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JavaWeb案例講解Servlet常用對(duì)象

 更新時(shí)間：2021年10月23日 09:37:02   作者：筆觸狂放  
Java Servlet 是運(yùn)行在 Web 服務(wù)器或應(yīng)用服務(wù)器上的程序，它是作為來(lái)自 Web 瀏覽器或其他 HTTP 客戶端的請(qǐng)求和 HTTP 服務(wù)器上的數(shù)據(jù)庫(kù)或應(yīng)用程序之間的中間層

概述

本次文章基于第三章的ServletConfig，ServletContext，HttpServletRequest，HttpServletResponse對(duì)象完成一個(gè)圖書訂閱系統(tǒng)的購(gòu)買圖書和查看圖書購(gòu)買記錄功能。

搭建項(xiàng)目主頁(yè)面

創(chuàng)建一個(gè)動(dòng)態(tài)網(wǎng)站項(xiàng)目，在src中新建包c(diǎn)om.book.servlet.

在包中，新建HomeServlet作為主頁(yè)。效果圖如下:

為了讓一訪問(wèn)項(xiàng)目根路徑地址就默認(rèn)進(jìn)入HomeServlet，這里需要將 HomeServlet的虛擬地址寫入web.xml文件中作為默認(rèn)的首頁(yè)地址。

<?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>Day07Jsp</display-name>
  <welcome-file-list>
    <welcome-file>HomeServlet</welcome-file>
  </welcome-file-list>
</web-app>

HomeServlet中要完成超鏈接的顯示，這里需要在該Servlet中定義兩個(gè)靜態(tài)數(shù)據(jù)，使用java注解的方式進(jìn)行定義，代碼如下：

package com.book.servlet;
 
import java.io.IOException;
import java.io.PrintWriter;
 
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebInitParam;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
/**
 * Servlet implementation class HomeServlet
 */
@WebServlet(urlPatterns = "/HomeServlet",
initParams = {
		@WebInitParam(name = "buy",value = "購(gòu)買圖書"),
		@WebInitParam(name = "selectOrder",value = "查看訂單")
})
public class HomeServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
	
    /**
     * @see HttpServlet#HttpServlet()
     */
    public HomeServlet() {
        super();
        // TODO Auto-generated constructor stub
    }
    
   
 
	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		
	}
 
	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}
 
}

然后在類中的空白處，重寫init方法，用于加載兩個(gè)靜態(tài)數(shù)據(jù)，因這兩個(gè)靜態(tài)數(shù)據(jù)需要在其他方法中被使用，因此定義成全局變量。代碼如下:

再重寫init方法，并通過(guò)兩個(gè)靜態(tài)數(shù)據(jù)，存儲(chǔ)至全局變量。

@Override
    public void init(ServletConfig config) throws ServletException {
    	buy=config.getInitParameter("buy");
    	selectOrder=config.getInitParameter("selectOrder");
    	
    }

因?yàn)g覽器訪問(wèn)服務(wù)器默認(rèn)使用Get請(qǐng)求，這里我們?cè)赿iGet方法中編寫兩個(gè)超鏈接發(fā)送給瀏覽器上顯示:

/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		//當(dāng)瀏覽器訪問(wèn)該Servlet的時(shí)候,servlet將靜態(tài)數(shù)據(jù)發(fā)給瀏覽器顯示
		response.setContentType("text/html");
		response.setCharacterEncoding("UTF-8");
		PrintWriter pw=response.getWriter();
		pw.append("<div align='center'>");
		pw.append("<a href=''>"+buy+"</a>&nbsp;");
		pw.append("<a href=''>"+selectOrder+"</a>&nbsp;");
		pw.append("</div>");
	}

這里運(yùn)行以后，可看到以上的效果圖所示的頁(yè)面。

定義圖書實(shí)體類

因?yàn)槲覀冃枰故径啾緢D書供用戶進(jìn)行購(gòu)買，而每一本圖書都需要包含，書名，作者，單價(jià)，出版社，購(gòu)買時(shí)間等等數(shù)據(jù)，因此為采用定義實(shí)體類的方式用于分別存儲(chǔ)每一本書的這些數(shù)據(jù)信息。

