Servlet（一）Servlet基础

Servlet基础

-Servlet概述

-Tomcat容器等级

-HelloServlet手工编写第一个Servlet

-HelloServlet使用eclipse编写第一个Servlet

-Servlet执行流程

-Tomacat装载Servlet的三种情况

-Servlet概述

jsp的前身就是Servlet

什么是Servlet：Servlet是在服务器上运行的小程序。一个Servlet就是一个Java类，并且可以通过“请求-响应”编程模型来访问的这个驻留在服务器内存里的Servlet程序

-Tomcat容器等级

Tomcat容器分为四个等级，

1. Container 容器，集装箱

2.Engine 引擎容器

3.Host 主机（）

4.Servlet容器（tomcat最低级别的容器）里面包含了一个或多个Context

—— Context （上下文，背景，环境）一个context对应一个web项目

—— Wrapper 容器里的封装部分。

-HelloServlet手工编写第一个Servlet

1. 继承HttpServlet

Servlet层级关系：

Servlet（接口）-->GenericServlet（抽象类，与协议无关的Servlet）-->HttpServlet（抽象类，实现了Http协议的Servlet）-->Custom Servlet（自定义的Servlet）。

如何创建和使用Servlet？

2. 重写doGet()和doPost方法

3. 注册Servlet

a) 在web.xml中进行如下配置：

<servlet-name>HelloServlet</servlet-name>

<servlet-class>servlet.HelloServlet</servlet-class>

</servlet>

<servlet-mapping>

<servlet-name>HelloServlet</servlet-name>

<url-pattern>/servlet/HelloServlet</url-pattern>

</servlet-mapping>

b)Servlet3.0之后可以使用注解来表示所有xml中的配置：

@WebServlet(name="HelloServlet",value={"/servlet/HelloServlet"})

测试:

在Eclipse中新建DynamicWebProject的时候不要直接点"完成"，在下一步有个勾选项(Generate web.xml deployment descriptor)，选上就会默认生成web.xml

选择Superclass,输入HttpServlet -选择第一项- OK

选择source-Override/Implement methods

勾选doGet和doPost

Index.jsp

<%@ page language="java" import="java.util.*"

    contentType="text/html; charset=utf-8" pageEncoding="utf-8"%>

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

<html>

<head>

<meta http-equiv="Content-Type" content="text/html; charset=utf-8">

<title>Insert title here</title>

</head>

<body>

    <h1>第一个Servlet小例子</h1>

    <hr>

    <a href="servlet/HelloServlet">Get方式请求HelloServlet</a><br>

    <form action="servlet/HelloServlet" method="post">

    <input type="submit" value="Post方式请求HelloServlet">

    </form>



</body>

</html>



HelloServlet.java

package servlet;



import java.io.IOException;

import java.io.PrintWriter;



import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

//继承于HttpServlet

public class HelloServlet extends HttpServlet {



    @Override

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

        // TODO Auto-generated method stub

        System.out.println("处理Get请求。。。");

        PrintWriter out=response.getWriter();

        out.println("<strong>Hello Servlet!</strong><br>");

    }



    @Override

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

        // TODO Auto-generated method stub

        System.out.println("处理Post请求。。。");

        PrintWriter out=response.getWriter();

        out.println("<strong>Hello Servlet!</strong><br>");

    }

   



}

Web.xml

<servlet-name>HelloServlet</servlet-name>

<servlet-class>servlet.HelloServlet</servlet-class>

</servlet>

<servlet-mapping>

<servlet-name>HelloServlet</servlet-name>

<url-pattern>/servlet/HelloServlet</url-pattern>

</servlet-mapping>

运行:

-HelloServlet使用eclipse编写第一个Servlet

Servlet不能自动配置web.xml的原因

建dynamic web project 时，dynamic web module version选择2.5就ok了。

新建servlet

已经自动配置了web.xml文件，选择Next

默认勾选了get和post等，finish。

测试:

HelloServlet.java

添加需要输出的脚本，留意其中注释掉的部分

package servlet;



import java.io.IOException;

import java.io.PrintWriter;



import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;



