在JSTL中使用枚举 [英] Using enum in JSTL
问题描述
我正在尝试使用jstl进行一些网站开发,我遇到了
以下问题:
I am trying to do some website development using jstl and I run into the following problem:
这里我试图创建一个下拉列表,其中显示的值是
国家/地区名称,值是国家/地区代码。要做到这一点,我
在后端java代码中有以下枚举:
Here I am trying to create a dropdown, where the displayed value is the country names, and the value is the country code. To do this I have the following enum in the backend java code:
public static enum CountryCodes implements EnumConstant {
USA, CAN, AUS, GBR, DEU, ESP, GUM, IND, ISR, MEX, NZL, PAN, PRI;
public final String toCountry(){
switch(this){
case USA:
return "United States";
case CAN:
return "Canada";
case AUS:
return "Australia";
case GBR:
return "Great Britan";
case DEU:
return "Germany";
case ESP:
return "Spain";
case GUM:
return "Guam";
case IND:
return "India";
case ISR:
return "Isreal";
case MEX:
return "Mexico";
case NZL:
return "New Zealand";
case PAN:
return "Panama";
case PRI:
return "Puerto Rico";
}
return this.toString();
}
}
jsp代码片段如下:
And the jsp code snippet is like the following:
<c:set var="countryCodes" value="<%=RequestConstants.CountryCodes.values()%>" />
<td>
<select id="<%=RequestConstants.CLModifyPage.COUNTRY_CODE%>"
name="<%=RequestConstants.CLModifyPage.COUNTRY_CODE%>">
<c:forEach items="${countryCodes}" var="countryCode">
<c:choose>
<c:when
test="${sessionScope.CURRENT_INSTITUTION.countryCode == countryCode}">
<option value="${countryCode}" selected="selected">
${countryCode.toCountry()}</option>
</c:when>
<c:otherwise>
<option value="${countryCode}">${countryCode.toCountry()}
</option>
</c:otherwise>
</c:choose>
</c:forEach>
</select>
</td>
但上面的代码有两个问题:
But the above code has two problems:
-
countryCode.toCountry()
不起作用......我不确定它应该是什么语法。
countryCode.toCountry()
doesn't really work... I am not sure what syntax it should be.
如果$ {sessionScope.CURRENT_INSTITUTION.countryCode}
不是有效的枚举值,即if它类似于AAA,然后比较失败并抛出java.lang.IllegalArgumentException:没有定义枚举const CountryCodes.AAA。我怎样才能解决这个问题?
if "${sessionScope.CURRENT_INSTITUTION.countryCode}"
is not a valid enum value, i.e, if it's something like "AAA", then the comparison fails and throws an java.lang.IllegalArgumentException: no enum const CountryCodes.AAA defined. How can I get around that?
推荐答案
你的方法太复杂了。
按如下方式重新设计你的枚举:
Redesign your enum as follows:
public enum CountryCode {
USA("United States"),
CAN("Canada"),
AUS("Australia");
// ...
private String label;
private CountryCode(String label) {
this.label = label;
}
public String getLabel() {
return label;
}
}
(注意它现在已经有了一个更值得且更有效的getter!)
在servlet的 init()期间将枚举值存储在应用程序范围中
方法,或者更好的是,在 <$ c $期间c> ServletContextListener 的 contextInitialized()
方法:
Store the enum values in the application scope during servlet's init()
method or, better, during ServletContextListener
's contextInitialized()
method:
servletContext.setAttribute("countryCodes", CountryCode.values());
最后遍历如下:
<select name="countryCode">
<c:forEach items="${countryCodes}" var="countryCode">
<option value="${countryCode}" ${institution.countryCode == countryCode ? 'selected' : ''}>${countryCode.label}</option>
</c:forEach>
</select>
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