java數據庫緩衝池的好處和基本原理(轉載)

package connectionpool;

import java.lang.reflect.Proxy;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Stack;

import test.TestInterface;

public class ConnectionPool {

 Stack<Connection> st = new Stack<Connection>();  //創建一個堆棧，作爲池子
 private static ConnectionPool instance = new ConnectionPool();  //單例模式
 public static int initialPoolSize = 5;
 public static String dbName = "test";
 public static String userName = "root";
 public static String userPasswd = "";

 private ConnectionPool() {
  for(int i = 0; i < initialPoolSize; i++)  //初始化緩衝池
   try {
    createConnection().close();
   } catch (Exception e) {
    e.printStackTrace();
   }
 }

 public synchronized static Connection getConnection() throws Exception {
  if (instance.st.size() > 0) return instance.st.pop();
  else return createConnection();
 }

 synchronized static void returnConnection(Connection conn) {
  instance.st.push(conn);
 }

 private static Connection createConnection() throws Exception { //以mysql爲例　創建數據庫連接
  String url="jdbc:mysql://localhost/"+dbName+"?user="+userName+"&password="+userPasswd;
  Class.forName("com.mysql.jdbc.Driver").newInstance();
  Connection connection=DriverManager.getConnection(url);
  ConnectionProxy handler = new ConnectionProxy(connection);
  Connection proxy = (Connection ) Proxy.newProxyInstance(  //創建代理
    connection.getClass().getClassLoader(),
    connection.getClass().getInterfaces(),handler);
  return proxy;
 }
}
接着實現代理類

package connectionpool;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.sql.Connection;

public class ConnectionProxy implements InvocationHandler{

 Connection delegate; 
 ConnectionProxy(Connection delegate) {
  this.delegate = delegate;
 }

 public Object invoke(Object proxy, Method method, Object[] args)
   throws Throwable {
  try {
   if ("close".equals(method.getName())) {  //在close函數處設置鉤子
    ConnectionPool.returnConnection((Connection) proxy);  
    //將數據庫連接歸還緩衝池，跳過了原來的close()函數
    // 這裏的proxy實際上就是Connection的一個代理實例
   }
   else return method.invoke(delegate, args);
  } catch (Exception e){
  }
  return null;
 }

}

使用緩衝池很簡單 ConnectionPool.getConnection();

使用完connection後，直接執行close()函數就行了，connection將返回緩衝池中而不是真正的關閉

當然這只是實現了很簡單的一個緩衝池，實用化還需要加上其他一些功能

比如關閉idle連接等等

接下來介紹一個實用的java數據庫緩衝池 c3p0。