Add newBuilder() API (#1142)

* Add Gson.newBuilder API.

* Remove redundant test.

* Address Codacy comments.

* Reduce visibility of GsonBuilder constructor.

gson/src/main/java/com/google/gson/Gson.java

@@ -25,6 +25,7 @@ import java.io.Writer;
 import java.lang.reflect.Type;
 import java.math.BigDecimal;
 import java.math.BigInteger;
+import java.text.DateFormat;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.HashMap;
@@ -124,18 +125,28 @@ public final class Gson {
 
   private final Map<TypeToken<?>, TypeAdapter<?>> typeTokenCache = new ConcurrentHashMap<TypeToken<?>, TypeAdapter<?>>();
 
-  private final List<TypeAdapterFactory> factories;
   private final ConstructorConstructor constructorConstructor;
-
-  private final Excluder excluder;
-  private final FieldNamingStrategy fieldNamingStrategy;
-  private final boolean serializeNulls;
-  private final boolean htmlSafe;
-  private final boolean generateNonExecutableJson;
-  private final boolean prettyPrinting;
-  private final boolean lenient;
   private final JsonAdapterAnnotationTypeAdapterFactory jsonAdapterFactory;
 
+  final List<TypeAdapterFactory> factories;
+
+  final Excluder excluder;
+  final FieldNamingStrategy fieldNamingStrategy;
+  final Map<Type, InstanceCreator<?>> instanceCreators;
+  final boolean serializeNulls;
+  final boolean complexMapKeySerialization;
+  final boolean generateNonExecutableJson;
+  final boolean htmlSafe;
+  final boolean prettyPrinting;
+  final boolean lenient;
+  final boolean serializeSpecialFloatingPointValues;
+  final String datePattern;
+  final int dateStyle;
+  final int timeStyle;
+  final LongSerializationPolicy longSerializationPolicy;
+  final List<TypeAdapterFactory> builderFactories;
+  final List<TypeAdapterFactory> builderHierarchyFactories;
+
   /**
    * Constructs a Gson object with default configuration. The default configuration has the
    * following settings:
@@ -175,23 +186,36 @@ public final class Gson {
         Collections.<Type, InstanceCreator<?>>emptyMap(), DEFAULT_SERIALIZE_NULLS,
         DEFAULT_COMPLEX_MAP_KEYS, DEFAULT_JSON_NON_EXECUTABLE, DEFAULT_ESCAPE_HTML,
         DEFAULT_PRETTY_PRINT, DEFAULT_LENIENT, DEFAULT_SPECIALIZE_FLOAT_VALUES,
-        LongSerializationPolicy.DEFAULT, Collections.<TypeAdapterFactory>emptyList());
+        LongSerializationPolicy.DEFAULT, null, DateFormat.DEFAULT, DateFormat.DEFAULT,
+        Collections.<TypeAdapterFactory>emptyList(), Collections.<TypeAdapterFactory>emptyList(),
+        Collections.<TypeAdapterFactory>emptyList());
   }
 
   Gson(final Excluder excluder, final FieldNamingStrategy fieldNamingStrategy,
       final Map<Type, InstanceCreator<?>> instanceCreators, boolean serializeNulls,
       boolean complexMapKeySerialization, boolean generateNonExecutableGson, boolean htmlSafe,
       boolean prettyPrinting, boolean lenient, boolean serializeSpecialFloatingPointValues,
-      LongSerializationPolicy longSerializationPolicy,
+      LongSerializationPolicy longSerializationPolicy, String datePattern, int dateStyle,
-      List<TypeAdapterFactory> typeAdapterFactories) {
+      int timeStyle, List<TypeAdapterFactory> builderFactories,
-    this.constructorConstructor = new ConstructorConstructor(instanceCreators);
+      List<TypeAdapterFactory> builderHierarchyFactories,
+      List<TypeAdapterFactory> factoriesToBeAdded) {
     this.excluder = excluder;
     this.fieldNamingStrategy = fieldNamingStrategy;
+    this.instanceCreators = instanceCreators;
+    this.constructorConstructor = new ConstructorConstructor(instanceCreators);
     this.serializeNulls = serializeNulls;
+    this.complexMapKeySerialization = complexMapKeySerialization;
     this.generateNonExecutableJson = generateNonExecutableGson;
     this.htmlSafe = htmlSafe;
     this.prettyPrinting = prettyPrinting;
     this.lenient = lenient;
+    this.serializeSpecialFloatingPointValues = serializeSpecialFloatingPointValues;
+    this.longSerializationPolicy = longSerializationPolicy;
+    this.datePattern = datePattern;
+    this.dateStyle = dateStyle;
+    this.timeStyle = timeStyle;
+    this.builderFactories = builderFactories;
+    this.builderHierarchyFactories = builderHierarchyFactories;
 
     List<TypeAdapterFactory> factories = new ArrayList<TypeAdapterFactory>();
 
@@ -202,8 +226,8 @@ public final class Gson {
     // the excluder must precede all adapters that handle user-defined types
     factories.add(excluder);
 
-    // user's type adapters
+    // users' type adapters
-    factories.addAll(typeAdapterFactories);
+    factories.addAll(factoriesToBeAdded);
 
