JDBC MySQL 01 JDBC operation MySQL (add, delete, modify and query)

Chapter vii. JDBC

One 、 Learning goals

1. understand JDBC principle
2. master Connection Use of interfaces
3. master Statement Use of interfaces
4. master ResultSet Use of interfaces
5. master PreparedStatement Use of interfaces

Two 、 What is? JDBC?

JDBC（Java DataBase Connectivity） yes Java Short for database connection technology . yes Java And the database bridge , It mainly provides the ability to connect various commonly used databases .

3、 ... and 、 Why JDBC?

Data needs to be persisted , It must be saved on disk , Not in memory . For the data in the program , We all use database management system to manage , Nothing more than adding, deleting, modifying and checking , that If in Java Database operation in the program ？ This requires the use of JDBC 了 . in fact , stay Java There are several techniques for operating databases in , For example, the most The original JDBC The way , be based on JDBC Packaged MyBatis frame , Or is it ORM frame Hibernate、SpirngDataJPA etc. .

So-called JDBC In fact, it is a typical case of interface oriented programming ,SUN The company is only responsible for defining JDBC API Interface ( That is to say interface class ), But I'm not responsible for writing specific implementation classes , The preparation of specific implementation classes is handed over to various database manufacturers to implement . The advantage of this is , Once the underlying database is replaced ,Java There is no need to change the program in the code . This group operates the database API be located Java The class library java.sql and javax.sql Two bags

Four 、JDBC Architecture

5、 ... and 、JDBC Programming steps

• stay Java Through the program JDBC The steps to operate the database are fixed , as follows ：

1. Load and register the driver Class.forName(“com.mysql.cj.jdbc.Driver”)
2. establish Connection Connection object ( namely Java The program is established between the client and the database server socket Connect , More specifically tcp Connect )
3. establish Statement object
4. perform SQL sentence
5. obtain ResultSet object ( If it is not a query operation , There will be no such step )
6. Release resources ( The network connection is always released , Otherwise, as the number of connections increases , The database server may crash when it is serious )

6、 ... and 、JDBC API

Provider ： Sun company

The main function ： Establish a connection to the database 、 perform SQL sentence 、 Processing results

​ Content ： Interfaces and classes for programmers to call , Integrated into the java.sql and javax.sql In bag Such as ：

​ 1、DriverManager class Driver management

​ 2、Connection Interface Connection object

​ 3、Statement Interface Perform object

​ 4、ResultSet Interface Result set

6.1DriverManager

• Provider ：Sun company
• effect ： Manage a variety of JDBC drive

6.2JDBC drive

• Provider ： Database vendors
• effect ： Responsible for connecting various databases

6.3JDBC API The main function ：

Establish a connection to the database 、 perform SQL sentence 、 Processing results

• DriverManager ： Depending on the database , management JDBC drive

• Connection ： Responsible for connecting to the database and the task of transferring data

• Statement ： from Connection produce 、 Responsible for the execution of SQL sentence

• ResultSet： Be responsible for the preservation of Statement The query result after execution

6.4Driver Interface

Driver The interface is provided by the database manufacturer , As java Developer , Just use Driver The interface will do . In programming, you should connect to the database , You must first load a specific vendor's database driver , Different databases have different loading methods . Such as ：

• load MySql drive ：Class.forName(“com.mysql.jdbc.Driver”);

• load Oracle drive ：Class.forName(“oracle.jdbc.driver.OracleDriver”);

6.5Connection Interface

Connection A connection to a specific database （ conversation ）, Execute in the connection context sql Statement and return the result .

DriverManager.getConnection(url, user, password) The method is based on JDBC URL Database defined in Connection Connected to the .

