Java 使用 JSTL 将值添加到 arraylist
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Add values to arraylist use JSTL
提问by Michel
is it possible to add values to an ArrayList instead of using a HashMap
是否可以将值添加到 ArrayList 而不是使用 HashMap
something like:
就像是：
<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">
${animal}<br>
</c:forEach>
now getting the error:
现在收到错误：
javax.servlet.jsp.JspTagException: Invalid property in <set>: "null"
thx
谢谢
采纳答案by BalusC
JSTL is not designed to do this kind of stuff. This really belongs in the business logic which is (in)directly to be controlled by a servlet class.
JSTL 不是为做这种事情而设计的。这确实属于业务逻辑，它（in）直接由 servlet 类控制。
Create a servlet which does like:
创建一个像下面这样的 servlet：
protected void doGet(HttpServletRequest request, HttpServletResponse response) {
List<String> animals = new ArrayList<String>();
animals.add("Sylvester");
animals.add("Goofy");
animals.add("Mickey");
request.setAttribute("animals", animals);
request.getRequestDispatcher("/WEB-INF/animals.jsp").forward(request, response);
}
Map this on an url-patternof /animals.
将此映射url-pattern到/animals。
Now create a JSP file in /WEB-INF/animals.jsp(place it in WEB-INFto prevent direct access):
现在创建一个 JSP 文件/WEB-INF/animals.jsp（将其放入WEB-INF以防止直接访问）：
<c:forEach items="${animals}" var="animal">
${animal}<br>
</c:forEach>
No need for jsp:useBeanas servlet has already set it.
不需要，jsp:useBean因为 servlet 已经设置了它。
Now call the servlet+JSP by http://example.com/context/animals.
现在通过 调用servlet+JSP http://example.com/context/animals。
回答by Sarvesh
The above code is not working.
上面的代码不起作用。
Following are the lines of code that has to be placed in file animals.jsp
以下是必须放在文件中的代码行 animals.jsp
<%@ taglib prefix="c" uri="http://java.sun.com/jstl/core" %>
<c:forEach var="animal" items="${animals}">
<c:set var="animalName" value="${animal}"/>
<c:out value="${animalName}"/>
</c:forEach>
回答by Marcos Gomes
To do add() to a List or others methods from Map, Set, etc... You have to use a unusable variable.
要从 Map、Set 等对 List 或其他方法执行 add() 操作...您必须使用不可用的变量。
<jsp:useBean id="list" class="java.util.ArrayList"/>
<c:set var="noUse" value="${list.add('YourThing')}"/>
<c:out value=${list} />
<jsp:useBean id="list" class="java.util.ArrayList"/>
<c:set var="noUse" value="${list.add('YourThing')}"/>
<c:out value=${list} />
