jdbc学习over

Posted 2022-12-29 cstdio1

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这次的代码和之前学习到一般的代码主要就是将一些很常见的操作（建立连接、清除连接）不管做什么操作都需要用到它们，所以将它们单独放到另一个工具类里面去。

用到的术语：

1.事务：https://www.cnblogs.com/cstdio1/p/11626657.html

2.缓冲池（数据源）：https://www.cnblogs.com/chy18883701161/p/11374731.html

主逻辑代码：

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import JDBCUtils.JDBCUtils;
import JDBCUtils.JDCPDataSource;

public class mysqlDemo1 

	public static void main(String[] args) 
		selectAll();
		//System.out.println(selectByUsernamePassword2("zs","123"));
		//sql注入
		//System.out.println(selectByUsernamePassword("zs","12347‘or‘1‘=‘1"));
		//PageSearch(1,2);
		//insert("sdf","249.1");
		//delete("sdf");
		//update("zs","123","000");
		transAccount("zs","ls",1000);
	
	public static void selectAll()
	// TODO Auto-generated method stub
	Connection con=null;
	Statement stmt=null;
	ResultSet rs=null;
	try 
		con = JDCPDataSource.getConnection();
		stmt = con.createStatement();
		String SqlRequest = "select * from student";
		rs= stmt.executeQuery(SqlRequest);
		while(rs.next())
		System.out.println(rs.getString(1)+" "+rs.getString(2)+" "+rs.getString(3)+" "+rs.getString(4));	
		//System.out.println(rs.getString("id")+" "+rs.getString("stu_name")+" "+rs.getString("stu_sex")+" "+rs.getString("stu_score"));
		
		
		
	 catch (Exception e) 
		// TODO Auto-generated catch block
		e.printStackTrace();
	finally
		JDCPDataSource.closeResource(rs, stmt, con);
		//JDBCUtils.closeResource(rs, stmt, con);
			
		
		
		
		

	
	public static boolean selectByUsernamePassword(String username,String password)//验证用户名和密码（字符串拼接的方式存在sql注入的问题）

		Connection con=null;
		Statement stmt=null;
		ResultSet rs=null;
		
		try 
			con = JDBCUtils.getConnection();
			stmt = con.createStatement();
			String requestSql="select * from user where u_name=‘"+username+"‘and u_password=‘"+password+"‘";
		   System.out.print(requestSql);
			rs = stmt.executeQuery(requestSql);
		     if(rs.next())
		    	 return true;
		     else
		    	 return false;
		     
			
		 catch (Exception e) 
			// TODO Auto-generated catch block
			e.printStackTrace();
		finally
			
			JDBCUtils.closeResource(rs, stmt, con);
		
		
		return false;
		
	

	public static boolean selectByUsernamePassword2(String username,String password)//验证用户名和密码(版本2可以防止sql注入)

		Connection con=null;
		PreparedStatement pstmt=null;
		ResultSet rs=null;
		
		try 
			con = JDBCUtils.getConnection();
		    String RequestSql="select *from user where u_name=? and u_password=? ";
			 pstmt = con.prepareStatement(RequestSql);
			
			pstmt.setString(1, username);
			pstmt.setString(2,password);
			rs = pstmt.executeQuery();
		     if(rs.next())
		    	 return true;
		     else
		    	 return false;
		     
			
		 catch (Exception e) 
			// TODO Auto-generated catch block
			e.printStackTrace();
		finally

			JDBCUtils.closeResource(rs, pstmt, con);
		
		
		return false;
		
		
		
	
	/*
	 *PageNum：查询第几页
	 *LineNum：总共显示多少行 
	 */
	public static void PageSearch(int PageNum,int LineNum)
               //分页查询
		Connection con=null;
		PreparedStatement pstmt=null;
		ResultSet rs=null;
		
		try 
			
			con = JDBCUtils.getConnection();
		       String RequestSql="select *from user limit ?,?";
			pstmt = con.prepareStatement(RequestSql);
			
			pstmt.setInt(1,(PageNum-1)*LineNum);
			pstmt.setInt(2,LineNum);
			rs = pstmt.executeQuery();
			while(rs.next())
				System.out.println(rs.getString(1)+" "+rs.getString(2));
			
			
			
		 catch (Exception e) 
			// TODO Auto-generated catch block
			e.printStackTrace();
		finally
			JDBCUtils.closeResource(rs, pstmt, con);
			
