JSP Java Servlet

2022-04-21
java java server pages

Java Servlet 即“服务器连接器”，主要用于创建Web应用，可在交互式地浏览和生成数据（动态Web内容）。当用户请求一个JSP页面的Web服务器，Servlet会自动生成一个对应的Java对文件。通过编译该Java文件用编译得到的字节码文件在服务器端创建一个Servlet对象。但在项目的实际需求之中，Web服应用需要Servlet对象有特定的功能，需要编写和创建Servlet对象和类就是本章重点介绍的一部分。

部署 Servlet

ID	DA
protected void doGet(HttpServletRequest request, HttpServletResponse response)	请求指定资源
protected void doPost(HttpServletRequest request, HttpServletResponse response)	向指定的资源提交要被处理的数据

创建一个Servlet类

Eclipse Web

package demofile;

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;

/**
 * Servlet implementation class NewFile
 */
@WebServlet("/NewFile")
public class NewFile extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public NewFile() {
        super();
        // TODO Auto-generated constructor stub
    }

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		response.getWriter().append("Served at: ").append(request.getContextPath());
		
		// 设置响应的内容类型
		response.setContentType("text/html;charset=utf-8");
		PrintWriter out = response.getWriter();
		out.println("<br>");
		out.println("Hello,world!");
	}

	/**
	 * @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);
	}

}

需要注意的事情是，Servlet可使用Eclipse Web 内自带的Servlet类型文件进行直接的创建，Servlet类必须要有一个包名，不然的话不是一个完整的Servlet类文件。在生成Servlet的同时，Eclipse会自动创建和部署有关的xml文件信息，通常该文件名称为web.xml。

@WebServlet

@WebServlet用于将一个类声明为Servlet对象，该注解将会在开始运行服务器时将部署时被Web容器根据Servlet对象进行处理.@WebServlet (name = "newfile", urlPatterns = {"newfile"}) 有兴趣的读者可自行进行了解或学习。

Servlet 生命周期

一个Servlet生命周期主要分为三个过程，分别为：初始化对象（int）、方法响应请求(service)、对象消亡(destroy)，也就是说当Servlet对象第一次被请求加载的时候会创建一个Servlet对象，主要调用int()方法进行初始化。Service()方法响应请求，创建的Servlet对象之后调用service()方法响应客户端进行请求。当服务器进行关闭时，Servlet对象会调用destroy()方法来使得对象销毁。

三个周期输出

package demofile;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class NewFile
 */
@WebServlet("/NewFile")
public class NewFile extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public NewFile() {
        super();
        // TODO Auto-generated constructor stub
    }
    	@Override
    public void init() throws ServletException {
    			System.out.println("初始化时输出");
    }

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
    	@Override
    protected void service(HttpServletRequest arg0, HttpServletResponse arg1) throws ServletException, IOException {
    			System.out.println("开启服务时输出");
    }
    @Override
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	@Override
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}
	@Override
	public void destroys() {
		System.out.println("结束时输出");
	}
}

JSP 调用Servlet

NewFile.jsp

<%@ 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>
	<form action="loginServlet" method="post">
	<%-- User = user \ Pass = pass 
				submit up \ reset set--%>
	<table>
			<tr>
				<td>User:</td>
				<td><input type="text" name="user"/></td>
				</tr>
			<tr>
				<td>pass:</td>	
				<td><input type="text" name="pass"/></td>
			</tr>
				<tr>
					<td><input type="submit" value="up"/></td>
					<td><input type="reset" value="set"></td>
					</tr>
		</table>
	</form>
</body>
</html>

loginServlet.java

package demofile;

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;

/**
 * Servlet implementation class loginServlet
 */
@WebServlet("/loginServlet")
public class loginServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public loginServlet() {
        super();
        // TODO Auto-generated constructor stub
    }


   protected void service (HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		response.setContentType("text/html;charset=UTF-8");
    		PrintWriter out = response.getWriter();
    		/*
    		 * Name
    		 * User
    		 */
    		String name = request.getParameter("user");
    		String password = request.getParameter("pass");
    		out.println("<html><body>");
    		
    		if (name == null || name.length() ==0) {
    				out.println("user null");
    		} else if(password == null || name.length() == 0) {
    				out.println("pass null");
    		} else if(name.length() > 0 && password.length() >0) {
    			if(name.equals("sun") && password.equals("kun")) {
    				out.println("ok");
    			} else {
    				out.println("no");
    			}
    		}
    		out.println("</body></html>");
    }
	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		response.getWriter().append("Served at: ").append(request.getContextPath());
	}

