Fix #502

Author: cowtowncoder

release-notes/VERSION-2.x

@@ -25,6 +25,7 @@ JSON library.
   `writeRaw(..)`) more efficiently
 #495: Create `StreamReadFeature` to move non-json specific `JsonParser.Feature`s to
 #496: Create `StreamWriteFeature` to take over non-json-specific `JsonGenerator.Feature`s
+#502: Make `DefaultPrettyPrinter.createInstance()` to fail for sub-classes
 
 2.9.8 (not yet released)
 

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

@@ -157,7 +157,7 @@ public DefaultPrettyPrinter withRootSeparator(SerializableString rootSeparator)
     }
 
     /**
-     * @since 2.6.0
+     * @since 2.6
      */
     public DefaultPrettyPrinter withRootSeparator(String rootSeparator) {
         return withRootSeparator((rootSeparator == null) ? null : new SerializedString(rootSeparator));
@@ -252,6 +252,10 @@ public DefaultPrettyPrinter withSeparators(Separators separators) {
 
     @Override
     public DefaultPrettyPrinter createInstance() {
+        if (getClass() != DefaultPrettyPrinter.class) { // since 2.10
+            throw new IllegalStateException("Failed `createInstance()`: "+getClass().getName()
+                    +" does not override method; it has to");
+        }
         return new DefaultPrettyPrinter(this);
     }
 

src/test/java/com/fasterxml/jackson/core/BaseTest.java

@@ -566,7 +566,12 @@ protected JsonFactory sharedStreamFactory() {
     protected JsonFactory newStreamFactory() {
         return new JsonFactory();
     }
-    
+
+    // @since 2.9.8
+    protected JsonFactoryBuilder streamFactoryBuilder() {
+        return (JsonFactoryBuilder) JsonFactory.builder();
+    }
+
     protected String fieldNameFor(int index)
     {
         StringBuilder sb = new StringBuilder(16);

src/test/java/com/fasterxml/jackson/core/util/TestDefaultPrettyPrinter.java

@@ -159,4 +159,19 @@ private String _printTestData(PrettyPrinter pp, boolean useBytes) throws IOExcep
         }
         return sw.toString();
     }
+
+    // [core#502]: Force sub-classes to reimplement `createInstance`
+    public void testInvalidSubClass() throws Exception
+    {
+        DefaultPrettyPrinter pp = new MyPrettyPrinter();
+        try {
+            pp.createInstance();
+            fail("Should not pass");
+        } catch (IllegalStateException e) {
+            verifyException(e, "does not override");
+        }
+    }
+
+    @SuppressWarnings("serial")
+    static class MyPrettyPrinter extends DefaultPrettyPrinter { }
 }