hello2 source anaylis

首先，我们先来看一看这一段的整体代码，

代码如下：

@WebServlet("/greeting")
public class GreetingServlet extends HttpServlet {

    @Override
    public void doGet(HttpServletRequest request,
            HttpServletResponse response)
            throws ServletException, IOException {

        response.setContentType("text/html");
        response.setBufferSize(8192);
        try (PrintWriter out = response.getWriter()) {
            out.println("<html lang=\"en\">"
                    + "<head><title>Servlet Hello</title></head>");

            // then write the data of the response
            out.println("<body  bgcolor=\"#ffffff\">"
                + "<img src=\"duke.waving.gif\" "
                + "alt=\"Duke waving his hand\">"
                + "<form method=\"get\">"
                + "<h2>Hello, my name is Duke. What's yours?</h2>"
                + "<input title=\"My name is: \"type=\"text\" "
                + "name=\"username\" size=\"25\">"
                + "<p></p>"
                + "<input type=\"submit\" value=\"Submit\">"
                + "<input type=\"reset\" value=\"Reset\">"
                + "</form>");

            String username = request.getParameter("username");
            if (username != null && username.length()> 0) {
                RequestDispatcher dispatcher =
                    getServletContext().getRequestDispatcher("/response");

                if (dispatcher != null) {
                    dispatcher.include(request, response);
                }
            }
            out.println("</body></html>");
        }
    }

对里面的部分代码分析：

String username = request.getParameter("username"); //获取通过URL或者form传递过来的数据并赋值给username
if (username != null && username.length() > 0) { //对数据进行验证，满足不为空和长度大于0的条件
RequestDispatcher dispatcher =
getServletContext().getRequestDispatcher("/response");
//获取jsp上下文里边存储了各变量的信息（值）,把一个命令发送到浏览器，让浏览器对指定的URL提出请求（此处的URL只能使用绝对路径）
if (dispatcher != null) {
dispatcher.include(request, response); //如果接收到的客户端的请求不为空时，记录保留request和response，以后不能再修改response里表示状态的信息。
}
}

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