JsonContext accepts a bean as target

ebean-api/src/main/java/io/ebean/text/json/JsonBeanReader.java

@@ -12,11 +12,18 @@ import io.ebean.bean.PersistenceContext;
  */
 public interface JsonBeanReader<T> {
 
+  /**
+   * Read the JSON into given bean. Will update existing properties.
+   */
+  T read(T target);
+
   /**
    * Read the JSON returning a bean.
    */
-  T read();
-
+  default T read() {
+    return read(null);
+  }
+  
   /**
    * Create a new reader taking the context from the existing one but using a new JsonParser.
    */

ebean-api/src/main/java/io/ebean/text/json/JsonContext.java

@@ -58,12 +58,60 @@ public interface JsonContext {
    */
   <T> T toBean(Class<T> cls, JsonParser parser, JsonReadOptions options) throws JsonIOException;
 
+  /**
+   * Read json parser input into a given Bean. <br>
+   * Note: This is a kind of "update". Only properties in the json will be modified. Embedded Lists and Maps will become new
+   * instances, so the object identity will not be preserved here.
+   *
+   * @throws JsonIOException When IOException occurs
+   */
+  <T> void toBean(T target, JsonParser parser) throws JsonIOException;
+
+  /**
+   * Read json parser input into a given Bean additionally using JsonReadOptions.<br>
+   * See {@link #toBean(Class, JsonParser)} for details modified.
+   *
+   * @throws JsonIOException When IOException occurs
+   */
+  <T> void toBean(T target, JsonParser parser, JsonReadOptions options) throws JsonIOException;
+
+  /**
+   * Read json reader input into a given Bean.<br>
+   * See {@link #toBean(Class, JsonParser)} for details
+   *
+   * @throws JsonIOException When IOException occurs
+   */
+  <T> void toBean(T target, Reader json) throws JsonIOException;
+
+  /**
+   * Read json reader input into a given Bean additionally using JsonReadOptions.<br>
+   * See {@link #toBean(Class, JsonParser)} for details modified.
+   *
+   * @throws JsonIOException When IOException occurs
+   */
+  <T> void toBean(T target, Reader json, JsonReadOptions options) throws JsonIOException;
+
+  /**
+   * Read json string input into a given Bean.<br>
+   * See {@link #toBean(Class, JsonParser)} for details
+   *
+   * @throws JsonIOException When IOException occurs
+   */
+  <T> void toBean(T target, String json) throws JsonIOException;
+
+  /**
+   * Read json string input into a given Bean additionally using JsonReadOptions.<br>
+   * See {@link #toBean(Class, JsonParser)} for details
+   *
+   * @throws JsonIOException When IOException occurs
+   */
+  <T> void toBean(T target, String json, JsonReadOptions options) throws JsonIOException;
+
   /**
    * Create and return a new bean reading for the bean type given the JSON options and source.
    * <p>
-   * Note that JsonOption provides an option for setting a persistence context and also enabling
-   * further lazy loading. Further lazy loading requires a persistence context so if that is set
-   * on then a persistence context is created if there is not one set.
+   * Note that JsonOption provides an option for setting a persistence context and also enabling further lazy loading. Further lazy
+   * loading requires a persistence context so if that is set on then a persistence context is created if there is not one set.
    */
   <T> JsonBeanReader<T> createBeanReader(Class<T> cls, JsonParser parser, JsonReadOptions options) throws JsonIOException;
 

ebean-core/src/main/java/io/ebeaninternal/server/deploy/BeanDescriptor.java

@@ -3381,12 +3381,12 @@ public class BeanDescriptor<T> implements BeanType<T>, STreeType, SpiBeanType {
     jsonHelp.jsonWriteProperties(writeJson, bean);
   }
 
-  public T jsonRead(SpiJsonReader jsonRead, String path) throws IOException {
-    return jsonHelp.jsonRead(jsonRead, path, true);
+  public T jsonRead(SpiJsonReader jsonRead, String path, T target) throws IOException {
+    return jsonHelp.jsonRead(jsonRead, path, true, target);
   }
 
-  T jsonReadObject(SpiJsonReader jsonRead, String path) throws IOException {
-    return jsonHelp.jsonRead(jsonRead, path, false);
+  T jsonReadObject(SpiJsonReader jsonRead, String path, T target) throws IOException {
+    return jsonHelp.jsonRead(jsonRead, path, false, target);
   }
 
   public List<BeanProperty[]> uniqueProps() {

ebean-core/src/main/java/io/ebeaninternal/server/deploy/BeanDescriptorElementEmbedded.java

@@ -61,13 +61,13 @@ class BeanDescriptorElementEmbedded<T> extends BeanDescriptorElement<T> {
   }
 
   @Override
-  public T jsonRead(SpiJsonReader jsonRead, String path) throws IOException {
-    return readJsonElement(jsonRead, path);
+  public T jsonRead(SpiJsonReader jsonRead, String path, T target) throws IOException {
+    return readJsonElement(jsonRead, path, target);
   }
 
