add cfg for hex values if we want upper or lowercase letters

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

@@ -250,8 +250,21 @@ public enum Feature {
          * @deprecated Use {@link com.fasterxml.jackson.core.StreamWriteFeature#USE_FAST_DOUBLE_WRITER} instead
          */
         @Deprecated
-        USE_FAST_DOUBLE_WRITER(false)
-        ;
+        USE_FAST_DOUBLE_WRITER(false),
+
+        /**
+         * Feature that specifies that hex values are encoded with capital letters.
+         *<p>
+         * Can be disabled to have a better possibility to compare between other Json
+         * writer libraries, such as JSON.stringify from Javascript.
+         *<p>
+         * Feature is enabled by default.
+         *
+         * @since 2.14
+         * @deprecated Use {@link com.fasterxml.jackson.core.json.JsonWriteFeature#WRITE_HEX_UPPER_CASE} instead
+         */
+        @Deprecated
+        WRITE_HEX_UPPER_CASE(true);
 
         private final boolean _defaultState;
         private final int _mask;

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

@@ -303,7 +303,7 @@ public JsonLocation startLocation(ContentReference srcRef) {
     public JsonLocation getStartLocation(Object srcRef) {
         return JsonLocation.NA;
     }
-    
+
     /**
      * Overridden to provide developer readable "JsonPath" representation
      * of the context.

src/main/java/com/fasterxml/jackson/core/io/CharTypes.java

@@ -5,12 +5,16 @@
 public final class CharTypes
 {
     protected final static char[] HC = "0123456789ABCDEF".toCharArray();
+    protected final static char[] HClower = "0123456789abcdef".toCharArray();
     protected final static byte[] HB;
+    protected final static byte[] HBlower;
     static {
         int len = HC.length;
         HB = new byte[len];
+        HBlower = new byte[len];
         for (int i = 0; i < len; ++i) {
             HB[i] = (byte) HC[i];
+            HBlower[i] = (byte) HClower[i];
         }
     }
 
@@ -242,6 +246,7 @@ public static char hexToChar(int ch)
         return HC[ch];
     }
 
+
     /**
      * Helper method for appending JSON-escaped version of contents
      * into specific {@link StringBuilder}, using default JSON specification
@@ -251,8 +256,7 @@ public static char hexToChar(int ch)
      *
      * @param content Unescaped String value to append with escaping applied
      */
-    public static void appendQuoted(StringBuilder sb, String content)
-    {
+    public static void appendQuoted(StringBuilder sb, String content) {
         final int[] escCodes = sOutputEscapes128;
         int escLen = escCodes.length;
         for (int i = 0, len = content.length(); i < len; ++i) {
@@ -285,11 +289,19 @@ public static void appendQuoted(StringBuilder sb, String content)
     }
 
     public static char[] copyHexChars() {
-        return (char[]) HC.clone();
+        return copyHexChars(true);
+    }
+
+    public static char[] copyHexChars(boolean uppercase) {
+        return (uppercase) ? HC.clone() : HClower.clone();
     }
 
     public static byte[] copyHexBytes() {
-        return (byte[]) HB.clone();
+        return copyHexBytes(true);
+    }
+
+    public static byte[] copyHexBytes(boolean uppercase) {
+        return (uppercase) ? HB.clone() : HBlower.clone();
     }
 
     /**

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

@@ -102,6 +102,14 @@ public abstract class JsonGeneratorImpl extends GeneratorBase
      */
     protected boolean _cfgUnqNames;
 
+
+    /**
+     * Write Hex values with uppercase letters
+     *
+     * @since 2.14
+     */
+    protected boolean _cfgWriteHexUppercase;
+
     /*
     /**********************************************************
     /* Life-cycle
@@ -117,6 +125,7 @@ public JsonGeneratorImpl(IOContext ctxt, int features, ObjectCodec codec)
             // inlined `setHighestNonEscapedChar()`
             _maximumNonEscapedChar = 127;
         }
+        _cfgWriteHexUppercase = Feature.WRITE_HEX_UPPER_CASE.enabledIn(features);
         _cfgUnqNames = !Feature.QUOTE_FIELD_NAMES.enabledIn(features);
     }
 