	/**
	 * @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);
	}

}

ID	DA
getParameter	获取input输出数据

Servlet MVC

MVC即“Model、View、Controller”的缩写，分别代表Web应用程序的三种职责，即：

ID	DA	FA
模型	用于存储数据以及处理用户请求的业务能力	一个或多个JavaBean对象、用于存储数据（实体模型）和处理业务逻辑
页面	向控制器提交数据，显示模型中的数据	一个或多个Jsp页面，向Servlet提交数据和为模型提供数据显示（JSP主要使用HTML来标记JavaBean来显示数据）
Servlet	根据页面提出的请求来判断将请求和数据交给那个模型中处理，处理后的那个页面更新显示	一个或多个Servlet对象，根据页面提交的请求进行控制。（即将请求转发给处理业务逻辑的JavaBean，并将处理结果存放在JavaBean中，市输出给视图显示）

JSP、Servlet、JavaBean实现MVC

通过使用JSP、Servlet、JavaBean来实现i个简单的MVC用户登录验证程序，其中包括MVC模型、页面、Servlet：

ID	DA	FA
User	用于创建模型，存储用户信息	JAVA
UserCheck	判断用户名和密码是否正确
LoginCheck	用于完成请求控制

loginCheak.jsp	用于编写登入界面	JSP
loginOk.jsp	登录成功页面

User.java

package demofile;
 
public class User {
 
	private String name;
	private String password;
	public String getName() {
		return name;
	}
	public void setName(String name){
		this.name = name;
	}
	
	public  String getPassword() {
		return password;
	}
	public  void setPassword(String password) {
		this.password = password;
	}
}

UserCheck (Service)

package service;
 
import demofile.User;
 
public class UserCheck {
	public  boolean validate(User user) {
		if(user!=null&&user.getName().equals("Sun")) {
             if(user.getPassword().equals("kun"))return true;
             else return false;
	}
     return false;
	}
}

LoginCheck (Servlet)

package servlet;
 
import java.io.IOException;
 
import javax.servlet.RequestDispatcher;
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 service.UserCheck;
import demofile.User;
 
/**
 * Servlet implementation class LoginCheckServlet
 */
@WebServlet(name="LoginCheckServlet",urlPatterns= {"/LoginCheckServlet"})
public class LoginCheck extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public LoginCheck() {
        super();
        // TODO Auto-generated constructor stub
    }
 
	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		 doPost(request, response);
	}
 
	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
          request.setCharacterEncoding("UTF-8");
          String nameuser = request.getParameter("nameuser");
          String password = request.getParameter("password");
          User user=new User();
         user.setName(nameuser);
         user.setPassword(password);
         UserCheck uc=new UserCheck();
         if(uc.validate(user)) {
        	 request.setAttribute("user", user);
        	 RequestDispatcher dis =request.getRequestDispatcher("loginOk.jsp");
        	 dis.forward(request, response);
         }else {
        	 response.sendRedirect("loginCheck.jsp"); 
         }
	}
 
}

loginCheak (Jsp)

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>loginCheck.jsp</title>
</head>
<body>
   <form action="LoginCheckServlet" methods="get">
   <table>
   <tr>
   <td>User：</td>
   <td><input type="text" name="nameuser"/></td>
   </tr>
   <tr>
   <td>Pass：</td>
   <td><input type="password" name="password"></td>
   </tr>
   <tr>
   <td><input type="submit" value="Up"/></td>
   <td><input type="reset" value="Set"/></td>
   </tr>
   </table>
   </form>
</body>
</html>

loginOK (Jsp)

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
    <%@page import="demofile.User" %>
<!DOCTYPE html">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>loginSuccess.jsp</title>
</head>
<body>
    <jsp:useBean id="user" type="demofile.User" scope="request"/>
    User:<jsp:getProperty property="name" name="user"/> success！
</body>
</html>

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