hello2源碼分析

時間 2019-12-10

標籤 hello2 hello 源碼分析简体版

原文原文鏈接

完整的源代碼html

/**
 * Copyright (c) 2014 Oracle and/or its affiliates. All rights reserved.
 *
 * You may not modify, use, reproduce, or distribute this software except in
 * compliance with  the terms of the License at:
 * https://github.com/javaee/tutorial-examples/LICENSE.txt
 */
package javaeetutorial.hello2;

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * This is a simple example of an HTTP Servlet. It responds to the GET method of
 * the HTTP protocol.
 */
@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=\"resources/images/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>");
        }
    }

    @Override
    public String getServletInfo() {
        return "The Hello servlet says hello.";

    }
}

分析
String userName=request.getParameter(「userName」):定義了一個叫userName的字符串變量，並給他賦值。request.getParameter(「userName」);這句的意思是從request中拿出名字叫userName的值，賦給了你剛纔定義的變量。request是負責頁面之間傳遞參數和數據的類，是java封裝好的，咱們只要把它當成一個工具就能夠了。而後判斷username是否爲空或者長度爲0，若是爲空或者長度爲0就實現Servlet之間的請求傳遞（頁面跳轉），最後輸出。java

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