... and add the writeFieldId() method actually

src/main/java/com/fasterxml/jackson/core/JsonGenerator.java

@@ -825,6 +825,20 @@ public void writeStartObject(Object forValue) throws IOException
      */
     public abstract void writeFieldName(SerializableString name) throws IOException;
 
+    /**
+     * Alternative to {@link #writeFieldName(String)} that may be used
+     * in cases where property key is of numeric type; either where
+     * underlying format supports such notion (some binary formats do,
+     * unlike JSON), or for convenient conversion into String presentation.
+     * Default implementation will simply convert id into <code>String</code>
+     * and call {@link #writeFieldName(String)}.
+     *
+     * @since 2.8
+     */
+    public void writeFieldId(long id) throws IOException {
+        writeFieldName(Long.toString(id));
+    }
+
     /*
     /**********************************************************
     /* Public API, write methods, scalar arrays (2.8)

src/main/java/com/fasterxml/jackson/core/json/JsonWriteContext.java

@@ -44,7 +44,7 @@ public class JsonWriteContext extends JsonStreamContext
      */
 
     /**
-     * Name of the field of which value is to be parsed; only
+     * Name of the field of which value is to be written; only
      * used for OBJECT contexts
      */
     protected String _currentName;
@@ -55,8 +55,8 @@ public class JsonWriteContext extends JsonStreamContext
     protected Object _currentValue;
 
     /**
-     * Marker used to indicate that we just received a name, and
-     * now expect a value
+     * Marker used to indicate that we just wrote a name, and
+     * now expect a value to write
      */
     protected boolean _gotName;
 

src/main/java/com/fasterxml/jackson/core/util/JsonGeneratorDelegate.java

@@ -203,7 +203,7 @@ public JsonGenerator setPrettyPrinter(PrettyPrinter pp) {
 
     @Override
     public void writeStartObject(Object forValue) throws IOException { delegate.writeStartObject(forValue); }
-    
+
     @Override
     public void writeEndObject() throws IOException { delegate.writeEndObject(); }
 
@@ -217,6 +217,11 @@ public void writeFieldName(SerializableString name) throws IOException {
         delegate.writeFieldName(name);
     }
 
+    @Override
+    public void writeFieldId(long id) throws IOException {
+        delegate.writeFieldId(id);
+    }
+
     @Override
     public void writeArray(int[] array, int offset, int length) throws IOException {
         delegate.writeArray(array, offset, length);