Yet more work for #1207; added DeserializationProblemHandler.handleMissingInstantiator() (and supporting functionality), to replace instantiationException(Class, String)

Author: cowtowncoder

src/main/java/com/fasterxml/jackson/databind/DeserializationContext.java

@@ -954,7 +954,6 @@ public Object handleWeirdNumberValue(Class<?> targetClass, Number value,
             String msg, Object... msgArgs)
         throws IOException
     {
-        // but if not handled, just throw exception
         if (msgArgs.length > 0) {
             msg = String.format(msg, msgArgs);
         }
@@ -977,46 +976,44 @@ public Object handleWeirdNumberValue(Class<?> targetClass, Number value,
     }
 
     /**
-     * Method that deserializers should call if they encounter a type id
-     * (for polymorphic deserialization) that can not be resolved to an
-     * actual type; usually since there is no mapping defined.
-     * Default implementation will try to call {@link DeserializationProblemHandler#handleUnknownTypeId}
-     * on configured handlers, if any, to allow for recovery; if recovery does not
-     * succeed, will throw exception constructed with {@link #unknownTypeIdException}.
-     *
-     * @param baseType Base type from which resolution starts
-     * @param id Type id that could not be converted
-     * @param extraDesc Additional problem description to add to default exception message,
-     *    if resolution fails.
+     * Method that deserializers should call if they fail to instantiate value
+     * due to lack of viable instantiator (usually creator, that is, constructor
+     * or static factory method). Method should be called at point where value
+     * has not been decoded, so that handler has a chance to handle decoding
+     * using alternate mechanism, and handle underlying content (possibly by
+     * just skipping it) to keep input state valid
      *
-     * @return {@link JavaType} that id resolves to
+     * @param instClass Type that was to be instantiated
+     * @param p Parser that points to the JSON value to decode
      *
-     * @throws IOException To indicate unrecoverable problem, if resolution can not
-     *    be made to work
+     * @return Object that should be constructed, if any; has to be of type <code>instClass</code>
      *
      * @since 2.8
      */
-    public JavaType handleUnknownTypeId(JavaType baseType, String id,
-            String extraDesc) throws IOException
+    public Object handleMissingInstantiator(Class<?> instClass, JsonParser p,
+            String msg, Object... msgArgs)
+        throws IOException
     {
+        if (msgArgs.length > 0) {
+            msg = String.format(msg, msgArgs);
+        }
         LinkedNode<DeserializationProblemHandler> h = _config.getProblemHandlers();
         while (h != null) {
             // Can bail out if it's handled
-            JavaType type = h.value().handleUnknownTypeId(this, baseType, id, extraDesc);
-            if (type != null) {
-                if (type.hasRawClass(Void.class)) {
-                    return null;
-                }
-                // But ensure there's type compatibility
-                if (type.isTypeOrSubTypeOf(baseType.getRawClass())) {
-                    return type;
+            Object instance = h.value().handleMissingInstantiator(this,
+                    instClass, p, msg);
+            if (instance != DeserializationProblemHandler.NOT_HANDLED) {
+                // Sanity check for broken handlers, otherwise nasty to debug:
+                if ((instance == null) || instClass.isInstance(instance)) {
+                    return instance;
                 }
-                throw unknownTypeIdException(baseType, id,
-                        "problem handler tried to resolve into non-subtype: "+type);
+                throw instantiationException(instClass, String.format(
+                        "DeserializationProblemHandler.handleMissingInstantiator() for type %s returned value of type %s",
+                        instClass, instance.getClass()));
             }
             h = h.next();
         }
-        throw unknownTypeIdException(baseType, id, extraDesc);
+        throw instantiationException(instClass, msg);
     }
 
     /**
@@ -1062,12 +1059,76 @@ public Object handleInstantiationProblem(Class<?> instClass, Object argument,
         throw instantiationException(instClass, t);
     }
 
