如何从Servlet获取对象作为参数

Question

我不知道如何将getParameter（）与对象配合使用，因为我知道这是不可能的。 那我该怎么办？

货币currency = req.getParameter（“ currencies”）;-不起作用。

我的servlet：

public class AddPurseServlet extends HttpServlet {
private PurseDao purseDao;
private CurrencyDao currencyDao;

@Override
public void init() throws ServletException {
    purseDao = (PurseDao) getServletContext().getAttribute("purseDao");
    currencyDao = (CurrencyDao) getServletContext().getAttribute("currencyDao");
}

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    List<Currency> currencies = currencyDao.getAll();

    req.setAttribute("currencies", currencies);

    req.getRequestDispatcher("WEB-INF/view/addPurse.jsp").forward(req, resp);
}

@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    HttpSession session = req.getSession();
    User user = (User) session.getAttribute("user");
    String amount = req.getParameter("amount");
    Currency currency = req.getParameter("currencies");

    Purse purse = new Purse(user, currency, new BigDecimal(amount), new Timestamp(System.currentTimeMillis()));

    purseDao.insert(purse);

    resp.sendRedirect("userPage");
}
}

在我的jsp页面上，我需要货币和金额参数：

<html>
<head>
<title>Title</title>
<link rel="stylesheet" href="//netdna.bootstrapcdn.com/bootstrap/3.3.2/css/bootstrap.min.css">
<link rel="stylesheet" href="//netdna.bootstrapcdn.com/bootstrap/3.3.2/css/bootstrap-theme.min.css">
<script src="//netdna.bootstrapcdn.com/bootstrap/3.3.2/js/bootstrap.min.js"></script>
</head>
<body>
<h1>Hello USER!</h1>
<div class="container">
<h1>Save User</h1>
<form method="post" action="addPurse">
    <div class="form-group">
        <label>Currency</label>
        <select>
            <c:forEach var="currency" items="${currencies}">
                <option value="${currency.id}">${currency.name}</option>
            </c:forEach>
        </select>
    </div>
    <div class="form-group">
        <label>Amount</label>
        <input class="form-control" name="amount" placeholder="Amount">
    </div>
    <input class="btn btn-default btn-xs" type="submit" value="Save">
    <a class="btn btn-default btn-xs" href="usersList" role="button">cancel</a>
</form>
</div>
</body>
</html>

Answer 1

参数是字符串。

如果您的货币是枚举

final String currencyStr = request.getParameter("currency");
final Currency currency = Stream.of(Currency.values()).filter(currency -> currency.code.equals(currencyStr)).findFirst().orElse(null));

Answer 2

因此，我从您的代码中了解到，您正在尝试填充货币列表，然后尝试为货币对象设置一些金额。

为此，您用唯一的ID来标识货币。 太完美了。现在您需要了解的是，您实际上并不需要JSP页面中的对象。 您只需要货币ID。

所以我会四处修改您的JSP：

<html>
<head>
<title>Title</title>
<link rel="stylesheet" href="//netdna.bootstrapcdn.com/bootstrap/3.3.2/css/bootstrap.min.css">
<link rel="stylesheet" href="//netdna.bootstrapcdn.com/bootstrap/3.3.2/css/bootstrap-theme.min.css">
<script src="//netdna.bootstrapcdn.com/bootstrap/3.3.2/js/bootstrap.min.js"></script>
</head>
<body>
<h1>Hello USER!</h1>
<div class="container">
<h1>Save User</h1>
<form method="post" action="addPurse">
    <div class="form-group">
        <label>Currency</label>
        <select id="currency" name="currency">
            <c:forEach var="currency" items="${currencies}">
                <option value="${currency.id}">${currency.name}</option>
            </c:forEach>
        </select>
    </div>
    <div class="form-group">
        <label>Amount</label>
        <input class="form-control" name="amount" placeholder="Amount">
    </div>
    <input class="btn btn-default btn-xs" type="submit" value="Save">
    <a class="btn btn-default btn-xs" href="usersList" role="button">cancel</a>
</form>
</div>
</body>
</html>

现在，进入您的servlet。 看到关键字“ DAO”和“ CurrencyDAO”，我假设您正在使用JPA / Hibernate。 因此，您需要使用以下内容修改代码：

@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    HttpSession session = req.getSession();
    User user = (User) session.getAttribute("user");
    String amount = req.getParameter("amount");
    String currencyid = req.getParameter("currency");
//Get your currency object from database
    Currency currencyToBeEdited = currencyDao.findById(Integer.parseInt(currencyid));

//Add the code to set the amount and save it back to the database

    Purse purse = new Purse(user, currency, new BigDecimal(amount), new Timestamp(System.currentTimeMillis()));

    purseDao.insert(purse);

    resp.sendRedirect("userPage");
}

注意：我不确定您的目标100％，但我提供了建议，希望能为您指明正确的方向

如何从Servlet获取对象作为参数

问题描述

2 个解决方案

解决方案1
1 2018-04-17 07:15:51

解决方案2
1 已采纳 2018-04-17 07:35:25

如何从Servlet获取对象作为参数

问题描述

2 个解决方案

解决方案1 1 2018-04-17 07:15:51

解决方案2 1 已采纳 2018-04-17 07:35:25

解决方案1
1 2018-04-17 07:15:51

解决方案2
1 已采纳 2018-04-17 07:35:25