近期我打算使用 java web 完成一个管理系统用于网博杯比赛使用
public CarCard checkUser(String username,String password){
try{
pstmt = ct.prepareStatement("select * from [CarCard] where CardID=? and CardPwd=?");
pstmt.setString(1,username);
pstmt.setString(2,password);
ResultSet rs = pstmt.executeQuery();
CarCard user = new CarCard();
while(rs.next()){
user.setCardID(rs.getString(1));
user.setCardPwd(rs.getString(2));
//....
return user;
}
return null;
}catch(Exception e){
e.printStackTrace();
return null;
}
}以上使用java连接数据库的时候使用这种方式可以提高效率
try {
pstmt.setString(1, username);
pstmt.setString(2, password);//相当于模式匹配
ResultSet rs = pstmt.executeQuery();//在上面的模式匹配下。完成查询。提高效率
if(rs.next()) {//说明查到了信息
isExists = true;
}
} catch (SQLException e) {
e.printStackTrace();
}finally {
MysqlDeal.getmysqlDeal().closeDBResources();
}在前后端交互的时候可以使用重定向将java的后端数据在传给前端
//登录成功重定向到index.jsp
response.sendRedirect("index.jsp");对于后端当在web.xml中使用servlet完成配置之后就可以通过request.getParameter（）获取后端的数据
String username =request.getParameter("username");
String password =request.getParameter("password");在web.xml中的额配置如下
<servlet>
<servlet-name>LoginServlet</servlet-name>
<servlet-class>com.byc.login.Login</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>LoginServlet</servlet-name>
<url-pattern>/login</url-pattern>
</servlet-mapping>在项目中 的com.byc.login包中有四个类
package com.byc.login;
import java.io.IOException;
import java.io.PrintWriter;
import javax.persistence.PrimaryKeyJoinColumn;
import javax.servlet.Servlet;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class Login extends HttpServlet implements Servlet {//本部分用来接收前端发来的信息然后进行处理
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//getParameter获取前端的信息
String username =request.getParameter("username");
String password =request.getParameter("password");
LoginInfo loginInfo =new LoginInfo(username,password);//通过构造函数将信息传出
//下面需要判断消息是否可以登录
LoginServlet loginServlet=new LoginServlet();
boolean legal =loginServlet.legal(loginInfo);//将信息移交审查并返回结果
//根据判断消息的对错做出不同的反应
if(legal)
{
//登录成功重定向到index.jsp
response.sendRedirect("index.jsp");
}
else {
//重定向到error.jsp
//response.sendRedirect("error.jsp");
//转发请求
request.getRequestDispatcher("error.jsp").forward(request, response);
}
}
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse respone)
throws ServletException, IOException {
doGet(request, respone);
}
}
package com.byc.login;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import com.byc.mysql.MysqlDeal;
import com.sun.org.apache.bcel.internal.generic.NEW;
public class LoginDao {
public boolean isExists(String username, String password) {
//从数据库中提取信息查看登录的用户是否在数据库中
boolean isExists = false;//初始化值设置为false
String sql = "select * from login where username=? and password=?";
//执行检查
PreparedStatement pstmt=MysqlDeal.getmysqlDeal().getPreparedStatement(sql);
try {
pstmt.setString(1, username);
pstmt.setString(2, password);//相当于模式匹配
ResultSet rs = pstmt.executeQuery();//在上面的模式匹配下。完成查询。提高效率
if(rs.next()) {//说明查到了信息
isExists = true;
}
} catch (SQLException e) {
e.printStackTrace();
}finally {
MysqlDeal.getmysqlDeal().closeDBResources();
}
return isExists;
}
}
package com.byc.login;
public class LoginInfo {
private String username;
private String password;
public LoginInfo(String username, String password) {//构造函数创建用户的信息
this.username = username;
this.password = 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;
}
}
package com.byc.login;
public class LoginServlet {
LoginDao logindao=new LoginDao();
public boolean legal(LoginInfo loginInfo) {//对LoginDao出来的信息进行审查
return logindao.isExists(loginInfo.getUsername(),loginInfo.getPassword());
}
}对于数据库的处理如下
package com.byc.mysql;
/*
* 对于数据库连接处理的模板在需要的时候可以直接拿来使用
*/
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.sql.Statement;
import javax.servlet.jsp.tagext.TryCatchFinally;
import com.sun.servicetag.Installer;
//数据库的连接管理
public class MysqlDeal {
static MysqlDeal mysqlDeal=new MysqlDeal();
private Connection conn;//声明连接的对象。连接之后获得连接的句柄
private Statement stmt;//创建statement类对象，用来执行SQL语句！
private PreparedStatement pstmt;//实例化SQL执行句柄pstmt
public static MysqlDeal getmysqlDeal()
{
return mysqlDeal;
}
public MysqlDeal() {
}
static {
//加载驱动
try {
Class.forName("com.mysql.jdbc.Driver");
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
//实例化数据库连接conn
public Connection getConnection() {
try {
conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/mylearn", "root", "root");
} catch (SQLException e) {
e.printStackTrace();
}
return conn;
}
//实例化SQL执行句柄stmt
public Statement getStatement() {
Connection conn = getConnection();//获得连接的对象
try {
if(conn != null) {
stmt = conn.createStatement();//如果连接成功
//创建statement类对象，用来执行SQL语句
//ResultSet rs = stmt.executeQuery(sql);
}
} catch (SQLException e) {
e.printStackTrace();
}
return stmt;
}
//实例化SQL执行句柄pstmt
public PreparedStatement getPreparedStatement(String sql) {
Connection conn = getConnection();
try {
if(conn != null) {
pstmt = conn.prepareStatement(sql);
}
}catch(SQLException e) {
e.printStackTrace();
}
return pstmt;
}
//关闭数据库连接资源
public void closeDBResources() {
try {
if(pstmt != null && !pstmt.isClosed()) {
pstmt.close();
}
if(stmt != null && !stmt.isClosed()) {//如果stmt不为空，并且还未关闭
stmt.close();
}
if(conn != null && !conn.isClosed()) {
conn.close();
}
}catch(SQLException e) {
e.printStackTrace();
}
}
}至此关于java作为后台的简单登录界面就已经完成了
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