blocks|key|1746167|text|因此，为了完全解决我的问题，我需要执行以下操作：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1746168|<%25+pageContext.setAttribute("old",+Status.OLD);+%25>|code-block|syntax|javascript|1746169|然后我就能做到：|1746170|<c:when+test="${someModel.status+==+old}"/>...</c:when>|1746171|它的工作效果与预期一致。|1746172|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

So to get my problem fully resolved I needed to do the following:

<pre class="lang-xml prettyprint-override"><code>&lt;% pageContext.setAttribute("old", Status.OLD); %&gt;
</code></pre>

Then I was able to do:

<pre class="lang-xml prettyprint-override"><code>&lt;c:when test="${someModel.status == old}"/&gt;...&lt;/c:when&gt;
</code></pre>

which worked as expected.

blocks|key|1531215|text|与字符串进行简单的比较是可行的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1531216|<c:when+test="${someModel.status+==+'OLD'}">|code-block|syntax|javascript|1531217|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

A simple comparison against string works:

<pre class="lang-xml prettyprint-override"><code>&lt;c:when test="${someModel.status == 'OLD'}"&gt;
</code></pre>

blocks|key|1531251|text|为此，我执行以下操作：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1531252|<c:set+var="abc">
++++<%25=Status.OLD.getStatus()%25>
</c:set>

<c:if+test="${someVariable+==+abc}">
++++....
</c:if>|code-block|syntax|javascript|1531253|它看起来很难看，但很管用！|1531254|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

For this purposes I do the following:

<pre class="lang-xml prettyprint-override"><code>&lt;c:set var="abc"&gt;
 &lt;%=Status.OLD.getStatus()%&gt;
&lt;/c:set&gt;

&lt;c:if test="${someVariable == abc}"&gt;
 ....
&lt;/c:if&gt;
</code></pre>

It's looks ugly, but works!

blocks|key|1531283|text|我通常认为将java代码混合到jsp/tag文件中是不好的做法。使用'eq‘应该可以解决这个问题：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1531284|<c:if+test="${dp.Status+eq+'OLD'}">
++...
</c:if>|code-block|syntax|javascript|1531285|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I generally consider it bad practice to mix java code into jsps/tag files. Using 'eq' should do the trick :

<pre><code>&lt;c:if test="${dp.Status eq 'OLD'}"&gt;
 ...
&lt;/c:if&gt;
</code></pre>

blocks|key|1531330|text|向枚举添加一个方法，如下所示：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1531331|public+String+getString()+{
++++return+this.name();
}|code-block|syntax|javascript|1531332|例如|1531333|public+enum+MyEnum+{
++++VALUE_1,
++++VALUE_2;
++++public+String+getString()+{
++++++++return+this.name();
++++}
}|1531334|然后，您可以使用：|1531335|<c:if+test="${myObject.myEnumProperty.string+eq+'VALUE_2'}">...</c:if>|1531336|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|U|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

Add a method to the enum like:

<pre><code>public String getString() {
 return this.name();
}
</code></pre>

For example

<pre><code>public enum MyEnum {
 VALUE_1,
 VALUE_2;
 public String getString() {
 return this.name();
 }
}
</code></pre>

Then you can use:

<pre><code>&lt;c:if test="${myObject.myEnumProperty.string eq 'VALUE_2'}"&gt;...&lt;/c:if&gt;
</code></pre>

blocks|key|1746352|text|我对Kornel的问题没有答案，但我对其他脚本示例有一个备注。大多数表达式都隐式信任toString()，但Enum.valueOf()需要来自/匹配Enum.name()属性的值。因此，应该使用例如：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1746353|<%25+pageContext.setAttribute("Status_OLD",+Status.OLD.name());+%25>
...
<c:when+test="${someModel.status+==+Status_OLD}"/>...</c:when>|code-block|syntax|javascript|1746354|entityMap^0|16|A|1I|E|23|B|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|U|8|@]|D|@]|E|$]]]|L|$]]

I do not have an answer to the question of Kornel, but I've a remark about the other script examples. Most of the expression trust implicitly on the <code>toString()</code>, but the <code>Enum.valueOf()</code> expects a value that comes from/matches the <code>Enum.name()</code> property. So one should use e.g.:

<pre><code>&lt;% pageContext.setAttribute("Status_OLD", Status.OLD.name()); %&gt;
...
&lt;c:when test="${someModel.status == Status_OLD}"/&gt;...&lt;/c:when&gt;
</code></pre>

blocks|key|1746374|text|如果使用Spring+MVC，Spring+Expression+Language+(SpEL)会很有帮助：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1746375|<spring:eval+expression="dp.status+==+T(com.example.Status).VALID"+var="isValid"+/>
<c:if+test="${isValid}">
+++isValid
</c:if>|code-block|syntax|javascript|1746376|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

