jdbc中的基本操作

本人是刚学jdbc的小萌新，记录一下java操作数据库的一些基本操作

1.建立与数据库的连接，关闭结果集，声明，连接

package jdbc;

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

public class JDBCUtils {

	private static final String CONNECTIONURL="jdbc:mysql://127.0.0.1:3305/runoob?characterEncoding=UTF-8";
	private static final String USERNAME="root";
	private static final String PASSWORD="zc2001313";
	public static Connection getConnection() {
		
        Connection c=null;
        try {
        	Class.forName("com.mysql.jdbc.Driver");//驱动
        	c = DriverManager.getConnection(CONNECTIONURL,USERNAME,PASSWORD);
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
        return c;
	}
	
		public static void close(ResultSet rs,Statement stmt,Connection c) {
		try {
			if(rs !=null)rs.close();
		}catch (SQLException e) {
			e.printStackTrace();
		}
		try {
			if(stmt !=null)stmt.close();
		}catch(SQLException e) {
			e.printStackTrace();
		}
		try {
			if(c !=null)c.close();
		}catch(SQLException e) {
			e.printStackTrace();
		}
	}
}

2.增删改查操作

package jdbc;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
  
public class TestJDBC { 
//查询表内所有内容
public static void SelectAll() {

    	Connection c=null;//定义在外面，而不是定义在try里面，这样就不是局部变量
    	Statement s =null;
        ResultSet rs=null;
    	try {
            c=JDBCUtils.getConnection();
            s=c.createStatement();//创建statement
            String sql =  "select * from runoob_tbl";//准备sql语句
            rs = s.executeQuery(sql);//执行语句得到结果集
            while(rs.next()) {//查询的两种方式：1.字段名查询（要加引号） 2.查找索引（数字）
            	System.out.println(rs.getInt("runoob_id")+","+rs.getString(2)+","+rs.getString(3)+","+rs.getString(4));
            }
        } catch (SQLException e) {
            
            e.printStackTrace();
        }finally {//谁最后打开，谁先关闭
        		jdbc.JDBCUtils.close(rs, s, c);
        }
  
    }

//按页查询表内内容，pageCount代表一页有几行，pageNumber代表第几页
public static void SelectUserByPage(int pageNumber,int pageCount){
	Connection c=null;//定义在外面，而不是定义在try里面，这样就不是局部变量
	PreparedStatement pstmt =null;
    ResultSet rs=null;
	try {
        c = JDBCUtils.getConnection();
        String sql =  "select * from runoob_tbl limit ?,?";//准备sql语句
        pstmt=c.prepareStatement(sql);//创建preparestatement,p不大写，也没有d
        pstmt.setInt(1, (pageNumber-1)*pageCount);
        pstmt.setInt(2, pageCount);
        rs= pstmt.executeQuery();
        while(rs.next()) {
        	System.out.println(rs.getInt(1)+","+rs.getString(2)+","+rs.getString(3)+","+rs.getString(4));
        }
    } catch (SQLException e) {
        
        e.printStackTrace();
    }finally {//谁最后打开，谁先关闭
    		jdbc.JDBCUtils.close(rs, pstmt, c);
    }
}
 
//这个好像只能插入非中文用户名
public static void insert(String username,String password,int money) {
	Connection c=null;
	PreparedStatement pstmt=null;
	ResultSet rs = null;
	
	c =JDBCUtils.getConnection();
	String sql ="insert into user(username,password,balance)values(?,?,?)";
	try {
		pstmt=c.prepareStatement(sql);
		pstmt.setString(1, username);
		pstmt.setString(2, password);
		pstmt.setInt(3, money);
		int result = pstmt.executeUpdate();
		
	} catch (SQLException e) {
		// TODO Auto-generated catch block
		e.printStackTrace();
	} finally {
		JDBCUtils.close(rs, pstmt, c);
	}
}

//删除操作
public static void delete(int id) {
	Connection c=null;
	PreparedStatement pstmt =null;
	ResultSet rs=null;
	
	c=JDBCUtils.getConnection()	;
	String sql = "delete from user where id = ?";
	
	try {
		pstmt = c.prepareStatement(sql);
		pstmt.setInt(1, id);
		int result = pstmt.executeUpdate();
		if(result >0)System.out.println("删除成功！");
		else System.out.println("删除失败！");
		