接著我們?cè)趕rc文件夾中定義包c(diǎn)om.book.entity,用于存儲(chǔ)創(chuàng)建的所有實(shí)體類，點(diǎn)右鍵新建class類，類名為Book,在Book中定義五個(gè)全局變量用于存儲(chǔ)以上五個(gè)信息，并對(duì)其進(jìn)行數(shù)據(jù)封裝，代碼如下:

package com.book.entity;
/**
 * 圖書的實(shí)體類
 * @author teacher
 *	2021/10/14
 */
public class Book {
	//java類的封裝
	private String bookName;//書名
	private String author;//作者
	private String price;//單價(jià)
	private String address;//出版社
	private String buyTime;//購(gòu)買時(shí)間
	public String getBookName() {
		return bookName;
	}
	public void setBookName(String bookName) {
		this.bookName = bookName;
	}
	public String getAuthor() {
		return author;
	}
	public void setAuthor(String author) {
		this.author = author;
	}
	public String getPrice() {
		return price;
	}
	public void setPrice(String price) {
		this.price = price;
	}
	public String getAddress() {
		return address;
	}
	public void setAddress(String address) {
		this.address = address;
	}
	public String getBuyTime() {
		return buyTime;
	}
	public void setBuyTime(String buyTime) {
		this.buyTime = buyTime;
	}
	
	//生成所有變量的get和set方法
	//構(gòu)造方法的作用:
	//1.用于創(chuàng)建這個(gè)類的對(duì)象
	//2.用于快速給變量進(jìn)行賦值
	//生成無(wú)參構(gòu)造方法
	public Book() {
		// TODO Auto-generated constructor stub
	}
	//生成有參構(gòu)造方法
	public Book(String bookName, String author, String price, String address, String buyTime) {
		super();
		this.bookName = bookName;
		this.author = author;
		this.price = price;
		this.address = address;
		this.buyTime = buyTime;
	}
	@Override
	public String toString() {
		return "Book [bookName=" + bookName + ", author=" + author + ", price=" + price + ", address=" + address
				+ ", buyTime=" + buyTime + "]";
	}
	
	//生成toString方法,為了在做功能的時(shí)候,
	//查看檢查這個(gè)對(duì)象中是否有數(shù)據(jù)
	
	
}

定義臨時(shí)圖書庫(kù)工具類

這里我們使用List集合臨時(shí)將多本圖書信息存儲(chǔ)起來(lái)，用于顯示在頁(yè)面上供用戶進(jìn)行購(gòu)買，這里我們?cè)趕rc文件夾中新建包c(diǎn)om.book.util,在包中新建類BookDBUtil，在類中定義方法，創(chuàng)建多本圖書信息，并將多本圖書存儲(chǔ)至List集合，代碼如下:

package com.book.util;
/**
 * 圖書信息的工具類
 * @author teahcer
 *	2021/10/14
 *用于臨時(shí)存儲(chǔ)一些圖書信息
 */
 
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
 
import com.book.entity.Book;
 
public class BookDataUtil {
 
	//定義方法,用于存儲(chǔ)多本書的信息
	public List<Book> getBooks(){
		Book book1=new Book("Java編程思想", "馬云", "120.0元", "人民郵電出版社", "");
		Book book2=new Book("MySQL數(shù)據(jù)庫(kù)教程", "任正非", "89.0元", "清華大學(xué)出版社", "");
		Book book3=new Book("Java瘋狂講義", "馬化騰", "108.0元", "電子工業(yè)出版社", "");
		Book book4=new Book("Python爬蟲技術(shù)", "李彥宏", "66.0元", "新華出版社", "");
		Book book5=new Book("C語(yǔ)言從入門到放棄", "李云龍", "56.0元", "江西出版社", "");
		//創(chuàng)建List用于存儲(chǔ)以上五本書
		List<Book> oBooks=new ArrayList<Book>();
		oBooks.add(book1);
		oBooks.add(book2);
		oBooks.add(book3);
		oBooks.add(book4);
		oBooks.add(book5);
		return oBooks;
	}
	
	//獲得當(dāng)前實(shí)時(shí)時(shí)間
	public static String getNowTime() {
		//獲得的現(xiàn)在實(shí)時(shí)時(shí)間是毫秒計(jì)算的
		Date date=new Date();
		//簡(jiǎn)單日期格式類  2021年10月20 日  13:55:30
		SimpleDateFormat sdf=
				new SimpleDateFormat("yyyy年MM月dd日  HH:mm:ss");
		//按照設(shè)定的格式進(jìn)行格式化
		String time=sdf.format(date);
		return time;
	}
}

創(chuàng)建圖書信息列表頁(yè)面供用戶購(gòu)買圖書

即多本圖書已準(zhǔn)備好，這里需要?jiǎng)?chuàng)建Servlet完成圖書信息列表頁(yè)面，類名為ShowBookInfoServlet，這里我們需要先從工具類中獲得所有圖書信息，并將該圖書已表格的形式發(fā)送給瀏覽器上顯示出來(lái)，其代碼如下:

package com.book.servlet;
 
import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;
 
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
import com.book.entity.Book;
import com.book.util.BookDataUtil;
 
