Fix for owlike#123 - Add support for preservation of unknown properties

genson/src/main/java/com/owlike/genson/Genson.java

@@ -9,6 +9,7 @@
 import com.owlike.genson.reflect.BeanDescriptor;
 import com.owlike.genson.reflect.BeanDescriptorProvider;
 import com.owlike.genson.reflect.RuntimePropertyFilter;
+import com.owlike.genson.reflect.UnknownPropertyHandler;
 import com.owlike.genson.stream.*;
 
 /**
@@ -72,6 +73,7 @@ public final class Genson {
   private final EncodingAwareReaderFactory readerFactory = new EncodingAwareReaderFactory();
   private final Map<Class<?>, Object> defaultValues;
   private final RuntimePropertyFilter runtimePropertyFilter;
+  private final UnknownPropertyHandler unknownPropertyHandler;
 
   /**
    * The default constructor will use the default configuration provided by the {@link GensonBuilder}.
@@ -81,7 +83,8 @@ public Genson() {
     this(_default.converterFactory, _default.beanDescriptorFactory,
       _default.skipNull, _default.htmlSafe, _default.aliasClassMap,
       _default.withClassMetadata, _default.strictDoubleParse, _default.indent,
-      _default.withMetadata, _default.failOnMissingProperty, _default.defaultValues, _default.runtimePropertyFilter);
+      _default.withMetadata, _default.failOnMissingProperty, _default.defaultValues,
+      _default.runtimePropertyFilter, _default.unknownPropertyHandler);
   }
 
   /**
@@ -108,11 +111,13 @@ public Genson() {
    * @param failOnMissingProperty throw a JsonBindingException when a key in the json stream does not match a property in the Java Class.
    * @param defaultValues contains a mapping from the raw class to the default value that should be used when the property is missing.
    * @param runtimePropertyFilter is used to define what bean properties should be excluded from ser/de at runtime.
+   * @param unknownPropertyHandler is used to handle unknown properties during ser/de.
    */
   public Genson(Factory<Converter<?>> converterFactory, BeanDescriptorProvider beanDescProvider,
                 boolean skipNull, boolean htmlSafe, Map<String, Class<?>> classAliases, boolean withClassMetadata,
                 boolean strictDoubleParse, boolean indent, boolean withMetadata, boolean failOnMissingProperty,
-                Map<Class<?>, Object> defaultValues, RuntimePropertyFilter runtimePropertyFilter) {
+                Map<Class<?>, Object> defaultValues, RuntimePropertyFilter runtimePropertyFilter,
+                UnknownPropertyHandler unknownPropertyHandler) {
     this.converterFactory = converterFactory;
     this.beanDescriptorFactory = beanDescProvider;
     this.skipNull = skipNull;
@@ -129,6 +134,7 @@ public Genson(Factory<Converter<?>> converterFactory, BeanDescriptorProvider bea
     this.indent = indent;
     this.withMetadata = withClassMetadata || withMetadata;
     this.failOnMissingProperty = failOnMissingProperty;
+    this.unknownPropertyHandler = unknownPropertyHandler;
   }
 
   /**
@@ -609,6 +615,10 @@ public RuntimePropertyFilter runtimePropertyFilter() {
     return runtimePropertyFilter;
   }
 
+  public UnknownPropertyHandler unknownPropertyHandler() {
+    return unknownPropertyHandler;
+  }
+
   /**
    * @deprecated use GensonBuilder
    */

genson/src/main/java/com/owlike/genson/GensonBuilder.java

@@ -76,6 +76,7 @@ public class GensonBuilder {
   private final Map<Class<?>, Object> defaultValues = new HashMap<Class<?>, Object>();
   private boolean failOnNullPrimitive = false;
   private RuntimePropertyFilter runtimePropertyFilter = RuntimePropertyFilter.noFilter;
+  private UnknownPropertyHandler unknownPropertyHandler;
 
   public GensonBuilder() {
     defaultValues.put(int.class, 0);
@@ -739,6 +740,11 @@ public GensonBuilder useRuntimePropertyFilter(RuntimePropertyFilter filter) {
     return this;
   }
 
+  public GensonBuilder useUnknownPropertyHandler(UnknownPropertyHandler handler) {
+    this.unknownPropertyHandler = handler;
+    return this;
+  }
+
   /**
    * Creates an instance of Genson. You may use this method as many times you want. It wont
    * change the state of the builder, in sense that the returned instance will have always the
@@ -824,7 +830,8 @@ protected Genson create(Factory<Converter<?>> converterFactory,
                           Map<String, Class<?>> classAliases) {
     return new Genson(converterFactory, getBeanDescriptorProvider(),
       isSkipNull(), isHtmlSafe(), classAliases, withClassMetadata,
-      strictDoubleParse, indent, metadata, failOnMissingProperty, defaultValues, runtimePropertyFilter);
+      strictDoubleParse, indent, metadata, failOnMissingProperty,
+      defaultValues, runtimePropertyFilter, unknownPropertyHandler);
   }
 
   /**

genson/src/main/java/com/owlike/genson/reflect/BeanDescriptor.java

@@ -4,7 +4,6 @@
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.Comparator;
-import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 
@@ -46,6 +45,8 @@ public class BeanDescriptor<T> implements Converter<T> {
   private final boolean _noArgCtr;
 
   private static final Object MISSING = new Object();
+  private static final GenericType<Object> UNKNOWN = new GenericType<Object>() {};
+
   // Used as a cache so we just copy it instead of recreating and assigning the default values
   private Object[] globalCreatorArgs;
 