// Connect MySql database ：
Connection conn = DriverManager.getConnection("jdbc:mysql://host:port/database", "user", "password");

// Connect Oracle database ：
Connection conn = DriverManager.getConnection("jdbc:oracle:thin:@host:port:database", "user", "password");

// Connect SqlServer database ：
Connection conn = DriverManager.getConnection("jdbc:microsoft:sqlserver://host:port; DatabaseName=database", "user", "password");

7、 ... and 、JDBC Working process diagram ：

8、 ... and 、JDBC Programming templates

Nine 、 Three elements of database connection

1. java.sql.Driver Implementation class of interface (JDBC API The connection with the corresponding database server depends on this interface , Otherwise, how to establish a relationship between the interface and the implementation class ？)

   • This driver implementation class is in the drivers provided by various database manufacturers

2. Connect URL( This url The network address and port number of the database server are specified in , And want to use DBMS Which database in )

   • This URL In fact, it is equivalent to a hyperlink , A website , But the protocol it uses is jdbc It's just an agreement . As shown in the figure below, the driver will be based on this URL The rules of , Take out URL Useful information in

3. User name and password ( To operate a database , You must provide the corresponding user name and password to verify your identity )
   • This is in JDBC API Can be specified separately in , You can also splice it directly to url In the parameters after

Ten 、 Use pure Java Way to connect MySql database ：

• from JDBC Drive direct access to the database

• advantage ： Completely Java Code , Fast 、 Cross platform

• shortcoming ： Access to different databases requires downloading dedicated JDBC drive

package cn.ketai.jdbc;

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

/** * @author Aiden */
public class JDBCDemo {
     
	/** *  preparation ： * 1. Download from official website MySql Drive pack ：https://dev.mysql.com/downloads/file/?id=494900 * 2. Introduce the drive package into the project  */
	public static void main(String[] args) {
     
		Connection conn = null;// Connection object 
		try {
     
			// 1. The load driver 
			Class.forName("com.mysql.cj.jdbc.Driver");
			// 2. Establish a database connection 
			conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/epet?serverTimezone=Asia/Shanghai", "root", "root");
			//  Determine if the connection is successful 
			if (conn != null) {
     
				System.out.println(" Successful connection .");
			} else {
     
				System.out.println(" The connection fails ！！！");
			}
		} catch (ClassNotFoundException e) {
     
			e.printStackTrace();
		} catch (SQLException e) {
     
			e.printStackTrace();
		} finally {
     
			if (conn != null) {
     // 3. If the connection is not empty, close the current connection 
				try {
     
					conn.close();
				} catch (SQLException e) {
     
					e.printStackTrace();
				}
			}
		}
	}
}

11、 ... and 、 Use Statement Execute the object to realize the new operation

package cn.ketai.jdbc;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;
/** * @author Aiden */
public class StatementDemo {
     

	public static void main(String[] args) {
     
		Connection conn = null;// Connection object 
		Statement stmt = null;// Perform object 
		try {
     
			// 1. The load driver 
			Class.forName("com.mysql.cj.jdbc.Driver");
			// 2. Establish a database connection 
			conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/epet?serverTimezone=Asia/Shanghai", "root", "root");
			// 3. Instantiate the execution object 
			stmt = conn.createStatement();
			// 4. Prepare the new to be executed Sql sentence ：
			String sql = "INSERT INTO `dog`(`name`,`health`,`love`,`strain`)VALUES (' A mu ',98,90,' Shepherd Dog ');";
			// 5. Start execution and return the execution result , Return the number of affected rows 
			int result = stmt.executeUpdate(sql);
			if (result > 0) {
     
				System.out.println(" Successful operation ");
			} else {
     
				System.out.println(" operation failed ！！！");
			}
		} catch (ClassNotFoundException e) {
     
			e.printStackTrace();
		} catch (SQLException e) {
     
			e.printStackTrace();
		} finally {
     
			if (stmt != null) {
     
				try {
     
					stmt.close();//  Close the execution object 
				} catch (SQLException e) {
     
					e.printStackTrace();
				}
			}
			if (conn != null) {
     
				try {
     
					conn.close();//  Close the current connection 
				} catch (SQLException e) {
     
					e.printStackTrace();
				}
			}
		}
	}
}

Twelve 、 Use Statement Execute object implementation modification

package cn.ketai.jdbc;

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

/** * @author Aiden */
public class StatementDemo2 {
     

	public static void main(String[] args) {
     
		Connection conn = null;// Connection object 
		Statement stmt = null;// Perform object 
		try {
     
			// 1. The load driver 
			Class.forName("com.mysql.cj.jdbc.Driver");
			// 2. Establish a database connection 
			conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/epet?serverTimezone=Asia/Shanghai", "root", "root");
			// 3. Instantiate the execution object 
			stmt = conn.createStatement();
			// 4. Prepare the modifications to be performed Sql sentence ：
			String sql = "update dog set love=90,health=100 where id=1;";// Change implemented sql sentence 
			// 5. Start execution and return the execution result , Return the number of affected rows 
			int result = stmt.executeUpdate(sql);
			if (result > 0) {
     