/**
 * Servlet implementation class ShowBookInfoServlet
 */
@WebServlet("/ShowBookInfoServlet")
public class ShowBookInfoServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public ShowBookInfoServlet() {
        super();
        // TODO Auto-generated constructor stub
    }
 
	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		//獲得所有圖書信息
		BookDataUtil util=new BookDataUtil();
		List<Book> oBooks=util.getBooks();
		response.setContentType("text/html");
		response.setCharacterEncoding("UTF-8");
		PrintWriter pw=response.getWriter();
		pw.append("<div align='center'>");
		pw.append("<table border='1' style='width:800px;text-align:center;'>");
		//寫標(biāo)題
		pw.append("<tr>");
		pw.append("<td>書名</td>");
		pw.append("<td>作者</td>");
		pw.append("<td>單價(jià)</td>");
		pw.append("<td>出版社</td>");
		pw.append("<td>操作</td>");
		pw.append("</tr>");
		for (int i=0;i<oBooks.size();i++) {
			pw.append("<tr>");
			pw.append("<td>"+oBooks.get(i).getBookName()+"</td>");
			pw.append("<td>"+oBooks.get(i).getAuthor()+"</td>");
			pw.append("<td>"+oBooks.get(i).getPrice()+"</td>");
			pw.append("<td>"+oBooks.get(i).getAddress()+"</td>");
			pw.append("<td><a href='BuyBookServlet?index="+i+"'><input type='button' "
					+ "style='background-color:green;' "
					+ "value='購(gòu)買'></a></td>");
			pw.append("</tr>");
		}
		pw.append("</table>");
		pw.append("</div>");
	}
 
	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}
 
}

并在HomeServlet的首頁(yè)的購(gòu)買圖書的超鏈接上添加圖書信息列表頁(yè)面的虛擬地址。

其運(yùn)行后，點(diǎn)擊購(gòu)買圖書即課跳轉(zhuǎn)至圖書信息列表頁(yè)面，效果如下:

完成存儲(chǔ)用戶購(gòu)買的圖書記錄信息

當(dāng)用戶點(diǎn)擊任意一本圖書進(jìn)行購(gòu)買的時(shí)候，這里我們采取發(fā)送給圖書的下標(biāo)給服務(wù)器的方式，能盡快的獲取用戶要購(gòu)買的圖書信息，這里新建一個(gè)Servlet類，類名為BuyBookServlet，用于接收用戶將要購(gòu)買的圖書的下標(biāo)，并查找出該圖書，并通過(guò)方法獲得當(dāng)前購(gòu)買圖書的下單的實(shí)時(shí)時(shí)間，存儲(chǔ)至該購(gòu)買的圖書中，然后將該圖書存儲(chǔ)至List集合，因?yàn)橛脩艨赡軙?huì)購(gòu)買多本圖書，最后將所喲購(gòu)買的圖書記錄信息存儲(chǔ)至ServletContext對(duì)象中。

package com.book.servlet;
 
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
 
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
import com.book.entity.Book;
import com.book.util.BookDataUtil;
 
/**
 * Servlet implementation class BuyBookServlet
 */
@WebServlet("/BuyBookServlet")
public class BuyBookServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public BuyBookServlet() {
        super();
        // TODO Auto-generated constructor stub
    }
 
	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		//獲得用于點(diǎn)擊購(gòu)買按鈕發(fā)送過(guò)來(lái)的請(qǐng)求
		//獲得瀏覽器發(fā)送過(guò)來(lái)的圖書的下標(biāo)
		String index=request.getParameter("index");
		//將接收的字符串類型轉(zhuǎn)換成int類型
		int i=Integer.parseInt(index);
		//根據(jù)用戶發(fā)送過(guò)來(lái)的下標(biāo)，去查找用戶將要購(gòu)買的書籍
		List<Book> oBooks=new BookDataUtil().getBooks();
		Book book=oBooks.get(i);
		//當(dāng)用戶購(gòu)買圖書的時(shí)候，需要獲得當(dāng)前實(shí)時(shí)時(shí)間
		book.setBuyTime(BookDataUtil.getNowTime());
		//獲得ServletContext對(duì)象
		ServletContext sc=getServletContext();
		//判斷ServletContext是否存在List集合
		Object object=sc.getAttribute("orders");
		List<Book> oList=null;
		if (object==null) {
			//說(shuō)明以前從來(lái)沒(méi)有購(gòu)買過(guò)書
			oList=new ArrayList<Book>();
			oList.add(book);
		}else {
			//以前有購(gòu)買書，只需要拿到List集合繼續(xù)添加購(gòu)買記錄即可
			//不需要重新創(chuàng)建List集合
			oList=(List<Book>) object;
			oList.add(book);
		}
		//保存完購(gòu)買記錄，之后存儲(chǔ)至ServletContext對(duì)象
		sc.setAttribute("orders", oList);
		//購(gòu)買成功之后，跳轉(zhuǎn)至提示頁(yè)面
		//使用請(qǐng)求轉(zhuǎn)發(fā)跳轉(zhuǎn)，因?yàn)檎?qǐng)求轉(zhuǎn)發(fā)可以攜帶數(shù)據(jù)跳轉(zhuǎn)頁(yè)面
		request.setAttribute("book", book);
		request.getRequestDispatcher("AlertServlet")
					.forward(request, response);
	}
 
