Dynamic Agent를 통한 DataSource

public class MyDataSource implements DataSource {

    private String username;
    private String password;
    private String url;
    private String driverClassName;

    private List<Connection> list = new ArrayList<Connection>();

    private boolean flag = true;

    private void init() throws ClassNotFoundException {
        flag = false;
        Class.forName(driverClassName);
        for(int i = 0; i < 5; i++) {
            Connection proxy2 = (Connection) Proxy.newProxyInstance(
                //    
                Thread.currentThread().getContextClassLoader(),
                //  
                new Class[]{Connection.class},
                //  
                (proxy, method, args) -> {
                //  close  
                if(method.getName().equals("close")) {
                    list.add((Connection)proxy);
                    return null;
                } else {
                    //      
                    return method.invoke(DriverManager.getConnection(url, username, password), args);
                }
            });
            list.add(proxy2);
        }
    }

    @Override
    public Connection getConnection() {
        if(flag) {
            try {
                init();
            } catch (ClassNotFoundException e) {
                e.printStackTrace();
            }
        }
        if(list.size() > 0) {
            return list.remove(0);
        }
        throw new RuntimeException();
    }
}