+    /**
+     * Method that deserializers should call if they encounter a type id
+     * (for polymorphic deserialization) that can not be resolved to an
+     * actual type; usually since there is no mapping defined.
+     * Default implementation will try to call {@link DeserializationProblemHandler#handleUnknownTypeId}
+     * on configured handlers, if any, to allow for recovery; if recovery does not
+     * succeed, will throw exception constructed with {@link #unknownTypeIdException}.
+     *
+     * @param baseType Base type from which resolution starts
+     * @param id Type id that could not be converted
+     * @param extraDesc Additional problem description to add to default exception message,
+     *    if resolution fails.
+     *
+     * @return {@link JavaType} that id resolves to
+     *
+     * @throws IOException To indicate unrecoverable problem, if resolution can not
+     *    be made to work
+     *
+     * @since 2.8
+     */
+    public JavaType handleUnknownTypeId(JavaType baseType, String id,
+            String extraDesc) throws IOException
+    {
+        LinkedNode<DeserializationProblemHandler> h = _config.getProblemHandlers();
+        while (h != null) {
+            // Can bail out if it's handled
+            JavaType type = h.value().handleUnknownTypeId(this, baseType, id, extraDesc);
+            if (type != null) {
+                if (type.hasRawClass(Void.class)) {
+                    return null;
+                }
+                // But ensure there's type compatibility
+                if (type.isTypeOrSubTypeOf(baseType.getRawClass())) {
+                    return type;
+                }
+                throw unknownTypeIdException(baseType, id,
+                        "problem handler tried to resolve into non-subtype: "+type);
+            }
+            h = h.next();
+        }
+        throw unknownTypeIdException(baseType, id, extraDesc);
+    }
+
     /*
     /**********************************************************
-    /* Methods for problem reporting
+    /* Methods for problem reporting, in cases where recovery
+    /* is not considered possible
     /**********************************************************
      */
 
+    /**
+     * Method for deserializers to call 
+     * when the token encountered was of type different than what <b>should</b>
+     * be seen at that position, usually within a sequence of expected tokens.
+     * Note that this method will throw a {@link JsonMappingException} and no
+     * recovery is attempted (via {@link DeserializationProblemHandler}, as
+     * problem is considered to be difficult to recover from, in general.
+     * 
+     * @since 2.8
+     */
+    public void reportWrongTokenException(JsonParser p,
+            JsonToken expToken, String msg, Object... msgArgs)
+        throws JsonMappingException
+    {
+        if (msgArgs.length > 0) {
+            msg = String.format(msg, msgArgs);
+        }
+        throw wrongTokenException(p, expToken, msg);
+    }
+    
     /**
      * Helper method for reporting a problem with unhandled unknown property.
      * 
@@ -1093,32 +1154,6 @@ public void reportUnknownProperty(Object instanceOrClass, String fieldName,
                 instanceOrClass, fieldName, propIds);
     }
 
-    /**
-     * @since 2.8
-     */
-    public void reportInstantiationException(Class<?> instClass,
-            String msg, Object... msgArgs)
-        throws JsonMappingException
-    {
-        if (msgArgs.length > 0) {
-            msg = String.format(msg, msgArgs);
-        }
-        throw instantiationException(instClass, msg);
-    }
-
-    /**
-     * @since 2.8
-     */
-    public JsonMappingException reportWrongTokenException(JsonParser p,
-            JsonToken expToken, String msg, Object... msgArgs)
-        throws JsonMappingException
-    {
-        if (msgArgs.length > 0) {
-            msg = String.format(msg, msgArgs);
-        }
-        throw wrongTokenException(p, expToken, msg);
-    }
-
     /**
      * @since 2.8
      */
@@ -1203,7 +1238,7 @@ public JsonMappingException mappingException(String msgTemplate, Object... args)
      */
 
     /**
-     * Helper method for constructing {@link JsonMappingException} to indicated
+     * Helper method for constructing {@link JsonMappingException} to indicate
      * that the token encountered was of type different than what <b>should</b>
      * be seen at that position, usually within a sequence of expected tokens.
      * Note that most of the time this method should NOT be directly called;
@@ -1288,6 +1323,21 @@ public JsonMappingException instantiationException(Class<?> instClass, Throwable
                         instClass.getName(), t.getMessage()), t);
     }
 
