Servlet(9)—HttpServlet和改进Servlet实例

1. 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。
2. 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 {

    @Override
    public 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 {

    @Override
    public 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);
        }
    }

    @Override
    public 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>