Preconditions for middleware module (#56)

* Add preconditions for parsers

* Remove redundant checks

* Refactored factory

* Add factory tests

* Change codestyle

* Fix PMD checks

middleware/src/main/java/com/nytimes/android/external/store/middleware/GsonParserFactory.java

@@ -17,18 +17,21 @@ public final class GsonParserFactory {
     private GsonParserFactory() {
     }
 
+    /**
+     * Returns a new Parser which parses from {@link Reader} to the specified type, using
+     * a new default configured {@link Gson} instance.
+     */
+    @NonNull
+    public static <T> Parser<Reader, T> createReaderParser(@NonNull Type type) {
+        return createReaderParser(new Gson(), type);
+    }
+
     /**
      * Returns a new Parser which parses from {@link Reader} to the specified type, using
      * the provided {@link Gson} instance.
      */
     @NonNull
     public static <T> Parser<Reader, T> createReaderParser(@NonNull Gson gson, @NonNull Type type) {
-        if (gson == null) {
-            throw new IllegalArgumentException("gson cannot be null.");
-        }
-        if (type == null) {
-            throw new IllegalArgumentException("type cannot be null.");
-        }
         return new GsonReaderParser<>(gson, type);
     }
 
@@ -37,11 +40,8 @@ public final class GsonParserFactory {
      * a new default configured {@link Gson} instance.
      */
     @NonNull
-    public static <T> Parser<Reader, T> createReaderParser(@NonNull Type type) {
+    public static <T> Parser<BufferedSource, T> createSourceParser(@NonNull Type type) {
-        if (type == null) {
+        return createSourceParser(new Gson(), type);
-            throw new IllegalArgumentException("type cannot be null.");
-        }
-        return new GsonReaderParser<>(new Gson(), type);
     }
 
     /**
@@ -50,52 +50,25 @@ public final class GsonParserFactory {
      */
     @NonNull
     public static <T> Parser<BufferedSource, T> createSourceParser(@NonNull Gson gson, @NonNull Type type) {
-        if (gson == null) {
-            throw new IllegalArgumentException("gson cannot be null.");
-        }
-        if (type == null) {
-            throw new IllegalArgumentException("type cannot be null.");
-        }
         return new GsonSourceParser<>(gson, type);
     }
 
-    /**
-     * Returns a new Parser which parses from {@link Reader} to the specified type, using
-     * a new default configured {@link Gson} instance.
-     */
-    @NonNull
-    public static <T> Parser<BufferedSource, T> createSourceParser(@NonNull Type type) {
-        if (type == null) {
-            throw new IllegalArgumentException("type cannot be null.");
-        }
-        return new GsonSourceParser<>(new Gson(), type);
-    }
-
-    /**
-     * Returns a new Parser which parses from a String to the specified type, using
-     * the provided {@link Gson} instance.
-     */
-    @NonNull
-    public static <T> Parser<String, T> createStringParser(@NonNull Gson gson, @NonNull Type type) {
-        if (gson == null) {
-            throw new IllegalArgumentException("gson cannot be null.");
-        }
-        if (type == null) {
-            throw new IllegalArgumentException("type cannot be null.");
-        }
-        return new GsonStringParser<>(gson, type);
-    }
-
     /**
      * Returns a new Parser which parses from a String to the specified type, using
      * a new default {@link Gson} instance.
      */
     @NonNull
     public static <T> Parser<String, T> createStringParser(@NonNull Class<T> type) {
-        if (type == null) {
+        return createStringParser(new Gson(), type);
-            throw new IllegalArgumentException("type cannot be null.");
+    }
-        }
+
-        return new GsonStringParser<>(new Gson(), type);
+    /**
+     * Returns a new Parser which parses from a String to the specified type, using
+     * the provided {@link Gson} instance.
+     */
+    @NonNull
+    public static <T> Parser<String, T> createStringParser(@NonNull Gson gson, @NonNull Type type) {
+        return new GsonStringParser<>(gson, type);
     }
 
 }

middleware/src/main/java/com/nytimes/android/external/store/middleware/GsonReaderParser.java

@@ -10,6 +10,8 @@ import java.lang.reflect.Type;
 
 import javax.inject.Inject;
 