				System.out.println(" Successful operation ");
			} else {
     
				System.out.println(" operation failed ！！！");
			}
		} catch (ClassNotFoundException e) {
     
			e.printStackTrace();
		} catch (SQLException e) {
     
			e.printStackTrace();
		} finally {
     
			if (stmt != null) {
     
				try {
     
					stmt.close();//  Close the execution object 
				} catch (SQLException e) {
     
					e.printStackTrace();
				}
			}
			if (conn != null) {
     
				try {
     
					conn.close();//  Close the current connection 
				} catch (SQLException e) {
     
					e.printStackTrace();
				}
			}
		}
	}

}

13、 ... and 、 Use Statement and ResultSet Implement query operation

package cn.ketai.jdbc;

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

/** * @author Aiden */
public class ResultSetDemo {
     

	public static void main(String[] args) {
     
		Connection conn = null;// Connection object 
		Statement stmt = null;// Perform object 
		ResultSet rs=null;// Result set 
		try {
     
			// 1. The load driver 
			Class.forName("com.mysql.cj.jdbc.Driver");
			// 2. Establish a database connection 
			conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/epet?serverTimezone=Asia/Shanghai", "root", "root");
			// 3. Instantiate the execution object 
			stmt = conn.createStatement();
			// 4. Prepare the query to be executed Sql sentence ：
			String sql = "SELECT `id`,`name`,`health`,`love`,`strain` FROM `dog`;";
			//5. Start execution and return the execution result 
			rs=stmt.executeQuery(sql) ;
			// Loop traversal display 
			System.out.println(" Number \t name \t Health value \t Intimacy \t Varieties ");
			while (rs.next()) {
     
				System.out.println(rs.getInt("id")+"\t"+rs.getString("name")+"\t"
			    +rs.getInt("health")+"\t"+rs.getInt("love")+"\t"+rs.getString("strain"));
			}
		} catch (ClassNotFoundException e) {
     
			e.printStackTrace();
		} catch (SQLException e) {
     
			e.printStackTrace();
		} finally {
     
			if(rs!=null) {
     
				try {
     
					rs.close();
				} catch (SQLException e) {
     
					e.printStackTrace();
				}
			}
			if (stmt != null) {
     
				try {
     
					stmt.close();//  Close the execution object 
				} catch (SQLException e) {
     
					e.printStackTrace();
				}
			}
			if (conn != null) {
     
				try {
     
					conn.close();//  Close the current connection 
				} catch (SQLException e) {
     
					e.printStackTrace();
				}
			}
		}
	}
}

fourteen 、Statement Common methods

Method name	say bright
ResultSet executeQuery(String sql)	perform SQL Query and get ResultSet object
int executeUpdate(String sql)	Insert can be performed 、 Delete 、 Update and other operations , The return value is the number of rows affected by the operation **
boolean execute(String sql)	Can execute any SQL sentence , Then get a Boolean value , Indicates whether to return ResultSet

15、 ... and 、ResultSet Common methods

Method name	say bright
boolean next( )	Moves the cursor down one line from its current position
boolean previous()	The cursor moves up one line from its current position
void close()	close ResultSet object
int getInt(int colIndex)	With int Get the specified column number value of the current row of the result set in the form of
int getInt(String colLabel)	With int Get the specified column name value of the current row of the result set in the form of
float getFloat(int colIndex)	With float Get the specified column number value of the current row of the result set in the form of
float getFloat(String colLabel)	With float Get the specified column name value of the current row of the result set in the form of
String getString(int colIndex)	With String Get the specified column number value of the current row of the result set in the form of
String getString(String colLabel)	With String Get the specified column name value of the current row of the result set in the form of

sixteen 、SQL Inject

package cn.ketai.jdbc;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Scanner;
/** * @author Aiden */
public class LoginDemo {
     
	public static void main(String[] args) {
     
		Connection conn = null;//  Connection object 
		Statement stmt = null;//  Perform object 
		ResultSet rs = null;//  Result set 
		Scanner input = new Scanner(System.in);
		try {
     