     // type adapters for basic platform types
     factories.add(TypeAdapters.STRING_FACTORY);
@@ -255,6 +279,16 @@ public final class Gson {
     this.factories = Collections.unmodifiableList(factories);
   }
 
+  /**
+   * Returns a new GsonBuilder containing all custom factories and configuration used by the current
+   * instance.
+   *
+   * @return a GsonBuilder instance.
+   */
+  public GsonBuilder newBuilder() {
+    return new GsonBuilder(this);
+  }
+
   public Excluder excluder() {
     return excluder;
   }

gson/src/main/java/com/google/gson/GsonBuilder.java

@@ -104,6 +104,31 @@ public final class GsonBuilder {
   public GsonBuilder() {
   }
 
+  /**
+   * Constructs a GsonBuilder instance from a Gson instance. The newly constructed GsonBuilder
+   * has the same configuration as the previously built Gson instance.
+   *
+   * @param gson the gson instance whose configuration should by applied to a new GsonBuilder.
+   */
+  GsonBuilder(Gson gson) {
+    this.excluder = gson.excluder;
+    this.fieldNamingPolicy = gson.fieldNamingStrategy;
+    this.instanceCreators.putAll(gson.instanceCreators);
+    this.serializeNulls = gson.serializeNulls;
+    this.complexMapKeySerialization = gson.complexMapKeySerialization;
+    this.generateNonExecutableJson = gson.generateNonExecutableJson;
+    this.escapeHtmlChars = gson.htmlSafe;
+    this.prettyPrinting = gson.prettyPrinting;
+    this.lenient = gson.lenient;
+    this.serializeSpecialFloatingPointValues = gson.serializeSpecialFloatingPointValues;
+    this.longSerializationPolicy = gson.longSerializationPolicy;
+    this.datePattern = gson.datePattern;
+    this.dateStyle = gson.dateStyle;
+    this.timeStyle = gson.timeStyle;
+    this.factories.addAll(gson.builderFactories);
+    this.hierarchyFactories.addAll(gson.builderHierarchyFactories);
+  }
+
   /**
    * Configures Gson to enable versioning support.
    *
@@ -572,7 +597,9 @@ public final class GsonBuilder {
     return new Gson(excluder, fieldNamingPolicy, instanceCreators,
         serializeNulls, complexMapKeySerialization,
         generateNonExecutableJson, escapeHtmlChars, prettyPrinting, lenient,
-        serializeSpecialFloatingPointValues, longSerializationPolicy, factories);
+        serializeSpecialFloatingPointValues, longSerializationPolicy,
+        datePattern, dateStyle, timeStyle,
+        this.factories, this.hierarchyFactories, factories);
   }
 
   @SuppressWarnings("unchecked")

gson/src/test/java/com/google/gson/GsonTest.java

@@ -17,8 +17,12 @@
 package com.google.gson;
 
 import com.google.gson.internal.Excluder;
+import com.google.gson.stream.JsonReader;
+import com.google.gson.stream.JsonWriter;
+import java.io.IOException;
 import java.lang.reflect.Field;
 import java.lang.reflect.Type;
+import java.text.DateFormat;
 import java.util.ArrayList;
 import java.util.HashMap;
 import junit.framework.TestCase;
@@ -43,12 +47,34 @@ public final class GsonTest extends TestCase {
   public void testOverridesDefaultExcluder() {
     Gson gson = new Gson(CUSTOM_EXCLUDER, CUSTOM_FIELD_NAMING_STRATEGY,
         new HashMap<Type, InstanceCreator<?>>(), true, false, true, false,
-        true, true, false, LongSerializationPolicy.DEFAULT,
+        true, true, false, LongSerializationPolicy.DEFAULT, null, DateFormat.DEFAULT,
-        new ArrayList<TypeAdapterFactory>());
+        DateFormat.DEFAULT, new ArrayList<TypeAdapterFactory>(),
+        new ArrayList<TypeAdapterFactory>(), new ArrayList<TypeAdapterFactory>());
 
     assertEquals(CUSTOM_EXCLUDER, gson.excluder());
     assertEquals(CUSTOM_FIELD_NAMING_STRATEGY, gson.fieldNamingStrategy());
     assertEquals(true, gson.serializeNulls());
     assertEquals(false, gson.htmlSafe());
   }
+
+  public void testClonedTypeAdapterFactoryListsAreIndependent() {
+    Gson original = new Gson(CUSTOM_EXCLUDER, CUSTOM_FIELD_NAMING_STRATEGY,
+        new HashMap<Type, InstanceCreator<?>>(), true, false, true, false,
+        true, true, false, LongSerializationPolicy.DEFAULT, null, DateFormat.DEFAULT,
+        DateFormat.DEFAULT, new ArrayList<TypeAdapterFactory>(),
+        new ArrayList<TypeAdapterFactory>(), new ArrayList<TypeAdapterFactory>());
+
+    Gson clone = original.newBuilder()
+        .registerTypeAdapter(Object.class, new TestTypeAdapter())
+        .create();
+
+    assertEquals(original.factories.size() + 1, clone.factories.size());
+  }
+
+  private static final class TestTypeAdapter extends TypeAdapter<Object> {
+    @Override public void write(JsonWriter out, Object value) throws IOException {
+      // Test stub.
+    }
+    @Override public Object read(JsonReader in) throws IOException { return null; }
+  }
 }