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MySQL——JDBC

2022-07-03 21:11:00 【Can't learn java】

List of articles

1、 Database driven
2、JDBC
3、 first JDBC Program
4、 Step summary
5、JDBC Object interpretation
6、 Write tool class
7、JDBC Operational transaction
8、 Database connection pool
- 8.1 、DBCP：
- 8.2、c3p0

1、 Database driven

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The program needs to be driven by database , Dealing with databases

2、JDBC

SUN Companies to simplify the development of （ Unification of data ） operation , Provides a （Java Operating the database ） standard , Be commonly called JDBC
For developers , Just master JDBC Interface operation

3、 first JDBC Program

Create test database

CREATE DATABASE `jdbcStudy` CHARACTER SET utf8 COLLATE utf8_general_ci;

USE `jdbcStudy`;

CREATE TABLE `users`(
 `id` INT PRIMARY KEY,
 `NAME` VARCHAR(40),
 `PASSWORD` VARCHAR(40),
 `email` VARCHAR(60),
 birthday DATE
);

 INSERT INTO `users`(`id`,`NAME`,`PASSWORD`,`email`,`birthday`)
VALUES('1','zhangsan','123456','[email protected]','1980-12-04'),
('2','lisi','123456','[email protected]','1981-12-04'),
('3','wangwu','123456','[email protected]','1979-12-04')

Import database driver

Write test code

package demo;

import java.sql.*;

// first JDBC Program 
public class JdbcFirstDemo {
      
    public static void main( String[] args ) throws ClassNotFoundException, SQLException {
      
        //1. The load driver 
        Class.forName("com.mysql.jdbc.Driver"); // Fixed writing , The load driver 

        //2. Connection information 
        String url = "jdbc:mysql://localhost:3306/jdbcstudy?useUnicode=true&characterEncoding=utf8&useSSL=false";
        String username = "root";
        String password = "123456";
        //3. Successful connection   Database objects  Connection  On behalf of the database 
        Connection connection = DriverManager.getConnection(url, username, password);
        //4. perform SQL The object of  Statement  perform sql The object of 
        Statement statement = connection.createStatement();
        //5. perform SQL The object of   Go to   perform SQL, There may be results , View return results 
        String sql="SELECT * FROM users";
        ResultSet resultSet = statement.executeQuery(sql);  // Return result set , The result set encapsulates all the query results 
        while (resultSet.next()){
      
            System.out.println("id="+resultSet.getObject(1));
            System.out.println("name="+resultSet.getObject(2));
            System.out.println("pwd="+resultSet.getObject(3));
            System.out.println("email="+resultSet.getObject(4));
            System.out.println("birthday="+resultSet.getObject(5));
            System.out.println("======================");
        }
        //6. Release the connection 
        resultSet.close();
        statement.close();
        connection.close();
    }
}

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4、 Step summary

The load driver
Connect to database DriverManager
Get executed sql The object of Statement
Get the returned result set

5、JDBC Object interpretation

Class.forName(“com.mysql.jdbc.Driver”); // The load driver
connection： Database objects , Get a database
statement： perform SQL sentence
1. statement.executeQuery(sql) // Query statement , return ResultSet Result set
2. statement.executeUpdate(sql) // UPDATE statement , Returns the number of updated rows
3. statement.execute(sql) // whatever SQL sentence
ResultSet： SQL Query result set , According to the type of database
1. resultSet.next() // The pointer , Move to the next data
2. resultSet.getInt( Parameters ); // Get integer data , It can be a subscript ( from 1 Start ), It can also be " Table field name "
3. resultSet.getString( Parameters ); // Get string data , It can be a subscript ( from 1 Start ), It can also be " Table field name "
4. resultSet.getObject( Parameters ); // Get arbitrary data , It can be a subscript ( from 1 Start ), It can also be " Table field name "
Release resources ：
1. resultSet.close();
2. statement.close();
3. connection.close();