If using Spring MVC, the Spring Expression Language (SpEL) can be helpful:

<pre class="lang-xml prettyprint-override"><code>&lt;spring:eval expression="dp.status == T(com.example.Status).VALID" var="isValid" /&gt;
&lt;c:if test="${isValid}"&gt;
 isValid
&lt;/c:if&gt;
</code></pre>

blocks|key|1746412|text|以下是另外两种可能性：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1746413|JSP+EL+3.0常量|1746414|只要您使用的EL版本至少为3.0，则可以将常量导入到您的页面中，如下所示：|1746415|<%25@+page+import="org.example.Status"+%25>
<c:when+test="${dp.status+eq+Status.VALID}">|code-block|syntax|javascript|1746416|然而，一些IDE还不能理解这一点(例如IntelliJ)，所以如果你输入错误，你不会得到任何警告，直到运行时。|offset|length|1746417|一旦获得适当的IDE支持，这将是我首选的方法。|1746418|帮助器方法|1746419|您可以只将getter添加到枚举中。|1746420|public+enum+Status+{+
++VALID("valid"),+OLD("old");

++private+final+String+val;

++Status(String+val)+{
++++this.val+=+val;
++}

++public+String+getStatus()+{
++++return+val;
++}

++public+boolean+isValid()+{
++++return+this+==+VALID;
++}

++public+boolean+isOld()+{
++++return+this+==+OLD;
++}
}|1746421|然后在你的JSP中：|1746422|<c:when+test="${dp.status.valid}">|1746423|这在所有IDE中都是受支持的，如果你还不能使用EL+3.0，它也会起作用。这就是我现在所做的，因为它将所有逻辑都封装在我的枚举中。|1746424|如果存储枚举的变量可能为null，也要小心。如果你的代码不能保证它不是空的，你需要首先检查它：|1746425|<c:when+test="${not+empty+db.status+and+dp.status.valid}">|1746426|我认为这种方法比那些在JSP中设置中间值的方法更好，因为您必须在需要使用枚举的每个页面上设置中间值。但是，使用此解决方案时，您只需声明一次getter。|1746427|entityMap|0|LINK|mutability|MUTABLE|url|https://youtrack.jetbrains.com/issue/IDEA-138230^0|0|0|0|0|J|8|0|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1G|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1H|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|1I|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|1J|8|@]|9|@]|A|$I|J]]|$1|K|3|L|5|6|7|1K|8|@]|9|@$M|1L|N|1M|1|1N]]|A|$]]|$1|O|3|P|5|6|7|1O|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|1P|8|@]|9|@]|A|$]]|$1|S|3|T|5|6|7|1Q|8|@]|9|@]|A|$]]|$1|U|3|V|5|H|7|1R|8|@]|9|@]|A|$I|J]]|$1|W|3|X|5|6|7|1S|8|@]|9|@]|A|$]]|$1|Y|3|Z|5|H|7|1T|8|@]|9|@]|A|$I|J]]|$1|10|3|11|5|6|7|1U|8|@]|9|@]|A|$]]|$1|12|3|13|5|6|7|1V|8|@]|9|@]|A|$]]|$1|14|3|15|5|H|7|1W|8|@]|9|@]|A|$I|J]]|$1|16|3|17|5|6|7|1X|8|@]|9|@]|A|$]]|$1|18|3|-4|5|6|7|1Y|8|@]|9|@]|A|$]]]|19|$1A|$5|1B|1C|1D|A|$1E|1F]]]]

Here are two more possibilities:
<h1>JSP EL 3.0 Constants</h1>
As long as you are using at least version 3.0 of EL, then you can import constants into your page as follows:
<pre><code>&lt;%@ page import=&quot;org.example.Status&quot; %&gt;
&lt;c:when test=&quot;${dp.status eq Status.VALID}&quot;&gt;
</code></pre>
However, some IDEs don't understand this yet (e.g. <a href="https://youtrack.jetbrains.com/issue/IDEA-138230" rel="noreferrer">IntelliJ</a>) so you won't get any warnings if you make a typo, until runtime.
This would be my preferred method once it gets proper IDE support.
<h1>Helper Methods</h1>
You could just add getters to your enum.
<pre><code>public enum Status { 
 VALID(&quot;valid&quot;), OLD(&quot;old&quot;);

 private final String val;

