Java：实现简单的连接池

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数据库连接是非常珍贵的资源，能够复用则尽量复用。这里我们实现数据库连接。

import java.sql.Connection;import java.sql.DriverManager;import java.sql.SQLException;import java.util.ArrayList;import java.util.List;public class ConnectionPool {    private List<ConnectionPair> connectionPairs;    private static final int DEFAULT_SIZE = 16;    private int size;    public ConnectionPool(String url, String username, String password) {        connectionPairs = new ArrayList<>(DEFAULT_SIZE);        size = DEFAULT_SIZE;        try {            Class.forName("com.mysql.jdbc.Driver");            for (int i = 0; i < size; i++) {                ConnectionPair pair = new ConnectionPair();                pair.connection = DriverManager.getConnection(url, username, password);                pair.isAvailable = true;                connectionPairs.add(pair);            }        } catch (ClassNotFoundException | SQLException e) {            e.printStackTrace();        }    }    // 同步获取connection，如果当前队列没有可用的connection，则阻塞    public synchronized Connection getConnectionSync() {        synchronized (this) {            for (int i = 0; i < size; i++) {                ConnectionPair pair = connectionPairs.get(i);                if (pair.isAvailable) {                    pair.isAvailable = false;                    return pair.connection;                }            }            // 进入阻塞态，等待可用的connection            // 可以用while(true)代替，但是while(true)消耗CPU运算            synchronized (this) {                try {                    this.wait();                } catch (InterruptedException e) {                    e.printStackTrace();                }            }            for (int i = 0; i < size; i++) {                ConnectionPair pair = connectionPairs.get(i);                if (pair.isAvailable) {                    return pair.connection;                }            }            return null;        }    }    public synchronized Connection getConnection() {        for (int i = 0; i < size; i++) {            ConnectionPair pair = connectionPairs.get(i);            if (pair.isAvailable) {                pair.isAvailable = false;                return pair.connection;            }        }        return null;    }    public void releaseConnection(Connection connection) {        for (int i = 0; i < size; i++) {            ConnectionPair pair = connectionPairs.get(i);            if (pair.connection == connection) {                pair.isAvailable = true;                synchronized (this) {                    this.notifyAll();                }                break;            }        }    }    public void releaseAll() {        for (int i = 0; i < size; i++) {            try {                connectionPairs.get(i).connection.close();            } catch (SQLException e) {                e.printStackTrace();            }        }    }    private class ConnectionPair {        Connection connection;        boolean isAvailable;    }}

这里实现了getConnectionSync()和getConnection()方法。
我们来做下测试：

public class MainClass {    public static void main(String[] args) throws Exception {        ConnectionPool pool = new ConnectionPool(                "jdbc:mysql://localhost:3306/mysql", "root", "");        for (int i = 0; i < 35; i++) {            Connection connection = pool.getConnectionSync();            final int j = i;            new Thread(() -> {                System.out.println("获取了第" + j + "个连接:" + connection);                try {                    Thread.sleep(1000);                } catch (InterruptedException e) {                    e.printStackTrace();                }                pool.releaseConnection(connection);                System.out.println("释放了第" + j + "个连接:" + connection);            }).start();        }        pool.releaseAll();    }}

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