   @SuppressWarnings("unchecked")
-  T readJsonElement(SpiJsonReader jsonRead, String path) throws IOException {
-    return (T)targetDescriptor.jsonRead(jsonRead, path);
+  T readJsonElement(SpiJsonReader jsonRead, String path, T target) throws IOException {
+    return (T)targetDescriptor.jsonRead(jsonRead, path, target);
   }
 
   void writeJsonElement(SpiJsonWriter ctx, Object element) {

ebean-core/src/main/java/io/ebeaninternal/server/deploy/BeanDescriptorElementEmbeddedMap.java

@@ -58,13 +58,13 @@ class BeanDescriptorElementEmbeddedMap<T> extends BeanDescriptorElementEmbedded<
       }
       if (stringKey) {
         parser.nextToken();
-        Object val = readJsonElement(readJson, null);
+        Object val = readJsonElement(readJson, null, null); // CHECKME: Update existing map entry here?
         add.addKeyValue(fieldName, val);
       } else {
         parser.nextFieldName();
         Object key = scalarTypeKey.jsonRead(parser);
         parser.nextFieldName();
-        Object val = readJsonElement(readJson, null);
+        Object val = readJsonElement(readJson, null, null); // CHECKME: Update existing map entry here?
         add.addKeyValue(key, val);
       }
     } while (true);

ebean-core/src/main/java/io/ebeaninternal/server/deploy/BeanDescriptorJsonHelp.java

@@ -65,7 +65,7 @@ final class BeanDescriptorJsonHelp<T> {
   }
 
   @SuppressWarnings("unchecked")
-  T jsonRead(SpiJsonReader jsonRead, String path, boolean withInheritance) throws IOException {
+  T jsonRead(SpiJsonReader jsonRead, String path, boolean withInheritance, T target) throws IOException {
     JsonParser parser = jsonRead.getParser();
     //noinspection StatementWithEmptyBody
     if (parser.getCurrentToken() == JsonToken.START_OBJECT) {
@@ -82,7 +82,7 @@ final class BeanDescriptorJsonHelp<T> {
     }
 
     if (desc.inheritInfo == null || !withInheritance) {
-      return jsonReadObject(jsonRead, path);
+      return jsonReadObject(jsonRead, path, target);
     }
 
     ObjectNode node = jsonRead.getObjectMapper().readTree(parser);
@@ -97,17 +97,25 @@ final class BeanDescriptorJsonHelp<T> {
     JsonNode discNode = node.get(discColumn);
     if (discNode == null || discNode.isNull()) {
       if (!desc.isAbstractType()) {
-        return desc.jsonReadObject(newReader, path);
+        return desc.jsonReadObject(newReader, path, target);
       }
       String msg = "Error reading inheritance discriminator - expected [" + discColumn + "] but no json key?";
       throw new JsonParseException(newParser, msg, parser.getCurrentLocation());
     }
 
-    return (T) inheritInfo.readType(discNode.asText()).desc().jsonReadObject(newReader, path);
+    BeanDescriptor<T> inheritDesc = (BeanDescriptor<T>) inheritInfo.readType(discNode.asText()).desc();
+    return inheritDesc.jsonReadObject(newReader, path, target);
   }
 
-  private T jsonReadObject(SpiJsonReader readJson, String path) throws IOException {
-    EntityBean bean = desc.createEntityBeanForJson();
+  private T jsonReadObject(SpiJsonReader readJson, String path, T target) throws IOException {
+    EntityBean bean;
+    if (target == null) {
+      bean = desc.createEntityBeanForJson();
+    } else if (desc.beanType.isInstance(target)) {
+      bean = (EntityBean) target;
+    } else {
+      throw new ClassCastException(target.getClass().getName() + " provided, but " + desc.beanType.getClass().getName() + " expected");
+    }
     return jsonReadProperties(readJson, bean, path);
   }
 

ebean-core/src/main/java/io/ebeaninternal/server/deploy/BeanPropertyAssocMany.java

@@ -1016,7 +1016,8 @@ public class BeanPropertyAssocMany<T> extends BeanPropertyAssoc<T> implements ST
     BeanCollection<?> collection = createEmpty(parentBean);
     BeanCollectionAdd add = beanCollectionAdd(collection);
     do {
-      EntityBean detailBean = (EntityBean) targetDescriptor.jsonRead(readJson, name);
+      // CHECKME: Update existing list entry here?
+      EntityBean detailBean = (EntityBean) targetDescriptor.jsonRead(readJson, name, null);
       if (detailBean == null) {
         // read the entire array
         break;

ebean-core/src/main/java/io/ebeaninternal/server/deploy/BeanPropertyAssocOne.java