@@ -86,11 +87,22 @@ public boolean isWritable() {
   }
 
   public void serialize(T obj, ObjectWriter writer, Context ctx) {
+    RuntimePropertyFilter  runtimePropertyFilter  = ctx.genson.runtimePropertyFilter();
+    UnknownPropertyHandler unknownPropertyHandler = ctx.genson.unknownPropertyHandler();
+
     writer.beginObject();
-    RuntimePropertyFilter runtimePropertyFilter = ctx.genson.runtimePropertyFilter();
     for (PropertyAccessor accessor : accessibleProperties) {
       if (runtimePropertyFilter.shouldInclude(accessor, ctx)) accessor.serialize(obj, writer, ctx);
     }
+    if (unknownPropertyHandler != null) {
+      Map<String, Object> props = unknownPropertyHandler.getUnknownProperties(obj);
+      if (props != null) {
+        for (String propName : props.keySet()) {
+          writer.writeName(propName);
+          ctx.genson.serialize(props.get(propName), writer, ctx);
+        }
+      }
+    }
     writer.endObject();
   }
 
@@ -110,8 +122,10 @@ public T deserialize(ObjectReader reader, Context ctx) {
   }
 
   public void deserialize(T into, ObjectReader reader, Context ctx) {
+    RuntimePropertyFilter  runtimePropertyFilter  = ctx.genson.runtimePropertyFilter();
+    UnknownPropertyHandler unknownPropertyHandler = ctx.genson.unknownPropertyHandler();
+
     reader.beginObject();
-    RuntimePropertyFilter runtimePropertyFilter = ctx.genson.runtimePropertyFilter();
     for (; reader.hasNext(); ) {
       reader.next();
       String propName = reader.name();
@@ -122,6 +136,8 @@ public void deserialize(T into, ObjectReader reader, Context ctx) {
         } else {
           reader.skipValue();
         }
+      } else if (unknownPropertyHandler != null) {
+        unknownPropertyHandler.onUnknownProperty(into, propName, ctx.genson.deserialize(UNKNOWN, reader, ctx));
       } else if (failOnMissingProperty) throw missingPropertyException(propName);
       else reader.skipValue();
     }
@@ -133,6 +149,7 @@ protected T _deserWithCtrArgs(ObjectReader reader, Context ctx) {
     List<String> names = new ArrayList<String>();
     List<Object> values = new ArrayList<Object>();
     RuntimePropertyFilter runtimePropertyFilter = ctx.genson.runtimePropertyFilter();
+    UnknownPropertyHandler unknownPropertyHandler = ctx.genson.unknownPropertyHandler();
 
     reader.beginObject();
     for (; reader.hasNext(); ) {
@@ -148,6 +165,10 @@ protected T _deserWithCtrArgs(ObjectReader reader, Context ctx) {
         } else {
           reader.skipValue();
         }
+      } else if (unknownPropertyHandler != null) {
+        Object propValue = ctx.genson.deserialize(UNKNOWN, reader, ctx);
+        names.add(propName);
+        values.add(propValue);
       } else if (failOnMissingProperty) throw missingPropertyException(propName);
       else reader.skipValue();
     }
@@ -175,7 +196,11 @@ protected T _deserWithCtrArgs(ObjectReader reader, Context ctx) {
     T bean = ofClass.cast(creator.create(creatorArgs));
     for (int i = 0; i < size; i++) {
       PropertyMutator property = mutableProperties.get(newNames[i]);
-      if (property != null) property.mutate(bean, newValues[i]);
+      if (property != null) {
+        property.mutate(bean, newValues[i]);
+      } else if (unknownPropertyHandler != null) {
+        unknownPropertyHandler.onUnknownProperty(bean, newNames[i], newValues[i]);
+      }
     }
     reader.endObject();
     return bean;

genson/src/main/java/com/owlike/genson/reflect/UnknownPropertyHandler.java

@@ -0,0 +1,43 @@
+package com.owlike.genson.reflect;
+
+import java.util.Map;
+
+/**
+ * An interface that defines callbacks that will be called when an
+ * unknown properties are encountered during deserialization, as well
+ * as to check if there are any unknown properties that should be
+ * written out during serialization.
+ * <p>
+ * The main purpose of this interface is to support schema evolution
+ * of objects that use JSON as a long term storage format, without
+ * loss of unknown properties across clients and severs using different
+ * versions of Java classes.
+ *
+ * @author Aleksandar Seovic  2018.05.09
+ */
+public interface UnknownPropertyHandler {
+    /**
+     * Called whenever a property is encountered in a JSON document
+     * that doesn't have a corresponding {@link PropertyMutator}.
+     * <p>
+     * Typically, the implementation of this interface concerned
+     * with schema evolution will handle this event by storing
+     * property value somewhere so it can be returned by the
+     * {@link #getUnknownProperties} method.
+     *
+     * @param target    the object we are deserializing JSON into
+     * @param propName  the name of the unknown property
+     * @param propValue the value of the unknown property
+     */
+    void onUnknownProperty(Object target, String propName, Object propValue);
+
+    /**
+     * Return a map of unknown properties encountered during
+     * deserialization, keyed by property name.
+     *
+     * @param source  the object we are serializing into JSON
+     *
+     * @return a map of unknown properties
+     */
+    Map<String, Object> getUnknownProperties(Object source);
+}