+import static com.nytimes.android.external.cache.Preconditions.checkNotNull;
+
 public class GsonReaderParser<Parsed> implements Parser<Reader, Parsed> {
 
     private final Gson gson;
@@ -17,6 +19,8 @@ public class GsonReaderParser<Parsed> implements Parser<Reader, Parsed> {
 
     @Inject
     public GsonReaderParser(Gson gson, Type type) {
+        checkNotNull(gson, "Gson can't be null");
+        checkNotNull(type, "Type can't be null");
         this.gson = gson;
         this.type = type;
     }

middleware/src/main/java/com/nytimes/android/external/store/middleware/GsonSourceParser.java

@@ -13,6 +13,8 @@ import javax.inject.Inject;
 
 import okio.BufferedSource;
 
+import static com.nytimes.android.external.cache.Preconditions.checkNotNull;
+
 /**
  * Parser to be used when going from a BufferedSource to any Parsed Type
  * example usage:
@@ -31,6 +33,8 @@ public class GsonSourceParser<Parsed> implements Parser<BufferedSource, Parsed>
 
     @Inject
     public GsonSourceParser(Gson gson, Type type) {
+        checkNotNull(gson, "Gson can't be null");
+        checkNotNull(type, "Type can't be null");
         this.gson = gson;
         this.type = type;
     }

middleware/src/main/java/com/nytimes/android/external/store/middleware/GsonStringParser.java

@@ -2,11 +2,11 @@ package com.nytimes.android.external.store.middleware;
 
 import com.google.gson.Gson;
 import com.nytimes.android.external.store.base.Parser;
-
 import java.lang.reflect.Type;
-
 import javax.inject.Inject;
 
+import static com.nytimes.android.external.cache.Preconditions.checkNotNull;
+
 public class GsonStringParser<Parsed> implements Parser<String, Parsed> {
 
     private final Gson gson;
@@ -14,6 +14,8 @@ public class GsonStringParser<Parsed> implements Parser<String, Parsed> {
 
     @Inject
     public GsonStringParser(Gson gson, Type parsedClass) {
+        checkNotNull(gson, "Gson can't be null");
+        checkNotNull(parsedClass, "Type can't be null");
         this.gson = gson;
         this.type = parsedClass;
     }

middleware/src/test/java/com/nytimes/android/external/store/GsonParserFactoryTest.java

@@ -0,0 +1,71 @@
+package com.nytimes.android.external.store;
+
+import com.google.gson.Gson;
+import com.nytimes.android.external.store.middleware.GsonParserFactory;
+
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+
+import java.lang.reflect.Type;
+
+public class GsonParserFactoryTest {
+
+    @Rule
+    public ExpectedException expectedException = ExpectedException.none();
+
+    @Mock
+    Type type;
+    private final Gson gson = new Gson();
+
+    @Before
+    public void setUp() throws Exception {
+        MockitoAnnotations.initMocks(this);
+    }
+
+    @Test
+    public void shouldCreateParsersProperly() {
+        GsonParserFactory.createReaderParser(gson, type);
+        GsonParserFactory.createSourceParser(gson, type);
+        GsonParserFactory.createStringParser(gson, type);
+    }
+
+    @Test
+    public void shouldThrowExceptionWhenCreatingReaderWithNullType() {
+        expectedException.expect(NullPointerException.class);
+        GsonParserFactory.createReaderParser(gson, null);
+    }
+
+    @Test
+    public void shouldThrowExceptionWhenCreatingReaderWithNullGson() {
+        expectedException.expect(NullPointerException.class);
+        GsonParserFactory.createReaderParser(null, type);
+    }
+
+    @Test
+    public void shouldThrowExceptionWhenCreatingSourceWithNullType() {
+        expectedException.expect(NullPointerException.class);
+        GsonParserFactory.createSourceParser(gson, null);
+    }
+
+    @Test
+    public void shouldThrowExceptionWhenCreatingSourceWithNullGson() {
+        expectedException.expect(NullPointerException.class);
+        GsonParserFactory.createSourceParser(null, type);
+    }
+
+    @Test
+    public void shouldThrowExceptionWhenCreatingStringWithNullType() {
+        expectedException.expect(NullPointerException.class);
+        GsonParserFactory.createStringParser(gson, null);
+    }
+
+    @Test
+    public void shouldThrowExceptionWhenCreatingStringWithNullGson() {
+        expectedException.expect(NullPointerException.class);
+        GsonParserFactory.createStringParser(null, type);
+    }
+}