java - 需要代码在java中创建连接池

Question

需要在java中创建连接池的代码吗？我们如何确保连接池不会返回已在使用的相同对象？如果客户端从连接池中取出连接后关闭连接会怎样？

更新 1:

我想用简单的 Java 术语创建它，并想看看它在多线程环境中是如何工作的。我的意思是哪些方法会被同步，哪些不是。这门课也会是公共(public)课吗？如果是，那么任何人都可以访问这个类并重新初始化连接池？

更新 2:

我有一些代码如下。但我不知道如何“关闭来自池的连接将其返回到池中，它不会物理关闭连接。”另外我不明白这个“因为如果从池中借用连接但尚未返回，则它不“可用”并且不能重新分配给池的另一个客户端。”

import java.util.*;
import java.sql.*;

class ConnectionPoolManager
{

 String databaseUrl = "jdbc:mysql://localhost:3306/myDatabase";
 String userName = "userName";
 String password = "userPass";

 Vector connectionPool = new Vector();

 public ConnectionPoolManager()
 {
  initialize();
 }

 public ConnectionPoolManager(
  //String databaseName,
  String databaseUrl,
  String userName,
  String password
  )
 {
  this.databaseUrl = databaseUrl;
  this.userName = userName;
  this.password = password;
  initialize();
 }

 private void initialize()
 {
  //Here we can initialize all the information that we need
  initializeConnectionPool();
 }

 private void initializeConnectionPool()
 {
  while(!checkIfConnectionPoolIsFull())
  {
   System.out.println("Connection Pool is NOT full. Proceeding with adding new connections");
   //Adding new connection instance until the pool is full
   connectionPool.addElement(createNewConnectionForPool());
  }
  System.out.println("Connection Pool is full.");
 }

 private synchronized boolean checkIfConnectionPoolIsFull()
 {
  final int MAX_POOL_SIZE = 5;

  //Check if the pool size
  if(connectionPool.size() < 5)
  {
   return false;
  }

  return true;
 }

 //Creating a connection
 private Connection createNewConnectionForPool()
 {
  Connection connection = null;

  try
  {
   Class.forName("com.mysql.jdbc.Driver");
   connection = DriverManager.getConnection(databaseUrl, userName, password);
   System.out.println("Connection: "+connection);
  }
  catch(SQLException sqle)
  {
   System.err.println("SQLException: "+sqle);
   return null;
  }
  catch(ClassNotFoundException cnfe)
  {
   System.err.println("ClassNotFoundException: "+cnfe);
   return null;
  }

  return connection;
 }

 public synchronized Connection getConnectionFromPool()
 {
  Connection connection = null;

  //Check if there is a connection available. There are times when all the connections in the pool may be used up
  if(connectionPool.size() > 0)
  {
   connection = (Connection) connectionPool.firstElement();
   connectionPool.removeElementAt(0);
  }
  //Giving away the connection from the connection pool
  return connection;
 }

 public synchronized void returnConnectionToPool(Connection connection)
 {
  //Adding the connection from the client back to the connection pool
  connectionPool.addElement(connection);
 }

 public static void main(String args[])
 {
  ConnectionPoolManager ConnectionPoolManager = new ConnectionPoolManager();
 }

}

Answer 1

Need code to create the connection pool in java?

不确定问题是什么，但不要创建另一个连接池，使用现有的解决方案，如 C3P0 , Apache DBCP , Proxool或 BoneCP (该领域的新玩家)。我会使用 C3P0。

How does we make sure that connection pool doesn't return the same object which is already in use?

因为如果一个连接已经从池中借用并且还没有返回，它只是不在池中并且不能分配给池的另一个客户端(资源被从池中移除直到它们被返回)。

How happens if client closed the connection after taking it out from Connection pool?

客户端从池中获得的连接并不是真正的 java.sql.Connection ，它是 java.sql.Connection 的包装器(代理)自定义某些方法的行为。 close() 方法就是其中之一，它不 关闭 Connection 实例，而是将其返回到池中。