第三十四章リンクプールを作成してリンクの多重化を実現する

リンクプールを使用してリンクを取得

public static void main(String[] args) throws SQLException{
		for(int i=0;i<20;i++){
			Connection conn = JdbcUtilsPool.getConnection();
			System.out.println(conn);
			JdbcUtilsPool.free(null, null, conn);
		}
	}

接続の取得と解除

package cn.itcast.jdbc;

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

/**
 *        Connection
 * @author Administrator
 *
 */
public class JdbcUtilsPool {
	private static MyDataSource myDataSource = null;
	private JdbcUtilsPool(){
		
	}
	static{
		try {
			Class.forName("com.mysql.jdbc.Driver");
			myDataSource = new MyDataSource();
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		}
	}
	
	/*    ，     */
	public static Connection getConnection() throws SQLException{
		return  myDataSource.getConnection();
	}
	public static void free(ResultSet rs, Statement st, Connection conn){
		if(rs!=null){
			try {
				rs.close();
			} catch (SQLException e) {
				e.printStackTrace();
			}finally{
				if(st!=null){
					try {
						st.close();
					} catch (SQLException e) {
						e.printStackTrace();
					}finally{
						if(conn != null){
							//conn.close();
							myDataSource.free(conn); //          ，       
						}
					}
				}
			}
		}
	}
	
}

接続プール

package cn.itcast.jdbc;

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

public class MyDataSource {
	
	private LinkedList<Connection> connectionsPool = new LinkedList<Connection>(); //   
	private static String username = "mysqlroot";
	private static String password = "mysqlroot";
	private static String url = "jdbc:mysql://localhost:3306/db_cityinfo";
	private static int initCount = 5; //      
	private static int maxCount = 10;  //      
	private static int currentCount = 0;  //          
	
	/*       */
	public MyDataSource(){
		for(int i=0; i<initCount; i++){
			try {
				this.connectionsPool.addLast(this.createConnection()); //       
				this.currentCount++;
			} catch (SQLException e) {
				throw new ExceptionInInitializerError(e);
			}
		}
	}
	
	/*        */
	public Connection getConnection() throws SQLException{
		synchronized (connectionsPool) {  //  
			if(this.connectionsPool.size() > 0){  //         ，     ，          
				return this.connectionsPool.removeFirst();
			}
			if(this.currentCount < maxCount){ //         ，     ，           
				this.currentCount++;
				return this.createConnection();
			}
			throw new SQLException("     ");  //            ，     
		}
	}
	
	/*    ,        */
	public void free(Connection conn){  
		this.connectionsPool.addLast(conn);
	}
	
	/*    */
	private Connection createConnection() throws SQLException{
		return DriverManager.getConnection(url,username,password);
	}
	
	
}