使用JSTL向arraylist添加值

问题描述：

是否可以将值添加到ArrayList而不是使用HashMap

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

类似:

<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>

现在出现错误:

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

thx

答

JSTL并非旨在执行此类操作.这确实属于业务逻辑，该业务逻辑将(间接)由Servlet类控制.

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.

创建一个如下所示的servlet:

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);
}

将此映射到/animals的url-pattern.

现在在/WEB-INF/animals.jsp中创建一个JSP文件(将其放置在WEB-INF中以防止直接访问):

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>

不需要jsp:useBean，因为servlet已经设置了它.

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

现在通过http://example.com/context/animals调用servlet + JSP.

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

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