Servlet(9)—HttpServlet和改进Servlet实例

本文主要是介绍Servlet(9)—HttpServlet和改进Servlet实例，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

HttpServlet：针对Http协议定义的一个Servlet基类，唯一的功能就是强制类型转换ServletRequest转换成HttpServletRequest，ServletResponse转换成HttpServletResponse，HttpServlet继承自GenericServlet，而GenericServlet实现了Servlet接口和ServletConfig接口。也就是说编写Servlet类不需要直接实现Servlet类，去继承HttpServlet就行。
好处：
- 不会产生多余无用的代码
- 不用在强制类型转换了（为了获取请求的方式是get还是post需要用到需要用request.getMethod()，其中request必须是HttpServletRequest类型的，HttpServlet在service(ServletRequest req, ServletResponse res)已经强制类型转换好了）
- 在service(HttpServletRequest req, HttpServletResponse resp)重载方法中获取请求方式，get请求会调用doget方法，post请求会执行dopost方法。所以我们可以再这2个方法中定义我们自己的业务逻辑

3 . Http中的方法：
HttpServlet()
doGet(HttpServletRequest, HttpServletResponse)
getLastModified(HttpServletRequest)
doHead(HttpServletRequest, HttpServletResponse)
doPost(HttpServletRequest, HttpServletResponse)
doPut(HttpServletRequest, HttpServletResponse)
doDelete(HttpServletRequest, HttpServletResponse)
getAllDeclaredMethods(Class< ? >)
doOptions(HttpServletRequest, HttpServletResponse)
doTrace(HttpServletRequest, HttpServletResponse)
service(HttpServletRequest, HttpServletResponse)
maybeSetLastModified(HttpServletResponse, long)
service(ServletRequest, ServletResponse)

改进后的实例:
HttpServlet

/*** 针对Http协议定义的一个Servlet基类*唯一的功能就是强制类型转换ServletRequest转换成HttpServletRequest，ServletResponse转换成*HttpServletResponse*/
public class MyHttpServlet extends MyGenericServlet {@Overridepublic void service(ServletRequest arg0, ServletResponse arg1)throws ServletException, IOException {if(arg0 instanceof HttpServletRequest){HttpServletRequest httpServletRequest = (HttpServletRequest) arg0;if(arg1 instanceof HttpServletResponse){HttpServletResponse httpServletResponse = (HttpServletResponse) arg1;service(httpServletRequest, httpServletResponse);}}   }public void service(HttpServletRequest arg0, HttpServletResponse arg1)throws ServletException, IOException {//1.获取请求方式String method = arg0.getMethod();//2.根据请求的方式再调用对应的处理方法if("GET".equalsIgnoreCase(method)){doGet(arg0, arg1);}else if("POST".equalsIgnoreCase(method)){doPost(arg0, arg1);}}public void doPost(HttpServletRequest arg0, HttpServletResponse arg1) throws ServletException, IOException{}public void doGet(HttpServletRequest arg0, HttpServletResponse arg1) throws ServletException, IOException{}
}

Servlet：

public class LoginServlet3 extends MyHttpServlet {@Overridepublic void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException  {//获取请求的方式String method = request.getMethod();System.out.println("请求方式：" + method);//1.获取请求参数username，password（获取的是表单信息）String username = request.getParameter("username");String password = request.getParameter("password");//2.获取当前web应用的初始化参数user，password。String initUser = getServletContext().getInitParameter("user");String initPassword = getServletContext().getInitParameter("password");PrintWriter out = response.getWriter();//3.比对if(initUser.equals(username) && initPassword.equals(password)){//4.打印响应字符串out.println("Hello: " + username);}else{out.println("Sorry: " + username);}}@Overridepublic void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException  {//获取请求的方式HttpServletRequest httpServletRequest = (HttpServletRequest) request;String method = httpServletRequest.getMethod();System.out.println("请求方式：" + method);//1.获取请求参数username，password（获取的是表单信息）String username = request.getParameter("username");String password = request.getParameter("password");//2.获取当前web应用的初始化参数user，password。String initUser = getServletContext().getInitParameter("user");String initPassword = getServletContext().getInitParameter("password");PrintWriter out = response.getWriter();//3.比对if(initUser.equals(username) && initPassword.equals(password)){//4.打印响应字符串out.println("Hello: " + username);}else{out.println("Sorry: " + username);}}
}

页面：

<body><form action="loginServlet" method="get">user：<input type="text" name="user"/><br>password：<input type="password" name="password"/><br>interesting：<input type="checkbox" name="interesting" value="read"/>read<input type="checkbox" name="interesting" value="walk"/>walk<input type="checkbox" name="interesting" value="swing"/>swing<input type="checkbox" name="interesting" value="shopping"/>shopping<input type="checkbox" name="interesting" value="tv"/>TV<br><input type="submit" value="Submit"/></form>
</body>