Display multi-valued hash map with one key and multiple values ​​in JSP

Question

I have the following MultiHashMap in a .java controller

MultiHashMap multimap= new MultiHashMap(); List<SampleList> list1 = (List<SampleList>) request.getPortletSession().getAttribute("list1"); Iterator<SampleList> sampleListIterator= list1.iterator(); while(sampleListIterator.hasNext()){ SampleList sampleList = sampleListIterator.next(); List <SubList> subList = sampleList.getsubList(); Iterator<SubList> subListIterator = subList.iterator(); while(subListIterator.hasNext() ){ SubList subList2 = subListIterator.next(); multimap.put(subList2.getCategorySubcategory(),subList2.getCost()); } } 

In jsp, I have a table that displays the above hashmap

 <table> <tbody> <c:foreach var="item" items="${multimap}"> <tr> <th> ${item.key}</th> <c:foreach var="valueList" items=${item.value}> <td> ${valueList}</td> </c:foreach> </tr> </c:foreach> </tbody> </table> 

I get an error when I try to display this value from the controller.

Answer 1

Apache Commons MultiHashMap is deprecated , you should use MultiValueMap instead.

Outdated . The class is now available as a MultiValueMap in the map subpackage. This version should be removed in v4.0 collections.

Both the MultiHashMap and MultiValueMap classes have a getCollection(Object key) method that returns a collection of values ​​for this particular key:

 java.util.Collection getCollection(java.lang.Object key) 

Gets the collection associated with the specified key.

You can iterate over it in JSP like any other collection using JSTL, OGNL, etc.

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EDIT

Surprisingly, there is not even one example of using this class in JSTL or OGNL all over the Internet ... I think your question will become popular, +1;)

Since the MultiValueMap (and the obsolete MultiHashMap) is a map with a collection of values ​​for each map key, it should be repeated in JSTL, like this one (untested, but supposedly correct) ( now TESTED on JSTL 1.1.2 in the Servlet 2.4 / JSP 2.0 container ) :

 <c:forEach var="entry" items="${multiMap}"> <br/>-> Key: <c:out value="${entry.key}"/> <br/>-> Values for this key: <c:forEach var="currentValue" items="${entry.value}"> <br/>|---> value: <c:out value="${currentValue}"/> </c:forEach> </c:forEach> 

Filling this type

 multiMap = new MultiValueMap(); multiMap.put("key1", "value1-1"); multiMap.put("key1", "value1-2"); multiMap.put("key1", "value1-3"); multiMap.put("key2", "value2-1"); multiMap.put("key2", "value2-2"); multiMap.put("key2", "value2-3"); multiMap.put("key3", "value3-1"); multiMap.put("key3", "value3-2"); multiMap.put("key3", "value3-3"); 

The result is this (copied and pasted from my JSP):

 -> Key: key1 -> Values for this key: |---> value: value1-1 |---> value: value1-2 |---> value: value1-3 -> Key: key3 -> Values for this key: |---> value: value3-1 |---> value: value3-2 |---> value: value3-3 -> Key: key2 -> Values for this key: |---> value: value2-1 |---> value: value2-2 |---> value: value2-3 

Then it works fine (except for the curious fact that key3 fits up to key2); if you still have problems, they are not code related, but in your configuration.

Please check out the JSTL wiki tags on SO , this good article or the numerous answers to JSTL problems from BalusC here on SO.

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As a final point, although looking at the code that you use to create the MultiValueMap, I highly recommend that you start creating some custom object , as object-oriented programming suggests, to avoid over-nesting lists and Maps, which can lead to unreadable, unreachable code.

Answer 2

I have not used MultiHashMaps before, but I usually display the contents of the HashMap on the jsp page (without the generics example):

 Iterator iter = map.entrySet().iterator(); while(iter.hasNext()){ Map.Entry entry = iter.next(); Object key = entry.getKey(); Object value = entry.getValue(); 

Answer 3

Using JTL Core taglibrary: <%

 Map<String, String> countryList = new HashMap<String, String>(); countryList.put("United States", "Washington DC"); countryList.put("India", "Delhi"); countryList.put("Germany", "Berlin"); countryList.put("France", "Paris"); countryList.put("Italy", "Rome"); request.setAttribute("capitalList", countryList); %> <c:forEach var="country" items="${capitalList}"> Country: ${country.key} - Capital: ${country.value} </c:forEach> 

If you use struts, you can arrange the logical tag library to repeat and display the map in JSP:

  <logic:iterate name="students" id="nameObj" scope="session"> <bean:write name="nameObj" property="key"/> <bean:write name="nameObj" property="value"/> </logic:iterate>