JavaWeb案例讲解Servlet常用对象

JavaWeb案例讲解Servlet常用对象

概述

本次文章基于第三章的ServletConfig，ServletContext，HttpServletRequest，HttpServletResponse对象完成一个图书订阅系统的购买图书和查看图书购买记录功能。

搭建项目主页面

创建一个动态网站项目，在src中新建包com.book.servlet.

在包中，新建HomeServlet作为主页。效果图如下:

为了让一访问项目根路径地址就默认进入HomeServlet，这里需要将 HomeServlet的虚拟地址写入web.xml文件中作为默认的首页地址。

Day07jsp

HomeServlet

HomeServlet中要完成超链接的显示，这里需要在该Servlet中定义两个静态数据，使用java注解的方式进行定义，代码如下：

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 = "购买图书"),

@WebInitParam(name = "selectOrder",value = "查看订单")

})

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);

}

}

然后在类中的空白处，重写init方法，用于加载两个静态数据，因这两个静态数据需要在其他方法中被使用，因此定义成全局变量。代码如下:

再重写init方法，并通过两个静态数据，存储至全局变量。

@Override

public void init(ServletConfig config) throws ServletException {

buy=config.getInitParameter("buy");

selectOrder=config.getInitParameter("selectOrder");

}

因浏览器访问服务器默认使用Get请求，这里我们在diGet方法中编写两个超链接发送给浏览器上显示:

/**

* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)

*/

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

//当浏览器访问该Servlet的时候,servlet将静态数据发给浏览器显示

response.setContentType("text/html");

response.setCharacterEncoding("UTF-8");

PrintWriter pw=response.getWriter();

pw.append("

pw.append(""+buy+" ");

pw.append(""+selectOrder+" ");

pw.append("

}

这里运行以后，可看到以上的效果图所示的页面。

定义图书实体类

接着我们在src文件夹中定义包com.book.entity,用于存储创建的所有实体类，点右键新建class类，类名为Book,在Book中定义五个全局变量用于存储以上五个信息，并对其进行数据封装，代码如下:

package com.book.entity;

/**

* 图书的实体类

* @author teacher

* 2021/10/14

*/

public class Book {

//javaVTBkTyGI类的封装

private String bookName;//书名

private String price;//单价

private String address;//出版社

private String buyTime;//购买时间

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;

}

//生成所有变量的get和set方法

//构造方法的作用:

//1.用于创建这个类的对象

//2.用于快速给变量进行赋值

//生成无参构造方法

public Book() {

// TODO Auto-generated constructor stub

}

//生成有参构造方法

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,为了在做功能的时候,

//查看检查这个对象中是否有数据

}

定义临时图书库工具类

这里我们使用List集合临时将多本图书信息存储起来，用于显示在页面上供用户进行购买，这里我们在src文件夹中新建包com.book.util,在包中新建类BookDBUtil，在类中定义方法，创建多本图书信息，并将多本图书存储至List集合，代码如下:

package com.book.util;

/**

* 图书信息的工具类

* @author teahcer

* 2021/10/14

*用于临时存储一些图书信息

*/

import java.text.SimpleDateFormat;

import java.util.ArrayList;

import java.util.Date;

import java.util.List;

import com.book.entity.Book;

public class BookDataUtil {

//定义方法,用于存储多本书的信息

public List getBooks(){

Book book1=new Book("Java编程思想", "马云", "120.0元", "人民邮电出版社", "");

Book book2=new Book("mysql数据库教程", "任正非", "89.0元", "清华大学出版社", "");

Book book3=new Book("Java疯狂讲义", "马化腾", "108.0元", "电子工业出版社", "");

Book book4=new Book("python爬虫技术", "李彦宏", "66.0元", "新华出版社", "");

Book book5=new Book("C语言从入门到放弃", "李云龙", "56.0元", "江西出版社", "");

//创建List用于存储以上五本书

List oBooks=new ArrayList();

oBooks.add(book1);

oBooks.add(book2);

oBooks.add(book3);

oBooks.add(book4);

oBooks.add(book5);

return oBooks;

}

//获得当前实时时间

public static String getNowTime() {

//获得的现在实时时间是毫秒计算的

Date date=new Date();

//简单日期格式类 2021年10月20 日 13:55:30

SimpleDateFormat sdf=

new SimpleDateFormat("yyyy年MM月dd日 HH:mm:ss");

//按照设定的格式进行格式化

String time=sdf.format(date);

return time;

}

}

创建图书信息列表页面供用户购买图书

即多本图书已准备好，这里需要创建Servlet完成图书信息列表页面，类名为ShowBookInfoServlet，这里我们需要先从工具类中获得所有图书信息，并将该图书已表格的形式发送给浏览器上显示出来，其代码如下:

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 {

//获得所有图书信息

BookDataUtil util=new BookDataUtil();