6、 Write tool class

stay src Create under directory db.properties file

driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/jdbcstudy?useUnicode=true&characterEncoding=utf8&useSSL=false
username = root
password = 123456

Create a tool class JdbcUtils

package demo;

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

public class JdbcUtils {
      
    private static String driver=null;
    private static String url=null;
    private static String username=null;
    private static String password=null;
    static {
      
        try{
      
            InputStream in = JdbcUtils.class.getClassLoader().getResourceAsStream("db.properties");
            Properties properties = new Properties();
            properties.load(in);
            driver= properties.getProperty("driver");
            url= properties.getProperty("url");
            username= properties.getProperty("username");
            password= properties.getProperty("password");
            // 1. The driver only loads once 
            Class.forName(driver);
        }catch (IOException e){
      
        } catch (ClassNotFoundException e) {
      
            e.printStackTrace();
        }
    }

    //  Get the connection 
    public static Connection getConnection() throws SQLException {
      
        return DriverManager.getConnection(url, username, password);
    }

    // Release resources 
    public static void release( Connection conn, Statement st,ResultSet rs ){
      
        if(rs!=null){
      
            try {
      
                rs.close();
            } catch (SQLException throwables) {
      
                throwables.printStackTrace();
            }
        }
        if(st!=null){
      
            try {
      
                st.close();
            } catch (SQLException throwables) {
      
                throwables.printStackTrace();
            }
        }
        if(conn!=null){
      
            try {
      
                conn.close();
            } catch (SQLException throwables) {
      
                throwables.printStackTrace();
            }
        }
    }
}

Use tool class

package demo;

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

public class TestInsert {
      
    public static void main( String[] args ) {
      
        Connection conn=null;
        Statement st=null;
        ResultSet rs=null;
        try {
      
            conn = JdbcUtils.getConnection();// Get database connection 
            st = conn.createStatement();    // get SQL Execution object of 
            String sql="INSERT\tINTO users(`id`,`NAME`,`PASSWORD`,`email`,`birthday`) " +
                    "VALUES(4,'Java be unable to learn how to do sth. ','123456','[email protected]','2022-07-02')";
            int i = st.executeUpdate(sql);
            if(i>0){
      
                System.out.println(" Insert the success ");
            }
        } catch (SQLException throwables) {
      
            throwables.printStackTrace();
        } finally {
      
            JdbcUtils.release(conn,st,rs);
        }

    }
}

7、JDBC Operational transaction

7.1、 Create table

--  Create a user table 
create table account(
    id int primary key auto_increment,
    name varchar(40),
    money float
);

--  insert data 
insert into account(name,money) values ('A',1000);
insert into account(name,money) values ('B',1000);
insert into account(name,money) values ('C',1000);

7.2、 Business

Either they all succeed , Or they all failed

ACID principle ：

Atomicity ： All or nothing , All or nothing
Uniformity ： The total remains unchanged
Isolation, ： Multiple threads do not interfere with each other
1. Dirty reading ： One transaction reads another transaction that is not committed
2. It can't be read repeatedly ： In the same business , Repeatedly read the data in the table , Table data has changed
3. Virtual reading （ Fantasy reading ）： In a business , Read the data inserted by others , It leads to inconsistent results before and after reading
persistence ： Once submitted, it's irreversible , Persist to database

package demo01;

import demo.JdbcUtils;

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

public class TestTransaction01 {
      
    public static void main( String[] args ) {
      
        Connection conn=null;
        PreparedStatement st=null;
        ResultSet rs=null;
        try {
      
            conn = JdbcUtils.getConnection();

            // Turn off automatic submission of the database , Automatically opens the transaction 
            conn.setAutoCommit(false);

