Autodetect classes in ObjectMapper

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

@@ -3055,6 +3055,23 @@ public <T> T readValue(JsonParser p, Class<T> valueType)
         return (T) _readValue(getDeserializationConfig(), p, _typeFactory.constructType(valueType));
     }
 
+    /**
+     * Reads the value from the given JSON content and automatically detects the class type.
+     *
+     * @param <T> the type of the object to read
+     * @param p the JsonParser
+     * @param reified don't pass any values here. It's a trick to detect the class type.
+     * @return the deserialized object
+     * @throws JsonProcessingException if there is a problem processing the JSON
+     */
+    public <T> T readValue(JsonParser p, T... reified) throws IOException {
+        if (reified.length > 0) {
+            throw new IllegalArgumentException("Please don't pass any values here. Java will detect class automatically.");
+        }
+
+        return readValue(p, _typeFactory.constructType(getClassOf(reified)));
+    }
+
     /**
      * Method to deserialize JSON content into a Java type, reference
      * to which is passed as argument. Type is passed using so-called
@@ -3855,6 +3872,34 @@ public <T> T readValue(String content, Class<T> valueType)
         return readValue(content, _typeFactory.constructType(valueType));
     }
 
+    /**
+     * Utility method to get the class type from a varargs array.
+     *
+     * @param <T> the generic type
+     * @param array the varargs array
+     * @return the class of the array component
+     */
+    private static <T> Class<T> getClassOf(T[] array) {
+        return (Class<T>) array.getClass().getComponentType();
+    }
+
+    /**
+     * Reads the value from the given JSON content and automatically detects the class type.
+     *
+     * @param <T> the type of the object to read
+     * @param content the JSON string
+     * @param reified don't pass any values here. It's a trick to detect the class type.
+     * @return the deserialized object
+     * @throws JsonProcessingException if there is a problem processing the JSON
+     */
+    public <T> T readValue(String content, T... reified) throws JsonProcessingException {
+        if (reified.length > 0) {
+            throw new IllegalArgumentException("Please don't pass any values here. Java will detect class automatically.");
+        }
+
+        return readValue(content, _typeFactory.constructType(getClassOf(reified)));
+    }
+
     /**
      * Method to deserialize JSON content from given JSON content String.
      *
@@ -3957,6 +4002,15 @@ public <T> T readValue(byte[] src, int offset, int len,
         return (T) _readMapAndClose(_jsonFactory.createParser(src, offset, len), _typeFactory.constructType(valueType));
     }
 
+    @SuppressWarnings("unchecked")
+    public <T> T readValue(byte[] src, int offset, int len, T... reified) throws IOException {
+        if (reified.length > 0) {
+            throw new IllegalArgumentException("Please don't pass any values here. Java will detect class automatically.");
+        }
+
+        return readValue(src, offset, len, _typeFactory.constructType(getClassOf(reified)));
+    }
+
     @SuppressWarnings({ "unchecked" })
     public <T> T readValue(byte[] src, TypeReference<T> valueTypeRef)
         throws IOException, StreamReadException, DatabindException

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

@@ -1492,7 +1492,7 @@ public void writeTree(JsonGenerator g, TreeNode rootNode) {
      * @param src Source to read content from
      */
     @SuppressWarnings("unchecked")
-    public <T> T readValue(InputStream src) throws IOException
+    private <T> T readValue(InputStream src) throws IOException
     {
         if (_dataFormatReaders != null) {
             return (T) _detectBindAndClose(_dataFormatReaders.findFormat(src), false);
@@ -1515,6 +1515,12 @@ public <T> T readValue(InputStream src, Class<T> valueType) throws IOException
         return (T) forType(valueType).readValue(src);
     }
 
+    @SuppressWarnings("unchecked")
+    public <T> T readValue(InputStream src, T... reified) throws IOException
+    {
+        return forType(getClassOf(reified)).readValue(src);
+    }
+
     /**
      * Method that binds content read from given input source,
      * using configuration of this reader.
@@ -1585,6 +1591,26 @@ public <T> T readValue(String src, Class<T> valueType) throws IOException
         return (T) forType(valueType).readValue(src);
     }
 
+    @SuppressWarnings("unchecked")
+    public <T> T readValue(String src, T... reified) throws IOException {
+        if (reified.length > 0) {
+            throw new IllegalArgumentException("Please don't pass any values here. Java will detect class automatically.");
+        }
+
+        return readValue(src, getClassOf(reified));
+    }
+
+    /**
+     * Utility method to get the class type from a varargs array.
+     *
+     * @param <T> the generic type
+     * @param array the varargs array
+     * @return the class of the array component
+     */
+    private static <T> Class<T> getClassOf(T[] array) {
+        return (Class<T>) array.getClass().getComponentType();
+    }
+
     /**
      * Method that binds content read from given byte array,
      * using configuration of this reader.

