码海拾遗：基于MySQL Connector/C++的MySQL操作(连接池)

1、MySQL安装及简单设置

　　(1)安装：在OSX系统下，可以使用万能的“brew install”命令来进行安装：brew isntall mysql(默认安装最新版的MySQL)

　　(2)启动：brew services start mysql

　　(3)修改密码：update user set authentication_string = password('password'), password_expired = 'N', password_last_changed = now() where user = 'root';

　　　　-->flush privileges;(让修改后的密码生效)

　　(4)允许远程访问：update mysql.user set host = '%' where user = 'root';

2、MySQL Connector/C++安装

　　(1)下载：MySQL Connector/C++源码可以从这里下载

　　(2)安装：解压后将“include”目录下的文件复制到“/usr/local/include”目录下，“lib”目录下的文件复制到“/usr/local/lib”目录下即可

3、示例代码（基于单例模式的懒汉模型）

CConnPool.h

/*
 * CConnPool.h
 *
 *  Created on: Mar 15, 2018
 *      Author: root
 */

#ifndef SRC_CCONNPOOL_H_
#define SRC_CCONNPOOL_H_

#include <list>
#include <string>

#include <pthread.h>

#include <mysql_connection.h>
#include <mysql_driver.h>
#include <cppconn/exception.h>
#include <cppconn/driver.h>
#include <cppconn/connection.h>
#include <cppconn/resultset.h>
#include <cppconn/prepared_statement.h>
#include <cppconn/statement.h>

using namespace sql;
using namespace std;

class CConnPool {
public:
	~CConnPool();
	void InitConnpool(string url, string user, string password, int maxSize);
	Connection* GetConnection();
	void ReleaseConnection(Connection* conn);
	static CConnPool *GetInstance();

private:
	CConnPool();
	Connection*CreateConnection(); //创建一个连接
	void InitConnection(int iInitialSize); //初始化数据库连接池
	void DestoryConnection(Connection *conn); //销毁数据库连接对象
	void DestoryConnPool(); //销毁数据库连接池
	CConnPool(string url, string user, string password, int maxSize); //构造方法

private:
	int curSize; //当前已建立的数据库连接数量
	int maxSize; //连接池中定义的最大数据库连接数
	string user;
	string password;
	string url;
	list<Connection*> connList; //连接池的容器队列  STL list 双向链表
	pthread_mutex_t lock; //线程锁
	static CConnPool *connPool;
	Driver*driver;
};

#endif /* SRC_CCONNPOOL_H_ */

CConnPool.cpp

/*
 * CConnPool.cpp
 *
 *  Created on: Mar 15, 2018
 *      Author: root
 */

#include <stdexcept>
#include <exception>
#include <cstdio>

#include "CConnPool.h"

CConnPool *CConnPool::connPool = NULL;
//CConnPool* CConnPool::connPool = new CConnPool();

CConnPool::CConnPool()
{
	// TODO Auto-generated constructor stub
}

void CConnPool::InitConnpool(string url, string user, string password,
							 int maxSize)
{
	this->maxSize = maxSize;
	this->curSize = 0;
	this->user = user;
	this->password = password;
	this->url = url;
	try
	{
		this->driver = sql::mysql::get_driver_instance();
	}
	catch (sql::SQLException &e)
	{
		perror("驱动连接出错;\n");
	}
	catch (std::runtime_error &e)
	{
		perror("运行出错了\n");
	}
	this->InitConnection(maxSize / 2);
	pthread_mutex_init(&lock, NULL);
}

CConnPool::CConnPool(string url, string user, string password, int maxSize)
{
	this->maxSize = maxSize;
	this->curSize = 0;
	this->user = user;
	this->password = password;
	this->url = url;
	try
	{
		this->driver = sql::mysql::get_driver_instance();
	}
	catch (sql::SQLException &e)
	{
		perror("驱动连接出错;\n");
	}
	catch (std::runtime_error &e)
	{
		perror("运行出错了\n");
	}
	this->InitConnection(maxSize / 2);
	pthread_mutex_init(&lock, NULL);
}

CConnPool *CConnPool::GetInstance()
{
	if (connPool == NULL)
		connPool = new CConnPool("tcp://127.0.0.1:3306", "root", "123456",
								 10);
	return connPool;
}

void CConnPool::InitConnection(int num)
{
	Connection *conn;
	pthread_mutex_lock(&lock);
	for (int i = 0; i < num; ++i)
	{
		conn = CreateConnection();
		if (conn)
		{
			connList.push_back(conn);
			++curSize;
		}
		else
		{
			perror("创建CONNECTION出错");
		}
	}
	pthread_mutex_unlock(&lock);
}

Connection *CConnPool::CreateConnection()
{
	Connection *conn;
	try
	{
		conn = driver->connect(url, user, password); //建立连接
		return conn;
	}
	catch (sql::SQLException &e)
	{
		perror(e.what());
		return NULL;
	}
	catch (std::runtime_error &e)
	{
		perror(e.what());
		return NULL;
	}
}

Connection *CConnPool::GetConnection()
{
	Connection *conn;
	pthread_mutex_lock(&lock);

	if (connList.size() > 0)
	{
		conn = connList.front();
		connList.pop_front();
		if (conn->isClosed())
		{
			delete conn;
			conn = CreateConnection();
		}
		if (conn == NULL)
			--curSize;
		pthread_mutex_unlock(&lock);
		return conn;
	}
	else
	{
		if (curSize < maxSize)
		{
			conn = CreateConnection();
			if (conn)
			{
				++curSize;
				pthread_mutex_unlock(&lock);
				return conn;
			}
			else
			{
				pthread_mutex_unlock(&lock);
				return NULL;
			}
		}
		else
		{
			pthread_mutex_unlock(&lock);
			return NULL;
		}
	}
}

void CConnPool::ReleaseConnection(Connection *conn)
{
	if (conn)
	{
		pthread_mutex_lock(&lock);
		connList.push_back(conn);
		pthread_mutex_unlock(&lock);
	}
}

CConnPool::~CConnPool()
{
	this->DestoryConnPool();
}

void CConnPool::DestoryConnPool()
{
	list<Connection *>::iterator iter;
	pthread_mutex_lock(&lock);
	for (iter = connList.begin(); iter != connList.end(); ++iter)
		this->DestoryConnection(*iter);
	curSize = 0;
	connList.clear();
	pthread_mutex_unlock(&lock);
}

void CConnPool::DestoryConnection(Connection *conn)
{
	if (conn)
	{
		try
		{
			conn->close();
		}
		catch (sql::SQLException &e)
		{
			perror(e.what());
		}
		catch (std::exception &e)
		{
			perror(e.what());
		}
		delete conn;
	}
}

main.cpp

#include <iostream>
#include <string>

#include "CConnPool.h"

using std::cout;
using std::endl;
using std::string;

CConnPool *connpool = CConnPool::GetInstance();

int main(int argc, char *argv[])
{
    Connection *conn;
    Statement *state;
    ResultSet *result;

    conn = connpool->GetConnection();
    state = conn->createStatement();
    state->execute("use mysql");

    result = state->executeQuery("select host,user from user");
    while (result->next())
    {
        try
        {
            string user = result->getString("user");
            string host = result->getString("host");
            cout << user << "@" << host << endl;
        }
        catch (sql::SQLException &e)
        {
            cout << e.what() << endl;
        }
    }

    delete result;
    delete state;
    connpool->ReleaseConnection(conn);

    getchar();
    return 0;
}