/**

 * Servlet implementation class HelloServlet

 */

public class HelloServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;

      

    /**

     * @see HttpServlet#HttpServlet()

     */

    public HelloServlet() {

        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());

        System.out.println("处理Get请求。。。");

        PrintWriter out=response.getWriter();

        out.println("<strong>Hello Servlet!</strong><br>");

    }



    /**

     * @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);

        System.out.println("处理Post请求。。。");

        PrintWriter out=response.getWriter();

        out.println("<strong>Hello Servlet!</strong><br>");

    }



}

Index.jsp

<h1>使用Eclipse创建Servlet小例子</h1>

<hr>

<a href="servlet/HelloServlet">Get方式请求HelloServlet</a><br>

</form>

Web.xml

需要修改一处

将<url-patternHelloServlet</url-pattern>改成

<url-pattern>/servlet/HelloServlet</url-pattern>即可

-Servlet执行流程

1.客户端发送请求给服务器。

2.服务器开始接受，先判断该请求的servlet实例是否存在，如果不存在先装载一个servlet类并创建实例。如果存在则直接调用该servlet的service方法，之后进行判断是调用doGet方法还是doPost方法。

3.servlet创建实例后，调用init方法进行初始化。之后调用servce方法，判断是调用doGet方法还是doPost方法。

4.最后判断服务是否关闭，如果关闭则调用destroy方法。

注:

编写Servlet的doPost方法时，需要抛出ServletExcpetion和IOException异常

-Tomacat装载Servlet的三种情况

1、自动装载：某些Servlet如果需要在Servlet容器启动时就加载，需要在web.xml下它的<Servlet>标签里中，添加优先级代码：

<load-on-startup>1<load-on-startup>

</Servlet>

数字越小表示该servlet的优先级越高，会先于其他自动装载的优先级较低的先装载

2、Servlet容器启动后，客户首次向某个Servlet发送请求时，Tomcat容器会加载它

3、当Servlet类文件被更新后，也会重新自动加载

Servlet是长期驻留在内存里的。某个Servlet一旦被加载，就会长期存在于服务器的内存里，直到服务器关闭

Servlet被装载后，Servlet容器创建一个Servlet实例并且调用Servlet的init()方法进行初始化。在Servlet的整个生命周期内，init()方法只被调用一次

-JSP与SerVlet对象的对应关系

Jsp内置对象out与servlet中response.getWriter()获得对象并不完全匹配，Jsp中是JspWriter类型，而servlet中获得是PrintWriter类型，其实一个是在Jsp中输出，一个是在servlet中输出，类型肯定不一样；

request、response内置对象可以通过service（）方法传到doGet（）、doPost（）里的request、response来获取；

session可以通过request.getSession()来获取；

application可以通过getServletContext()来获取；

exception可以通过Throwable 来获得；

page对应this对象；

pageContext对象对应PageContext对象；

config可以通过getServletConfig()来获取。

-通过Servlet获取表单数据

1.建立JavaBean类；

2.在Servlet类中的 doPost方法内编写代码；

a)实例化JavaBean对象，通过 getParameter(String param);获取表单值，通过 getParameterValues(String param); 获取多个同name的表单值；通过setter()方法给JavaBean对象传值；

b)将JavaBean对象保存到session中；

c)进行页面跳转。

3.jsp页面中创建Servlet对象，通过<jsp:getProperty />或对象的get()方法获取值。

<jsp:useBean id="idName" class="classPath" scope="session"></jsp:useBean>

<jsp:getProperty name=" idName " property="propertyName"/>

<% String[] favorites=userReg.getFavorites();

for(String favorite:favorites){

<%=favorite %>  

<% }%>

注意事项:

1.在 jsp 页面中可以使用<% %> 写 java 代码;

2.日期转换时需要注意格式 '-';

3.复选框需要使用 getParameterValues 方式获取;

4.注意复选框是否为 null ;

5.注意javaBean属性名不与表单属性名冲突!

