JavaWeb+Servlet：（一）實現簡單登入
阿新 • • 發佈：2018-12-10
注：專案常見錯誤
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tomcat無法啟動；報錯：Failed to start component [StandardEngine[Catalina].StandardHost[localhost].
web.xml檔案servlet配置（注意斜槓）：<url-pattern>/login/loginServlet</url-pattern>
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eclipse 新建 Dynamic Web Project；建立專案後報錯：**The superclass "javax.servlet.http.HttpServlet" was not found on the Java Build Path**
表示未新增執行環境：1. 選擇專案，右鍵 選擇 Build Path ---> Configura Build Path
一、連線資料庫（mysql），編寫dao層
0. 資料庫資訊；
主鍵id；欄位username 唯一，即不重複
CREATE TABLE `admin` ( `id` int(11) NOT NULL AUTO_INCREMENT COMMENT '主鍵', `username` varchar(25) NOT NULL COMMENT '管理員，姓名', `password` varchar(25) NOT NULL COMMENT '登入密碼', PRIMARY KEY (`id`), UNIQUE KEY `UNIQUE` (`username`) ) ENGINE=InnoDB AUTO_INCREMENT=10 DEFAULT CHARSET=utf8
1. JDBCUtil工具類，獲取jdbc連線
//獲取jdbc 連線 public class JDBCUtil { private Connection conn; private final String Driver = "com.mysql.jdbc.Driver"; private final String url = "jdbc:mysql://localhost:3306/myblog"; private final String username = "root" ; private final String password = "123456" ; public Connection getConnection(){ try { Class.forName(Driver); conn = DriverManager.getConnection(url, username, password); } catch (ClassNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); }catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } return conn; } }
2. dao層登入註冊（UserDao.java）
public class UserDao {
private JDBCUtil jdbcUtil = new JDBCUtil();
private Connection conn ;
private PreparedStatement pstmt ;
private ResultSet rs ;
private int i = 0 ;
public UserDao() {
conn = jdbcUtil.getConnection();
}
//登入
public String isLogin(String username ,String password){
String sql = "select * from admin where username='"+username+"'";
System.out.println("sql:"+sql);
try {
pstmt = conn.prepareStatement(sql);
rs = pstmt.executeQuery();
//判斷使用者名稱是否正確
rs.last(); //將結果集 移動到最後一行 ;判斷是否有資料
if(rs.getRow() == 0){ //無資料
return "username is not exits";
}else{
//有資料，rs結果集移動到第一個
rs.beforeFirst();
//判斷密碼是否正確
while(rs.next()){
if(password.equals(rs.getString("password"))){
return "success" ;
}
}
}
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
try {
rs.close();
pstmt.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
return "password Error";
}
/*
註冊
*/
//註冊 ；插入資料
public int isRegister(String username ,String password){
String sql = "insert into admin(id,username,password) value(null,?,?)";
int executeUpdate = 0 ;
try {
pstmt = conn.prepareStatement(sql);
pstmt.setString(1, username);
pstmt.setString(2, password);
//執行插入更新；返回int型別，表示更新的行數（受影響的行數）；無資料更新或者插入返回0
executeUpdate = pstmt.executeUpdate();
System.out.println("executeUpdate:"+executeUpdate);
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
try {
pstmt.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
return executeUpdate;
}
//判斷是否有該使用者
public String isUsernameExist(String username){
String sql = "select * from admin where username='"+username+"'";
System.out.println("sql:"+sql);
try {
pstmt = conn.prepareStatement(sql);
rs = pstmt.executeQuery();
rs.last(); //將結果集 移動到最後一行 ;判斷是否有資料
if(rs.getRow() == 0){
return "noExist";
}
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally{
try {
rs.close();
pstmt.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
return "exist";
}
}
3. servlet類（LoginServlet.java）
servlet 兩種配置方式：一是web.xml配置方式；二是註解方式（@WebServlet）如下
但需要注意的是使用註解方式： web.xml檔案中metadata-complete="false"；即 <web-app metadata-complete="false" >
//註解方式配置servlet路徑
/*@WebServlet("/login/loginServlet")*/
public class LoginServlet{
private UserDao userDao ;
public LoginServlet() {
super();
userDao = new UserDao();
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
request.setCharacterEncoding("utf-8");
//1. 獲取表單資訊
String username = request.getParameter("username");
String password = request.getParameter("password");
System.out.println("username:"+username);
System.out.println("password:"+password);
//2. 呼叫userDao,並與資料庫資訊進行判斷，返回判斷結果
String isLogin = userDao.isLogin(username, password);
System.out.println("是否登入："+isLogin);
//3. 是否登入成功並 轉發或者重定向頁面
if("success".equals(isLogin)){ //登入成功
//帳號密碼正確
/*request.setAttribute("username", username);
request.setAttribute("password", password);*/
//將使用者資訊儲存到session域中
HttpSession session = request.getSession();
session.setAttribute("username", username);
session.setAttribute("password", password);
request.getRequestDispatcher("/success.jsp").forward(request, response);
}else{ //登入失敗
System.out.println("錯誤原因："+isLogin);
//重定向登入介面
response.sendRedirect(request.getContextPath()+"/index.jsp");
}
//搭建環境測試；使用固定帳號密碼實現重定向
/*if("asdf".equals(username) && "asdf".equals(password)){
System.out.println("帳號密碼正確");
//轉發 success介面
request.setAttribute("username", username);
request.setAttribute("password", password);
request.getRequestDispatcher("/success.jsp").forward(request, response);
}else{
System.out.println("帳號或密碼錯誤");
//重定向登入介面
response.sendRedirect(request.getContextPath()+"/index.jsp");
}*/
}
}4. web.xml 配置servlet
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
<display-name>JavaWebTest</display-name>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
<servlet>
<servlet-name>loginServlet</servlet-name>
<servlet-class>com.space.servlet.LoginServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>loginServlet</servlet-name>
<url-pattern>/login/loginServlet</url-pattern>
</servlet-mapping>
</web-app>5. index.jsp登入頁面
<!-- 第一種設定全域性路徑：
使用方式如： <form
action=" ${APP_PATH}/LoginServlet"
等同於: ${pageContext.request.contextPath}
-->
<% pageContext.setAttribute("APP_PATH", request.getContextPath()); %>
<!-- 第二種設定全域性路徑：
<\%=request.getContextPath() %>
-->
<form id="form" action="<%=request.getContextPath() %>/login/loginServlet" method="POST">
username:<input type="text" name="username"/><br>
password:<input type="password" name="password" /><br>
<input type="submit" value="登入"/><button type="button" id="ajaxBtn">後臺登入</button><br>
<button type="button" id="btnRegister">註冊</button>
</form>6. success.jsp登入成功頁面
<body>
<h1>登入成功</h1>
登入使用者名稱："${username}" <br>
登入密碼："${password }"
</body>
具體專案程式碼訪問 GitHub：連結