Provide a generic json mapper for any entity.

data/src/main/java/com/fernandocejas/android10/sample/data/entity/mapper/EntityJsonMapper.java

@@ -0,0 +1,90 @@
+/**
+ * Copyright (C) 2015 Fernando Cejas Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.fernandocejas.android10.sample.data.entity.mapper;
+
+import com.google.gson.Gson;
+import com.google.gson.JsonSyntaxException;
+import com.google.gson.reflect.TypeToken;
+
+import java.lang.reflect.ParameterizedType;
+import java.lang.reflect.Type;
+import java.util.List;
+
+/**
+ * Class used to transform from Strings representing json to valid objects.
+ */
+public class EntityJsonMapper<T> {
+
+  private final Gson gson;
+  private final Type type;
+  private ParameterizedType parameterizedType;
+
+  public EntityJsonMapper(Class<T> clazz) {
+    this.gson = new Gson();
+    this.type = clazz;
+  }
+
+  /**
+   * Transform from valid json string to an object type {@link T}.
+   *
+   * @param json A json representing an object type {@link T}.
+   * @return {@link T}.
+   * @throws com.google.gson.JsonSyntaxException if the json string is not a valid json structure.
+   */
+  public T transformEntity(String json) throws JsonSyntaxException {
+    try {
+      return gson.fromJson(json, type);
+    } catch (JsonSyntaxException jsonException) {
+      throw jsonException;
+    }
+  }
+
+  /**
+   * Transform from valid json string to List of {@link T}.
+   *
+   * @param json A json representing a collection of objects type {@link T}.
+   * @return List of {@link T}.
+   * @throws com.google.gson.JsonSyntaxException if the json string is not a valid json structure.
+   */
+  public List<T> transformEntityCollection(String json)
+      throws JsonSyntaxException {
+    try {
+      return gson.fromJson(json, getParameterizedType());
+    } catch (JsonSyntaxException jsonException) {
+      throw jsonException;
+    }
+  }
+
+  private ParameterizedType getParameterizedType() {
+    if (parameterizedType == null) {
+      parameterizedType = new ParameterizedType() {
+        @Override public Type[] getActualTypeArguments() {
+          return new Type[] {type};
+        }
+
+        @Override public Type getOwnerType() {
+          return null;
+        }
+
+        @Override public Type getRawType() {
+          return List.class;
+        }
+      };
+    }
+
+    return parameterizedType;
+  }
+}

data/src/main/java/com/fernandocejas/android10/sample/data/net/RestApiImpl.java

@@ -19,7 +19,7 @@
 import android.net.ConnectivityManager;
 import android.net.NetworkInfo;
 import com.fernandocejas.android10.sample.data.entity.UserEntity;
-import com.fernandocejas.android10.sample.data.entity.mapper.UserEntityJsonMapper;
+import com.fernandocejas.android10.sample.data.entity.mapper.EntityJsonMapper;
 import com.fernandocejas.android10.sample.data.exception.NetworkConnectionException;
 import io.reactivex.Observable;
 import java.net.MalformedURLException;
@@ -31,20 +31,20 @@
 public class RestApiImpl implements RestApi {
 
   private final Context context;
-  private final UserEntityJsonMapper userEntityJsonMapper;
+  private final EntityJsonMapper<UserEntity> entityJsonMapper;
 
   /**
    * Constructor of the class
    *
    * @param context {@link android.content.Context}.
-   * @param userEntityJsonMapper {@link UserEntityJsonMapper}.
+   * @param entityJsonMapper {@link EntityJsonMapper}.
    */
-  public RestApiImpl(Context context, UserEntityJsonMapper userEntityJsonMapper) {
-    if (context == null || userEntityJsonMapper == null) {
+  public RestApiImpl(Context context, EntityJsonMapper entityJsonMapper) {
+    if (context == null || entityJsonMapper == null) {
       throw new IllegalArgumentException("The constructor parameters cannot be null!!!");
     }
     this.context = context.getApplicationContext();
-    this.userEntityJsonMapper = userEntityJsonMapper;
+    this.entityJsonMapper = entityJsonMapper;
   }
 
