Add values to arraylist use JSTL

问题

is it possible to add values to an ArrayList instead of using a HashMap

something like:

<jsp:useBean id="animalList" class="java.util.ArrayList" />

<c:set target="${animalList}" value="Sylvester"/>

<c:set target="${animalList}" value="Goofy"/>

<c:set target="${animalList}" value="Mickey"/>

<c:forEach items="${animalList}" var="animal">

${animal}<br>

</c:forEach>

now getting the error:

javax.servlet.jsp.JspTagException: Invalid property in &lt;set&gt;:  "null"

thx

回答1:

JSTL is not designed to do this kind of stuff. This really belongs in the business logic which is (in)directly to be controlled by a servlet class.

Create a servlet which does like:

protected void doGet(HttpServletRequest request, HttpServletResponse response) {
    List<String> animals = new ArrayList<String>();
    animals.add("Sylvester");
    animals.add("Goofy");
    animals.add("Mickey");
    request.setAttribute("animals", animals);
    request.getRequestDispatcher("/WEB-INF/animals.jsp").forward(request, response);
}

Map this on an url-pattern of /animals.

Now create a JSP file in /WEB-INF/animals.jsp (place it in WEB-INF to prevent direct access):

<c:forEach items="${animals}" var="animal">
    ${animal}<br>
</c:forEach>

No need for jsp:useBean as servlet has already set it.

Now call the servlet+JSP by http://example.com/context/animals.

回答2:

The above code is not working.

Following are the lines of code that has to be placed in file animals.jsp

<%@ taglib prefix="c" uri="http://java.sun.com/jstl/core" %>
<c:forEach var="animal" items="${animals}">
   <c:set var="animalName" value="${animal}"/>
   <c:out value="${animalName}"/>
</c:forEach>

回答3:

To do add() to a List or others methods from Map, Set, etc... You have to use a unusable variable.

<jsp:useBean id="list" class="java.util.ArrayList"/> <c:set var="noUse" value="${list.add('YourThing')}"/> <c:out value=${list} />

来源：https://stackoverflow.com/questions/1835061/add-values-to-arraylist-use-jstl

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java

jstl