为什么servlet响应没有显示在我的JavaScript中

Why is servlet response not showing in my JavaScript

本文关键字：我的 JavaScript 显示 servlet 响应 为什么      更新时间：2023-09-26

我正在翻阅一本学习ajax的书，但由于Servlet响应（只是文本）没有在JavaScript中显示在警报中，我陷入了困境。当单击该按钮时，它会调用一个JavaScript函数，然后异步发送一个http请求。

我不明白为什么String没有显示在响应中。感谢任何人对此提供的线索。

编辑：此外，在发送"获取"请求后，我得到了200的状态代码。当我在控制台下查看firebug时，我看到了带有200状态代码的Get请求。有三个选项卡-参数、标题和XML。在"参数"下，我看到我在请求中发送的伪参数。在Headers下有2个节点-响应标头和请求标头。当我展开响应头节点时，我看到一个叫做内容长度的东西，后面有一个0。这是否意味着我的响应中没有任何内容？？？

这是我的HTML

<html>
 <head>
  <title>Boards 'R' Us</title>
  <link rel="stylesheet" type="text/css" href="boards.css" media="screen" />
  <script type="text/javascript" src="ajax.js"> </script>
  <script type="text/javascript" src="text-utils.js"> </script>
  <script type="text/javascript" src="boards.js"> </script>
 </head>
 <body>
  <h1>Boards 'R' Us :: How Much Butt We're Kicking</h1>
  <div id="boards">
   <table>
    <tr><th>Snowboards Sold</th>
     <td><span id="boards-sold">1672</span></td></tr>
    <tr><th>What I Sell 'em For</th>
     <td>$<span id="boards-price">249.95</span></td></tr>
    <tr><th>What it Costs Me</th>
     <td>$<span id="boards-cost">84.22</span></td></tr>
   </table>
   <table>
    <tr><th>Boots Sold</th>
     <td><span id="boots-sold">312</span></td></tr>
    <tr><th>What I Sell 'em For</th>
     <td>$<span id="boots-price">175.47</span></td></tr>
    <tr><th>What it Costs Me</th>
     <td>$<span id="boots-cost">54.23</span></td></tr>
   </table>
   <table>
    <tr><th>Bindings Sold</th>
     <td><span id="bindings-sold">82</span></td></tr>
    <tr><th>What I Sell 'em For</th>
     <td>$<span id="bindings-price">146.92</span></td></tr>
    <tr><th>What it Costs Me</th>
     <td>$<span id="bindings-cost">98.03</span></td></tr>
   </table>
   <h2>Cash for the Slopes: 
    $<span id="cash">318936.42</span></h2>
   <form>
    <input value="Show Me the Money" type="button" 
           onClick="getNewTotals();" /> 
   </form>
  </div>
 </body>
</html>

和我的JavaScript

function getNewTotals() {
    console.log("Getting new totals");
    var url = "boards.do";
    url = url + "?dummy=" + new Date().getTime();
    request.open("GET", url, true);
    request.onreadystatechange = updatePage;
    request.send(null);
}
function updatePage() {
    if (request.readyState == 4) {
        if (request.status == 200) {
            var reply = request.responseText;
            alert("returned: " + reply);
        } else {
            alert("Error! Request status = " + request.status);
        }
    }
}

和我的Servlet

import java.io.IOException;
import java.io.PrintWriter;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.gmail.gmjord.controller.BoardSalesController;
/**
 * Servlet implementation class BoardSalesController
 */
//@WebServlet("/BoardSalesController")
public class BoardSalesController extends HttpServlet {
    private static final long serialVersionUID = 1L;
    private static final Logger LOGGER = Logger.getLogger(BoardSalesController.class.getClass().getName());
    private static final Level INFO = Level.INFO;
    private static final Level[] LEVELS = {Level.SEVERE, Level.WARNING, Level.INFO, Level.CONFIG,
        Level.FINE, Level.FINER, Level.FINEST};
    /**
     * @see HttpServlet#HttpServlet()
     */
    public BoardSalesController() {
        super();
        // TODO Auto-generated constructor stub
    }
    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        LOGGER.log(INFO, "in doGet()");
        String info = request.getParameter("dummy");
        LOGGER.log(INFO, "Request info: " + info);
        response.setContentType("text/plain");
        response.setCharacterEncoding("UTF-8");
        String reply = "Do you see this?";
        response.getWriter().write(reply);

    }
    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
    }
}

我知道您正确地调用了servlet，并得到了http-header状态为200的响应，但您没有收到字符串内容，不是吗？

然后我认为您必须调用编写器上的flush()来提交响应。如果你检查javax.servlet.ServletResponse文档中的getWriter()，它是javax.servlet.http.HttpServletResponse的接口，你可以看到：

在PrintWriter上调用flush（）将提交响应。

然而，这通常是不必要的，因为servlet container为您做到了这一点，但在您的情况下，似乎不需要尝试在servlet上的doGet方法中使用此代码：

String reply = "Do you see this?";
PrintWriter writer = response.getWriter();
writer.write(reply);
writer.flush();

希望这有帮助，

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