6. request.setCharacterEncoding("UTF-8");//防止中文乱码

7.留意勾选框一直false的情况

if(request.getParameterValues("isAccept")!=null){

isAccept = request.getParameter("isAccept");

}else{

isAccept = "false";

}

u.setFlag("true".equals(isAccept)?true:false);

<input type="checkbox" name="isAccept" value="true">是否接受霸王条款

8.留意格式，若为mm则一直是1月，出现错误

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");

测试:

Users.java


package entity;



import java.util.Date;



//用户类

public class Users {

    private String username;// 用户名

    private String mypassword;// 密码

    private String email;// 邮箱

    private String gender;// 性别

    private Date birthday;// 出生日期

    private String[] favorites;// 爱好

    private String introduce;// 自我介绍

    private boolean flag;// 是否接受协议



    public Users() {



    }



    public String getUsername() {

        return username;

    }



    public void setUsername(String username) {

        this.username = username;

    }



    public String getMypassword() {

        return mypassword;

    }



    public void setMypassword(String mypassword) {

        this.mypassword = mypassword;

    }



    public String getEmail() {

        return email;

    }



    public void setEmail(String email) {

        this.email = email;

    }



    public String getGender() {

        return gender;

    }



    public void setGender(String gender) {

        this.gender = gender;

    }



    public Date getBirthday() {

        return birthday;

    }



    public void setBirthday(Date birthday) {

        this.birthday = birthday;

    }



    public String[] getFavorites() {

        return favorites;

    }



    public void setFavorites(String[] favorites) {

        this.favorites = favorites;

    }



    public String getIntroduce() {

        return introduce;

    }



    public void setIntroduce(String introduce) {

        this.introduce = introduce;

    }



    public boolean isFlag() {

        return flag;

    }



    public void setFlag(boolean flag) {

        this.flag = flag;

    }



}

RegServlet.java

package servlet;



import java.io.IOException;

import java.text.SimpleDateFormat;

import java.util.Date;



import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;



import entity.Users;



/**

 * Servlet implementation class RegServlet

 */

public class RegServlet extends HttpServlet {





    /**

     * @see HttpServlet#HttpServlet()

     */

    public RegServlet() {

        super();

        // TODO Auto-generated constructor stub

    }

    public void destroy() {

        super.destroy(); // Just puts "destroy" string in log

        // Put your code here

    }



    /**

     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse

     *      response)

     */

    public void doGet(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        // TODO Auto-generated method stub

        doPost(request, response);

    }



    /**

     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse

     *      response)

     */

    public void doPost(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        // TODO Auto-generated method stub

        Users u = new Users();

        String username, mypassword, gender, email, introduce, isAccept;

        Date birthday;

        String[] favorites;

        request.setCharacterEncoding("UTF-8");

        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");

        try {

            username = request.getParameter("username");

            mypassword = request.getParameter("mypassword");

            gender = request.getParameter("gender");

            email = request.getParameter("email");

            birthday = sdf.parse(request.getParameter("birthday"));

            favorites = request.getParameterValues("favorite");

            introduce=request.getParameter("introduce");

            if(request.getParameterValues("isAccept")!=null)

            {

              isAccept = request.getParameter("isAccept");

            }

            else

            {

              isAccept = "false";

            }



            u.setUsername(username);

            u.setMypassword(mypassword);

            u.setGender(gender);

            u.setEmail(email);

            u.setBirthday(birthday);

            u.setFavorites(favorites);

            u.setIntroduce(introduce);

            u.setFlag("true".equals(isAccept)?true:false);

           



            // 把注册成功的用户对象保存到session中

            request.getSession().setAttribute("regUser", u);

            // 跳转到注册成功页面

            request.getRequestDispatcher("../userinfo.jsp").forward(request, response);



        } catch (Exception ex) {

            ex.printStackTrace();

        }

    }

    public void init() throws ServletException {

        // Put your code here

    }





}

userinfo.jsp

<%@ page language="java" import="java.util.*,java.text.*" contentType="text/html; charset=utf-8"%>



<%

String path = request.getContextPath();

String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";

%>



<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>

  <head>

    <base href="<%=basePath%>">

   

    <title>My JSP 'userinfo.jsp' starting page</title>

   

