JSP标记文件,它可以输出其主体或以变量形式返回它 [英] JSP tag file that either outputs its body or returns it in a variable
问题描述
我在".tag"文件中有一个自定义标签,该标签计算并输出一个值.因为我无法在此处发布代码,所以让我们假设一个简单的示例.
I have a custom tag in a ".tag" file that computes and outputs a value. Because I cannot post the code here, let's assume a simple example.
mytag.tag文件的内容:
Content of file mytag.tag:
<@tag dynamic-attributes="dynamicParameters">
<%@attribute name="key" required="true"%> <%-- this works fine, in spite of dynamic-attributes --%>
<jsp:doBody var="bodyContent/">
<%-- ... here is some code to compute the value of variable "output" --%>
${output}
呼叫者可以像这样轻松地调用它:
The caller can easily call it like this:
<prefix:mytag key="foo">Body content...</prefix:mytag>
这将插入标签的输出.但是我还可以使调用者执行以下操作:
This will insert the output of the tag. But I would also enable the caller to do something like this:
<prefix:mytag key="foo" var="mytagOutput">Body content...</prefix:mytag>
在这种情况下,实际上不会写入输出,而是将输出分配给调用方可以使用的变量"mytagOutput".
In this case, the output would not actually be written, but assigned to the variable "mytagOutput", which the caller then can use.
我知道调用者可以通过将自定义标签包装在c:set
中来实现此目的,但是这比简单地声明"var"要优雅.我还知道,可以将带有name-from-attribute
的@variable
指令用于实现此目的.但是然后,我不知道属性"var"是否已由调用者提供. (如果有的话,我想将${output}
分配给该变量,否则我只想写出${output}
.)
I know that the caller can achieve this by wrapping the custom tag in a c:set
, but this is less elegant than simply declaring a "var". I also know that the @variable
directive with the name-from-attribute
can be used to achieve this. But then, I do not know if the attribute "var" has been given by the caller or not. (If given, I want to assign ${output}
to that variable, otherwise I want to just write out ${output}
.)
有没有一种方法可以确定是否已传递"var"属性?
Is there a way how I can find out if the "var" attribute has been passed in or not?
另一种选择是创建第二个自定义标签,可能称为"getMytag",该标签始终期望使用"var"属性,并将"mytag"包装在c:set
中.如果我在这里找不到解决方案,那我会去的.
Another option would be to create a second custom tag, maybe called "getMytag", which always expects the "var" attribute and just wraps the "mytag" in a c:set
. If I don't find a solution here, I will go for that.
(如果以前曾问过这个问题,请指向我.我进行了快速搜索,但没有找到类似的问题.)
(If this question has been asked before, please point me to it. I did a quick search, but did not find a similar question.)
推荐答案
遇到同样的问题,并找到了解决此问题的方法,而无需在".jsp"和".tag"之间进行匹配的硬编码"变量名. >
Ran into this same issue and found a way to this without a "hard-coded" variable name that has to match between .jsp and .tag.
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%><%@
taglib prefix="s" uri="http://www.springframework.org/tags" %>
<jsp:directive.attribute name="someInput" type="java.lang.Object" required="true" rtexprvalue="true" description="Input object" />
<jsp:directive.attribute name="var" type="java.lang.String" required="false" rtexprvalue="false" description="Optional return var name" />
<s:eval expression="@someService.someMethod(someInput)" var="someOutput" />
<c:choose>
<c:when test="${not empty var}">
${pageContext.request.setAttribute(var, someOutput)}
</c:when>
<c:otherwise>
${someOutput}
</c:otherwise>
</c:choose>
此标记可以通过两种方式使用:
This tag can be used in two ways:
<%-- Option 1: renders the output of the tag directly to the page --%>
<some:tagname someInput="${yourVar}" />
<%-- Option 2: stores the output of the tag in variable called "result" and lets the caller render the output on his own --%>
<some:tagname someInput="${yourVar}" var="result" />
<c:out value="${result}"/>
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