Fix #3002

release-notes/VERSION-2.x

@@ -8,6 +8,8 @@ Project: jackson-databind
 
 #2828: Add `DatabindException` as intermediate subtype of `JsonMappingException`
 #3001: Add mechanism for setting default `ContextAttributes` for `ObjectMapper`
+#3002: Add `DeserializationContext.readTreeAsValue()` methods for more convenient
+  conversions for deserializers to use
 #3035: Add `removeMixIn()` method in `MapperBuilder`
 #3036: Backport `MapperBuilder` lambda-taking methods: `withConfigOverride()`,
   `withCoercionConfig()`, `withCoercionConfigDefaults()`

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

@@ -31,6 +31,7 @@
 import com.fasterxml.jackson.databind.jsontype.TypeDeserializer;
 import com.fasterxml.jackson.databind.jsontype.TypeIdResolver;
 import com.fasterxml.jackson.databind.node.JsonNodeFactory;
+import com.fasterxml.jackson.databind.node.TreeTraversingParser;
 import com.fasterxml.jackson.databind.type.LogicalType;
 import com.fasterxml.jackson.databind.type.TypeFactory;
 import com.fasterxml.jackson.databind.util.*;
@@ -912,6 +913,10 @@ public <T> T readValue(JsonParser p, JavaType type) throws IOException {
      * for reading one-off values for the composite type, taking into account
      * annotations that the property (passed to this method -- usually property that
      * has custom serializer that called this method) has.
+     *
+     * @param p Parser that points to the first token of the value to read
+     * @param prop Logical property of a POJO being type
+     * @return Value of type {@code type} that was read
      * 
      * @since 2.4
      */
@@ -920,6 +925,10 @@ public <T> T readPropertyValue(JsonParser p, BeanProperty prop, Class<T> type) t
     }
 
     /**
+     * Same as {@link #readPropertyValue(JsonParser, BeanProperty, Class)} but with
+     * fully resolved {@link JavaType} as target: needs to be used for generic types,
+     * for example.
+     *
      * @since 2.4
      */
     @SuppressWarnings("unchecked")
@@ -934,6 +943,13 @@ public <T> T readPropertyValue(JsonParser p, BeanProperty prop, JavaType type) t
     }
 
     /**
+     * Convenience method for reading the value that passed {@link JsonParser}
+     * points to as a {@link JsonNode}.
+     *
+     * @param p Parser that points to the first token of the value to read
+     *
+     * @return Value read as {@link JsonNode}
+     *
      * @since 2.10
      */
     public JsonNode readTree(JsonParser p) throws IOException {
@@ -951,6 +967,71 @@ public JsonNode readTree(JsonParser p) throws IOException {
                 .deserialize(p, this);
     }
 
+    /**
+     * Helper method similar to {@link ObjectReader#treeToValue(TreeNode, Class)}
+     * which will read contents of given tree ({@link JsonNode})
+     * and bind them into specified target type. This is often used in two-phase
+     * deserialization in which content is first read as a tree, then manipulated
+     * (adding and/or removing properties of Object values, for example),
+     * and finally converted into actual target type using default deserialization
+     * logic for the type.
+     *<p>
+     * NOTE: deserializer implementations should be careful not to try to recursively
+     * deserialize into target type deserializer has registered itself to handle.
+     *
+     * @param n Tree value to convert, if not {@code null}: if {@code null}, will simply
+     *     return {@code null}
+     * @param targetType Type to deserialize contents of {@code n} into (if {@code n} not {@code null})
+     *
+     * @return Either {@code null} (if {@code n} was {@code null} or a value of
+     *     type {@code type} that was read from non-{@code null} {@code n} argument
+     *
+     * @since 2.13
+     */
+    public <T> T readTreeAsValue(JsonNode n, Class<T> targetType) throws IOException
+    {
+        if (n == null) {
+            return null;
+        }
+        try (TreeTraversingParser p = _treeAsTokens(n)) {
+            return readValue(p, targetType);
+        }
+    }
+
+    /**
+     * Same as {@link #readTreeAsValue(JsonNode, Class)} but will fully resolved
+     * {@link JavaType} as {@code targetType}
+     *<p>
+     * NOTE: deserializer implementations should be careful not to try to recursively
+     * deserialize into target type deserializer has registered itself to handle.
+     *
+     * @param n Tree value to convert
+     * @param targetType Type to deserialize contents of {@code n} into
+     *
+     * @return Value of type {@code type} that was read
+     *
+     * @since 2.13
+     */
+    public <T> T readTreeAsValue(JsonNode n, JavaType targetType) throws IOException
+    {
+        if (n == null) {
+            return null;
+        }
+        try (TreeTraversingParser p = _treeAsTokens(n)) {
+            return readValue(p, targetType);
+        }
+    }
+
+    private TreeTraversingParser _treeAsTokens(JsonNode n) throws IOException
+    {
+        // Not perfect but has to do...
+        ObjectCodec codec = (_parser == null) ? null : _parser.getCodec();
+        TreeTraversingParser p = new TreeTraversingParser(n, codec);
+        // important: must initialize...
+        p.nextToken();
+        return p;
+    }
+
     /*
     /**********************************************************
     /* Methods for problem handling