List oBooks=util.getBooks();

response.setContentType("text/html");

response.setCharacterEncoding("UTF-8");

PrintWriter pw=response.getWriter();

pw.append("

pw.append("

//写标题

pw.append("

pw.append("

pw.append("

pw.append("

pw.append("

pw.append("

pw.append("

for (int i=0;i

pw.append("

");

pw.append("

"+oBooks.get(i).getBookName()+"");

pw.append("

"+oBooks.get(i).getAuthor()+"");

pw.append("

"+oBooks.get(i).getPrice()+"");

pw.append("

"+oBooks.get(i).getAddress()+"");

pw.append("

+ "style='background-color:green;' "

+ "value='购买'>

");

pw.append("

");

pw.append("

pw.append("

pw.append("

pw.append("

pw.append("

pw.append("

+ "style='background-color:green;' "

+ "value='购买'>

pw.append("

}

pw.append("

pw.append("

}

/**

* @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的首页的购买图书的超链接上添加图书信息列表页面的虚拟地址。

其运行后，点击购买图书即课跳转至图书信息列表页面，效果如下:

完成存储用户购买的图书记录信息

当用户点击任意一本图书进行购买的时候，这里我们采取发送给图书的下标给服务器的方式，能尽快的获取用户要购买的图书信息，这里新建一个Servlet类，类名为BuyBookServlet，用于接收用户将要购买的图书的下标，并查找出该图书，并通过方法获得当前购买图书的下单的实时时间，存储至该购买的图书中，然后将该图书存储至List集合，因为用户可能会购买多本图书，最后将所哟购买的图书记录信息存储至ServletContext对象中。

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 {

//获得用于点击购买按钮发送过来的请求

//获得浏览器发送过来的图书的下标

String index=request.getParameter("index");

//将接收的字符串类型转换成int类型

int i=Integer.parseInt(index);

//根据用户发送过来的下标，去查找用户将要购买的书籍

List oBooks=new BookDataUtil().getBooks();

Book book=oBooks.get(i);

//当用户购买图书的时候，需要获得当前实时时间

book.setBuyTime(BookDataUtil.getNowTime());

//获得ServletContext对象

ServletContext sc=getServletContext();

//判断ServletContext是否存在List集合

Object object=sc.getAttribute("orders");

List oList=null;

if (object==null) {

//说明以前从来没有购买过书

oList=new ArrayList();

oList.add(book);

}else {

//以前有购买书，只需要拿到List集合继续添加购买记录即可

//不需要重新创建List集合

oList=(List) object;

oList.add(book);

}

//保存完购买记录，之后存储至ServletContext对象

sc.setAttribute("orders", oList);

//购买成功之后，跳转至提示页面

//使用请求转发跳转，因为请求转发可以携带数据跳转页面

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);

}

}

创建提示信息页面

在图书记录信息存储后，需要提示用户购买的图书下单完成，是否需要继续购买的提示，这里新建一个Servlet类，类名为：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()+"》购买成功，"

+ "如果继续购买请点击这里，"

+ "或者5秒之后自动跳回首页";

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:

完成查看图书记录信息列表页面

用户在购买完图书信息之后，需要查看当前购买的所有图书的记录信息，这里我们新建Servlet类，类名为:SelectOrderServlet,从ServletContext类中获得所有的图书记录信息，展示在表格上，并需要判断是否有购买图书记录信息，其代码如下:

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 {

//因为用户购买的图书信息被存储在ServletContext对象中

//要展示用户的购买记录，需要先获得ServletContext对象

ServletContext sc=getServletContext();

//从该对象中获得存储图书记录的List集合

Object object=sc.getAttribute("orders");

response.setContentType("text/html");

response.setCharacterEncoding("UTF-8");

PrintWriter pw=response.getWriter();

if (object!=null) {

oBooks=(List) object;

pw.append("

pw.append("

//写标题

pw.append("

pw.append("

pw.append("

pw.append("

pw.append("

pw.append("

pw.append("

for (int i=0;i

pw.append("

");

pw.append("

"+oBooks.get(i).getBookName()+"");

pw.append("

"+oBooks.get(i).getAuthor()+"");

pw.append("

"+oBooks.get(i).getPrice()+"");

pw.append("

"+oBooks.get(i).getAddress()+"");

pw.append("

"+oBooks.get(i).getBuyTime()+"");

pw.append("

");

pw.append("

pw.append("

pw.append("

pw.append("

pw.append("

pw.append("

pw.append("

}

pw.append("

pw.append("

}else {

pw.print("当前还没有购买图书的记录，请先购买再查看！！！");

}

}

/**

* @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);

}

}

并把给Servlet的虚拟地址添加至主页面的第二个超链接上，

其运行的效果如下:

初学者可根据代码完成以上功能，可自行扩展修改图书信息以及删除购买记录的功能等等。

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