如何循环遍历 servlet 中的值并在其中显示它们 table？

Question

我正在使用 servlet 容器的 doPost 方法编写一个 servlet 计算器。

 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //show result page

        PrintWriter out = response.getWriter();
        out.println("<html>");
        out.println("<head>SIMPLE CALCULATOR<br><br><br></head>");
        out.println("<body>");
        out.println("<form method = 'post' action = 'calc'>");
        out.println("enter the first number:<br>");
        out.println("<input type = 'text' name='number1'><br><br>");
        out.println("enter the second number:<br>");
        out.println("<input type = 'text' name='number2'><br><br>");
        out.println("enter the operation:<br><br>");
        out.println("<input type ='radio' name = 'op' value = '+'>add<br>");
        out.println("<input type = 'radio' name = 'op' value = '-'>sub<br>");
        out.println("<input type = 'radio' name = 'op' value = '*'>mul<br>");
        out.println("<input type = 'radio' name = 'op' value = '/'>div<br><br>");
        out.println("<input type = 'submit' name = 'result' value = 'submit'><br>");
        out.println("</body>");
        out.println("</html>");
        int a1= Integer.parseInt(request.getParameter("number1"));
        int a2= Integer.parseInt(request.getParameter("number2"));
        String operation = request.getParameter("op");
        int result = 0;
        if(operation.equals("+"))
        {
            result = a1 + a2;
            out.println("The result of " + a1 + " " + operation + " "+ a2 + " = "+ result);
        }
        if(operation.equals("-"))
        {
            result = a1 - a2;
            out.println("The result of " + a1 + " " + operation + " " + a2 + " = "+ result);
        }
        if(operation.equals("*"))
        {
            result = a1 * a2;
            out.println("The result of " + a1 + " " + operation + " " + a2 + " = "+ result);
        }if(operation.equals("/"))
        {
            result = a1 / a2;
            out.println("The result of " + a1 + operation + a2 + " = "+ result);
        }

        out.println("<table border=1>");
        out.println("<tr>");
        out.println("<th>first</th>");
        out.println("<th>operation</th>");
        out.println("<th>second</th>");
        out.println("<th>result</th>");
        out.println("</tr>");
        out.println("<tr>");
        out.println("<td>" + a1 + "</td>");
        out.println("<td>" + operation + "</td>");
        out.println("<td>" + a2 + "</td>");
        out.println("<td>" + result + "</td>");
        out.println("</tr>");
        out.println("</table>");
        
        out.flush();
    }

我想在每次计算并单击提交按钮时显示值、操作和结果。我现在看到的是只显示第一个计算值，当我执行第二个计算值时，它会更改前一个计算值并自行显示。预期输出是

我现在看到了有人有帮助吗？

Answer 1

我的解决方案是使用字符串列表来存储历史记录。如果您想要一个更好的解决方案，您可以编写一个 class，其中包含第一个、第二个和运算符，以便您可以检索每个属性。我将列表存储在会话中，以便 JSP 页面可以访问它。我只是在写一个最小的解决方案。您可以根据自己的要求重写它。

JSP 页

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%@page contentType="text/html" pageEncoding="UTF-8"%>

<form action="ComputeServlet" method="post">
<input type="text" name="firstNumber" size="5"> 
<select name="operator">
  <option value="+">+</option>
  <option value="+">-</option>
  <option value="+">*</option>
  <option value="+">/</option>
</select>
<input type="text" name="secondNumber" size="5"> 
<input type="submit" name="submit" value="submit">

<c:forEach var="problem" items="${history}">
  <p>${problem}</p>
</c:forEach>
<input type="submit" name="clear" value="clear">
</form>

Servlet

protected void processRequest(HttpServletRequest request, HttpServletResponse response)
          throws ServletException, IOException {
    
  if (request.getParameter("clear")!=null){
    List<String> history = (List<String>) request.getSession().getAttribute("history");
    if (history == null){
      history = new ArrayList<>();
      request.getSession().setAttribute("history", history);
    } else {
      history.clear();
    }     
  } else if (request.getParameter("submit")!=null){
     int first = Integer.parseInt(request.getParameter("firstNumber"));
     int second = Integer.parseInt(request.getParameter("secondNumber"));
     String op = request.getParameter("operator");
     int result = 0;
     switch(op){
       case "+": result = first+second; break;
       case "*": result = first*second; break;
       case "/": result = first/second; break;
       case "-": result = first-second; break;
      }
    List<String> history = (List<String>) request.getSession().getAttribute("history");
    if (history == null){
      history = new ArrayList<>();
      request.getSession().setAttribute("history", history);
    }
    history.add("" + first + op + second + "=" + result);
  }
  getServletContext().getRequestDispatcher("/index.jsp").forward(request, response);
}

输出

<form action="ComputeServlet" method="post">
<input type="text" name="firstNumber" size="5"> 
<select name="operator">
  <option value="+">+</option>
  <option value="+">-</option>
  <option value="+">*</option>
  <option value="+">/</option>
</select>
<input type="text" name="secondNumber" size="5"> 
<input type="submit" name="submit" value="submit">

  <p>4+5=9</p>
  <p>2+6=8</p>
  <p>3+2=5</p>
  <p>3+2=5</p>

<input type="submit" name="clear" value="clear">
</form>

如何循环遍历 servlet 中的值并在其中显示它们 table？

how to loop over values in servlets and display them in them table?

java

forms

servlets