java web 开发入门实例
学习是个技巧活,关键是要找到重点的地方,新手在这方面的坑尤其多。看别人的教程一步一步的跟着做,隔几步就遇到一个新知识点,忍不住就百度往深处了解,一晃半天就过去了。
有的知识点要深入学习的,有的是了解下就行的。我个人感觉这个度的把握是最难的。当然这也是饶不过去的坑。
最近跟着网上的一个教程学习JAVA WEB开发,将中间遇到的坑和教训标记下:
1、JAVAC编译时,提示找不到自定义类的问题。(如果是用记事本编辑,用命令行Javac编译,需要 在环境变量中,设置CLASSPATH 指向你的classes目录);
2、关于JDBC:MYSQL的端口号,如果没有指定,会连接失败。切记根据本机的端口设置正确
3、有条件还是用ECLIPSE来编译执行,可以从控制台看到详细的错误日志。
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附:入门代码及注释
1、文件及目录结构(存在TOMCAT的WEBAPPS目录下)
2、登录页面效果
3、主要代码(运行前提:需安装JDK及MYSQL)
(1)、在MYSQL 中创建数据库user ,创建用户表tb_user;
mysql -u root -p 123456 ; create database user; use user; create table tb_user ( username varchar(20) primary key, password varchar(20));
(2)创建两个JSP文件 (index.jsp mesage.jsp)
index.jsp 中需要用到login.jpg ,要放在images目录下面。
<%@ page contentType="text/html;charset=UTF-8" language="java" %> <html> <head> <title>JAVA 学习Reg</title> </head> <body> <center><img src="images/login.jpg"/></center> <center><font size=5 color="blue"><B>用户注册页面</B></font></center> <form action="RegServlet" method="post"> <!-- 指定将该表单交给RegServlet来处理--> <table align="center" width="450" border="0"> <!--用户名行--> <tr> <td align="right">Username:</td> <td> <input type="text" name="username"> </td> </tr> <!--密码行--> <tr> <td align="right">Password:</td> <td> <input type="password" name="password"> </td> </tr> <!--确认密码行--> <tr> <td align="right">Confirm Password:</td> <td> <input type="password" name="repassword"> </td> </tr> <!--提交 重置行--> <tr> <td colspan="2" align="center"> <input type="submit" value="Reg"> <input type="reset" value="Reset"> </td> </tr> </table> </form> </body> </html>
message.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %> <body> <center><img src="images/regfail.jpg"/></center> <% String info = (String)request.getAttribute("info"); if(info != null) { out.print("<center>"); out.print("<font size=10>"); out.print("<B>"); out.print(info); out.print("</B>"); out.print("</font>"); out.print("</center>"); } %> </body>
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以上就是展示层,结束后,可以在浏览器中输入http://localhost:8080/reg/index.jsp看下效果。(注意你TOMCAT的端口号,我用的是8080)
(3)、建立 JAVA BEAN模型层
共有4个文件,分别放在beans dao service utils 目录下
文件名为 :UserBean.java UserDao.java SignInServlet.java DataBaseUtil.java
UserBean.java
package beans; /** 用户信息javabean **/ public class UserBean { private String username; private String password; public String getUsername() { return username; } public void setUsername(String username) { this.username = username; } public String getPassword() { return password; } public void setPassword(String password) { this.password = password; } }
UserDao.java
package dao; import utils.DataBaseUtil; import beans.UserBean; import java.sql.*; public class UserDao { public boolean isUserExist(String username) { //create a connection Connection connection = DataBaseUtil.getConnection(); String sql ="select * from tb_user WHERE username=?"; try{ PreparedStatement ps = connection.prepareStatement(sql); ps.setString(1, username); ResultSet resultSet = ps.executeQuery(); if(!resultSet.next()) { return true; } }catch(SQLException e) { System.out.println(e.toString()); e.printStackTrace(); }catch(NullPointerException f){ f.printStackTrace(); }finally { DataBaseUtil.closeConnection(connection); } return false; } public boolean isPasswordConfirm(String password, String repassword) { return password.equals(repassword); } public void saveUser(UserBean user) { Connection connection = DataBaseUtil.getConnection(); String sql = "insert into tb_user (username, password) values(?,?) "; try { PreparedStatement ps = connection.prepareStatement(sql); ps.setString(1, user.getUsername()); ps.setString(2, user.getPassword()); ps.executeUpdate(); }catch(SQLException e) { e.printStackTrace(); }finally { DataBaseUtil.closeConnection(connection); } } }
