public class Source220V {
    public int outVoltage220v(){
        return 220;
    }
}

public interface Destination5V {
    /**
     *
     * @return
     */
    int outVoltage5v();
}

public class VoltageAdapter extends Source220V implements Destination5V{
    @Override
    public int outVoltage5v() {
        int voltage220v = outVoltage220v();
        return voltage220v/44;
    }
}

public class Client {
    public static void main(String[] args) {
        VoltageAdapter voltageAdapter = new VoltageAdapter();
        voltageAdapter.outVoltage5v();
    }
}

public class VoltageAdapter  implements Destination5V{
    /**
     * 直接持有需要被适配的类（Source）
     */
    private Source220V source220V;

    public VoltageAdapter(Source220V source220V) {
        this.source220V = source220V;
    }

    @Override
    public int outVoltage5v() {
        int voltage220v = source220V.outVoltage220v();
        return voltage220v/44;
    }
}

public class Client {
    public static void main(String[] args) {
        VoltageAdapter voltageAdapter = new VoltageAdapter(new Source220V());
        voltageAdapter.outVoltage5v();
    }
}

public interface Destination {
    /**
     *
     * @return
     */
    int outVoltage5v();

    /**
     * @return
     */
    int outVoltage10v();

    /**
     * @return
     */
    int outVoltage36v();

    /**
     * @return
     */
    int outVoltage220v();
}

public  abstract class AbstractVoltageAdapter implements Destination{
    @Override
    public int outVoltage5v() {
        return 5;
    }

    @Override
    public int outVoltage10v() {
        return 10;
    }

    @Override
    public int outVoltage36v() {
        return 36;
    }

    @Override
    public int outVoltage220v() {
        return 220;
    }
}

public class VoltageAdapter extends AbstractVoltageAdapter{
    @Override
    public int outVoltage5v() {
        int voltage220v = outVoltage220v();
        return voltage220v/44;
    }
}

public class Client {
    public static void main(String[] args) {
        VoltageAdapter voltageAdapter = new VoltageAdapter();
        voltageAdapter.outVoltage5v();
    }
}

public class DispatcherServlet extends FrameworkServlet {
...
    /**
	 * Return the HandlerAdapter for this handler object.
	 * @param handler the handler object to find an adapter for
	 * @throws ServletException if no HandlerAdapter can be found for the handler. This is a fatal error.
	 */
	protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
		for (HandlerAdapter ha : this.handlerAdapters) {
			if (logger.isTraceEnabled()) {
				logger.trace("Testing handler adapter [" + ha + "]");
			}
			if (ha.supports(handler)) {
				return ha;
			}
		}
		throw new ServletException("No adapter for handler [" + handler +
				"]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");
	}
...
}

public interface HandlerAdapter {

	/**
	 * Given a handler instance, return whether or not this {@code HandlerAdapter}
	 * can support it. Typical HandlerAdapters will base the decision on the handler
	 * type. HandlerAdapters will usually only support one handler type each.
	 * <p>A typical implementation:
	 * <p>{@code
	 * return (handler instanceof MyHandler);
	 * }
	 * @param handler handler object to check
	 * @return whether or not this object can use the given handler
	 */
	boolean supports(Object handler);

	/**
	 * Use the given handler to handle this request.
	 * The workflow that is required may vary widely.
	 * @param request current HTTP request
	 * @param response current HTTP response
	 * @param handler handler to use. This object must have previously been passed
	 * to the {@code supports} method of this interface, which must have
	 * returned {@code true}.
	 * @throws Exception in case of errors
	 * @return ModelAndView object with the name of the view and the required
	 * model data, or {@code null} if the request has been handled directly
	 */
	ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception;

	/**
	 * Same contract as for HttpServlet's {@code getLastModified} method.
	 * Can simply return -1 if there's no support in the handler class.
	 * @param request current HTTP request
	 * @param handler handler to use
	 * @return the lastModified value for the given handler
	 * @see javax.servlet.http.HttpServlet#getLastModified
	 * @see org.springframework.web.servlet.mvc.LastModified#getLastModified
	 */
	long getLastModified(HttpServletRequest request, Object handler);

}