@@ -783,7 +783,8 @@ public class BeanPropertyAssocOne<T> extends BeanPropertyAssoc<T> implements STr
   @Override
   public void jsonRead(SpiJsonReader readJson, EntityBean bean) throws IOException {
     if (jsonDeserialize && targetDescriptor != null) {
-      T assocBean = targetDescriptor.jsonRead(readJson, name);
+      T target = (T) value(bean);
+      T assocBean = targetDescriptor.jsonRead(readJson, name, target);
       setValue(bean, assocBean);
     }
   }

ebean-core/src/main/java/io/ebeaninternal/server/text/json/DJsonBeanReader.java

@@ -36,9 +36,9 @@ public final class DJsonBeanReader<T> implements JsonBeanReader<T> {
   }
 
   @Override
-  public T read() {
+  public T read(T target) {
     try {
-      return desc.jsonRead(readJson, null);
+      return desc.jsonRead(readJson, null, target);
     } catch (IOException e) {
       throw new PersistenceIOException(e);
     }

ebean-core/src/main/java/io/ebeaninternal/server/text/json/DJsonContext.java

@@ -125,7 +125,43 @@ public final class DJsonContext implements SpiJsonContext {
 
     BeanDescriptor<T> desc = getDescriptor(cls);
     try {
-      return desc.jsonRead(new ReadJson(desc, parser, options, determineObjectMapper(options)), null);
+      return desc.jsonRead(new ReadJson(desc, parser, options, determineObjectMapper(options)), null, null);
+    } catch (IOException e) {
+      throw new JsonIOException(e);
+    }
+  }
+
+  @Override
+  public <T> void toBean(T target, String json) throws JsonIOException {
+    toBean(target, new StringReader(json));
+  }
+
+  @Override
+  public <T> void toBean(T target, String json, JsonReadOptions options) throws JsonIOException {
+    toBean(target, new StringReader(json), options);
+  }
+
+  @Override
+  public <T> void toBean(T target, Reader jsonReader) throws JsonIOException {
+    toBean(target, createParser(jsonReader));
+  }
+
+  @Override
+  public <T> void toBean(T target, Reader jsonReader, JsonReadOptions options) throws JsonIOException {
+    toBean(target, createParser(jsonReader), options);
+  }
+
+  @Override
+  public <T> void toBean(T target, JsonParser parser) throws JsonIOException {
+    toBean(target, parser, null);
+  }
+
+  @Override
+  public <T> void toBean(T target, JsonParser parser, JsonReadOptions options) throws JsonIOException {
+  
+    BeanDescriptor<T> desc = (BeanDescriptor<T>) getDescriptor(target.getClass());
+    try {
+      desc.jsonRead(new ReadJson(desc, parser, options, determineObjectMapper(options)), null, target);
     } catch (IOException e) {
       throw new JsonIOException(e);
     }
@@ -188,7 +224,8 @@ public final class DJsonContext implements SpiJsonContext {
 
       List<T> list = new ArrayList<>();
       do {
-        T bean = desc.jsonRead(readJson, null);
+        // CHECKME: Should we update the list
+        T bean = desc.jsonRead(readJson, null, null); 
         if (bean == null) {
           break;
         } else {

ebean-test/src/test/java/org/tests/text/json/TestJsonBeanDescriptorParse.java

@@ -26,12 +26,9 @@ public class TestJsonBeanDescriptorParse extends BaseTestCase {
 
     BeanDescriptor<Customer> descriptor = server.descriptor(Customer.class);
 
-    StringReader reader = new StringReader("{\"id\":123,\"name\":\"Hello rob\"}");
-    JsonParser parser = server.json().createParser(reader);
+    SpiJsonReader readJson = createRead(server, descriptor);
 
-    SpiJsonReader readJson = new ReadJson(descriptor, parser, null, null);
-
-    Customer customer = descriptor.jsonRead(readJson, null);
+    Customer customer = descriptor.jsonRead(readJson, null, null);
 
     assertEquals(Integer.valueOf(123), customer.getId());
     assertEquals("Hello rob", customer.getName());
@@ -42,6 +39,21 @@ public class TestJsonBeanDescriptorParse extends BaseTestCase {
     assertEquals(2, loadedProps.size());
     assertTrue(loadedProps.contains("id"));
     assertTrue(loadedProps.contains("name"));
+    
+    customer.setName("Hello Roland");
+    customer.setId(234);
+    readJson = createRead(server, descriptor);
+    descriptor.jsonRead(readJson, null, customer);
+    assertEquals(Integer.valueOf(123), customer.getId());
+    assertEquals("Hello rob", customer.getName());
+  }
+
+  private SpiJsonReader createRead(SpiEbeanServer server, BeanDescriptor<Customer> descriptor) {
+    StringReader reader = new StringReader("{\"id\":123,\"name\":\"Hello rob\"}");
+    JsonParser parser = server.json().createParser(reader);
+
+    SpiJsonReader readJson = new ReadJson(descriptor, parser, null, null);
+    return readJson;
   }
 
 }