 Status(String val) {
 this.val = val;
 }

 public String getStatus() {
 return val;
 }

 public boolean isValid() {
 return this == VALID;
 }

 public boolean isOld() {
 return this == OLD;
 }
}
</code></pre>
Then in your JSP:
<pre><code>&lt;c:when test=&quot;${dp.status.valid}&quot;&gt;
</code></pre>
This is supported in all IDEs and will also work if you can't use EL 3.0 yet. This is what I do at the moment because it keeps all the logic wrapped up into my enum.
Also be careful if it is possible for the variable storing the enum to be null. You would need to check for that first if your code doesn't guarantee that it is not null:
<pre><code>&lt;c:when test=&quot;${not empty db.status and dp.status.valid}&quot;&gt;
</code></pre>
I think this method is superior to those where you set an intermediary value in the JSP because you have to do that on each page where you need to use the enum. However, with this solution you only need to declare the getter once.

blocks|key|1746463|text|在使用MVC框架时，我在控制器中放入了以下内容。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1746464|request.setAttribute(RequestParameterNamesEnum.INBOX_ACTION.name(),+RequestParameterNamesEnum.INBOX_ACTION.name());|code-block|syntax|javascript|1746465|这允许我在我的JSP页面中使用以下代码。|1746466|<script>+var+url+=+'http://www.nowhere.com/?${INBOX_ACTION}='+%2B+someValue;</script>|1746467|它也可以用于您的比较|1746468|<c:when+test="${someModel.action+==+INBOX_ACTION}">|1746469|我更喜欢它而不是放入字符串文字。|1746470|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|W|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|Y|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

When using a MVC framework I put the following in my controller.

<pre><code>request.setAttribute(RequestParameterNamesEnum.INBOX_ACTION.name(), RequestParameterNamesEnum.INBOX_ACTION.name());
</code></pre>

This allows me to use the following in my JSP Page.

<pre><code>&lt;script&gt; var url = 'http://www.nowhere.com/?${INBOX_ACTION}=' + someValue;&lt;/script&gt;
</code></pre>

It can also be used in your comparison

<pre><code>&lt;c:when test="${someModel.action == INBOX_ACTION}"&gt;
</code></pre>

Which I prefer over putting in a string literal.

blocks|key|1531514|text|当有很多点要用的时候，我会这样做。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1531515|public+enum+Status+{+

++++VALID("valid"),+OLD("old");

++++private+final+String+val;

++++Status(String+val)+{
++++++++this.val+=+val;
++++}

++++public+String+getStatus()+{
++++++++return+val;
++++}

++++public+static+void+setRequestAttributes(HttpServletRequest+request)+{
++++++++Map<String,String>+vals+=+new+HashMap<String,String>();
++++++++for+(Status+val+:+Status.values())+{
++++++++++++vals.put(val.name(),+val.value);
++++++++}
++++++++request.setAttribute("Status",+vals);
++++}

}|code-block|syntax|javascript|1531516|JSP|1531517|<%25@+page+import="...Status"+%25>
<%25+Status.setRequestAttributes(request)+%25>

<c:when+test="${dp.status+eq+Status.VALID}">
...|1531518|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

I do it this way when there are many points to use...

<pre><code>public enum Status { 

 VALID("valid"), OLD("old");

 private final String val;

 Status(String val) {
 this.val = val;
 }

 public String getStatus() {
 return val;
 }

 public static void setRequestAttributes(HttpServletRequest request) {
 Map&lt;String,String&gt; vals = new HashMap&lt;String,String&gt;();
 for (Status val : Status.values()) {
 vals.put(val.name(), val.value);
 }
 request.setAttribute("Status", vals);
 }

}
</code></pre>

JSP

<pre><code>&lt;%@ page import="...Status" %&gt;
&lt;% Status.setRequestAttributes(request) %&gt;

&lt;c:when test="${dp.status eq Status.VALID}"&gt;
...
</code></pre>

I have an Enum called Status defined as such:

<pre><code>public enum Status { 

 VALID("valid"), OLD("old");

 private final String val;

 Status(String val) {
 this.val = val;
 }

 public String getStatus() {
 return val;
 }

}
</code></pre>

I would like to access the value of <code>VALID</code> from a JSTL tag. Specifically the <code>test</code> attribute of the <code>&lt;c:when&gt;</code> tag. E.g.

<pre><code>&lt;c:when test="${dp.status eq Status.VALID"&gt;
</code></pre>

I'm not sure if this is possible.

Access Enum value using EL with JSTL

我有一个名为Status的枚举，定义如下：public enum Status {     VALID("valid"), OLD("old");    private final String val;    Status(String val) {        this.val = val;    }    pu...

问使用EL和JSTL访问枚举值
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