Database connection pool and dbutils tool

Database connection pool
What is a database connection pool ：
In the use of JDBC When programming , Each time you access the database, you need to create an object , After the access is completed, you also need to disconnect （ Destroy object ）. To avoid frequent creation of database connections , Put forward the database connection pool technology .
The application does not need to create and disconnect objects , Instead, it is left to the database connection pool management .
Database connection pool disconnected , Not destroy objects , Instead, return the connection object to the connection pool .
The database connection pool is responsible for allocation 、 Manage and release database connections , It allows applications to reuse existing database connections , Instead of re establishing .

Schematic diagram of using database connection pool to operate database ：

advantage ： Manage connection objects through database connection pool , Reduce the creation and destruction of database connection objects , Improved database access efficiency .

Basic parameters of database connection pool ：
1. Initialization size ： The number of initial connection objects in the database connection pool
2. maximum connection ： The maximum number of connection objects in the database connection pool
3. Maximum waiting time ： When the user fetches the connection object through the connection pool , The world that needs to wait
4. Maximum free connection ： Database connection pool , When user access tends to stabilize , Maximum number of idle connections
5. Minimum free connection ： At the peak of user access , The minimum number of remaining connection objects in the database connection pool .

DataSource Interface
In order to get the database connection object （Connection）,JDBC Provides javax.sql.DataSource Interface , It is responsible for establishing a connection with the database , And defines the return value Connection Object method ：
Connection getConnection()
Connection getConnection(String username,String password)
Habitually realized javax.sql.DataSource The class of an interface is called a data source , That is, the source of the data . All the information of establishing database connection is stored in the data source .

DBCP data source
DBCP Data source connection pool （DataBase Connection Pool）, By apache Database connection pool technology provided by the organization , Free open source .
In project development , Use DBCP Basic steps ：
Premise import DBCP Of jar package ：commons-dbcp.jar,commons-pool.jar
DBCP Get the connection object ： Set connection parameters . Four connection parameters ：driverName,url,username,password

package cn.itcast.chapter10.example;

import java.sql.Connection;
import java.sql.DatabaseMetaData;
import java.sql.SQLException;

import javax.sql.DataSource;

import org.apache.commons.dbcp.BasicDataSource;


public class Example01 {
    
	public static DataSource ds = null;
	static {
    
		// obtain DBCP The data source implements class objects 
		BasicDataSource bds = new BasicDataSource();
		// Set the four connection parameters required to connect to the database 
		bds.setDriverClassName("com.mysql.jdbc.Driver");
		bds.setUrl("jbdc:mysql://localhost:3306/jdbc");
		bds.setUsername("root");
		bds.setPassword(null);
		// Set connection pool parameters 
		bds.setInitialSize(5);  // Initialize parameters 
		bds.setMaxIdle(10); 
		ds = bds;
	}
	public static void main(String[] args) throws SQLException {
    
		// Database connection pool gets connection object 
		Connection con = ds.getConnection();
		// Get connection parameters 
		DatabaseMetaData metaData = con.getMetaData();
		System.out.println(metaData.getURL());
		System.out.println(metaData.getUserName());
		System.out.println(metaData.getDriverName());
	}
}

BasicDataSource Common methods of class ：

C3P0 data source
C3P0 Data source is one of the most popular database connection pool technologies , Its performance is more superior , It also provides a framework for later data hibernate Good support , It's open source and free .
In project development , Use C3P0 Basic steps ：
Premise import C3P0 Of jar package , Provides C3P0 Core class methods for
Set connection parameters ： Four connection parameters ：driverName,url,username,password

package cn.itcast.chapter10.example;

import java.beans.PropertyVetoException;
import java.sql.SQLException;

import javax.sql.DataSource;

import com.mchange.v2.c3p0.ComboPooledDataSource;

public class Example02 {
    
	public static DataSource ds = null;
	//  initialization C3P0 data source 
	static {
    
		ComboPooledDataSource cpds = new ComboPooledDataSource();

		try {
    
			//  Set four connection parameters 
			cpds.setDriverClass("com.mysql.jdbc.Driver");
			cpds.setJdbcUrl("jdbc:mysql://localhost:3306/jdbc");
			cpds.setUser("root");
			cpds.setPassword("");
			//  Set connection pool parameters 
			cpds.setInitialPoolSize(5);
			cpds.setMaxPoolSize(15);
			ds = cpds;
		} catch (PropertyVetoException e) {
    
			// TODO  Automatically generated  catch  block 
			e.printStackTrace();
		}
	}
	public static void main(String[] args) throws SQLException {
    
		System.out.println(ds.getConnection());
	}
}

ComboPooledDataSource Class ：

DBUtils Tools
DBUtils Tool is introduced ： By apache Provide . yes commons Component one . It's right jdbc Simple encapsulation , Reduce the code for operating the database . Before using , Import required DBUtils Of jar package .
QueryRunner class
QueryRunner Class is DBUtils Core classes under components , Usually and ResultSetHandler Interface with , Yes jdbc The code is simply encapsulated , Reduce the large amount of code for operating the database .
ResultSetHandler Interface
ResultSetHandler The interface is used to handle ResultSet Result set , It can convert the data in the result set into different forms .
ResultSetHandler Provides a set of common implementation classes , As follows ：