+    /**
+     * Helper method for constructing instantiation exception for specified type,
+     * to indicate that instantiation failed due to missing instantiator
+     * (creator; constructor or factory method).
+     *<p>
+     * Note that most of the time this method should NOT be called; instead,
+     * {@link #handleMissingInstantiator} should be called which will call this method
+     * if necessary.
+     */
+    public JsonMappingException instantiationException(Class<?> instClass, String msg) {
+        return JsonMappingException.from(_parser,
+                String.format("Can not construct instance of %s: %s",
+                        instClass.getName(), msg));
+    }
+
     /**
      * Helper method for constructing exception to indicate that given type id
      * could not be resolved to a valid subtype of specified base type, during
@@ -1313,16 +1363,6 @@ public JsonMappingException unknownTypeIdException(JavaType baseType, String typ
     /**********************************************************
      */
 
-    /**
-     * @deprecated Since 2.8 use {@link #reportInstantiationException} instead
-     */
-    @Deprecated
-    public JsonMappingException instantiationException(Class<?> instClass, String msg) {
-        return JsonMappingException.from(_parser,
-                String.format("Can not construct instance of %s: %s",
-                        instClass.getName(), msg));
-    }
-
     /**
      * @since 2.5
      *

src/main/java/com/fasterxml/jackson/databind/deser/AbstractDeserializer.java

@@ -146,11 +146,8 @@ public Object deserializeWithType(JsonParser p, DeserializationContext ctxt,
     public Object deserialize(JsonParser p, DeserializationContext ctxt)
         throws IOException
     {
-        // This method should never be called...
-        ctxt.reportInstantiationException(_baseType.getRawClass(),
+        return ctxt.handleMissingInstantiator(_baseType.getRawClass(), p,
                 "abstract types either need to be mapped to concrete types, have custom deserializer, or be instantiated with additional type information");
-        // 05-May-2016, tatu: Unlikely work as is but...
-        return null;
     }
 
     /*

src/main/java/com/fasterxml/jackson/databind/deser/BeanDeserializer.java

@@ -30,6 +30,14 @@ public class BeanDeserializer
 
     private static final long serialVersionUID = 1L;
 
+    /**
+     * Lazily constructed exception used as root cause if reporting problem
+     * with creator method that returns <code>null</code> (which is not allowed)
+     *
+     * @since 3.8
+     */
+    protected transient Exception _nullFromCreator;
+    
     /*
     /**********************************************************
     /* Life-cycle, construction, initialization
@@ -397,10 +405,8 @@ protected Object _deserializeUsingPropertyBased(final JsonParser p, final Deseri
                         bean = wrapInstantiationProblem(e, ctxt);
                     }
                     if (bean == null) {
-                        ctxt.reportInstantiationException(_beanType.getRawClass(),
-                                "JSON Creator returned null");
-                        // 05-May-2016, tatu: This won't really work well at all but...
-                        return null;
+                        return ctxt.handleInstantiationProblem(handledType(), null,
+                                _creatorReturnedNullException());
                     }
                     // [databind#631]: Assign current value, to be accessible by custom serializers
                     p.setCurrentValue(bean);
@@ -906,4 +912,17 @@ protected Object deserializeUsingPropertyBasedWithExternalTypeId(JsonParser p, D
             return wrapInstantiationProblem(e, ctxt);
         }
     }
+
+    /**
+     * Helper method for getting a lazily construct exception to be reported
+     * to {@link DeserializationContext#handleInstantiationProblem(Class, Object, Throwable)}.
+     *
+     * @since 2.8
+     */
+    protected Exception _creatorReturnedNullException() {
+        if (_nullFromCreator == null) {
+            _nullFromCreator = new NullPointerException("JSON Creator returned null");
+        }
+        return _nullFromCreator;
+    }
 }