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

@@ -1973,7 +1973,20 @@ public <T> T treeToValue(TreeNode n, Class<T> valueType) throws JsonProcessingEx
         } catch (IOException e) { // should not occur, no real i/o...
             throw JsonMappingException.fromUnexpectedIOE(e);
         }
-    }    
+    }
+
+    // @since 2.13
+    public <T> T treeToValue(TreeNode n, JavaType valueType) throws JsonProcessingException
+    {
+        _assertNotNull("n", n);
+        try {
+            return readValue(treeAsTokens(n), valueType);
+        } catch (JsonProcessingException e) {
+            throw e;
+        } catch (IOException e) { // should not occur, no real i/o...
+            throw JsonMappingException.fromUnexpectedIOE(e);
+        }
+    }
 
     @Override
     public void writeValue(JsonGenerator gen, Object value) throws IOException {

src/test/java/com/fasterxml/jackson/databind/ObjectReaderTest.java

@@ -447,8 +447,13 @@ public void testTreeToValue() throws Exception
         ObjectReader r = MAPPER.readerFor(String.class);
         List<?> list = r.treeToValue(n, List.class);
         assertEquals(1, list.size());
+
+        // since 2.13:
+        String[] arr = r.treeToValue(n, MAPPER.constructType(String[].class));
+        assertEquals(1, arr.length);
+        assertEquals("xyz", arr[0]);
     }
-    
+
     public void testCodecUnsupportedWrites() throws Exception
     {
         ObjectReader r = MAPPER.readerFor(String.class);

src/test/java/com/fasterxml/jackson/databind/deser/TestCustomDeserializers.java

@@ -313,13 +313,42 @@ public Object deserialize(JsonParser p, DeserializationContext ctxt)
         }
     }
 
+    @JsonDeserialize(using = NamedPointDeserializer.class)
+    static class NamedPoint
+    {
+        public Point point;
+        public String name;
+
+        public NamedPoint(String name, Point point) {
+            this.point = point;
+            this.name = name;
+        }
+    }
+
+    static class NamedPointDeserializer extends StdDeserializer<NamedPoint>
+    {
+        public NamedPointDeserializer() {
+            super(NamedPoint.class);
+        }
+
+        @Override
+        public NamedPoint deserialize(JsonParser p, DeserializationContext ctxt)
+                throws IOException
+        {
+            JsonNode tree = ctxt.readTree(p);
+            String name = tree.path("name").asText(null);
+            Point point = ctxt.readTreeAsValue(tree.get("point"), Point.class);
+            return new NamedPoint(name, point);
+        }
+    }
+
     /*
     /**********************************************************
     /* Unit tests
     /**********************************************************
      */
 
-    final ObjectMapper MAPPER = objectMapper();
+    private final ObjectMapper MAPPER = newJsonMapper();
 
     public void testCustomBeanDeserializer() throws Exception
     {
@@ -388,7 +417,6 @@ public Immutable convert(JsonNode value)
     // [databind#623]
     public void testJsonNodeDelegating() throws Exception
     {
-        ObjectMapper mapper = new ObjectMapper();
         SimpleModule module = new SimpleModule("test", Version.unknownVersion());
         module.addDeserializer(Immutable.class,
             new StdNodeBasedDeserializer<Immutable>(Immutable.class) {
@@ -399,7 +427,9 @@ public Immutable convert(JsonNode root, DeserializationContext ctxt) throws IOEx
                     return new Immutable(x, y);
                 }
         });
-        mapper.registerModule(module);
+        ObjectMapper mapper = jsonMapperBuilder()
+                .addModule(module)
+                .build();
         Immutable imm = mapper.readValue("{\"x\":-10,\"y\":3}", Immutable.class);
         assertEquals(-10, imm.x);
         assertEquals(3, imm.y);
@@ -485,7 +515,7 @@ public JsonDeserializer<?> modifyDeserializer(DeserializationConfig config,
     }
 
     // [databind#2452]
-    public void testCustomSerializerWithReadTree() throws Exception
+    public void testCustomDeserializerWithReadTree() throws Exception
     {
         ObjectMapper mapper = jsonMapperBuilder()
                 .addModule(new SimpleModule()
@@ -499,4 +529,26 @@ public void testCustomSerializerWithReadTree() throws Exception
         assertEquals(3, n.size());
         assertEquals(123, n.get(2).intValue());
     }
+
+    // [databind#3002]
+    public void testCustomDeserializerWithReadTreeAsValue() throws Exception
+    {
+        final String json = a2q("{'point':{'x':13, 'y':-4}, 'name':'Foozibald' }");
+        NamedPoint result = MAPPER.readValue(json, NamedPoint.class);
+        assertNotNull(result);
+        assertEquals("Foozibald", result.name);
+        assertEquals(new Point(13, -4), result.point);
+
+        // and with JavaType variant too
+        result = MAPPER.readValue(json, MAPPER.constructType(NamedPoint.class));
+        assertNotNull(result);
+        assertEquals("Foozibald", result.name);
+        assertEquals(new Point(13, -4), result.point);
+
+        // also, try some edge conditions
+        result = MAPPER.readValue(a2q("{'name':4})"), NamedPoint.class);
+        assertNotNull(result);
+        assertEquals("4", result.name);
+        assertNull(result.point);
+    }
 }