Servlet实现简单的登录页面

 package emp;

 import java.io.IOException;
 import java.io.PrintWriter;
 import java.sql.Connection;
 import java.sql.PreparedStatement;
 import java.sql.ResultSet;
 import java.sql.SQLException;

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

 import util.DBUtil;

 public class EmpServlet extends HttpServlet {
     private static final long serialVersionUID = 1L;
     private Connection conn;
     private PrintWriter pw;
     private String username1;
     private String password1;

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

     }

     protected void doPost(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         //设置解码所使用的字符集，注意要与客户端保持一致
         request.setCharacterEncoding("utf-8");
         //告诉浏览器，服务器返回的数据类型和编码格式(通过设置content-type消息头的值)
         response.setContentType("text/html;charset=utf-8");
         //调用request对象提供的方法来读取请求参数值
         String name = request.getParameter("username");
         String passw = request.getParameter("password");
         try {
             //使用JDBC工具类来获取Connection对象
             conn = DBUtil.getConnection();
             //通过response(响应对象)获得一个输出流
             pw = response.getWriter();
             String sql = "select username,password from user_zyd where username=?";
             PreparedStatement ps = conn.prepareStatement(sql);
             //给sql赋值
             ps.setString(1, name);
             //查询返回的结果集(是一个集合)
             ResultSet rs = ps.executeQuery();
             while (rs.next()) {
                 //获取用户查询数据库的内容
                 username1 = rs.getString("username");
                 password1 = rs.getString("password");
                 System.out.println(username1);
                 System.out.println(password1);
                 //判断用户查询的内容是否正确
             }
             if (username1==null) {
                 pw.println("用户名或密码错误");
             } else if(username1.equals(name) & password1.equals(passw)){
                 pw.println("用户名或密码错误");
             } else {
                 pw.println("登陆成功");
             }
         } catch (SQLException e) {
             e.printStackTrace();
         } finally {
             DBUtil.close(conn);
             pw.close();
         }
     }
 }
 //db.properties
 # connection parameters
 driver=oracle.jdbc.driver.OracleDriver
 url=jdbc:oracle:thin:@localhost:1521:xe
 user=system
 password=123456
 # datasouce parameters
 initSize=1
 maxSize=2

 //DBUtil
 package util;

 import java.io.IOException;
 import java.sql.Connection;
 import java.sql.SQLException;
 import java.util.Properties;

 import org.apache.commons.dbcp.BasicDataSource;

 public class DBUtil {
     private static BasicDataSource ds;
     static {
         Properties p = new Properties();
         try {
             p.load(DBUtil.class.getClassLoader().getResourceAsStream("db.properties"));
             String driver = p.getProperty("driver");
             String url = p.getProperty("url");
             String user = p.getProperty("user");
             String password = p.getProperty("password");
             String initSize = p.getProperty("initSize");
             String maxSize = p.getProperty("maxSize");
             ds = new BasicDataSource();
             ds.setDriverClassName(driver);
             ds.setUrl(url);
             ds.setUsername(user);
             ds.setPassword(password);
             ds.setInitialSize(Integer.parseInt(initSize));
             ds.setMaxActive(Integer.parseInt(maxSize));
         } catch (IOException e) {
             e.printStackTrace();
             throw new RuntimeException(e);
         }
     }

     public static Connection getConnection() throws SQLException {
         return ds.getConnection();
     }

     public static void close(Connection conn) {
         if (conn != null)
             try {
                 conn.close();
             } catch (SQLException e) {
                 e.printStackTrace();
                 throw new RuntimeException(e);
             }
     }
 }