我在 Servlet 上创建列表时遇到问题。我有以下代码:
protected void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
List lIngredients = new ArrayList<>();
String ingrediente = request.getParameter("Ingredientes");
String action = request.getParameter("action"); //elegimos a qué pantalla pasar en función de la acción que nos llegue de la interfaz
if ("Buscar todas las recetas".equalsIgnoreCase(action)) {
request.setAttribute("AllReceipes", RecetaDao.getAllReceipes());
request.getRequestDispatcher("receipes.jsp").forward(request, response);
}else if ("Buscar por ingredientes".equalsIgnoreCase(action)){
lIngredients.add(ingrediente);
request.setAttribute("AllIngredients", RecetaDao.getSomeReceipes(lIngredients));
request.getRequestDispatcher("perIngredient.jsp").forward(request, response);
}else if ("Agregar ingrediente".equalsIgnoreCase(action)){
lIngredients.add(ingrediente);
}
}
问题是我一直保存相同的值。我不知道是否可以重置我创建的“ingrediente”和“action”字符串，并让用户从 JSP 中选择其他值。
谢谢。
这是 JSP:
`<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>JSP Page</title>
</head>
<body>
<form action="./optionServlet" method="POST">
<table border="1">
<form action="demo_form.asp" autocomplete="on">
<th><FONT FACE="Times New Roman" SIZE=3> Ingredientes: </th>
<td><input type="text" name="Ingredientes" value="${Receta.Ingredientes}" list="datalist1" /></td>
<datalist id="datalist1">
<option value="Aceite"><option value="AceiteOliva"> <option value="AceitunasNegras"><option value="Ajo"><option value="Albahaca">
<option value="AlbahacaFresca"><option value="Azucar"><option value="CarnePicada"><option value="Cebolla"><option value="CebollaMorada">
<option value="Croutons"><option value="DienteDeAjo"><option value="Espinaca"><option value="FileteSalmon"><option value="Guisantes">
<option value="Harina"><option value="Huevo"><option value="LaminaParaCanelones"><option value="Lechuga"><option value="Macarrones">
<option value="Mantequilla"><option value="MasaPizza"><option value="Miel"><option value="Mostaza"><option value="Oregano">
<option value="PanRallado"><option value="Patata"><option value="PechugaPollo"><option value="Pepino"><option value="Perejil"><option value="Pimienta">
<option value="PimientoRojo"><option value="QuesoFeta"><option value="QuesoMozzarella"><option value="QuesoParmesano"><option value="QuesoRicota">
<option value="Sal"><option value="SalsaQueso"><option value="Tomate"><option value="TomateTriturado"><option value="Zanahoria">
</datalist>
<button><input type="submit" name="action" value="Buscar todas las recetas" /></button>
<button><input type="submit" name="action" value="Buscar por ingredientes" /></button>
<button><input type="submit" name="action" value="Agregar ingrediente" /></button>
<table>
<tr>
<td> <font color="#74DF00"><b><c:out value="${mensajesOK}"/></b></font> </td>`
这是正确的代码:
protected void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
HttpSession session = request.getSession();
List lIngredients = (List) session.getAttribute("Ingredientes");
response.setContentType("text/html;charset=UTF-8");
if (lIngredients == null) {
lIngredients = new ArrayList<>();
session.setAttribute("Ingredientes", lIngredients);
}
String ingrediente = request.getParameter("Ingredientes");
String action = request.getParameter("action"); //elegimos a qué pantalla pasar en función de la acción que nos llegue de la interfaz
if ("Buscar todas las recetas".equalsIgnoreCase(action)) {
request.setAttribute("AllReceipes", RecetaDao.getAllReceipes());
request.getRequestDispatcher("receipes.jsp").forward(request, response);
}else if ("Buscar por ingredientes".equalsIgnoreCase(action)){
lIngredients.add(ingrediente);
request.setAttribute("AllIngredients", RecetaDao.getSomeReceipes(lIngredients));
request.getRequestDispatcher("perIngredient.jsp").forward(request, response);
}else if ("Agregar ingrediente".equalsIgnoreCase(action)){
lIngredients.add(ingrediente);
request.getRequestDispatcher("option.jsp").forward(request, response);
ingrediente = request.getParameter("Ingredientes");
action = request.getParameter("action");
}
}
最佳答案
问题是您在每次请求时都会创建一个新的List。
List lIngredients = new ArrayList<>();
因为它是一个局部变量，所以请求完成后它就不再存在。因此，当用户最终决定搜索菜谱时，您可以使用之前的值，您需要将成分 List 保存到 session 中。
HttpSession session = request.getSession();
List lIngredients = (List) session.getAttribute("Ingredientes");
if (lIngredients == null) {
List lIngredients = new ArrayList<>();
session.setAttribute("Ingredientes", lIngredientes);
}
关于java - 在 Servlet 上创建 ArrayList，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/28305838/