Add JsonGeneratorDecorator to allow decorating JsonGenerators

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

@@ -7,6 +7,8 @@
 import java.io.*;
 import java.lang.ref.SoftReference;
 import java.net.URL;
+import java.util.ArrayList;
+import java.util.List;
 import java.util.Objects;
 
 import com.fasterxml.jackson.core.format.InputAccessor;
@@ -317,6 +319,9 @@ public static int collectDefaults() {
      */
     protected final char _quoteChar;
 
+    /** @since 2.16 */
+    protected List<JsonGeneratorDecorator> _generatorDecorators = new ArrayList<>();
+
     /*
     /**********************************************************
     /* Construction
@@ -393,6 +398,7 @@ public JsonFactory(JsonFactoryBuilder b) {
         _rootValueSeparator = b._rootValueSeparator;
         _maximumNonEscapedChar = b._maximumNonEscapedChar;
         _quoteChar = b._quoteChar;
+        _generatorDecorators = new ArrayList<>(b._generatorDecorators);
     }
 
     /**
@@ -1892,7 +1898,14 @@ protected JsonGenerator _createGenerator(Writer out, IOContext ctxt) throws IOEx
         if (rootSep != DEFAULT_ROOT_VALUE_SEPARATOR) {
             gen.setRootValueSeparator(rootSep);
         }
-        return gen;
+        return _decorate(gen);
+    }
+
+    private JsonGenerator _decorate(JsonGenerator result) {
+        for(JsonGeneratorDecorator decorator : _generatorDecorators) {
+            result = decorator.decorate(this, result);
+        }
+        return result;
     }
 
     /**
@@ -1925,7 +1938,7 @@ protected JsonGenerator _createUTF8Generator(OutputStream out, IOContext ctxt) t
         if (rootSep != DEFAULT_ROOT_VALUE_SEPARATOR) {
             gen.setRootValueSeparator(rootSep);
         }
-        return gen;
+        return _decorate(gen);
     }
 
     protected Writer _createWriter(OutputStream out, JsonEncoding enc, IOContext ctxt) throws IOException

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

@@ -0,0 +1,13 @@
+package com.fasterxml.jackson.core;
+
+public interface JsonGeneratorDecorator {
+    /**
+     * Allow to decorate {@link JsonGenerator} instances returned by {@link JsonFactory}.
+     * 
+     * @since 2.16
+     * @param factory The factory which was used to build the original generator
+     * @param generator The generator to decorate. This might already be a decorated instance, not the original.
+     * @return decorated generator
+     */
+    JsonGenerator decorate(JsonFactory factory, JsonGenerator generator);
+}

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

@@ -1,5 +1,8 @@
 package com.fasterxml.jackson.core;
 
+import java.util.ArrayList;
+import java.util.List;
+
 import com.fasterxml.jackson.core.io.InputDecorator;
 import com.fasterxml.jackson.core.io.OutputDecorator;
 import com.fasterxml.jackson.core.json.JsonReadFeature;
@@ -84,6 +87,9 @@ public abstract class TSFBuilder<F extends JsonFactory,
      */
     protected StreamReadConstraints _streamReadConstraints;
 
+    /** @since 2.16 */
+    protected List<JsonGeneratorDecorator> _generatorDecorators = new ArrayList<>();
+
     /*
     /**********************************************************************
     /* Construction
@@ -284,6 +290,11 @@ public B streamReadConstraints(StreamReadConstraints streamReadConstraints) {
 
     // // // Other methods
 
+    public B decorateWith(JsonGeneratorDecorator decorator) {
+        _generatorDecorators.add(decorator);
+        return _this();
+    }
+
     /**
      * Method for constructing actual {@link TokenStreamFactory} instance, given
      * configuration.