Trying to create a dropdown in my jsp page

Question

I am trying to create a dropdown which will have dynamic values in my jsp page but getting an exception, i am trying to use spring form tags here.

WebController.java

 @RequestMapping(value="/addAchivement",method=RequestMethod.GET)
public String addAchievements(){

    Object object=null;
    try {
        object = genericAppProcessor.checkLogin(username, password,null,null);
    } catch (ParseException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    SchoolLoginDetails sld=new SchoolLoginDetails();
    sld=(SchoolLoginDetails)object;
    List<GroupDetails> list=new ArrayList<GroupDetails>();
    list=(List<GroupDetails>) sld.getGroupDetails();
    Set<Object> addedClass = new HashSet<Object>();
    Set<Object> addedSection = new HashSet<Object>();

    Map referenceData = new HashMap();
    Map<Object,Object> classs = new LinkedHashMap<Object,Object>();        

    for(int i=0;i<list.size();i++){
    Object obj=list.get(i).getClazz();
    Object objj=list.get(i).getSection();
    addedClass.add(obj);
    addedSection.add(objj);
    List<Object> convertTolist=new ArrayList<Object>(addedClass);
    classs.put(convertTolist.get(0),convertTolist.get(0));
    addedClass.clear();
    }



    referenceData.put("classList",classs);

    return "addAchivement"; 
}

addAchivement.jsp

<form:form method="POST" role="form" action="/GenericApp/addWebAchievement" enctype="multipart/form-data">

<form:select path="classs">
        <form:options items="${classList}" />
</form:select>

Exception :-

 org.apache.jasper.JasperException: An exception occurred processing JSP page /WEB-INF/jsp/addAchivement.jsp at line 72

<div class="input-field col s12 m4 l3"  >
   <!--Line 72 -->   <form:select path="classs" class="text-black custom-select">
                      <form:options items="${classList}" />
                     </form:select>

Answer 1

you need to return model and view instead of just returning a view Use Below Code :

// Java Code

     @RequestMapping(value="/addAchivement",method=RequestMethod.GET)
     public ModelAndView addAchievements(){
   Object object=null;
try {
    object = genericAppProcessor.checkLogin(username, password,null,null);
} catch (ParseException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
}
SchoolLoginDetails sld=new SchoolLoginDetails();
sld=(SchoolLoginDetails)object;
List<GroupDetails> list=new ArrayList<GroupDetails>();
list=(List<GroupDetails>) sld.getGroupDetails();
Set<Object> addedClass = new HashSet<Object>();
Set<Object> addedSection = new HashSet<Object>();

Map referenceData = new HashMap();
Map<Object,Object> classs = new LinkedHashMap<Object,Object>();        

for(int i=0;i<list.size();i++){
Object obj=list.get(i).getClazz();
Object objj=list.get(i).getSection();
addedClass.add(obj);
addedSection.add(objj);
List<Object> convertTolist=new ArrayList<Object>(addedClass);
classs.put(convertTolist.get(0),convertTolist.get(0));
addedClass.clear();
}



referenceData.put("classList",classs);
ModelAndView mav = new ModelAndView("addAchivement", referenceData);

return mav; 

}

You are assigning a path to classs in your jsp

 <!--Line 72 -->   <form:select path="classs" class="text-black custom-select">

but you are not sending anything from model on which this class variable can map so you need to use modelAttribute in your spring form so that this class variable can map .

for eg . : you need to make a class object which has a class as member :

below is java code change :

  referenceData.put("classList",classs);
  referenceData.put("classObject",class); // Here class is a object that has    class attribute by which that value in jsp will bind .
  ModelAndView mav = new ModelAndView("addAchivement", referenceData);

Here is Jsp Code change :

<form:form method="POST" role="form" action="/GenericApp/addWebAchievement" enctype="multipart/form-data" modelAttribute="classObject">

<form:select path="classs">
        <form:options items="${classList}" />
</form:select>

Sample class object :

 public Class{

 String classs ;

 // getter setter for classs member variable .

  }