JDK API动态代理模拟数据库连接池

JDK API动态代理模拟数据库连接池

实现：在MyDataSource类中，编写静态方法getConnection，使该方法能够返回一个Connection的代理对象，该代理对象对Connection的close方法进行增强，使close方法不再直接关闭数据库连接而是将数据库连接返回到MyDataSource的连接池（链表或是其他的数据结构）中。

这样，外部通过MyDataSource获取Connection代理对象，外部调用Connection代理对象的close方法，即可将Connection对象归还到MyDataSource的连接池中。

PS:
MyDataSourceAdapter.java可有可无，不使用MyDataSourceAdapter.java的话，请在MyDataSource.java中实现DataSource接口

MyDataSourceAdapter.java

package DataSrouceTest;

import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.SQLException;
import java.sql.SQLFeatureNotSupportedException;
import java.util.logging.Logger;

import javax.sql.DataSource;

public abstract class MyDataSourceAdapter implements DataSource {

	@Override
	public PrintWriter getLogWriter() throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public void setLogWriter(PrintWriter out) throws SQLException {
		// TODO Auto-generated method stub

	}

	@Override
	public void setLoginTimeout(int seconds) throws SQLException {
		// TODO Auto-generated method stub

	}

	@Override
	public int getLoginTimeout() throws SQLException {
		// TODO Auto-generated method stub
		return 0;
	}

	@Override
	public Logger getParentLogger() throws SQLFeatureNotSupportedException {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public <T> T unwrap(Class<T> iface) throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public boolean isWrapperFor(Class<?> iface) throws SQLException {
		// TODO Auto-generated method stub
		return false;
	}

	@Override
	public Connection getConnection(String username, String password) throws SQLException {
		// TODO Auto-generated method stub
		return null;
	}

}

MyDataSource.java

package DataSrouceTest;

import java.io.IOException;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.LinkedList;
import java.util.Properties;

public class MyDataSource extends MyDataSourceAdapter {

	private static LinkedList<Connection> pool;
	private static final int DEFAULT_SIZE = 5;
	private static String username;
	private static String password;
	private static String url;

	static {
		pool = new LinkedList<Connection>();
		Properties prop = new Properties();
		try {
			prop.load(MyDataSource.class.getClassLoader().getResourceAsStream("db_server.properties"));
			username = prop.getProperty("username");
			password = prop.getProperty("password");
			url = prop.getProperty("url");
			try {
				Class.forName(prop.getProperty("driverClassName"));
			} catch (ClassNotFoundException e) {
				e.printStackTrace();
			}
		} catch (IOException e) {
			e.printStackTrace();
		}
		for (int i = 0; i < DEFAULT_SIZE; i++) {
			try {
				pool.add(DriverManager.getConnection(url, username, password));
			} catch (SQLException e) {
				e.printStackTrace();
			}
		}
	}

	/**
	 * 返回一个Connection的代理对象
	 */
	@Override
	public Connection getConnection() throws SQLException {
		Connection connection = pool.remove();
		System.out.println("数据库连接被借走，当前数据库连接池中连接数为：" + pool.size());
		Connection proxy = (Connection) Proxy.newProxyInstance(connection.getClass().getClassLoader(),
				new Class<?>[] { Connection.class }, new InvocationHandler() {
					@Override
					public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
						if ("close".equals(method.getName())) {
							pool.add(connection);
							System.out.println("数据库连接被归还，当前数据库连接池中连接数为：" + pool.size());
							return null;
						} else {
							return method.invoke(connection, args);
						}
					}
				});
		return proxy;
	}

}