		
			
			
	

	public static void insert(String UserName,String Password)
               //新注册的信息进行插入操作
		
		Connection con=null;
		PreparedStatement pstmt=null;
		ResultSet rs=null;
		int mark=0;
		try 
			con = JDBCUtils.getConnection();
		    String RequestSql="insert into user(u_name,u_password) values(?,?)";
			pstmt = con.prepareStatement(RequestSql);
			
			pstmt.setString(1, UserName);
			pstmt.setString(2,Password);
			mark = pstmt.executeUpdate();
			if(mark>0)
				System.out.println("插入成功");
			else
				System.out.println("插入失败");
			
			
		 catch (Exception e) 
			// TODO Auto-generated catch block
			e.printStackTrace();
		finally

			JDBCUtils.closeResource(rs, pstmt, con);
		
		
		
		
		
	

	public static void delete(String UserName)

		Connection con=null;
		PreparedStatement pstmt=null;
		ResultSet rs=null;
		int mark=0;
		try 
			con = JDBCUtils.getConnection();
		    String RequestSql="delete from user where u_name = ?";
			pstmt = con.prepareStatement(RequestSql);
			
			pstmt.setString(1, UserName);
			mark = pstmt.executeUpdate();
			if(mark>0)
				System.out.println("删除成功");
			else
				System.out.println("删除失败");
			

			
		 catch (Exception e) 
			// TODO Auto-generated catch block
			e.printStackTrace();
		finally

			JDBCUtils.closeResource(rs, pstmt, con);
		
	

	public static void update(String UserName,String OldPassword,String NewPassword)
		//修改用户密码

		Connection con=null;
		PreparedStatement pstmt=null;
		ResultSet rs=null;
		int mark=0;
		try 
			con = JDBCUtils.getConnection();
		    String RequestSql="update user set u_password = ? where u_name = ? and u_password = ? ";
			pstmt = con.prepareStatement(RequestSql);
			
			pstmt.setString(1, NewPassword);
			pstmt.setString(2, UserName);
			pstmt.setString(3, OldPassword);
			mark = pstmt.executeUpdate();
			if(mark>0)
				System.out.println("修改成功");
			else
				System.out.println("修改失败");
			

			
		 catch (Exception e) 
			// TODO Auto-generated catch block
			e.printStackTrace();
		finally

			JDBCUtils.closeResource(rs, pstmt, con);
		
	

	public static void transAccount(String UserName1,String UserName2,int money)
	//转账操作(利用事务)
		Connection con=null;
		PreparedStatement pstmt1=null;
		PreparedStatement pstmt2=null;
		ResultSet rs=null;
		try 
			con = JDBCUtils.getConnection();
			con.setAutoCommit(false);//开启事务
		        String sql="update user set u_balance = u_balance - ? where u_name = ? ";
			pstmt1 = con.prepareStatement(sql);
			
			pstmt1.setInt(1, money);
			pstmt1.setString(2, UserName1);
			pstmt1.executeUpdate();
		
//			String s=null;模拟异常情况(断电、数据库崩溃)
//			s.charAt(2);

			sql = "update user set u_balance = u_balance + ? where u_name = ? ";
			pstmt2 = con.prepareStatement(sql);
			pstmt2.setInt(1, money);
			pstmt2.setString(2, UserName2);
			pstmt2.executeUpdate();			
			
			con.commit();//事务完成
			
		 catch (Exception e) 
			// TODO Auto-generated catch block
			e.printStackTrace();
		finally

			JDBCUtils.closeResource(rs, pstmt1, con);
			JDBCUtils.closeResource(null, pstmt2, null);

分页查询的公式：

技术图片

JDBC工具类：

package JDBCUtils;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;

public class JDBCUtils 
	private static final String url="jdbc:mysql://localhost:3306/dy?useUnicode=true&characterEncoding=utf-8&useSSL=false"; 
	private static final String user="root";
	private static final String password="root";
	private static ArrayList <Connection> Clist = new ArrayList<Connection>();//保存连接
	
	static
		for(int i=0;i<10;i++)
		Connection con = createConnection();//创建连接
		Clist.add(con);//添加到容器中
		
