并发示例——实现简易的数据库连接池

约定不等于承诺〃 2022-03-16 01:36 200阅读 0赞

## 一、引言 ##

在前一篇文章中[线程间通信][Link 1]，介绍了线程间的通信。主要对实现该机制的两种方式：synchronized+wait-notify模式和 Lock+Condition 模式进行介绍。下面用上面的两种机制，实现简易的数据库连接池，加深理解。

## 二、数据库连接池，方式一 ##

package com.scorpios.mybatis.thread;
    
    import java.sql.Connection;
    import java.sql.DriverManager;
    import java.sql.SQLException;
    import java.util.LinkedList;
    
    public class MyDataSource { 
    
    	private LinkedList<Connection> pool = new LinkedList<>();// 用于存放数据库连接池
    
    	private static final int INIT_CONNECTIONS = 10;// 连接池大小
    
    	private static final String DRIVER_CLASS = "";
    
    	private static final String USER = "";
    
    	private static final String PASSWORD = "";
    
    	private static final String URL = "";
    
    	static { 
    		try { 
    			Class.forName(DRIVER_CLASS);// 模拟加载数据库驱动
    		} catch (ClassNotFoundException e) { 
    			e.printStackTrace();
    		}
    	}
    
    	public MyDataSource2() { 
    		// 循环创建10个连接池
    		for (int i = 0; i < INIT_CONNECTIONS; i++) { 
    			try { 
    				Connection conn = DriverManager.getConnection(URL, USER, PASSWORD);
    				// 加到队列中
    				pool.addLast(conn);
    			} catch (SQLException e) { 
    				e.printStackTrace();
    			}
    		}
    	}
    
    	// 从队列中获取连接
    	public synchronized Connection getConnect() { 
    		Connection result = null;
    		synchronized (pool) { 
    			// 如果连接池中没有连接，则要等待
    			while (pool.size() <= 0) { // 这地方一定要用while，而不是if
    				try { 
    					wait();
    				} catch (InterruptedException e) { 
    					e.printStackTrace();
    				}
    			}
    			// 连接池中有连接
    			if (!pool.isEmpty()) { 
    				result = pool.removeFirst();
    			}
    			return result;
    		}
    	}
    
    	// 释放连接，把连接放回到连接池中
    	public synchronized void release(Connection conn) { 
    		if (conn != null) { 
    			synchronized (pool) { 
    				pool.addLast(conn);
    				notifyAll();
    			}
    		}
    	}
    
    }

## 三、数据库连接池，方式二 ##

package com.scorpios.mybatis.thread;
    
    import java.sql.Connection;
    import java.sql.DriverManager;
    import java.sql.SQLException;
    import java.util.LinkedList;
    import java.util.concurrent.locks.Condition;
    import java.util.concurrent.locks.Lock;
    import java.util.concurrent.locks.ReentrantLock;
    
    public class MyDataSource2 { 
    
    	private LinkedList<Connection> pool = new LinkedList<>();// 用于存放数据库连接池
    
    	private static final int INIT_CONNECTIONS = 10;// 连接池大小
    
    	private static final String DRIVER_CLASS = "";
    
    	private static final String USER = "";
    
    	private static final String PASSWORD = "";
    
    	private static final String URL = "";
    
    	private Lock lock = new ReentrantLock(); // 获取Lock
    	private Condition c1 = lock.newCondition();// 获得Condition
    
    	static { 
    		try { 
    			Class.forName(DRIVER_CLASS);// 模拟加载数据库驱动
    		} catch (ClassNotFoundException e) { 
    			e.printStackTrace();
    		}
    	}
    
    	public MyDataSource() { 
    		// 循环创建10个连接池
    		for (int i = 0; i < INIT_CONNECTIONS; i++) { 
    			try { 
    				Connection conn = DriverManager.getConnection(URL, USER, PASSWORD);
    				// 加到队列中
    				pool.addLast(conn);
    			} catch (SQLException e) { 
    				e.printStackTrace();
    			}
    		}
    	}
    
    	// 从队列中获取连接
    	public Connection getConnect() { 
    		Connection result = null;
    		lock.lock();
    		try { 
    			while (pool.size() <= 0) { 
    				try { 
    					c1.await();
    				} catch (InterruptedException e) { 
    					e.printStackTrace();
    				}
    			}
    			if (!pool.isEmpty()) { 
    				result = pool.removeFirst();
    			}
    			return result;
    		} finally { 
    			lock.unlock();
    		}
    	}
    
    	// 释放连接，把连接放回到连接池中
    	public void release(Connection conn) { 
    		if (conn != null) { 
    			lock.lock();
    			try { 
    				pool.addLast(conn);
    				c1.signal();
    			} finally { 
    				lock.unlock();
    			}
    		}
    	}
    
    }

[Link 1]: https://blog.csdn.net/zxd1435513775/article/details/84862038