JSP导入文件 [英] JSP importing a file
问题描述
美好的一天！
运行JSP程序时遇到以下错误.
java.lang.IllegalStateException: PWC3991: getOutputStream() has already been called for this response
似乎我的JSP中的html文件不起作用. 我的代码如下:
<%@page import = "java.util.*"%>
<%@page import = "javax.servlet.*"%>
<%@page import = "javax.servlet.http.*"%>
<%@page import= "session.*" %>
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>JSP Page</title>
</head>
<body>
<%
Item item = (Item) request.getAttribute("invenItem");
if (item != null) {
out.println("<html><title>Inventory Item</title>");
out.println("<body><h1>Inventory Item Details:</h1>");
out.println("Stock ID : " + item.getStockID() + "<br/>");
out.println("Name : " + item.getItemName() + "<br/>");
out.println("Unit Price: " + item.getUnitPrice() + "<br/>");
out.println("On Stock : " + item.getOnStock() + "<br/>");
out.println("</body>");
out.println("</html>");
} else {
RequestDispatcher rd = request.getRequestDispatcher("DataForm.html"); //NOT WORKING
rd.include(request, response);
out.println("<br>Item not found...<br>");
rd = request.getRequestDispatcher("ItemEntry.html"); //NOT WORKING
rd.include(request, response);
}
%>
</body>
</html>
我的html文件位于文件夹 WEB-INF 中.我该如何运作?我还需要导入吗?谢谢.
不要使用 scriptlets (那些<% %>东西). JSP是HTML的模板技术.对于HTML，您不需要所有这些讨厌的out.println()东西.只需在JSP中编写纯HTML.
所以，而不是
<%
out.println("<html><title>Inventory Item</title>");
%>
只是做
<html><title>Inventory Item</title>
(请注意，这会导致HTML无效，HTML页面中应该只有一个<html>标签，而<head>中应该只有一个<title>，但这是一个不同的问题， w3 HTML验证器应该给出很多提示和答案，并让您自己学习一些HTML教程)
JSP提供 EL (表达语言，那些${ }东西)来访问后端数据，即在page，request，session和application范围中作为属性出现.可以使用属性名称进行访问.
所以，而不是
<%
Item item = (Item) request.getAttribute("invenItem");
%>
使用
${invenItem}
而不是
<%
out.println("Stock ID : " + item.getStockID() + "<br/>");
%>
使用
Stock ID: ${invenItem.stockID}<br/>
JSP还提供了诸如 JSTL 之类的标签库来控制页面流和输出.
所以，而不是
<%
if (item != null) {
} else {
}
%>
使用
<c:choose>
<c:when test="${invenItem != null}">
</c:when>
<c:otherwise>
</c:otherwise>
</c:choose>
JSP还提供了<jsp:include>标记以包含页面片段.
所以，而不是
<%
RequestDispatcher rd = request.getRequestDispatcher("DataForm.html"); //NOT WORKING
rd.include(request, response);
%>
使用
<jsp:include page="/WEB-INF/DataForm.jsp" />
(并将其重命名为.jsp)
该异常将消失.
另请参见:
与具体问题无关，此答案中的几乎所有链接都已经(间接)在您先前的问题中直接提供给您.认真对待他们.要成为一名优秀的程序员(如您在问题/评论中曾经说过的)，请花一些时间来使自己熟悉那些链接(以及链接中的链接).
Good day!
I encountered the following error upon running my JSP program.
java.lang.IllegalStateException: PWC3991: getOutputStream() has already been called for this response
It seems like the html file inside my JSP doesn't work. My code is as follows:
<%@page import = "java.util.*"%>
<%@page import = "javax.servlet.*"%>
<%@page import = "javax.servlet.http.*"%>
<%@page import= "session.*" %>
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>JSP Page</title>
</head>
<body>
<%
Item item = (Item) request.getAttribute("invenItem");
if (item != null) {
out.println("<html><title>Inventory Item</title>");
out.println("<body><h1>Inventory Item Details:</h1>");
out.println("Stock ID : " + item.getStockID() + "<br/>");
out.println("Name : " + item.getItemName() + "<br/>");
out.println("Unit Price: " + item.getUnitPrice() + "<br/>");
out.println("On Stock : " + item.getOnStock() + "<br/>");
out.println("</body>");
out.println("</html>");
} else {
RequestDispatcher rd = request.getRequestDispatcher("DataForm.html"); //NOT WORKING
rd.include(request, response);
out.println("<br>Item not found...<br>");
rd = request.getRequestDispatcher("ItemEntry.html"); //NOT WORKING
rd.include(request, response);
}
%>
</body>
</html>
My html Files are located inside the folder WEB-INF. How can I make it work? DO i need to import it also? Thank you.
Don't use scriptlets (those <% %> things). JSP is a template technology for HTML. You don't need all those nasty out.println() things for HTML. Just write HTML plain in JSP.
So, instead of
<%
out.println("<html><title>Inventory Item</title>");
%>
just do
<html><title>Inventory Item</title>
(note that this results in invalid HTML, there should be only one <html> tag in a HTML page and only one <title> in the <head>, but that's a different problem, the w3 HTML validator should give a lot of hints and answers, also get yourself through some HTML tutorials)
JSP offers EL (Expression Language, those ${ } things) to access backend data, i.e. the data which is present as attribute in page, request, session and application scopes. It can be accessed using the attribute name.
So, instead of
<%
Item item = (Item) request.getAttribute("invenItem");
%>
use
${invenItem}
and instead of
<%
out.println("Stock ID : " + item.getStockID() + "<br/>");
%>
use
Stock ID: ${invenItem.stockID}<br/>
JSP also offers taglibs like JSTL to control the page flow and output.
So, instead of
<%
if (item != null) {
} else {
}
%>
use
<c:choose>
<c:when test="${invenItem != null}">
</c:when>
<c:otherwise>
</c:otherwise>
</c:choose>
JSP also offers <jsp:include> tag to include page fragments.
So, instead of
<%
RequestDispatcher rd = request.getRequestDispatcher("DataForm.html"); //NOT WORKING
rd.include(request, response);
%>
use
<jsp:include page="/WEB-INF/DataForm.jsp" />
(and rename it to .jsp)
And the exception will disappear.
See also:
Unrelated to the concrete problem, almost all of the links in this answer was already (in)directly given to you in your previous questions. Take them serious. To become a great programmer (as you ever stated in a question/comment), take some time to get yourself through those links (and the links in the links).
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