Java EE WEB工程师培训-JDBC+Servlet+JSP整合开发之12.Servlet基础(1)-优快云博客

本文详细介绍了Servlet的基本概念，包括提交表单的方法(get与post的区别)，Servlet的生命周期，如何使用Servlet输出HTML页面，以及如何获取Servlet的初始化参数等内容。

–提交表单的方法
• get
• post
–Servlet 生命周期
–使用Servlet 输出HTML页面
–获得Servlet初始化参数
–页面导航
• 请求重定向
–response.sendRedirect(“url”);
• 请求转发
–request.getRequestDispatcher(“url”).forward(request,response);
• 请求包含
–request.getRequestDispatcher(“url”).include(request,response);

############Michael分割线################

ServletBasic.java

package com.michael.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;

public class ServletBasic extends HttpServlet {

         /**
         * Constructor of the object.
         */
         public ServletBasic() {
                 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 {

                response.setContentType( "text/html");
                PrintWriter out = response.getWriter();
                out
                                .println( "<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
                out.println("<HTML>");
                out.println("    <HEAD><TITLE>A Servlet</TITLE></HEAD>");
                out.println("    <BODY>");
                out.print("        This is ");
                out.print(this.getClass());
                out.println(", using the GET method");
                out.println("    </BODY>");
                out.println("</HTML>");
                out.flush();
                out.close();
        }

        /**
         * 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 {

                response.setContentType("text/html");
                PrintWriter out = response.getWriter();
                out
                                .println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
                out.println("<HTML>");
                out.println("    <HEAD><TITLE>A Servlet</TITLE></HEAD>");
                out.println("    <BODY>");
                out.print("        This is ");
                out.print(this.getClass());
                out.println(", using the POST method");
                out.println("    </BODY>");
                out.println("</HTML>");
                out.flush();
                out.close();
        }

        /**
         * Initialization of the servlet. <br>
         *
         * @throws ServletException if an error occure
         */
        public void init() throws ServletException {
                // Put your code here
        }

}

web.xml

测试页面

############Michael分割线################

• 提交表单的方法
–提交表单的常用方法有两种
• get
–将请求参数显示在URL中
–调用Servlet的doGet方法
• post
–不在URL终显示请求参数
–调用Servlet的doPost方法

login.html

< !DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" >
< html >
     < head >
         < title >login.html </title>
         < meta http-equiv ="keywords" content ="keyword1,keyword2,keyword3" >
         < meta http-equiv ="description" content ="this is my page" >
         < meta http-equiv ="content-type" content ="text/html; charset=UTF-8" >
         < ! --<link rel="stylesheet" type="text/css" href="./styles.css">-->

     </head>
     < body >
         < form name ="f1" id ="f1" action ="/Servlet_Basic/servlet/ServletBasic" method ="post" >
             < table border ="0" >
                 < tr >
                     < td >帐号: </td>
                     < td > < input type ="text" name ="username" id ="login" > </td>
                 </tr>
                 < tr >
                     < td >密码: </td>
                     < td > < input type ="password" name ="password" id ="password" > </td>
                 </tr>
                 < tr >
                     < td colspan ="2" align ="center" > < input type ="submit" value ="登录" > </td>
                 </tr>
             </table>
         </form>
     </body>
</html>

测试页面

现在将method设置为get

看下测试页面

get会将用户密码显示在url中，而post不会哈~

• Servlet 生命周期
–Servlet生命周期的四个步骤
• 加载实例化Servlet
–创建一个Servlet实例
• 调用init方法
–仅被调用一次
• 调用service方法（doGet或者doPost)
–被调用多次（每次请求调用）
• 调用destory方法
–调用一次（销毁Servlet）

ServletBasic.java

package com.michael.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;

public class ServletBasic extends HttpServlet {

         /**
         * Constructor of the object.
         */
         public ServletBasic() {
                 super();
                System.out.println( "-----ServletBasic-----");
        }

         /**
         * Destruction of the servlet. <br>
         */
         public void destroy() {
                 super.destroy();
                System.out.println( "-----destroy-----");
        }

         /**
         * 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 {
                System.out.println( "-----doGet-----");

                response.setContentType( "text/html");
                PrintWriter out = response.getWriter();
                out
                                .println( "<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
                out.println("<HTML>");
                out.println("    <HEAD><TITLE>A Servlet</TITLE></HEAD>");
                out.println("    <BODY>");
                out.print("        This is ");
                out.print(this.getClass());
                out.println(", using the GET method");
                out.println("    </BODY>");
                out.println("</HTML>");
                out.flush();
                out.close();
        }

        /**
         * 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 {
                System.out.println("-----doPost-----");
                response.setContentType("text/html");
                PrintWriter out = response.getWriter();
                out
                                .println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
                out.println("<HTML>");
                out.println("    <HEAD><TITLE>A Servlet</TITLE></HEAD>");
                out.println("    <BODY>");
                out.print("        This is ");
                out.print(this.getClass());
                out.println(", using the POST method");
                out.println("    </BODY>");
                out.println("</HTML>");
                out.flush();
                out.close();
        }

        /**
         * Initialization of the servlet. <br>
         *
         * @throws ServletException if an error occure
         */
        public void init() throws ServletException {
                System.out.println("-----init-----");
        }

