java手写数据库连接池

以下是一个简单的Java手写数据库连接池的示例代码：

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

public class ConnectionPool {
    private static final String URL = "jdbc:mysql://localhost:3306/test";
    private static final String USERNAME = "root";
    private static final String PASSWORD = "password";
    private static final int INITIAL_POOL_SIZE = 5;
    private static final int MAX_POOL_SIZE = 10;

    private List<Connection> connections;

    public ConnectionPool() {
        connections = new ArrayList<>(INITIAL_POOL_SIZE);

        try {
            for (int i = 0; i < INITIAL_POOL_SIZE; i++) {
                Connection connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);
                connections.add(connection);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

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

        if (connections.size() > 0) {
            connection = connections.remove(connections.size() - 1);
        } else if (connections.size() < MAX_POOL_SIZE) {
            try {
                connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        return connection;
    }

    public synchronized void releaseConnection(Connection connection) {
        if (connections.size() < MAX_POOL_SIZE) {
            connections.add(connection);
        } else {
            try {
                connection.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

    public synchronized void closeAllConnections() {
        for (Connection connection : connections) {
            try {
                connection.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        connections.clear();
    }
}

这个连接池使用了一个ArrayList作为连接池，使用synchronized关键字保证线程安全。连接池的初始化和连接获取、释放以及连接池关闭的方法都已经实现。使用时只需要创建一个ConnectionPool对象，并调用getConnection()方法获取连接，调用releaseConnection()方法释放连接，最后调用closeAllConnections()方法关闭连接池即可。