    <meta http-equiv="pragma" content="no-cache">

    <meta http-equiv="cache-control" content="no-cache">

    <meta http-equiv="expires" content="0">   

    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">

    <meta http-equiv="description" content="This is my page">

    <!--

    <link rel="stylesheet" type="text/css" href="styles.css">

    -->

    <style type="text/css">

     .title{

         width: 30%;

         background-color: #CCC;

         font-weight: bold;

     }

     .content{

         width:70%;

         background-color: #CBCFE5;

     }

     

   </style> 

  </head>

 

  <body>

    <h1>用户信息</h1>

    <hr>

    <center>

     <jsp:useBean  id="regUser" class="entity.Users" scope="session"/>  

     <table width="600" cellpadding="0" cellspacing="0" border="1">

        <tr>

          <td class="title">用户名：</td>

          <td class="content">&nbsp;<jsp:getProperty name="regUser" property="username"/></td>

        </tr>

        <tr>

          <td class="title">密码：</td>

          <td class="content">&nbsp;<jsp:getProperty name="regUser" property="mypassword"/></td>

        </tr>

        <tr>

          <td class="title">性别：</td>

          <td class="content">&nbsp;<jsp:getProperty name="regUser" property="gender"/></td>

        </tr>

        <tr>

          <td class="title">E-mail：</td>

          <td class="content">&nbsp;<jsp:getProperty name="regUser" property="email"/></td>

        </tr>

        <tr>

          <td class="title">出生日期：</td>

          <td class="content">&nbsp;

            <%

               SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日");

               String date = sdf.format(regUser.getBirthday());

              

            %>

             <%=date%>

          </td>

        </tr>

        <tr>

          <td class="title">爱好：</td>

          <td class="content">&nbsp;

            <%

               String[] favorites = regUser.getFavorites();

               for(String f:favorites)

               {

            %>

                <%=f%> &nbsp;&nbsp;

            <%

               }

            %>

          </td>

        </tr>

        <tr>

          <td class="title">自我介绍：</td>

          <td class="content">&nbsp;<jsp:getProperty name="regUser" property="introduce"/></td>

        </tr>

        <tr>

          <td class="title">是否介绍协议：</td>

          <td class="content">&nbsp;<jsp:getProperty name="regUser" property="flag"/></td>

        </tr>

     </table>

    </center>

  </body>

</html>

reg.jsp

<%@ page language="java" import="java.util.*" contentType="text/html; charset=utf-8"%>

<%

String path = request.getContextPath();

String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";

%>



<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>

  <head>

    <base href="<%=basePath%>">

   

    <title>My JSP 'reg.jsp' starting page</title>

   

    <meta http-equiv="pragma" content="no-cache">

    <meta http-equiv="cache-control" content="no-cache">

    <meta http-equiv="expires" content="0">   

    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">

    <meta http-equiv="description" content="This is my page">

    <!--

    <link rel="stylesheet" type="text/css" href="styles.css">

    -->

    <style type="text/css">

     .label{

          width: 20%

     }

     .controler{

          width: 80%

     }

   </style> 

   <script type="text/javascript" src="js/Calendar3.js"></script>

  </head>

 

  <body>

    <h1>用户注册</h1>

    <hr>

    <form name="regForm" action="servlet/RegServlet" method="post" >

              <table border="0" width="800" cellspacing="0" cellpadding="0">

                <tr>

                <td class="lalel">用户名：</td>

                <td class="controler"><input type="text" name="username" /></td>

                </tr>

                <tr>

                <td class="label">密码：</td>

                <td class="controler"><input type="password" name="mypassword" ></td>

               

                </tr>

                <tr>

                <td class="label">确认密码：</td>

                <td class="controler"><input type="password" name="confirmpass" ></td>

               

                </tr>

                <tr>

                <td class="label">电子邮箱：</td>

                <td class="controler"><input type="text" name="email" ></td>

               

                </tr>

                <tr>

                <td class="label">性别：</td>

                <td class="controler"><input type="radio" name="gender" checked="checked" value="Male">男<input type="radio" name="gender" value="Female">女</td>

               

                </tr>

              