            String sql1="update account set money = money-100 where name ='A'";
            st = conn.prepareStatement(sql1);
            st.execute();

            int x = 1/0;    // Report errors 

            String sql2="update account set money = money+100 where name ='B'";
            st = conn.prepareStatement(sql2);
            st.execute();
            // Commit transaction 
            conn.commit();
            System.out.println(" Successful operation ");
        } catch (SQLException throwables) {
      
            try {
      
                conn.rollback();    // If it fails, roll back , Rollback by default 
            } catch (SQLException e) {
      
                e.printStackTrace();
            }
        } finally {
      
            JdbcUtils.release(conn,st,rs);
        }


    }
}

7.3、 summary

Start business ： conn.setAutoCommit(false);
A set of business execution completed , Commit transaction
Can be in catch The definition shown in the statement , Rollback statement , By default, failure rolls back

8、 Database connection pool

Database connection —— completion of enforcement —— Release
Connect —— It is a waste of system resources
Pool technology ： Prepare some resources in advance , Come and connect with the prepared
1. Minimum connections
2. maximum connection
3. Waiting for timeout
Write connection pools , Implement an interface DataSource
1. Open source data source implementation
2. DBCP
3. C3P0
4. Druid
- Only , In project development, there is no need to write code to connect to the database

8.1 、DBCP：

establish dbcpconfig.properties file

# connections setting up   The nouns in this , yes DBCP Defined in the data source 
driverClassName=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/jdbcstudy?userUnicode=true&characterEncoding=utf8&useSSL=false
username=root
password=123456

#<!--  Initialize connection  -->
initialSize=10

# Maximum number of connections 
maxActive=50

#<!--  Maximum free connection  -->
maxIdle=20

#<!--  Minimum free connection  -->
minIdle=5

#<!--  Timeout wait time in milliseconds  6000 millisecond /1000 be equal to 60 second  -->
maxWait=60000

#JDBC The format of the connection attribute attribute attached to the driver when establishing the connection must be as follows ：【 Property name =property;】
# Be careful ："user"  And  "password"  Two attributes are explicitly passed , So there's no need to include them .
connectionProperties=useUnicode=true;characterEncoding=utf8

# Specifies the automatic commit of connections created by the connection pool （auto-commit） state .
defaultAutoCommit=true

#driver default  Specifies the read-only... Of the connection created by the connection pool （read-only） state .
# If the value is not set , be “setReadOnly” Method will not be called .（ Some drivers do not support read-only mode , Such as ：Informix）
defaultReadOnly=

#driver default  Specify the transaction level of the connection created by the connection pool （TransactionIsolation）.
# The available values are one of the following ：（ Details visible javadoc.）NONE,READ_UNCOMMITTED, READ_COMMITTED, REPEATABLE_READ, SERIALIZABLE
defaultTransactionIsolation=READ_COMMITTED

Tool class

package demo02;

import demo.JdbcUtils;
import org.apache.commons.dbcp2.BasicDataSource;
import org.apache.commons.dbcp2.BasicDataSourceFactory;

import java.io.InputStream;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Properties;

public class JdbcUtils_DBCP {
      
    private static BasicDataSource dataSource = null;
    static {
      
        try{
      
            InputStream in = JdbcUtils.class.getClassLoader().getResourceAsStream("dbcpconfig.properties");
            Properties properties = new Properties();
            properties.load(in);

            // create data source   Factory mode --> Create objects 
            dataSource = BasicDataSourceFactory.createDataSource(properties);

        }catch (Exception e){
      
        }
    }

    //  Get the connection 
    public static Connection getConnection() throws SQLException {
      
        return dataSource.getConnection();  // Get the connection from the data source 
    }

    // Release resources 
    public static void release( Connection conn, Statement st, ResultSet rs ){
      
        if(rs!=null){
      
            try {
      
                rs.close();
            } catch (SQLException throwables) {
      
                throwables.printStackTrace();
            }
        }
        if(st!=null){
      
            try {
      
                st.close();
            } catch (SQLException throwables) {
      
                throwables.printStackTrace();
            }
        }
        if(conn!=null){
      
            try {
      
                conn.close();
            } catch (SQLException throwables) {
      
                throwables.printStackTrace();
            }
        }
    }
}

Test code

package demo02;

