java - Process list stream and collect into map/ImmutableMap with only non null values -

how process list of string , collec map or immutable map value present

string anotherparam = "xyz"; map.builder<string,string> resultmap = immutablemap.builder(..)   listofitems.stream()             .filter(objects::nonnull)             .distinct()             .foreach(                     item -> {                         final optional<string> result =          getprocesseditem(item,anotherparam);                          if (result.ispresent()) {      resultmap.put(item, result.get());                         }                     });         return resultmap.build(); 

please tell, there better way achieve via collect?

if have access apache commons library can make use of pair.class

map<string, string> resultmap = immutablemap.copyof(listofitems()     .stream()     .filter(objects::nonnull)     .distinct()     .map(it -> pair.of(it, getprocesseditem(it,anotherparam))     .filter(pair -> pair.getvalue().ispresent())     .collect(tomap(pair::getkey, pair -> pair.getvalue().get()))) 

but it's practice make special data classes describes mapping item->result more specificly

here example, create class this:

static class itemresult(){     public final string item;     public final optional<string> result;      public itemresult(string item, optional<string> result){         this.item = item;         this.result = result;     }      public boolean ispresent(){         return this.result.ispresent();     }      public string getresult(){         return result.get();     } } 

and use that:

map<string, string> resultmap = immutablemap.copyof(listofitems()     .stream()     .filter(objects::nonnull)     .distinct()     .map(it -> new itemresult(it, getprocesseditem(it,anotherparam))     .filter(itemresult::ispresent)     .collect(tomap(itemresult::item, itemresult::getresult))) 

you can read here why google gave idea of tuples , pairs , don't use them in cases

if after don't want use other class can leverage api of optional:

map.builder<string,string> resultmap = immutablemap.builder(..)  listofitems.stream()         .filter(objects::nonnull)         .distinct()         .foreach(item -> getprocesseditem(item,anotherparam)                          .ifpresent(result -> resultmap.put(item result));     return resultmap.build();