	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}
 
}

創(chuàng)建提示信息頁(yè)面

在圖書記錄信息存儲(chǔ)后，需要提示用戶購(gòu)買的圖書下單完成，是否需要繼續(xù)購(gòu)買的提示，這里新建一個(gè)Servlet類，類名為：AlertServlet

package com.book.servlet;
 
import java.io.IOException;
import java.io.PrintWriter;
 
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
import com.book.entity.Book;
 
/**
 * Servlet implementation class AlertServlet
 */
@WebServlet("/AlertServlet")
public class AlertServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public AlertServlet() {
        super();
        // TODO Auto-generated constructor stub
    }
 
	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		Book book=(Book) request.getAttribute("book");
		String info="您的《"+book.getBookName()+"》購(gòu)買成功，"
				+ "如果繼續(xù)購(gòu)買請(qǐng)<a href='ShowBookInfoServlet'>點(diǎn)擊這里</a>，"
				+ "或者5秒之后自動(dòng)跳回首頁(yè)";
		response.setHeader("refresh", "5;url=HomeServlet");
		response.setContentType("text/html");
		response.setCharacterEncoding("UTF-8");
		PrintWriter pw=response.getWriter();
		pw.print(info);
	}
 
	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}
 
}

效果如下:

完成查看圖書記錄信息列表頁(yè)面

用戶在購(gòu)買完圖書信息之后，需要查看當(dāng)前購(gòu)買的所有圖書的記錄信息，這里我們新建Servlet類，類名為:SelectOrderServlet,從ServletContext類中獲得所有的圖書記錄信息，展示在表格上，并需要判斷是否有購(gòu)買圖書記錄信息，其代碼如下:

package com.book.servlet;
 
import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;
 
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
import com.book.entity.Book;
 
/**
 * Servlet implementation class SelectOrderServlet
 */
@WebServlet("/SelectOrderServlet")
public class SelectOrderServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public SelectOrderServlet() {
        super();
        // TODO Auto-generated constructor stub
    }
 
	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		//因?yàn)橛脩糍?gòu)買的圖書信息被存儲(chǔ)在ServletContext對(duì)象中
		//要展示用戶的購(gòu)買記錄，需要先獲得ServletContext對(duì)象
		ServletContext sc=getServletContext();
		//從該對(duì)象中獲得存儲(chǔ)圖書記錄的List集合
		Object object=sc.getAttribute("orders");
		response.setContentType("text/html");
		response.setCharacterEncoding("UTF-8");
		PrintWriter pw=response.getWriter();
		List<Book> oBooks=null;
		if (object!=null) {
			oBooks=(List<Book>) object;
			pw.append("<div align='center'>");
			pw.append("<table border='1' style='width:800px;text-align:center;'>");
			//寫標(biāo)題
			pw.append("<tr>");
			pw.append("<td>書名</td>");
			pw.append("<td>作者</td>");
			pw.append("<td>單價(jià)</td>");
			pw.append("<td>出版社</td>");
			pw.append("<td>購(gòu)買時(shí)間</td>");
			pw.append("</tr>");
			for (int i=0;i<oBooks.size();i++) {
				pw.append("<tr>");
				pw.append("<td>"+oBooks.get(i).getBookName()+"</td>");
				pw.append("<td>"+oBooks.get(i).getAuthor()+"</td>");
				pw.append("<td>"+oBooks.get(i).getPrice()+"</td>");
				pw.append("<td>"+oBooks.get(i).getAddress()+"</td>");
				pw.append("<td>"+oBooks.get(i).getBuyTime()+"</td>");
				pw.append("</tr>");
			}
			pw.append("</table>");
			pw.append("</div>");
		}else {
			pw.print("當(dāng)前還沒(méi)有購(gòu)買圖書的記錄，請(qǐng)先購(gòu)買再查看?。?！");
		}
		
	}
	
 
	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}
 
}

并把給Servlet的虛擬地址添加至主頁(yè)面的第二個(gè)超鏈接上，

其運(yùn)行的效果如下:

初學(xué)者可根據(jù)代碼完成以上功能，可自行擴(kuò)展修改圖書信息以及刪除購(gòu)買記錄的功能等等。

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