}

输入信息进行登录

页面调用Servlet

现在我们再重新登录下,Servlet重新执行了一次doGet或者doPost方法，而不会重新构造及初始化Servlet

doGet或者doPost方法最终都会调用service方法,我们测试下，先覆盖service方法

ServletBasic.java

重新部署tomcat后执行登录操作

现在Servlet不再调用doGet或者doPost方法而直接调用service方法

• 使用Servlet 输出HTML页面
–获得输出流
• PrintWriter out = response.getWriter();
–输出HTML页面

• 获得Servlet初始化参数
–获得全局参数
• web.xml 配置

• 获得

web.xml

<? xml version ="1.0" encoding ="UTF-8" ?>
< web-app version ="2.4"
         xmlns ="http://java.sun.com/xml/ns/j2ee"
         xmlns:xsi ="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd" >
         < context-param >
                 < param-name >driver </ param-name >
                 < param-value >com.mysql.jdbc.Driver </ param-value >
         </ context-param >
         < context-param >
                 < param-name >url </ param-name >
                 < param-value >jdbc:mysql://localhost:3306/jdbc_db </ param-value >
         </ context-param >
     < servlet >
         < description >This is the description of my J2EE component </ description >
         < display-name >This is the display name of my J2EE component </ display-name >
         < servlet-name >ServletBasic </ servlet-name >
         < servlet-class >com.michael.servlet.ServletBasic </ servlet-class >
     </ servlet >

     < servlet-mapping >
         < servlet-name >ServletBasic </ servlet-name >
         < url-pattern >/servlet/ServletBasic </ url-pattern >
     </ servlet-mapping >

</ web-app >

ServletBasic.java

package com.michael.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;

public class ServletBasic extends HttpServlet {

         /**
         * Constructor of the object.
         */
         public ServletBasic() {
                 super();
                System.out.println( "-----ServletBasic-----");
        }

         /**
         * Destruction of the servlet. <br>
         */
         public void destroy() {
                 super.destroy();
                System.out.println( "-----destroy-----");
        }

         /**
         * 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 {
                System.out.println( "-----doGet-----");

                response.setContentType( "text/html");
                PrintWriter out = response.getWriter();
                out
                                .println( "<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
                out.println("<HTML>");
                out.println("    <HEAD><TITLE>A Servlet</TITLE></HEAD>");
                out.println("    <BODY>");
                out.print("        This is ");
                out.print(this.getClass());
                out.println(", using the GET method");
                out.println("    </BODY>");
                out.println("</HTML>");
                out.flush();
                out.close();
        }

        /**
         * 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 {
                System.out.println("-----doPost-----");
                response.setContentType("text/html");
                PrintWriter out = response.getWriter();
                out
                                .println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
                out.println("<HTML>");
                out.println("    <HEAD><TITLE>A Servlet</TITLE></HEAD>");
                out.println("    <BODY>");
                out.print("        This is ");
                out.print(this.getClass());
                out.println(", using the POST method");
                out.println("    </BODY>");
                out.println("</HTML>");
                out.flush();
                out.close();
        }

        /**
         * Initialization of the servlet. <br>
         *
         * @throws ServletException if an error occure
         */
        public void init() throws ServletException {
                String driver = this.getServletContext().getInitParameter("driver");
                String url = this.getServletContext().getInitParameter("url");
                System.out.println(driver);
                System.out.println(url);
                System.out.println("-----init-----");
        }

        @Override
        protected void service(HttpServletRequest arg0, HttpServletResponse arg1) throws ServletException, IOException {
                // TODO Auto-generated method stub
                System.out.println("-----service-----");
        }
}

重新登录测试下

还可以使用第二种方法

ServletBasic.java

package com.michael.servlet;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ServletBasic extends HttpServlet {

         /**
         * Constructor of the object.
         */
         public ServletBasic() {
                 super();
                System.out.println( "-----ServletBasic-----");
        }

         /**
         * Destruction of the servlet. <br>
         */
         public void destroy() {
                 super.destroy();
                System.out.println( "-----destroy-----");
        }

         /**
         * 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 {
                System.out.println( "-----doGet-----");

                response.setContentType( "text/html");
                PrintWriter out = response.getWriter();
                out
                                .println( "<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
                out.println("<HTML>");
                out.println("    <HEAD><TITLE>A Servlet</TITLE></HEAD>");
                out.println("    <BODY>");
                out.print("        This is ");
                out.print(this.getClass());
                out.println(", using the GET method");
                out.println("    </BODY>");
                out.println("</HTML>");
                out.flush();
                out.close();
        }

        /**
         * 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 {
                System.out.println("-----doPost-----");
                response.setContentType("text/html");
                PrintWriter out = response.getWriter();
                out
                                .println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
                out.println("<HTML>");
                out.println("    <HEAD><TITLE>A Servlet</TITLE></HEAD>");
                out.println("    <BODY>");
                out.print("        This is ");
                out.print(this.getClass());
                out.println(", using the POST method");
                out.println("    </BODY>");
                out.println("</HTML>");
                out.flush();
                out.close();
        }

        /**
         * Initialization of the servlet. <br>
         *
         * @throws ServletException if an error occure
         */
        public void init() throws ServletException {
                //第一种方法
                /*
                String driver = this.getServletContext().getInitParameter("driver");
                String url = this.getServletContext().getInitParameter("url");
                System.out.println(driver);
                System.out.println(url);
                */
                //第二种方法
                Enumeration enu = this.getServletContext().getInitParameterNames();
                while(enu.hasMoreElements()){
                        String name = (String) enu.nextElement();
                        String value = this.getServletContext().getInitParameter(name);
                        System.out.println(name+":"+value);
                }
                System.out.println("-----init-----");
        }

        @Override
        protected void service(HttpServletRequest arg0, HttpServletResponse arg1) throws ServletException, IOException {
                // TODO Auto-generated method stub
                System.out.println("-----service-----");
        }
}

执行登录进行测试