feat : variants implementation

Author: reeshika-h

src/main/java/com/contentstack/sdk/Entry.java

@@ -1099,4 +1099,39 @@ public Entry includeMetadata() {
         params.put("include_metadata", true);
         return this;
     }
+
+    /**
+    * @method variants
+    * @memberof Entry
+    * @description The variant header will be added to client
+    * @returns {Entry}
+    * @example
+    * import contentstack from '@contentstack/delivery-sdk'
+    *
+    * Stack stack = contentstack.Stack("apiKey", "deliveryToken", "environment");
+    * Entry entry = stack.contentType("user").entry("entry_uid").variant("variant_uid").fetch();
+    */
+   public Entry variants(@NotNull String variants){
+   if (variants != null && variants.length() > 0) {
+      this.headers.put("x-cs-variant-uid", variants.trim());
+    }
+    return this;
+  
+  }
+  public Entry variants(@NotNull String[] variants){
+    if (variants != null && variants.length > 0) {
+        List<String> variantList = new ArrayList<>();
+        for (String variant : variants) {
+            if(variant != null && !variant.trim().isEmpty())
+            variantList.add(variant.trim());
+        }
+        if(!variantList.isEmpty()){
+            this.headers.put("x-cs-variant-uid", String.join(", ", variantList));
+        }
+    }
+    return this;
+  }
+  public LinkedHashMap<String, Object> getHeaders() {
+    return headers;
+}
 }

src/test/java/com/contentstack/sdk/TestEntry.java

@@ -7,6 +7,8 @@
 import java.util.GregorianCalendar;
 import java.util.logging.Logger;
 
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 @TestInstance(TestInstance.Lifecycle.PER_CLASS)
@@ -62,6 +64,50 @@ public void onCompletion(ResponseType responseType, Error error) {
         });
         logger.info("passed..");
     }
+    @Test
+    void VariantsTestSingleUid(){
+        entry = stack.contentType(CONTENT_TYPE).entry(entryUid).variants("  cs672c33271558d8b0 ");
+        entry.fetch(new EntryResultCallBack() {
+            @Override
+            public void onCompletion(ResponseType responseType, Error error) {
+                assertEquals("cs672c33271558d8b0", entry.getHeaders().get("x-cs-variant-uid"));
+               System.out.println(entry.toJSON());
+            }
+        });
+    }
+    @Test
+    void VariantsTestArray(){
+        entry = stack.contentType(CONTENT_TYPE).entry(entryUid).variants(new String[]{" cs672c33271558d8b0"," cs321fbc07ec71861b"," cs321fbc07ec71861b "});
+        entry.fetch(new EntryResultCallBack() {
+            @Override
+            public void onCompletion(ResponseType responseType, Error error) {
+               System.out.println(entry.toJSON());
+            }
+        });
+    }
+    
+    @Test
+    void VariantsTestArrayWithMixedElements() {
+        entry = stack.contentType(CONTENT_TYPE).entry(entryUid).variants(new String[]{"", " cs672c33271558d8b0 ", null, "   "});
+        entry.fetch(new EntryResultCallBack() {
+            @Override
+            public void onCompletion(ResponseType responseType, Error error) {
+                System.out.println(entry.toJSON());
+            }
+        });
+    }
+
+    @Test
+    void VariantsTestNullString() {
+    entry = stack.contentType(CONTENT_TYPE).entry(entryUid).variants((String) null);
+    entry.fetch(new EntryResultCallBack() {
+        @Override
+        public void onCompletion(ResponseType responseType, Error error) {
+            assertNull(entry.getHeaders().get("x-cs-variant-uid"));
+            System.out.println(entry.toJSON());
+        }
+    });
+    }
 
     @Test
     @Order(4)