@@ -143,6 +152,8 @@ public JsonGenerator enable(Feature f) {
         super.enable(f);
         if (f == Feature.QUOTE_FIELD_NAMES) {
             _cfgUnqNames = false;
+        } else if ( f == Feature.WRITE_HEX_UPPER_CASE) {
+            _cfgWriteHexUppercase = true;
         }
         return this;
     }
@@ -153,6 +164,8 @@ public JsonGenerator disable(Feature f) {
         super.disable(f);
         if (f == Feature.QUOTE_FIELD_NAMES) {
             _cfgUnqNames = true;
+        } else if ( f == Feature.WRITE_HEX_UPPER_CASE) {
+            _cfgWriteHexUppercase = false;
         }
         return this;
     }
@@ -162,6 +175,7 @@ public JsonGenerator disable(Feature f) {
     protected void _checkStdFeatureChanges(int newFeatureFlags, int changedFeatures) {
         super._checkStdFeatureChanges(newFeatureFlags, changedFeatures);
         _cfgUnqNames = !Feature.QUOTE_FIELD_NAMES.enabledIn(newFeatureFlags);
+        _cfgWriteHexUppercase = Feature.WRITE_HEX_UPPER_CASE.enabledIn(newFeatureFlags);
     }
 
     @Override

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

@@ -147,7 +147,7 @@ public Object getCurrentValue() {
     public void setCurrentValue(Object v) {
         _currentValue = v;
     }
-    
+
     /*
     /**********************************************************
     /* Factory methods

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

@@ -72,6 +72,19 @@ public enum JsonWriteFeature
     @SuppressWarnings("deprecation")
     ESCAPE_NON_ASCII(false, JsonGenerator.Feature.ESCAPE_NON_ASCII),
 
+    /**
+     * Feature that specifies that hex values are encoded with capital letters.
+     *<p>
+     * Can be disabled to have a better possibility to compare between other Json
+     * writer libraries, such as JSON.stringify from Javascript.
+     *<p>
+     * Feature is enabled by default.
+     *
+     * @since 2.14
+     */
+    @SuppressWarnings("deprecation")
+    WRITE_HEX_UPPER_CASE(true, JsonGenerator.Feature.WRITE_HEX_UPPER_CASE),
+
 //23-Nov-2015, tatu: for [core#223], if and when it gets implemented
     /*
      * Feature that specifies handling of UTF-8 content that contains

src/main/java/com/fasterxml/jackson/core/json/UTF8JsonGenerator.java

@@ -29,12 +29,17 @@ public class UTF8JsonGenerator
     // intermediate copies only made up to certain length...
     private final static int MAX_BYTES_TO_BUFFER = 512;
 
-    private final static byte[] HEX_CHARS = CharTypes.copyHexBytes();
+    private final static byte[] HEX_CHARS_UPPER = CharTypes.copyHexBytes(true);
+    private final static byte[] HEX_CHARS_LOWER = CharTypes.copyHexBytes(false);
 
     private final static byte[] NULL_BYTES = { 'n', 'u', 'l', 'l' };
     private final static byte[] TRUE_BYTES = { 't', 'r', 'u', 'e' };
     private final static byte[] FALSE_BYTES = { 'f', 'a', 'l', 's', 'e' };
 
+    private byte[] getHexChars() {
+        return _cfgWriteHexUppercase ? HEX_CHARS_UPPER : HEX_CHARS_LOWER;
+    }
+
     /*
     /**********************************************************
     /* Configuration
@@ -2136,6 +2141,7 @@ protected final void _outputSurrogates(int surr1, int surr2) throws IOException
      */
     private final int _outputMultiByteChar(int ch, int outputPtr) throws IOException
     {
+        byte[] HEX_CHARS = getHexChars();
         byte[] bbuf = _outputBuffer;
         if (ch >= SURR1_FIRST && ch <= SURR2_LAST) { // yes, outside of BMP; add an escape
             // 23-Nov-2015, tatu: As per [core#223], may or may not want escapes;
@@ -2175,6 +2181,7 @@ private final void _writeNull() throws IOException
     private int _writeGenericEscape(int charToEscape, int outputPtr) throws IOException
     {
         final byte[] bbuf = _outputBuffer;
+        byte[] HEX_CHARS = getHexChars();
         bbuf[outputPtr++] = BYTE_BACKSLASH;
         bbuf[outputPtr++] = BYTE_u;
         if (charToEscape > 0xFF) {

