将ArrayList从servlet传递给JSP

Question

我试图将包含从servlet的对象的ArrayList传递给JSP.但

Servlet文件:

request.setAttribute("servletName", categoryList); //categorylist is an arraylist      contains object of class category  
getServletConfig().getServletContext().getRequestDispatcher("/GetCategory.jsp").forward(request,response);

JSP文件:

//category class    
<% Category category = new Category();
//creating arraylist object of type category class
ArrayList<Category> list = ArrayList<Category>();
//storing passed value from jsp
list = request.getAttribute("servletName");

for(int i = 0; i < list.size(); i++) {

category = list.get(i);

out.println( category.getId());

out.println(category.getName());

out.println(category.getMainCategoryId() );
}
%>

Answer 1

在servlet代码中,使用该指令request.setAttribute("servletName", categoryList)将列表保存在请求对象中,并使用名称"servletName"来引用它.
顺便说一下,使用名称"servletName"作为列表是相当混乱的,也许最好称之为"列表"或类似的东西: request.setAttribute("list", categoryList)
无论如何,假设你不改变你的serlvet代码,并使用名称"servletName"存储列表".当您到达JSP时,需要从请求中检索列表,为此您只需要该request.getAttribute(...)方法.

<%  
// retrieve your list from the request, with casting 
ArrayList<Category> list = (ArrayList<Category>) request.getAttribute("servletName");

// print the information about every category of the list
for(Category category : list) {
    out.println(category.getId());
    out.println(category.getName());
    out.println(category.getMainCategoryId());
}
%>

Answer 2

request.getAttribute("servletName")方法将返回Object您需要转换为ArrayList

ArrayList<Category> list =new ArrayList<Category>();
//storing passed value from jsp
list = (ArrayList<Category>)request.getAttribute("servletName");