java 在 JSP 中迭代枚举常量
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iterating over Enum constants in JSP
提问by Dónal
I have an Enum like this
我有一个这样的枚举
package com.example;
public enum CoverageEnum {
COUNTRY,
REGIONAL,
COUNTY
}
I would like to iterate over these constants in JSP without using scriptlet code. I know I can do it with scriptlet code like this:
我想在不使用 scriptlet 代码的情况下在 JSP 中迭代这些常量。我知道我可以用这样的 scriptlet 代码做到这一点：
<c:forEach var="type" items="<%= com.example.CoverageEnum.values() %>">
${type}
</c:forEach>
But can I achieve the same thing without scriptlets?
但是我可以在没有脚本的情况下实现同样的目标吗？
Cheers, Don
干杯，唐
回答by Ted Pennings
If you're using Spring MVC, you can accomplish your goal with the following syntactic blessing:
如果您使用的是 Spring MVC，则可以通过以下语法祝福来实现您的目标：
<form:form method="post" modelAttribute="cluster" cssClass="form" enctype="multipart/form-data">
<form:label path="clusterType">Cluster Type
<form:errors path="clusterType" cssClass="error" />
</form:label>
<form:select items="${clusterTypes}" var="type" path="clusterType"/>
</form:form>
where your model attribute (ie, bean/data entity to populate) is named cluster and you have already populated the model with an enum array of values named clusterTypes. The <form:error>part is very much optional.
其中您的模型属性（即要填充的 bean/数据实体）被命名为 cluster，并且您已经使用名为 clusterTypes 的值的枚举数组填充模型。该<form:error>部分是非常可选的。
In Spring MVC land, you can also auto-populate clusterTypesinto your model like this
在 Spring MVC 领域，您还可以clusterTypes像这样自动填充到您的模型中
@ModelAttribute("clusterTypes")
public MyClusterType[] populateClusterTypes() {
return MyClusterType.values();
}
回答by Garth Gilmour
If you are using Tag Libraries you could encapsulate the code within an EL function. So the opening tag would become:
如果您使用标签库，您可以将代码封装在 EL 函数中。所以开始标签将变成：
<c:forEach var="type" items="${myprefix:getValues()}">
EDIT: In response to discussion about an implementation that would work for multiple Enum types just sketched out this:
编辑：为了回应有关适用于多种 Enum 类型的实现的讨论，只是勾勒出这一点：
public static <T extends Enum<T>> Enum<T>[] getValues(Class<T> klass) {
try {
Method m = klass.getMethod("values", null);
Object obj = m.invoke(null, null);
return (Enum<T>[])obj;
} catch(Exception ex) {
//shouldn't happen...
return null;
}
}