			// 1. The load driver 
			Class.forName("com.mysql.cj.jdbc.Driver");
			// 2. Establish a database connection 
			conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/epet?serverTimezone=Asia/Shanghai", "root", "root");
			// 3. Instantiate the execution object 
			stmt = conn.createStatement();
			System.out.println(" Please enter a user name ：");
			String name = input.next();
			System.out.println(" Please input a password ：");
			String password = input.next();
			// 4. Splice login query statements ：
			String sql = " SELECT * FROM `master` WHERE `name`='" + name + "' AND `password`='" + password + "';";
			// 5. Start execution and return the execution result 
			rs = stmt.executeQuery(sql);
			if (rs.next()) {
     
				System.out.println(" Login successful .");
			}else {
     
				System.out.println(" Login failed , Wrong username and password ！");
			}

		} catch (ClassNotFoundException e) {
     
			e.printStackTrace();
		} catch (SQLException e) {
     
			e.printStackTrace();
		} finally {
     
			if (rs != null) {
     
				try {
     
					rs.close();
				} catch (SQLException e) {
     
					e.printStackTrace();
				}
			}
			if (stmt != null) {
     
				try {
     
					stmt.close();//  Close the execution object 
				} catch (SQLException e) {
     
					e.printStackTrace();
				}
			}
			if (conn != null) {
     
				try {
     
					conn.close();//  Close the current connection 
				} catch (SQLException e) {
     
					e.printStackTrace();
				}
			}
		}
	}
}

test result ：

 Please enter a user name ：
 Li Ming 
 Please input a password ：
123'or'1'='1
 Login successful .

seventeen 、 How to avoid SQL Injection potential ？

Use PreparedStatement Interface

• Inherited from Statement Interface
• Than Statement Objects are more flexible to use , More efficient
• Improved code maintainability , Improved security .

eighteen 、PreparedStatement Perform object

package cn.ketai.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;
import java.util.Scanner;

/** * @author Aiden */
public class PreparedStatementDemo {
     
	public static void main(String[] args) {
     
		Connection conn = null;//  Connection object 
		PreparedStatement pstmt = null;//  Perform object 
		ResultSet rs = null;//  Result set 
		Scanner input = new Scanner(System.in);
		try {
     
			// 1. The load driver 
			Class.forName("com.mysql.cj.jdbc.Driver");
			// 2. Establish a database connection 
			conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/epet?serverTimezone=Asia/Shanghai", "root", "root");
			//  User control day input 
			System.out.println(" Please enter a user name ：");
			String name = input.next();
			System.out.println(" Please input a password ：");
			String password = input.next();
			// 3. Login validation query statement ：
			String sql = " SELECT * FROM `master` WHERE `name`=? AND `password`=?;";
			// 4. Instantiate the execution object 
			pstmt = conn.prepareStatement(sql);
			//5. Set parameters 
			pstmt.setObject(1, name);
			pstmt.setObject(2, password);
			// 5. Start execution and return the execution result 
			rs = pstmt.executeQuery();
			if (rs.next()) {
     
				System.out.println(" Login successful .");
			} else {
     
				System.out.println(" Login failed , Wrong username and password ！");
			}
		} catch (ClassNotFoundException e) {
     
			e.printStackTrace();
		} catch (SQLException e) {
     
			e.printStackTrace();
		} finally {
     
			if (rs != null) {
     
				try {
     
					rs.close();
				} catch (SQLException e) {
     
					e.printStackTrace();
				}
			}
			if (pstmt != null) {
     
				try {
     
					pstmt.close();//  Close the execution object 
				} catch (SQLException e) {
     
					e.printStackTrace();
				}
			}
			if (conn != null) {
     
				try {
     
					conn.close();//  Close the current connection 
				} catch (SQLException e) {
     
					e.printStackTrace();
				}
			}
		}
	}
}

nineteen 、 Common mistakes

Use JDBC When connecting to the database , Frequent mistakes

1. JDBC The name of the driver class is written incorrectly , Lead to ClassNotFoundException abnormal
2. Data connection string 、 Database user name 、 Wrong password , Lead to SQLException abnormal
3. After the database operation , The database connection is not closed , As a result, system resources are still occupied
4. The close database connection statement is not put into finally In the block , As a result, the statement may not be executed

twenty 、 Summary of this chapter