javaweb入門（四）-----Servlet與JSP進階

HTTP請求

HTTP請求的結構

HTTP請求包含三部分：請求行、請求頭、請求體。

HTTP響應的結構

HTTP常見狀態碼

ContentType的作用

ContentType

示例：

/**
 * Servlet implementation class ContentTypeServlet
 */
@WebServlet("/ct")
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 res) throws ServletException, IOException {
		// TODO Auto-generated method stub
		String output = "<h1><a href='http://www.baidu.com'>百度</a></h1>";
		res.setContentType("text/html;charset=utf-8");
		res.getWriter().println(output);
	}
}

請求轉發與重定向

• 多個Servlet（JSP）之間跳轉有兩種方式：
  request.getRequestDispatcher().forward() 請求轉發： 請求轉發是服務器跳轉，只會產生一次請求
  response.sendRedirect() 響應重定向：重定向是瀏覽器端跳轉會產生2次請求。

protected void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
		// TODO Auto-generated method stub
		req.setAttribute("username", "admin");
		//實現了請求轉發的功能
//		req.getRequestDispatcher("/direct/index").forward(req,res);
		//響應重定向需要增加contextPath
		res.sendRedirect("/myJsp/direct/index");
	}

設置請求自定義屬性

請求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)

瀏覽器Cookie

• Cookie是瀏覽器保存在本地的文本內容
• Cookie常用於保存登錄狀態、用戶資料等小文本
• Cookie具有時效性， Cookie內容會伴隨請求發送給Tomcat
  設置cookie

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		Cookie coo = new Cookie("name","張三");
		coo.setMaxAge(60*60*24);
		response.addCookie(coo);
		response.getWriter().println("login ok ");
	}

獲取

protected void doGet(HttpServletRequest req, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		Cookie[] cs = req.getCookies();
		if(cs==null) {
			response.getWriter().println("user not login");
			return;
		}
		String user = null;
		for(Cookie c : cs) {
			System.out.println(c.getName() + ":" + c.getValue());
			if(c.getName().equals("name")) {
				user = c.getValue();
				break;
			}
		}
		
		if(user == null) {
			response.getWriter().println("user not login");
		}else {
			response.getWriter().println("user:" + user);
		}

Session 用戶會話

• Session 用於保存於“瀏覽器窗口”對應的數據
• Session 的數據存在服務器的內存中，具有時效性
• Session 通過瀏覽器Cookie的SessionId值提取用戶數據

Session 常用方法

• request.getSession() --獲取 Session對象
• getAttribute() setAttribute() removeAttribute() – 獲取 設置 刪除Session屬性
• setMaxInactiveInterval — 設置Session超時時間

protected void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
		// TODO Auto-generated method stub
		HttpSession session = req.getSession();
		String sessionId = session.getId();
		System.out.print(sessionId);
		session.setAttribute("name", "lucy");
		req.getRequestDispatcher("/session/index").forward(req, res);
	}

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		HttpSession session = request.getSession();
		String sessionId = session.getId();
		String name = (String)session.getAttribute("name");
		response.setContentType("text/html;charset=utf-8");
		response.getWriter().println("這是首頁，當前用戶爲:" + name);
	}

ServletContext

ServletContext（Servlet上下文對象），是web應用全局對象。
一個web應用只會創建一個ServletContext對象。
ServletContext隨着web應用啓動而自動創建。

Java Web三大作用域對象

HttpServletRequest ---- 請求對象
HttpSession ----- 用戶會話對象
ServletContext ---- web應用全局對象。

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		ServletContext context = request.getServletContext();
		String copyright = context.getInitParameter("copyright");
		context.setAttribute("copyright", copyright);
		String title = context.getInitParameter("title");
		context.setAttribute("title", title);
		response.getWriter().println("init success");
	}

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		ServletContext context = (ServletContext)request.getServletContext();
		String copyright = (String)context.getAttribute("copyright");
		String title = (String)context.getAttribute("title");
		response.setContentType("text/html;charset=utf-8");
		response.getWriter().println("<h1>"+title+"</h1>"+copyright);
	}

web應用的中文亂碼問題

Tomcat默認使用字符集ISO-8859-1，屬於西歐字符集。
解決亂碼的核心思路是將ISO-8859-1轉換爲UTF-8
Servlet中請求與相應都要設置值utf-8字符集。

web.xml常用配置

• 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等狀態碼默認頁面

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
  <display-name>servlet_advanced</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
  	<servlet-name>patternServlet</servlet-name>
  	<servlet-class>pattern.PatternServlet</servlet-class>
  </servlet>
  <servlet-mapping>
  	<servlet-name>patternServlet</servlet-name>
  	<url-pattern>/pattern/*</url-pattern>
  </servlet-mapping>
  <context-param>
  	<param-name>copyright</param-name>
  	<param-value>© 12003892號-22</param-value>
  </context-param>
  <context-param>
  	<param-name>title</param-name>
  	<param-value>淘寶</param-value>
  </context-param>
  <!-- 指定錯誤頁面 -->
  <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>
</web-app>

JSP九大內置對象

Tomcat常用配置

• 修改web應用端口號
• 修改ContextPath上下文路徑
• 設置應用自動重載
  server.xml文件修改配置。

JAVA WEB打包與發佈

• Java Web應用採用war包進行發佈
• 發佈路徑爲: {TOMCAT_HOME}/webapps
• Eclipse支持war包導出
  項目上右鍵，Export ---->WAR file