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

public class TestDBCP {
      
    public static void main( String[] args ) {
      
        Connection conn=null;
        Statement st=null;
        ResultSet rs=null;
        try {
      
            conn = JdbcUtils_DBCP.getConnection();// Get database connection 
            st = conn.createStatement();    // get SQL Execution object of 
            String sql="INSERT INTO users(`id`,`NAME`,`PASSWORD`,`email`,`birthday`) " +
                    "VALUES(6,'JavaStudy','123456','[email protected]','2022-07-02')";
            int i = st.executeUpdate(sql);
            if(i>0){
      
                System.out.println(" Insert the success ");
            }
        } catch (SQLException throwables) {
      
            throwables.printStackTrace();
        } finally {
      
            JdbcUtils_DBCP.release(conn,st,null);
        }

    }
}

8.2、c3p0

establish c3p0-config.xml file

<?xml version="1.0"  encoding="UTF-8"?>
<c3p0-config>
    <default-config>
        <property name="driverClass">com.mysql.jdbc.Driver</property>
        <property name="jdbcUrl">jdbc:mysql://localhost:3306/jdbcstudy?userUnicode=true&amp;characterEncoding=utf8&amp;useSSL=false&amp;</property>
        <property name="user">root</property>
        <property name="password">123456</property>

        <property name="acquiredIncrement">5</property>
        <property name="initialPoolSize">10</property>
        <property name="minPoolSize">5</property>
        <property name="maxPoolSize">20</property>
    </default-config>
    <name-config name="MySQL">
        <property name="driverClass">com.mysql.jdbc.Driver</property>
        <property name="jdbcUrl">jdbc:mysql://localhost:3306/jdbcstudy?userUnicode=true&amp;characterEncoding=utf8&amp;useSSL=false&amp;</property>
        <property name="user">root</property>
        <property name="password">123456</property>
        <property name="acquiredIncrement">5</property>
        <property name="initialPoolSize">10</property>
        <property name="minPoolSize">5</property>
        <property name="maxPoolSize">20</property>
    </name-config>

</c3p0-config>

Tool class ：

package demo02;

import com.mchange.v2.c3p0.ComboPooledDataSource;

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

public class JdbcUtils_c3p0 {
      
    private static ComboPooledDataSource dataSource = null;
    static {
      
        try{
      

            // create data source   Factory mode --> Create objects 
            dataSource = new ComboPooledDataSource();

        }catch (Exception e){
      
        }
    }

    //  Get the connection 
    public static Connection getConnection() throws SQLException {
      
        return dataSource.getConnection();  // Get the connection from the data source 
    }

    // Release resources 
    public static void release( Connection conn, Statement st, ResultSet rs ){
      
        if(rs!=null){
      
            try {
      
                rs.close();
            } catch (SQLException throwables) {
      
                throwables.printStackTrace();
            }
        }
        if(st!=null){
      
            try {
      
                st.close();
            } catch (SQLException throwables) {
      
                throwables.printStackTrace();
            }
        }
        if(conn!=null){
      
            try {
      
                conn.close();
            } catch (SQLException throwables) {
      
                throwables.printStackTrace();
            }
        }
    }
}

Test code ：

package demo02;

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

public class Testc3p0 {
      
    public static void main( String[] args ) {
      
        Connection conn=null;
        Statement st=null;
        ResultSet rs=null;
        try {
      
            conn = JdbcUtils_c3p0.getConnection();// Get database connection 
            st = conn.createStatement();    // get SQL Execution object of 
            String sql="INSERT INTO users(`id`,`NAME`,`PASSWORD`,`email`,`birthday`) " +
                    "VALUES(10,'JavaStudy','123456','[email protected]','2022-07-02')";
            int i = st.executeUpdate(sql);
            if(i>0){
      
                System.out.println(" Insert the success ");
            }
        } catch (SQLException throwables) {
      
            throwables.printStackTrace();
        } finally {
      
            JdbcUtils_DBCP.release(conn,st,null);
        }

    }
}