一般我們要建立一個數據連線池存放一些Connection連線，當然了，不要放太多，比方說我這裡就只放了三個做例子而已。

每當我們需要使用Connection連線的時候就從中取出來，當他沒有了的時候就等待，等有用完了歡回來了就再取。

當一個事務完成了就會將連線還回去。

具體示例：

配置檔案jdbc.properties

#mysql
driver=com.mysql.jdbc.Driver
url=jdbc:mysql:///mydata?useUnicode=true&characterEncoding=utf-8
userName=root
password=
 

連線池ConnsUtil.java

package cn.hncu.pool;

import java.sql.Connection;
import java.sql.DriverManager;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;

import cn.hncu.utils.ConnectionFactory;

public class ConnsUtil {
	private static List<Connection> pool=new ArrayList<Connection>();
	private static int num=3;
	static {
		try {
			//讀取配置檔案
			Properties p=new Properties();
			p.load(ConnectionFactory.class.getClassLoader().getResourceAsStream("jdbc.properties"));
			String driver=p.getProperty("driver");
			String url=p.getProperty("url");
			String userName=p.getProperty("userName");
			String password=p.getProperty("password");
			Class.forName(driver);
			
			for (int i=0;i<num;i++){
				Connection con=DriverManager.getConnection(url, userName, password);
				pool.add(con);
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
	public static synchronized Connection getConnection() throws Exception{
		if (pool.size()<=0){
			Thread.sleep(100);
			return getConnection();
		}
		return pool.remove(0);
	}
	public static void back(Connection con){
		pool.add(con);
		System.out.println("還回來一個連線");
	}
}
 

package cn.hncu.pool;

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

public class TestPool {

	public static void main(String[] args) {
		Connection con=null;
		try {
			con=ConnsUtil.getConnection();
			con.setAutoCommit(false);
			new SecondThread(1).start();
			new SecondThread(2).start();
			new SecondThread(3).start();
			new SecondThread(4).start();
			new SecondThread(5).start();
			
			Statement st=con.createStatement();
			String sql="insert into stud values('p3001','鳳姐',50)";
			st.execute(sql);
			sql="insert into stud values('p3002','芙蓉姐',40)";
			st.execute(sql);
			
			System.out.println("主執行緒準備提交");
			con.commit();
			System.out.println("主執行緒提交完畢");
		} catch (Exception e) {
			try {
				con.rollback();
				System.out.println("主執行緒回滾了");
			} catch (SQLException e1) {
				throw new RuntimeException("主執行緒事務回滾失敗", e1);
			}
		} finally {
			try {
				if (con!=null){
					con.setAutoCommit(true);
					ConnsUtil.back(con);
					//con.close();//如果要把close內部的功能換成還連線，就需要我們以後的技術來實現
				}
			} catch (SQLException e) {
				throw new RuntimeException("主執行緒連線關閉失敗", e);
			}
		}
	}
}

class SecondThread extends Thread{
	private int n;
	public SecondThread(int n) {
		this.n=n;
	}

	@Override
	public void run() {
		Connection con=null;
		try {
			con=ConnsUtil.getConnection();
			con.setAutoCommit(false);
			Statement st=con.createStatement();
			String sql="insert into stud values('p400"+n+"','鳳姐2',50)";
			st.execute(sql);
			sql="insert into stud values('p410"+n+"','芙蓉姐2',40)";
			st.execute(sql);
			
			System.out.println("第"+n+"個執行緒準備提交");
			con.commit();
			System.out.println("第"+n+"個執行緒提交完畢");
		} catch (Exception e) {
			try {
				con.rollback();
				System.out.println("第"+n+"個執行緒回滾了");
			} catch (SQLException e1) {
				throw new RuntimeException("第"+n+"個事務回滾失敗", e1);
			}
		} finally {
			try {
				if (con!=null){
					con.setAutoCommit(true);
					//con.close();
					ConnsUtil.back(con);
				}
			} catch (SQLException e) {
				throw new RuntimeException("第"+n+"個連線關閉失敗", e);
			}
		}
	}
}