Java Web学习之HttpServlet

一、HttpServlet

1. HttpServlet是一个 Servlet，继承自 GenericServlet。针对于 HTTP 协议所定制。
2. 实际开发中，直接继承 HttpServlet，并根据请求方式复写 doXxx() 方法即可。
3. 优点：直接由针对性的覆盖 doXxx() 方法；直接使用 HttpServletRequest 和 HttpServletResponse，不再需要强转。

二、具体实现

1. 在 service() 方法中直接把 ServletReuqest 和 ServletResponse 转为 HttpServletRequest 和 HttpServletResponse。并调用了重载的service(HttpServletRequest, HttpServletResponse)。

2. 在 service(HttpServletRequest, HttpServletResponse) 获取了请求方式：request.getMethod()。根据请求方式有创建了
   doXxx() 方法(xxx 为具体的请求方式, 比如 Get, Post)。

三、源码

public class HttpServlet extends GenericServlet {

	@Override
	/*在 service() 方法中直接把 ServletReuqest 和 ServletResponse 转为 HttpServletRequest 和 HttpServletResponse。
	并调用了重载的service(HttpServletRequest, HttpServletResponse)*/
	public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {

		HttpServletRequest request;
		HttpServletResponse response;

		try {
			request = (HttpServletRequest) req;
			response = (HttpServletResponse) res;
		} catch (ClassCastException e) {
			throw new ServletException("non-HTTP request or response");
		}
		service(request, response);
	}

	public void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// 1. 获取请求方式.
		String method = request.getMethod();

		// 2. 根据请求方式再调用对应的处理方法
		if ("GET".equalsIgnoreCase(method)) {
			doGet(request, response);
		} else if ("POST".equalsIgnoreCase(method)) {
			doPost(request, response);
		}
	}

	public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub

	}

	public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub

	}
}