	
	
	public static Connection getConnection()
		if(Clist.isEmpty()==false)
			Connection con = Clist.get(0);//得到容器中的连接
			Clist.remove(con);
			return con;
		else
			return createConnection();//创建连接
		
	
	public static Connection createConnection()
		try 
			Class.forName("com.mysql.jdbc.Driver");
			return DriverManager.getConnection(url,user,password);//建立和mysql数据库的连接
		 catch (Exception e) 
			// TODO Auto-generated catch block
			e.printStackTrace();
		//选择注册驱动
		
		return null;
	
	
	public static void closeResource(ResultSet rs,Statement stmt,Connection con)
		try 
			if(rs!=null)
			rs.close();
		 catch (SQLException e) 
			// TODO Auto-generated catch block
			e.printStackTrace();
		
	
		try 
			if(stmt!=null)
			stmt.close();
		 catch (SQLException e) 
			// TODO Auto-generated catch block
			e.printStackTrace();
		

//		try 
//			if(con!=null)
//			con.close();
//		 catch (SQLException e) 
//			// TODO Auto-generated catch block
//			e.printStackTrace();
//		
		Clist.add(con);
	
	
	public static void closeResource(ResultSet rs,PreparedStatement pstmt,Connection con)
		try 
			if(rs!=null)
			rs.close();
		 catch (SQLException e) 
			// TODO Auto-generated catch block
			e.printStackTrace();
		
	
		try 
			if(pstmt!=null)
			pstmt.close();
		 catch (SQLException e) 
			// TODO Auto-generated catch block
			e.printStackTrace();
		

//		try 
//			if(con!=null)
//			con.close();
//		 catch (SQLException e) 
//			// TODO Auto-generated catch block
//			e.printStackTrace();
//		
		Clist.add(con);//这里的连接不需要关闭，因为在不断建立连接和取消连接的过程会消耗很多时间，所以引入了缓冲池（数据源）的概念

我们上面的工具类的数据源是我们自己利用容器去模拟它去实现的，实际上已经有一些现成的我们可以直接使用的，例如：dbcp、c3p0。

DBCP数据源（工具类版本2）：

package JDBCUtils;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import org.apache.commons.dbcp2.BasicDataSource;

public class JDCPDataSource 
	private static final String url="jdbc:mysql://localhost:3306/dy?useUnicode=true&characterEncoding=utf-8&useSSL=false"; 
	private static final String user="root";
	private static final String password="root";
	private static BasicDataSource ds;
	
	static
		ds = new BasicDataSource();
		ds.setDriverClassName("com.mysql.jdbc.Driver");
		ds.setUrl(url);
		ds.setUsername(user);
		ds.setPassword(password);
		
		ds.setInitialSize(5);//设置初始连接
		ds.setMaxTotal(20);//设置最大连接数
		ds.setMinIdle(3);//设置最小空闲连接（一旦小于最小空闲连接它会自动创建连接以达到最小空闲连接）
	
	public static Connection getConnection()
		
		try 
			return ds.getConnection();
		 catch (SQLException e) 
			// TODO Auto-generated catch block
			e.printStackTrace();
		
		
		return null;
	
	public static void closeResource(ResultSet rs,Statement stmt,Connection con)
		try 
			if(rs!=null)
			rs.close();
		 catch (SQLException e) 
			// TODO Auto-generated catch block
			e.printStackTrace();
		
	
		try 
			if(stmt!=null)
			stmt.close();
		 catch (SQLException e) 
			// TODO Auto-generated catch block
			e.printStackTrace();
		

		try 
			if(con!=null)
			con.close();
		 catch (SQLException e) 
			// TODO Auto-generated catch block
			e.printStackTrace();
		
		
	
	
	public static void closeResource(ResultSet rs,PreparedStatement pstmt,Connection con)
		try 
			if(rs!=null)
			rs.close();
		 catch (SQLException e) 
			// TODO Auto-generated catch block
			e.printStackTrace();
		
	
		try 
			if(pstmt!=null)
			pstmt.close();
		 catch (SQLException e) 
			// TODO Auto-generated catch block
			e.printStackTrace();
		

		try 
			if(con!=null)
			con.close();
		 catch (SQLException e) 
			// TODO Auto-generated catch block
			e.printStackTrace();

注意：使用dbcp时需要下载：第一个是核心包、后面两个都是核心包所依赖的东西，不下程序会显示找不到Class

技术图片

c3p0使用方法类似，不做过多演示　

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