DataBaseUtil.java
1 package utils; 2 3 import java.sql.Connection; 4 import java.sql.DriverManager; 5 import java.sql.SQLException; 6 7 public class DataBaseUtil { 8 9 public static Connection getConnection() { 10 Connection connection = null; 11 try{ 12 Class.forName("com.mysql.jdbc.Driver"); 13 String url = "jdbc:mysql://localhost:3306/user"; 14 connection = DriverManager.getConnection(url, "root", "123456"); 15 return connection; 16 17 }catch(ClassNotFoundException nfe) { 18 nfe.printStackTrace(); 19 }catch(SQLException sqle) { 20 sqle.printStackTrace(); 21 } 22 return connection; 23 } 24 25 public static void closeConnection(Connection connection) { 26 if(connection != null) { 27 try{ 28 connection.close(); 29 }catch(SQLException sqle) { 30 sqle.printStackTrace(); 31 } 32 } 33 } 34 }
(3)、控制层 SignInServlet
SignInServlet.java
1 package service; 2 3 import beans.UserBean; 4 import dao.UserDao; 5 6 import javax.servlet.ServletException; 7 import javax.servlet.http.HttpServlet; 8 import javax.servlet.http.HttpServletRequest; 9 import javax.servlet.http.HttpServletResponse; 10 import java.io.IOException; 11 12 public class SignInServlet extends HttpServlet{ 13 14 @Override 15 public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException{ 16 String username = request.getParameter("username"); 17 String password = request.getParameter("password"); 18 String repassword = request.getParameter("repassword"); 19 20 UserDao userDao = new UserDao(); 21 if(username != null && !username.isEmpty()) { 22 //用户名不存在可以注册 23 if(userDao.isUserExist(username) && userDao.isPasswordConfirm(password, repassword)) { 24 UserBean userBean = new UserBean(); 25 userBean.setPassword(password); 26 userBean.setUsername(username); 27 userDao.saveUser(userBean); 28 request.setAttribute("info", "Congratulations! Reg successfully!"); 29 }else { 30 if(!userDao.isUserExist(username)) 31 request.setAttribute("info", "Sorry! Username exists!"+username+" "+password); 32 if(!userDao.isPasswordConfirm(password, repassword)) 33 request.setAttribute("info", "Sorry! Password not confirmed!"); 34 } 35 } 36 //forward to message.jsp 37 request.getRequestDispatcher("message.jsp").forward(request, response); 38 } 39 }
(4)、配置web.xml文件
在WEB-INF目录下创建web.xml文件,指定程序的相关配置信息
1 <?xml version="1.0" encoding="UTF-8"?> 2 <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee" 3 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 4 xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" 5 version="3.1"> 6 <!-- 欢迎页面 --> 7 <welcome-file-list> 8 <welcome-file>index.jsp</welcome-file> 9 </welcome-file-list> 10 <servlet> 11 <servlet-name>SignInServlet</servlet-name> 12 <servlet-class>service.SignInServlet</servlet-class> 13 </servlet> 14 <servlet-mapping> 15 <servlet-name>SignInServlet</servlet-name> 16 <url-pattern>/RegServlet</url-pattern> 17 </servlet-mapping> 18 </web-app>
(5)、下载相关JAR包
从网上下载JDBC-MySQL驱动,放入lib目录中(我用的是:mysql-connector-java-5.1.30.jar)
(6)、编译JAVA文件
打开reg/web-inf/CLASSES 文件夹,按住shift在窗口中点鼠标右键,选择 “在此处打开命令窗口w” 进入cmd窗口,先进入相关的子目录 ,一个一个的执行 javac **.java 将文件编译为.class文件;
上述工作完成后,启动浏览器,输入 http://localhost:8080/reg/ 如果能打开页面如下,祝贺你,你的 WEB项目成功了;
真诚感谢 Easy sir :
新手推荐JSP+JavaBean+Servlet MVC模式用户注册模块
代码基本照搬,改了JSP的编码类型为 UTF-8 ,顺序略有调整。