准备工作

准备工作
- 新建maven web项目
- 测试Tomcat
导入相关依赖：
数据库准备

supermarket:smbms_address,smbms_bill,smbms_provider,smbms_role,smbms_user

构建相应的实体类
编写配置文件

db.properties

编写数据库的公共类
参考：https://blog.csdn.net/qq_42647047/article/details/116503457

  package com.test.dao;

  import java.io.IOException;
  import java.io.InputStream;
  import java.sql.*;
  import java.util.Properties;

  /**
   * 操作数据库的基类--静态类
   * @author Administrator
   *
   */
  public class BaseDao {
  	
  	static{//静态代码块,在类加载的时候执行
  		init();
  	}
  	
  	private static String driver;
  	private static String url;
  	private static String user;
  	private static String password;
  	
  	//初始化连接参数,从配置文件里获得
  	public static void init(){
  		Properties params=new Properties();
  		InputStream is=BaseDao.class.getClassLoader().getResourceAsStream("db.properties");
  		try {
  			params.load(is);
  		} catch (IOException e) {
  			e.printStackTrace();
  		}
  		driver=params.getProperty("driver");
  		url=params.getProperty("url");
  		user=params.getProperty("user");
  		password=params.getProperty("password");

  	}   
  		
  	/**
  	 * 获取数据库连接
  	 * @return
  	 */
  	public static Connection getConnection(){
  		Connection connection = null;
  		try {
  			Class.forName(driver);
  			connection = DriverManager.getConnection(url, user, password);
  		} catch (Exception e) {
  			e.printStackTrace();
  		}
  		
  		return connection;
  	}
  	/**
  	 * 查询操作
  	 * @param connection
  	 * @param pstm
  	 * @param rs
  	 * @param sql
  	 * @param params
  	 * @return
  	 */
  	public static ResultSet execute(Connection connection,PreparedStatement pstm,ResultSet rs, String sql,Object[] params) throws Exception{
  		pstm = connection.prepareStatement(sql);
  		//向sql中的占位符加载参数Object[] params
  		for(int i = 0; i < params.length; i++){
  			pstm.setObject(i+1, params[i]);
  		}
  		rs = pstm.executeQuery();
  		return rs;
  	}
  	/**
  	 * 更新操作
  	 * @param connection
  	 * @param pstm
  	 * @param sql
  	 * @param params
  	 * @return
  	 * @throws Exception
  	 */
  	public static int execute(Connection connection,PreparedStatement pstm, String sql,Object[] params) throws Exception{
  		int updateRows = 0;
  		pstm = connection.prepareStatement(sql);
  		for(int i = 0; i < params.length; i++){
  			pstm.setObject(i+1, params[i]);
  		}
  		updateRows = pstm.executeUpdate();
  		return updateRows;
  	}
  	
  	/**
  	 * 释放资源
  	 * @param connection
  	 * @param pstm
  	 * @param rs
  	 * @return
  	 */
  	public static boolean closeResource(Connection connection,PreparedStatement pstm,ResultSet rs){
  		boolean flag = true;
  		if(rs != null){
  			try {
  				rs.close();
  				rs = null; //如果rs.close()没关上，让其等于null，使垃圾回收器自动回收。
  			} catch (SQLException e) {
  				e.printStackTrace();
  				flag = false;
  			}
  		}
  		if(pstm != null){
  			try {
  				pstm.close();
  				pstm = null;//GC回收
  			} catch (SQLException e) {
  				// TODO Auto-generated catch block
  				e.printStackTrace();
  				flag = false;
  			}
  		}
  		if(connection != null){
  			try {
  				connection.close();
  				connection = null;//GC回收
  			} catch (SQLException e) {
  				// TODO Auto-generated catch block
  				e.printStackTrace();
  				flag = false;
  			}
  		}
  		
  		return flag;
  	}

  }