	} catch (SQLException e) {
		// TODO Auto-generated catch block
		e.printStackTrace();
	} finally {
		JDBCUtils.close(rs, pstmt, c);
	}
	
}

//更新密码操作
public static void update(int id,String newPassword) {
	Connection c=null;
	PreparedStatement pstmt =null;
	ResultSet rs=null;
	
	c=JDBCUtils.getConnection()	;
	String sql = "update user set password = ? where id = ?";
	
	try {
		pstmt = c.prepareStatement(sql);
		pstmt.setString(1, newPassword);
		pstmt.setInt(2, id);
		int result = pstmt.executeUpdate();
		if(result >0)System.out.println("修改成功！");
		else System.out.println("修改失败！");
		
	} catch (SQLException e) {
		// TODO Auto-generated catch block
		e.printStackTrace();
	} finally {
		JDBCUtils.close(rs, pstmt, c);
	}
}
}

3.转账操作（用到事务）

目标是将用户1：username1 的 money元 转给用户2：username2

//转账的事务操作,所谓事务，即要么其中的操作都完成，要么都失败
public static void transferAccount(String username1,String username2,int money) {
	Connection c = null;
	PreparedStatement pstmt1= null;
	PreparedStatement pstmt2= null;
	ResultSet rs = null;
	
	c=JDBCUtils.getConnection();
    
    try {
    	c.setAutoCommit(false);//开启事务
    	
    	String sql = "update user set balance = balance - ? where username = ?";
    	pstmt1 = c.prepareStatement(sql);
    	pstmt1.setInt(1, money);
    	pstmt1.setString(2, username1);
    	pstmt1.executeUpdate();
    	
    	sql = "update user set balance = balance + ? where username = ?";
    	pstmt2 = c.prepareStatement(sql);
    	pstmt2.setInt(1, money);
    	pstmt2.setString(2,username2);
    	pstmt2.executeUpdate();
    	
    	c.commit();//提交事务
    	
	} catch (SQLException e) {
		// TODO Auto-generated catch block
		e.printStackTrace();
	}finally {
		JDBCUtils.close(rs, pstmt1, c);
		JDBCUtils.close(rs, pstmt2, c);
	}

}

4.验证密码

以下方法为1.0，不太聪明的方法，因为如果有高手的话，会利用sql语句强行登陆

public static boolean CheckUserPassword(String username,String password) {
    	Connection c=null;//定义在外面，而不是定义在try里面，这样就不是局部变量
    	Statement stmt =null;
        ResultSet rs=null;
    	try {
            c = jdbc.JDBCUtils.getConnection();
            stmt=c.createStatement();//创建statement
            String sql =  "select * from user where username='"+username+"' and password='"+password+"'";//准备sql语句
            rs = stmt.executeQuery(sql);//执行语句得到结果集
            if(rs.next()) {
            	return true;
            }else {
            	return false;
            }
        }catch (SQLException e) {
            
            e.printStackTrace();
        }finally {//谁最后打开，谁先关闭
        		jdbc.JDBCUtils.close(rs, stmt, c);
        		
        }
    	return false;//不能讲return false 写在finally 里面，java与c语言不同，java执行return之后，会继续执行下面的语句
    }
    

验证密码1.0版本，这虽然能验证密码，但是由于sql语句注入的问题，这种方法不太安全，所以我们采用2.0的升级版本，用到了preparedstatement

//与下面的验证密码方法1.0相比，2.0升级版可以解决sql注入问题，即输入sql语句强行登陆
public static boolean CheckUserPasswordUp(String username,String password) {
	Connection c=null;//定义在外面，而不是定义在try里面，这样就不是局部变量
	PreparedStatement pstmt =null;
    ResultSet rs=null;
	try {
        c=JDBCUtils.getConnection();
        
        String sql ="select * from user where username=? and password=?";
        pstmt = c.prepareStatement(sql);
        pstmt.setString(1,username);
        pstmt.setString(2,password);
        rs= pstmt.executeQuery();
        if(rs.next())return true;
        else return false;
    } catch (SQLException e) {
        
        e.printStackTrace();
    }finally {//谁最后打开，谁先关闭
    		JDBCUtils.close(rs, pstmt, c);
    		
    }
	return false;//不能讲return false 写在finally 里面，java与c语言不同，java执行return之后，会继续执行下面的语句
}