Servlet通配符映射及初始化參數 * 設置404，500等狀態碼首頁 **修改web應用默認首頁** ~~~ <welcome-file-list>  <welcome-file>index.html</welcome-file> <welcome-file>default.html</welcome-file> </welcome-file-list> ~~~ **通配符映射，利用地址傳參（非get提交）** ~~~ public class PatternServlet extends HttpServlet{ @Override protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //查詢員工的基本信息 //獲取當前訪問的URL String url = request.getRequestURL().toString(); System.out.println(url); String id = url.substring(url.lastIndexOf("/") + 1); int eid = Integer.parseInt(id); response.setContentType("text/html;charset=utf-8"); PrintWriter out = response.getWriter(); out.println(id); if(eid == 1) { out.println("張三"); }else if(eid == 2) { out.println("李四"); }else { out.println("其他員工"); } } } ~~~ ~~~ <servlet> <servlet-name>patternServlet</servlet-name> <servlet-class>com.dodoke.servlet.pattern.PatternServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>patternServlet</servlet-name>  <url-pattern>/pattern/*</url-pattern> </servlet-mapping> ~~~ **設置全局參數** 在之前的學習中，我們在設置網站備案信息和版權信息時，是將內容寫死在程序中的，這其實對我們的程序來說不算友好，現在我們可以嘗試著將這些全局信息寫入到配置文件中。 ~~~ <context-param> <param-name>copyright</param-name> <param-value>Powered by EduSoho v8.6.4 ?2014-2020 課程存檔 \n課程內容版權均歸南通在渡教育咨詢有限公司所有蘇ICP備18015371號</param-value> </context-param> <context-param> <param-name>title</param-name> <param-value>渡課IT教育</param-value> </context-param> ~~~ ~~~ @WebServlet("/servletcontext/init") public class ServletContextInitServlet extends HttpServlet { private static final long serialVersionUID = 1L; public ServletContextInitServlet() { super(); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { ServletContext context = request.getServletContext(); //獲取ServletContext對象通過配置文件設置的初始化參數 String copyright = context.getInitParameter("copyright"); context.setAttribute("copyright", copyright); String title = context.getInitParameter("title"); context.setAttribute("title", title); response.getWriter().println("init success"); } } ~~~ **設置404，500等狀態碼首頁** ~~~  <error-page> <error-code>404</error-code> <location>/error/404.html</location> </error-page> <error-page> <error-code>500</error-code> <location>/error/500.jsp</location> </error-page> ~~~ ~~~ <!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <title>Insert title here</title> </head> <body> 資源不存在 </body> </html> ~~~ ~~~ <!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <title>Insert title here</title> </head> <body> 服務器內部錯誤，請聯系管理員 </body> </html> ~~~ ## JSP九大內置對象內置對象，又叫做隱含對象，不需要預先聲明就可以在腳本代碼和表達式中隨意使用 1\. 由JSP規范提供,不用編寫者實例化。? 2\. 通過Web容器實現和管理? 3\. 所有JSP頁面均可使用? 4\. 只有在腳本元素的表達式或代碼段中才可使用 ![](https://img.kancloud.cn/30/a3/30a360c3b59eb052cec2413058bf403a_781x522.png) ~~~ <%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8" %> <!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <title>Insert title here</title> </head> <body> <% String url = request.getRequestURL().toString(); // HttpServletRequest response.getWriter().println(url);//HttpServletResponse %> <% out.println("<br>ABCCC"); session.setAttribute("user", "張三"); out.println((String)session.getAttribute("user")); %> <% String cp = application.getInitParameter("copyright") ; //ServletContext out.println("<hr/>"); out.println(cp); //pageContext可以幫助我們快速獲取其他對象 pageContext.getRequest(); pageContext.getResponse(); pageContext.getSession(); pageContext.getServletContext(); %> </body> </html> ~~~ 利用exception對象顯示錯誤信息。 ~~~  <%@ page contentType="text/html;charset=utf-8" isErrorPage="true"%> <!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <title>Insert title here</title> </head> <body> 服務器內部錯誤，請聯系管理員 ,錯誤信息如下： <% String msg = exception.getMessage(); out.print("<br>" + exception.getClass().getSimpleName() + ":" + msg); %> </body> </html> ~~~ ## Java Web的打包與發布在編寫完成代碼后，就需要正式的進行程序的上線了，那么我們該如何進行程序的上線呢？ ![](https://img.kancloud.cn/cc/53/cc53624402c6babeaa11cf47fbadb729_890x413.png) ![](https://img.kancloud.cn/b6/07/b60718c050814901204124073071aea1_525x550.png) ![](https://img.kancloud.cn/fb/de/fbde58940fc7701af139ed19cbeee146_525x550.png) 直接將這樣的war包，保存到Tomcat的webapp目錄中，啟動Tomcat就可以了。注意： * 端口可以改為80，避免輸入端口號 * 項目路徑可以只保留斜杠，避免輸入項目路徑 * ![](https://img.kancloud.cn/21/96/21961c142ea3c3722fe4fd28da5b3809_1151x97.png)