Refactor Retrofit samples (#2568)

libraries/src/main/java/com/baeldung/retrofit/basic/GitHubBasicService.java

@@ -1,54 +1,60 @@
 package com.baeldung.retrofit.basic;
 
-import java.io.IOException;
-import java.util.ArrayList;
-import java.util.Collections;
-import java.util.List;
-import java.util.stream.Collectors;
-
 import com.baeldung.retrofit.models.Contributor;
 import com.baeldung.retrofit.models.Repository;
-
 import retrofit2.Retrofit;
 import retrofit2.converter.gson.GsonConverterFactory;
 
-public class GitHubBasicService {
-    
+import java.io.IOException;
+import java.util.Collections;
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+class GitHubBasicService {
+
     private GitHubBasicApi gitHubApi;
-    
-    public GitHubBasicService() {
+
+    GitHubBasicService() {
         Retrofit retrofit = new Retrofit.Builder()
-            .baseUrl("https://api.github.com/")
-            .addConverterFactory(GsonConverterFactory.create())
-            .build();
-          
-          gitHubApi = retrofit.create(GitHubBasicApi.class);
+          .baseUrl("https://api.github.com/")
+          .addConverterFactory(GsonConverterFactory.create())
+          .build();
+
+        gitHubApi = retrofit.create(GitHubBasicApi.class);
     }
-    
-    public List<String> getTopContributors(String userName) throws IOException {
+
+    List<String> getTopContributors(String userName) throws IOException {
         List<Repository> repos = gitHubApi
           .listRepos(userName)
           .execute()
           .body();
-        
-        List<Contributor> topContributors = new ArrayList<>();
-        for(Repository repo : repos) {
-            List<Contributor> contributers = gitHubApi
-              .listRepoContributors(userName, repo.getName())
-              .execute()
-              .body();
-            
-            List<Contributor> repoTopContributors = contributers.stream()
-              .filter(c -> c.getContributions() > 100)
-              .collect(Collectors.toList());
-            topContributors.addAll(repoTopContributors);
-        }
-        
-        Collections.sort(topContributors, (a, b) -> b.getContributions() - a.getContributions());
-        return topContributors.stream()
-          .map(c -> c.getName())
+
+        repos = repos != null ? repos : Collections.emptyList();
+
+        return repos.stream()
+          .flatMap(repo -> getContributors(userName, repo))
+          .sorted((a, b) -> b.getContributions() - a.getContributions())
+          .map(Contributor::getName)
           .distinct()
+          .sorted()
           .collect(Collectors.toList());
     }
 
+    private Stream<Contributor> getContributors(String userName, Repository repo) {
+        List<Contributor> contributors = null;
+        try {
+            contributors = gitHubApi
+              .listRepoContributors(userName, repo.getName())
+              .execute()
+              .body();
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+
+        contributors = contributors != null ? contributors : Collections.emptyList();
+
+        return contributors.stream()
+          .filter(c -> c.getContributions() > 100);
+    }
 }