Java JSP 包含指令、jsp:include 动作、相对路径与绝对路径

JSP include directive, jsp:include action, relative vs. absolute paths

提问by Matt Mc

I am doing some basic templating in my JSP-based webapp. For example, I want to have a standard header and footer (basic HTML) that I pull into each of my JSPs.

我正在我的基于 JSP 的 web 应用程序中做一些基本的模板。例如，我想要将标准页眉和页脚（基本 HTML）拉入我的每个 JSP 中。

My content JSP is at /WEB-INF/jsp/home.jsp, and I have template JSPs at /WEB-INF/jsp/template/, such as /WEB-INF/jsp/template/Body-Footer.jsp.

我的内容 JSP 位于/WEB-INF/jsp/home.jsp，并且我的模板 JSP 位于/WEB-INF/jsp/template/，例如/WEB-INF/jsp/template/Body-Footer.jsp.

So now, within home.jsp, I want to pull in my template files. First, I try the jsp:includeaction:

所以现在，在 内home.jsp，我想拉入我的模板文件。首先，我尝试以下jsp:include操作：

<jsp:include page="template/Body-Footer.jsp"></jsp:include>

It generates the error javax.servlet.ServletException: File "/template/Body-Footer.jsp" not found

它产生错误 javax.servlet.ServletException: File "/template/Body-Footer.jsp" not found

Strange to me, considering that Eclipse says that the path is valid.

对我来说很奇怪，考虑到 Eclipse 说路径是有效的。

Okay, so then I switch to the include directive:

好的，那么我切换到包含指令：

<%@ include file="template/Body-Footer.jsp" %>

This works just fine, pulls in my footer HTML.

这工作得很好，拉入我的页脚 HTML。

But why does the jsp:includenot work? After some experimentation, I find that putting in the absolute path does get it to work:

但为什么不起作用jsp:include？经过一些实验，我发现放入绝对路径确实可以让它工作：

<jsp:include page="/WEB-INF/jsp/template/Body-Footer.jsp"></jsp:include>

Now it works fine, no errors.

现在它工作正常，没有错误。

So here's my question: why? Why do I (apparently) need to use an absolute path with the jsp:includeaction, but not with the include directive?

所以这是我的问题：为什么？为什么我（显然）需要在操作中使用绝对路径jsp:include，而不是在 include 指令中使用？

采纳答案by developerwjk

/WEB-INF/jsp/template/Body-Footer.jspis not an absolute path. Its also a relative path. The problem is that template/Body-Footer.jspis an incomplete relative path, whereas the other is complete. That is, the paths are relative to your app path. Since /WEB-INF/is under your app path, you have to include it. Absolute path means like C:/program files/tomcat/webapps/yourapp/WEB-INF/jsp/template/Body-Footer.jsp

/WEB-INF/jsp/template/Body-Footer.jsp不是绝对路径。它也是一个相对路径。问题是这template/Body-Footer.jsp是一个不完整的相对路径，而另一个是完整的。也就是说，路径是相对于您的应用程序路径的。由于/WEB-INF/在您的应用程序路径下，您必须包含它。绝对路径意味着像C:/program files/tomcat/webapps/yourapp/WEB-INF/jsp/template/Body-Footer.jsp

回答by dejanmr

Answer to WHY - The jsp:includeis a runtime directive unlike the <%@ include ... %>directive which happens to be a compile time directive (translation time, actually).

对 WHY 的回答 - 这jsp:include是一个运行时指令，与<%@ include ... %>恰好是编译时指令（实际上是翻译时间）的指令不同。

See more on: JSP Performance using jsp:include

查看更多关于：使用 jsp:include 的 JSP 性能

Bottom line - directives are run against different folders as a base.

底线 - 指令针对不同的文件夹作为基础运行。

Btw. JSP pages should be outside of WEB-INF folder, if you want to follow official recommendation:

顺便提一句。JSP 页面应该在 WEB-INF 文件夹之外，如果你想遵循官方建议：

The Java EE 6 Tutorial - Web Module Structure

Java EE 6 教程 - Web 模块结构

回答by gavenkoa

I read JSP 2.0 spec and here:

我阅读了 JSP 2.0 规范和这里：

 Relative URL Specifications

 * A context-relative path is a path that starts with a slash (/).
 It is to be interpreted as relative to the application to which
 the JSP page or tag file belongs. That is, its ServletContext
 object provides the base context URL.

 * A page relative path is a path that does not start with a
 slash (/). It is to be in- terpreted as relative to the current
 JSP page, or the current JSP file or tag file, depending on where
 the path is being used.

For now javax.servlet.ServletContext.getRealPath("/WEB-INF/test/test.jsp")is null for security reason.

出于javax.servlet.ServletContext.getRealPath("/WEB-INF/test/test.jsp")安全原因，现在为空。

Assume that context-relative pathis path from your WAR root.

假设上下文相关路径是来自您的 WAR 根的路径。