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

@@ -19,7 +19,12 @@ public class WriterBasedJsonGenerator
 {
     protected final static int SHORT_WRITE = 32;
 
-    protected final static char[] HEX_CHARS = CharTypes.copyHexChars();
+    protected final static char[] HEX_CHARS_UPPER = CharTypes.copyHexChars(true);
+    protected final static char[] HEX_CHARS_LOWER = CharTypes.copyHexChars(false);
+
+    private char[] getHexChars() {
+        return _cfgWriteHexUppercase ? HEX_CHARS_UPPER : HEX_CHARS_LOWER;
+    }
 
     /*
     /**********************************************************
@@ -1814,6 +1819,7 @@ private void _prependOrWriteCharacterEscape(char ch, int escCode)
             return;
         }
         if (escCode != CharacterEscapes.ESCAPE_CUSTOM) { // std, \\uXXXX
+            char[] HEX_CHARS = getHexChars();
             if (_outputTail >= 6) { // fits, prepend to buffer
                 char[] buf = _outputBuffer;
                 int ptr = _outputTail - 6;
@@ -1902,6 +1908,7 @@ private int _prependOrWriteCharacterEscape(char[] buffer, int ptr, int end,
             return ptr;
         }
         if (escCode != CharacterEscapes.ESCAPE_CUSTOM) { // std, \\uXXXX
+            char[] HEX_CHARS = getHexChars();
             if (ptr > 5 && ptr < end) { // fits, prepend to buffer
                 ptr -= 6;
                 buffer[ptr++] = '\\';
@@ -1980,6 +1987,7 @@ private void _appendCharacterEscape(char ch, int escCode)
             }
             int ptr = _outputTail;
             char[] buf = _outputBuffer;
+            char[] HEX_CHARS = getHexChars();
             buf[ptr++] = '\\';
             buf[ptr++] = 'u';
             // We know it's a control char, so only the last 2 chars are non-0

src/test/java/com/fasterxml/jackson/core/write/UTF8GeneratorTest.java

@@ -11,6 +11,8 @@
 
 import java.io.ByteArrayOutputStream;
 
+import static com.fasterxml.jackson.core.json.JsonWriteFeature.WRITE_HEX_UPPER_CASE;
+
 public class UTF8GeneratorTest extends BaseTest
 {
     private final JsonFactory JSON_F = new JsonFactory();
@@ -114,4 +116,33 @@ public void testFilteringWithEscapedChars() throws Exception
         assertNull(p.nextToken());
         p.close();
     }
+
+    public void testHexLowercase() throws Exception
+    {
+        ByteArrayOutputStream bytes = new ByteArrayOutputStream();
+        JsonFactory factory = JsonFactory.builder().disable(WRITE_HEX_UPPER_CASE).build();
+        JsonGenerator gen = factory.createGenerator(bytes);
+        String str = "\u001b";
+        gen.writeString(str);
+        gen.flush();
+        gen.close();
+
+        String result = bytes.toString();
+        assertEquals("\"\\u001b\"", result);
+    }
+
+    public void testHexUppercase() throws Exception
+    {
+        ByteArrayOutputStream bytes = new ByteArrayOutputStream();
+        JsonFactory factory = JsonFactory.builder().enable(WRITE_HEX_UPPER_CASE).build();
+        JsonGenerator gen = factory.createGenerator(bytes);
+        String str = "\u001b";
+        gen.writeString(str);
+        gen.flush();
+        gen.close();
+
+        String result = bytes.toString();
+        assertEquals("\"\\u001B\"", result);
+    }
+
 }