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

@@ -45,6 +45,9 @@ public void testBoundsWithByteArrayInput() throws Exception {
         final JavaType TYPE = MAPPER.constructType(String.class);
         _testBoundsWithByteArrayInput(
                 (data,offset,len)->MAPPER.readValue(data, offset, len, TYPE));
+
+        _testBoundsWithByteArrayInput(
+                (data,offset,len)->MAPPER.readValue(data, offset, len));
     }
 
     private void _testBoundsWithByteArrayInput(ByteBackedCreation creator) throws Exception

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

@@ -385,6 +385,16 @@ public void testJsonFactoryLinkage()
         assertSame(m, f.getCodec());
     }
 
+    @Test
+    public void testAutoDetectClasses() throws Exception
+    {
+        ObjectMapper m = new ObjectMapper();
+        final String JSON = "{ \"x\" : 3 }";
+
+        Bean bean = m.readValue(JSON);
+        assertNotNull(bean);
+    }
+
     @Test
     public void testProviderConfig() throws Exception
     {

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

@@ -454,6 +454,9 @@ public void testCanPassResultToOverloadedMethod() throws Exception {
         ObjectReader reader = MAPPER.readerFor(POJO.class).at("/foo/bar/caller");
 
         process(reader.readValue(source, POJO.class));
+
+        POJO pojo = reader.readValue(source);
+        process(pojo);
     }
 
     void process(POJO pojo) {

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

@@ -82,6 +82,50 @@ public void testTokenBufferWithSample() throws Exception
         }
     }
 
+    @Test
+    public void testTokenBufferWithSequenceWithAutoDetectClass() throws Exception
+    {
+        final ObjectMapper mapper = jsonMapperBuilder()
+                .disable(DeserializationFeature.FAIL_ON_TRAILING_TOKENS)
+                .build();
+
+        // and then sequence of other things
+        JsonParser p = mapper.createParser("[ 32, [ 1 ], \"abc\", { \"a\" : true } ]");
+        assertToken(JsonToken.START_ARRAY, p.nextToken());
+
+        assertToken(JsonToken.VALUE_NUMBER_INT, p.nextToken());
+        TokenBuffer buf = mapper.readValue(p);
+
+        // check manually...
+        JsonParser bufParser = buf.asParser();
+        assertToken(JsonToken.VALUE_NUMBER_INT, bufParser.nextToken());
+        assertEquals(32, bufParser.getIntValue());
+        assertNull(bufParser.nextToken());
+
+        // then bind to another
+        buf = mapper.readValue(p);
+        bufParser = buf.asParser();
+        assertToken(JsonToken.START_ARRAY, bufParser.nextToken());
+        assertToken(JsonToken.VALUE_NUMBER_INT, bufParser.nextToken());
+        assertEquals(1, bufParser.getIntValue());
+        assertToken(JsonToken.END_ARRAY, bufParser.nextToken());
+        assertNull(bufParser.nextToken());
+
+        // third one, with automatic binding
+        buf = mapper.readValue(p);
+        String str = mapper.readValue(buf.asParser());
+        assertEquals("abc", str);
+
+        // and ditto for last one
+        buf = mapper.readValue(p, TokenBuffer.class);
+        Map<?,?> map = mapper.readValue(buf.asParser());
+        assertEquals(1, map.size());
+        assertEquals(Boolean.TRUE, map.get("a"));
+
+        assertEquals(JsonToken.END_ARRAY, p.nextToken());
+        assertNull(p.nextToken());
+    }
+
     @SuppressWarnings("resource")
     @Test
     public void testTokenBufferWithSequence() throws Exception

src/test/java/com/fasterxml/jackson/databind/deser/jdk/LocaleDeserTest.java

@@ -268,6 +268,15 @@ public void testLocaleFuzz47034() throws Exception
         assertNotNull(loc);
     }
 
+    @Test
+    public void testLocaleFuzz47034WithAutoDetectClss() throws Exception
+    {
+        Locale loc = MAPPER.reader()
+                .without(DeserializationFeature.FAIL_ON_TRAILING_TOKENS)
+                .readValue(getClass().getResourceAsStream("/fuzz/oss-fuzz-47034.json"));
+        assertNotNull(loc);
+    }
+
     // https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=47036
     // @since 2.14
     @Test