src/main/java/com/fasterxml/jackson/databind/deser/BeanDeserializerBase.java

@@ -1186,11 +1186,13 @@ protected Object deserializeFromObjectUsingNonDefault(JsonParser p,
         }
         // should only occur for abstract types...
         if (_beanType.isAbstract()) {
-            throw JsonMappingException.from(p, "Can not instantiate abstract type "+_beanType
-                    +" (need to add/enable type information?)");
+            return ctxt.handleMissingInstantiator(_beanType.getRawClass(), p,
+                    "Can not instantiate abstract type %s (need to add/enable type information?)",
+                    _beanType);
         }
-        throw JsonMappingException.from(p, "No suitable constructor found for type "
-                +_beanType+": can not instantiate from JSON object (missing default constructor or creator, or perhaps need to add/enable type information?)");
+        return ctxt.handleMissingInstantiator(_beanType.getRawClass(), p,
+                "No suitable constructor found for type %s: can not instantiate from JSON object (missing default constructor or creator, or perhaps need to add/enable type information?)",
+                _beanType);
     }
 
     protected abstract Object _deserializeUsingPropertyBased(final JsonParser p,
@@ -1237,8 +1239,8 @@ public Object deserializeFromNumber(JsonParser p, DeserializationContext ctxt) t
             }
             return bean;
         }
-        ctxt.reportInstantiationException(handledType(), "no suitable creator method found to deserialize from JSON integer number");
-        return null;
+        return ctxt.handleMissingInstantiator(handledType(), p,
+                "no suitable creator method found to deserialize from JSON integer number");
     }
 
     public Object deserializeFromString(JsonParser p, DeserializationContext ctxt) throws IOException
@@ -1287,9 +1289,8 @@ public Object deserializeFromDouble(JsonParser p, DeserializationContext ctxt) t
         if (_delegateDeserializer != null) {
             return _valueInstantiator.createUsingDelegate(ctxt, _delegateDeserializer.deserialize(p, ctxt));
         }
-        ctxt.reportInstantiationException(handledType(),
+        return ctxt.handleMissingInstantiator(handledType(), p,
                 "no suitable creator method found to deserialize from JSON floating-point number");
-        return null;
     }
 
     /**

src/main/java/com/fasterxml/jackson/databind/deser/DeserializationProblemHandler.java

@@ -206,6 +206,39 @@ public Object handleInstantiationProblem(DeserializationContext ctxt,
         return NOT_HANDLED;
     }
 
+    /**
+     * Method called when instance creation for a type fails due to lack of an
+     * instantiator. Method is called before actual deserialization from input
+     * is attempted, so handler may do one of following things:
+     *<ul>
+     * <li>Indicate it does not know what to do by returning {@link #NOT_HANDLED}
+     *  </li>
+     * <li>Throw a {@link IOException} to indicate specific fail message (instead of
+     *    standard exception caller would throw
+     *  </li>
+     * <li>Handle content to match (by consuming or skipping it), and return actual
+     *    instantiated value (of type <code>targetType</code>) to use as replacement;
+     *    value may be `null` as well as expected target type.
+     *  </li>
+     * </ul>
+     *
+     * @param instClass Type that was to be instantiated
+     * @param p Parser to use for accessing content that needs handling, to either
+     *   use it or skip it (latter with {@link JsonParser#skipChildren()}.
+     *
+     * @return Either {@link #NOT_HANDLED} to indicate that handler does not know
+     *    what to do (and exception may be thrown), or value to use as key (possibly
+     *    <code>null</code>
+     *
+     * @since 2.8
+     */
+    public Object handleMissingInstantiator(DeserializationContext ctxt,
+            Class<?> instClass, JsonParser p, String msg)
+        throws IOException
+    {
+        return NOT_HANDLED;
+    }
+    
     /**
      * Handler method called if resolution of type id from given String failed
      * to produce a subtype; usually because logical id is not mapped to actual

src/main/java/com/fasterxml/jackson/databind/deser/std/MapDeserializer.java

@@ -334,9 +334,8 @@ public Map<Object,Object> deserialize(JsonParser p, DeserializationContext ctxt)
                     _delegateDeserializer.deserialize(p, ctxt));
         }
         if (!_hasDefaultCreator) {
-            ctxt.reportInstantiationException(getMapClass(), "No default constructor found");
-            // 05-May-2016, tatu: Unlikely to really work...
-            return null;
+            return (Map<Object,Object> ) ctxt.handleMissingInstantiator(getMapClass(), p,
+                    "No default constructor found");
         }
         // Ok: must point to START_OBJECT, FIELD_NAME or END_OBJECT
         JsonToken t = p.getCurrentToken();