                <tr>

                <td class="label">出生日期：</td>

                <td class="controler">

                  <input name="birthday" type="text" id="control_date" size="10"

                      maxlength="10" onclick="new Calendar().show(this);" readonly="readonly" />

                </td>

                </tr>

                <tr>

                <td class="label">爱好：</td>

                <td class="controler">

                <input type="checkbox" name="favorite" value="nba"> NBA &nbsp;

                  <input type="checkbox" name="favorite" value="music"> 音乐 &nbsp;

                  <input type="checkbox" name="favorite" value="movie"> 电影 &nbsp;

                  <input type="checkbox" name="favorite" value="internet"> 上网 &nbsp;

                </td>

                </tr>

                <tr>

                <td class="label">自我介绍：</td>

                <td class="controler">

                     <textarea name="introduce" rows="10" cols="40"></textarea>

                </td>

                </tr>

                <tr>

                <td class="label">接受协议：</td>

                <td class="controler">

                     <input type="checkbox" name="isAccept" value="true">是否接受霸王条款

                </td>

                </tr>

                <tr>

                <td colspan="2" align="center">

                     <input type="submit" value="注册"/>&nbsp;&nbsp;

                    <input type="reset" value="取消"/>&nbsp;&nbsp;

                </td>

                </tr>

              </table>

            </form>

  </body>

</html>

-Servlet的路径跳转

一、JSP跳转到Servlet

1、相对路径,如href="servlet/TestServlet"

***注意：如果写成"/servlet/TestServlet"会报错，因为第一个'/'表示的是【服务器根目录：http://localhost:8080/】

2、绝对路径，通过内置成员变量path实现，如href="<%=path%>/servlet/TestServlet"。

***注意：这里的path得到的是项目根目录，如【http://localhost:8080/Servlet002_GetFormDemo】

二、Servlet跳转JSP

1、请求重定向：response.sendRedirect(request.getContextPath()+"/xxx.jsp");这里通过request.getContextPath()方法获得项目根目录，或者通过"../xxx.jsp"取得上层路径得到

2、服务器内部转发：request.getRequestDispatcher("../xxx.jsp").forward(req,resp);

***小结：都可以通过../xxx.jsp得到

应用:用Server实现用户登录

JSP项目链接: https://blog.csdn.net/RayMa0305/article/details/81603914

删除com.DAO、dologin.jsp

新建一个servlet/Loginservlet

在login.jsp中把action=”dologin.jsp” 改为<form action="servlet/LoginServlet" method="post">

Loginservlet.java

package servlet;



import java.io.IOException;

import java.io.PrintWriter;



import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;



import com.po.Users;



public class LoginServlet extends HttpServlet {



         /**

          * Constructor of the object.

          */

         public LoginServlet() {

                   super();

         }



         /**

          * Destruction of the servlet. <br>

          */

         public void destroy() {

                   super.destroy(); // Just puts "destroy" string in log

                   // Put your code here

         }



         /**

          * The doGet method of the servlet. <br>

          *

          * This method is called when a form has its tag value method equals to get.

          *

          * @param request

          *            the request send by the client to the server

          * @param response

          *            the response send by the server to the client

          * @throws ServletException

          *             if an error occurred

          * @throws IOException

          *             if an error occurred

          */

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



                   doPost(request, response);

         }



         /**

          * The doPost method of the servlet. <br>

          *

          * This method is called when a form has its tag value method equals to post.

          *

          * @param request

          *            the request send by the client to the server

          * @param response

          *            the response send by the server to the client

          * @throws ServletException

          *             if an error occurred

          * @throws IOException

          *             if an error occurred

          */

         public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

                   Users u = new Users();

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

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



                   u.setUsername(username);

                   u.setPassword(password);

                   // 判断用户名和密码是否正确

                   if (u.getUsername().equals("admin") && u.getPassword().equals("admin")) {

                            response.sendRedirect(request.getContextPath() + "/login_success.jsp");

                   } else {

                            response.sendRedirect(request.getContextPath() + "/login_failure.jsp");

                   }



         }



         /**

          * Initialization of the servlet. <br>

          *

          * @throws ServletException

          *             if an error occurs

          */

         public void init() throws ServletException {

                   // Put your code here

         }



}