   @Override public Observable<List<UserEntity>> userEntityList() {
@@ -53,7 +53,7 @@ public RestApiImpl(Context context, UserEntityJsonMapper userEntityJsonMapper) {
         try {
           String responseUserEntities = getUserEntitiesFromApi();
           if (responseUserEntities != null) {
-            emitter.onNext(userEntityJsonMapper.transformUserEntityCollection(
+            emitter.onNext(entityJsonMapper.transformEntityCollection(
                 responseUserEntities));
             emitter.onComplete();
           } else {
@@ -74,7 +74,7 @@ public RestApiImpl(Context context, UserEntityJsonMapper userEntityJsonMapper) {
         try {
           String responseUserDetails = getUserDetailsFromApi(userId);
           if (responseUserDetails != null) {
-            emitter.onNext(userEntityJsonMapper.transformUserEntity(responseUserDetails));
+            emitter.onNext(entityJsonMapper.transformEntity(responseUserDetails));
             emitter.onComplete();
           } else {
             emitter.onError(new NetworkConnectionException());

data/src/main/java/com/fernandocejas/android10/sample/data/repository/datasource/UserDataStoreFactory.java

@@ -18,7 +18,8 @@
 import android.content.Context;
 import android.support.annotation.NonNull;
 import com.fernandocejas.android10.sample.data.cache.UserCache;
-import com.fernandocejas.android10.sample.data.entity.mapper.UserEntityJsonMapper;
+import com.fernandocejas.android10.sample.data.entity.UserEntity;
+import com.fernandocejas.android10.sample.data.entity.mapper.EntityJsonMapper;
 import com.fernandocejas.android10.sample.data.net.RestApi;
 import com.fernandocejas.android10.sample.data.net.RestApiImpl;
 import javax.inject.Inject;
@@ -58,8 +59,8 @@ public UserDataStore create(int userId) {
    * Create {@link UserDataStore} to retrieve data from the Cloud.
    */
   public UserDataStore createCloudDataStore() {
-    final UserEntityJsonMapper userEntityJsonMapper = new UserEntityJsonMapper();
-    final RestApi restApi = new RestApiImpl(this.context, userEntityJsonMapper);
+    final EntityJsonMapper<UserEntity> entityJsonMapper = new EntityJsonMapper<>(UserEntity.class);
+    final RestApi restApi = new RestApiImpl(this.context, entityJsonMapper);
 
     return new CloudUserDataStore(restApi, this.userCache);
   }

data/src/test/java/com/fernandocejas/android10/sample/data/entity/mapper/UserEntityJsonMapperTest.java → data/src/test/java/com/fernandocejas/android10/sample/data/entity/mapper/EntityMapperUtilTest.java

@@ -30,7 +30,7 @@
 import static org.hamcrest.MatcherAssert.assertThat;
 
 @RunWith(MockitoJUnitRunner.class)
-public class UserEntityJsonMapperTest {
+public class EntityMapperUtilTest {
 
   private static final String JSON_RESPONSE_USER_DETAILS = "{\n"
       + "    \"id\": 1,\n"
@@ -51,19 +51,19 @@ public class UserEntityJsonMapperTest {
       + "    \"followers\": 1381\n"
       + "}]";
 
-  private UserEntityJsonMapper userEntityJsonMapper;
+  private EntityJsonMapper<UserEntity> entityJsonMapper;
 
   @Rule
   public ExpectedException expectedException = ExpectedException.none();
 
   @Before
   public void setUp() {
-    userEntityJsonMapper = new UserEntityJsonMapper();
+    entityJsonMapper = new EntityJsonMapper<UserEntity>(UserEntity.class);
   }
 
   @Test
   public void testTransformUserEntityHappyCase() {
-    UserEntity userEntity = userEntityJsonMapper.transformUserEntity(JSON_RESPONSE_USER_DETAILS);
+    UserEntity userEntity = entityJsonMapper.transformEntity(JSON_RESPONSE_USER_DETAILS);
 
     assertThat(userEntity.getUserId(), is(1));
     assertThat(userEntity.getFullname(), is(equalTo("Simon Hill")));
@@ -73,7 +73,7 @@ public void testTransformUserEntityHappyCase() {
   @Test
   public void testTransformUserEntityCollectionHappyCase() {
     Collection<UserEntity> userEntityCollection =
-        userEntityJsonMapper.transformUserEntityCollection(
+        entityJsonMapper.transformEntityCollection(
             JSON_RESPONSE_USER_COLLECTION);
 
     assertThat(((UserEntity) userEntityCollection.toArray()[0]).getUserId(), is(1));
@@ -84,12 +84,12 @@ public void testTransformUserEntityCollectionHappyCase() {
   @Test
   public void testTransformUserEntityNotValidResponse() {
     expectedException.expect(JsonSyntaxException.class);
-    userEntityJsonMapper.transformUserEntity("ironman");
+    entityJsonMapper.transformEntity("ironman");
   }
 
   @Test
   public void testTransformUserEntityCollectionNotValidResponse() {
     expectedException.expect(JsonSyntaxException.class);
-    userEntityJsonMapper.transformUserEntityCollection("Tony Stark");
+    entityJsonMapper.transformEntityCollection("Tony Stark");
   }
 }