问题
In JSP/JSTL, how can I set values for a usebean of class="java.util.ArrayList".
If I try using c:set property or value, I get the following error: javax.servlet.jsp.JspTagException: Invalid property in : "null"
回答1:
That isn't directly possible. There are the <c:set>
and <jsp:setProperty>
tags which allows you to set properties in a fullworthy javabean through a setter method. However, the List
interface doesn't have a setter, just an add()
method.
A workaround would be to wrap the list in a real javabean like so:
public class ListBean {
private List<Object> list = new ArrayList<Object>();
public void setChild(Object object) {
list.add(object);
}
public List<Object> getList() {
return list;
}
}
and set it by
<jsp:useBean id="listBean" class="com.example.ListBean" scope="request" />
<jsp:setProperty name="listBean" property="child" value="foo" />
<jsp:setProperty name="listBean" property="child" value="bar" />
<jsp:setProperty name="listBean" property="child" value="waa" />
But that makes little sense. How to solve it rightly depends on the sole functional requirement. If you want to preserve some List
upon a GET request, then you should be using a preprocessing servlet. Create a servlet which does the following in doGet()
method:
List<String> list = Arrays.asList("foo", "bar", "waa");
request.setAttribute("list", list);
request.getRequestDispatcher("/WEB-INF/page.jsp").forward(request, response);
When you invoke the servlet by its URL, then the list is in the forwarded JSP available by
${list}
without the need for old fashioned <jsp:useBean>
tags. In a servlet you've all freedom to write Java code the usual way. This way you can use JSP for pure presentation only without the need to gobble/hack some preprocessing logic by <jsp:useBean>
tags.
See also:
- Our servlets wiki page
来源:https://stackoverflow.com/questions/6024435/how-to-add-values-to-an-arraylist-referenced-by-jspusebean