JavaScript/Jsp 实现对数据库的增删改查和简单的下载上传文件

完成目标：在页面显示数据库的信息，并且完成对数据库的增删改查，并且增加分页功能。在页面实现图片或文本的下载。

1.增删改查操作

User实体类代码：

package com.jredu.web.entity;

public class User {
	private int id;
	private String userName;
	private String pwd;
	private String displayName;

	public User() {
	};

	public User(int id, String userName, String pwd, String displayName) {
		super();
		this.id = id;
		this.userName = userName;
		this.pwd = pwd;
		this.displayName = displayName;
	}

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public String getUserName() {
		return userName;
	}

	public void setUserName(String userName) {
		this.userName = userName;
	}

	public String getPwd() {
		return pwd;
	}

	public void setPwd(String pwd) {
		this.pwd = pwd;
	}

	public String getDisplayName() {
		return displayName;
	}

	public void setDisplayName(String displayName) {
		this.displayName = displayName;
	}
}

UserDao代码：

package com.jredu.web.dao;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;
import com.jredu.web.db.DBConnection;
import com.jredu.web.entity.User;
import java.sql.*;

public class UserDao {
	public List<User> selectAll() {
		Connection con = DBConnection.getConnection();
		Statement stmt;
		List<User> list = new ArrayList<User>();
		try {
			stmt = con.createStatement();
			ResultSet rs = stmt.executeQuery("SELECT * FROM users");
			while(rs.next()) {
				User user = new User();
				user.setId(rs.getInt("id"));
				user.setUserName(rs.getString("user_name"));
				user.setPwd(rs.getString("pwd"));
				user.setDisplayName(rs.getString("display_name"));
				list.add(user);
			}	
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} finally {
			DBConnection.closeConnection();
		}
		return list;	
	}
	public List<User> selectPage(int from,int rows) {
		Connection con = DBConnection.getConnection();
		Statement stmt;
		List<User> list = new ArrayList<User>();
		try {
			stmt = con.createStatement();
			ResultSet rs = stmt.executeQuery("SELECT * FROM users LIMIT "+from+","+rows);
			while(rs.next()) {
				User user = new User();
				user.setId(rs.getInt("id"));
				user.setUserName(rs.getString("user_name"));
				user.setPwd(rs.getString("pwd"));
				user.setDisplayName(rs.getString("display_name"));
				list.add(user);
			}	
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} finally {
			DBConnection.closeConnection();
		}
		return list;	
	}
	// " where user_name = '' and pwd = '' "
	public User selectWhere(String whereOption) {
		Connection con = DBConnection.getConnection();
		Statement stmt;
		User user = null;
		try {
			stmt = con.createStatement();
			String sql = "SELECT * FROM users ";
			if(!whereOption.equals("")) {
				sql += whereOption;
			}
			ResultSet rs = stmt.executeQuery(sql);
			if(rs.next()) {
				user = new User();
				user.setUserName(rs.getString("user_name"));
				user.setPwd(rs.getString("pwd"));
				user.setDisplayName(rs.getString("display_name"));
			}	
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} finally {
			DBConnection.closeConnection();
		}
		return user;
	}
	public int selectCount() {
		Connection con = DBConnection.getConnection();
		Statement stmt;
		int count = 0;
		try {
			stmt = con.createStatement();
			String sql = "SELECT count(1) as count FROM users ";
			ResultSet rs = stmt.executeQuery(sql);
			if(rs.next()) {
				count = rs.getInt("count");
			}	
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} finally {
			DBConnection.closeConnection();
		}
		return count;
	}
	public int insert(User user){
		Connection con = DBConnection.getConnection();
		PreparedStatement pstmt = null;
		int count =0;
		String sql = " insert into users(user_name,pwd,display_name) values(?,?,?)";
	    try {
			pstmt =con.prepareStatement(sql);
			pstmt.setString(1, user.getUserName());
			pstmt.setString(2, user.getPwd());
			pstmt.setString(3, user.getDisplayName());
			count = pstmt.executeUpdate();
			/*if(count==0){
				throw new DataAlreadyExistException();
			}*/
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}finally{
			try {
				pstmt.close();
			} catch (SQLException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
			DBConnection.closeConnection();
		}
	    return count;		
	}
	
	public int update