Question

I have a requirement where some data has to be obtained by connecting to an API.

I have mapped the object returned by query to a hashmap, using the following code–

        untypedResult=wt.QueryPermissions();
        resp.getWriter().println(" Response for QueryPermissions----");
        if(wt.errormsg=="No Error")
        {   
            hMap = (HashMap<String, Integer>) untypedResult;

            Set set = hMap.entrySet();

            Iterator i = set.iterator();

            while(i.hasNext()){
              Map.Entry me = (Map.Entry)i.next();
              resp.getWriter().println(me.getKey() + " : " +     me.getValue());

The output as returned by using above code —

 Response for QueryPermissions----
 get_all_words_popularity : {keyphrase_limit=999, timeout_limit=99, cost_per_call=99, result_limit=999}

Now I tried to map the response (in object) to the following class—

public class wt_queryperm_class {

public Integer keyphrase_limit;
public Integer timeout_limit;
public Integer cost_per_call;
public Integer result_limit;


}

Also, now I modified the code used to display the data as shown below–

    //declare new object to store result of QueryPermissions
        wt_queryperm_class a;

    untypedResult=wt.QueryPermissions();
        resp.getWriter().println(" Response for QueryPermissions----");
        if(wt.errormsg=="No Error")
        {   
            hMap = (HashMap<String, Integer>) untypedResult;

            Set set = hMap.entrySet();

            Iterator i = set.iterator();

            while(i.hasNext()){
              Map.Entry me = (Map.Entry)i.next();
              a= (wt_queryperm_class)(me.getValue());
              resp.getWriter().println(me.getKey() + " :  Cost per call=" + a.cost_per_call + "Keyphrase limit=" + a.keyphrase_limit + " Result limit=" + a.result_limit +" Timeout limit=" +  a.timeout_limit );
            }

However I get the following error when I run the above code–

Problem accessing /keywords_trial_application. Reason:

java.util.HashMap cannot be cast to com.taurusseo.keywords.wt_queryperm_class
Caused by:

java.lang.ClassCastException: java.util.HashMap cannot be cast to com.taurusseo.keywords.wt_queryperm_class

What am I doing wrong here? How do I cast the response correctly so that I can extract each of the 4 values correctly?

Answer 1

The result of the query, given what’s printed and the error you got is a Map<String, Map<String, Integer>> (or a Map<String, Map<String, String>> if the numbers are stored as Strings).

The map has one single key : "get_all_words_popularity". The associated valud contains 4 keys : "keyphrase_limit", "timeout_limit", "cost_per_call", "result_limit".

So your code should rather look like this:

untypedResult = wt.queryPermissions();
resp.getWriter().println(" Response for QueryPermissions----");
if("No Error".equals(wt.errormsg)) {   
    Map<String, Map<String, Integer> hMap = 
        (Map<String, Map<String, Integer>) untypedResult;

    for (Map.Entry<String, Map<String, Integer>> me : hMap.entrySet()) {
        Map<String, Integer> value = me.getValue();
        WtQueryPerm perm = new WtQueryPerm(value.get("keyphrase_limit"),
                                           value.get("timeout_limit"),
                                           value.get("cost_per_call"),
                                           value.get("result_limit"));
        resp.getWriter().println(me.getKey() 
                                 + " :  Cost per call=" + perm.getCostPerCall() 
                                 + ", Keyphrase limit=" + perm.getKeyphraseLimit() 
                                 + ", Result limit=" + perm.getResultLimit() 
                                 + ", Timeout limit=" +  perm.getTimeoutLimit());

    }
}

Note that my code

• respects the Java naming conventions
• always uses generic types, which avoid casts and compilation warnings
• doesn’t compare Strings with ==, but uses equals, because == only compares the references and not the values.
• declare the variables with the smaller scope possible, only when needed.
• use getters to access the state of the constructed object.

Also understand that a cast doesn’t magically transform an object into another object type. It just allows referencing an object of type A as another type B, and only works if the object is effectively of type B (and thus B has A as ancestor or interface)