Fixes #776: Add settings for the kind of newline to use

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

@@ -69,7 +69,7 @@
  *
  * <p>You can create a Gson instance by invoking {@code new Gson()} if the default configuration
  * is all you need. You can also use {@link GsonBuilder} to build a Gson instance with various
- * configuration options such as versioning support, pretty printing, custom
+ * configuration options such as versioning support, pretty printing, custom newline, custom
  * {@link JsonSerializer}s, {@link JsonDeserializer}s, and {@link InstanceCreator}s.</p>
  *
  * <p>Here is an example of how Gson is used for a simple Class:
@@ -142,6 +142,7 @@ public final class Gson {
   static final boolean DEFAULT_JSON_NON_EXECUTABLE = false;
   static final boolean DEFAULT_LENIENT = false;
   static final boolean DEFAULT_PRETTY_PRINT = false;
+  static final NewlineStyle DEFAULT_NEWLINE_STYLE = NewlineStyle.LF;
   static final boolean DEFAULT_ESCAPE_HTML = true;
   static final boolean DEFAULT_SERIALIZE_NULLS = false;
   static final boolean DEFAULT_COMPLEX_MAP_KEYS = false;
@@ -179,6 +180,7 @@ public final class Gson {
   final boolean generateNonExecutableJson;
   final boolean htmlSafe;
   final boolean prettyPrinting;
+  final NewlineStyle newlineStyle;
   final boolean lenient;
   final boolean serializeSpecialFloatingPointValues;
   final boolean useJdkUnsafe;
@@ -199,6 +201,8 @@ public final class Gson {
    *   <li>The JSON generated by <code>toJson</code> methods is in compact representation. This
    *   means that all the unneeded white-space is removed. You can change this behavior with
    *   {@link GsonBuilder#setPrettyPrinting()}. </li>
+   *   <li>When the JSON generated contains more than one line, the kind of newline to use
+   *   can be configured with {@link GsonBuilder#setNewlineStyle(NewlineStyle)}.</li>
    *   <li>The generated JSON omits all the fields that are null. Note that nulls in arrays are
    *   kept as is since an array is an ordered list. Moreover, if a field is not null, but its
    *   generated JSON is empty, the field is kept. You can configure Gson to serialize null values
@@ -230,8 +234,8 @@ public Gson() {
     this(Excluder.DEFAULT, DEFAULT_FIELD_NAMING_STRATEGY,
         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,
-        DEFAULT_USE_JDK_UNSAFE,
+        DEFAULT_PRETTY_PRINT, DEFAULT_NEWLINE_STYLE, DEFAULT_LENIENT,
+        DEFAULT_SPECIALIZE_FLOAT_VALUES, DEFAULT_USE_JDK_UNSAFE,
         LongSerializationPolicy.DEFAULT, DEFAULT_DATE_PATTERN, DateFormat.DEFAULT, DateFormat.DEFAULT,
         Collections.<TypeAdapterFactory>emptyList(), Collections.<TypeAdapterFactory>emptyList(),
         Collections.<TypeAdapterFactory>emptyList(), DEFAULT_OBJECT_TO_NUMBER_STRATEGY, DEFAULT_NUMBER_TO_NUMBER_STRATEGY,
@@ -241,8 +245,8 @@ public Gson() {
   Gson(Excluder excluder, FieldNamingStrategy fieldNamingStrategy,
       Map<Type, InstanceCreator<?>> instanceCreators, boolean serializeNulls,
       boolean complexMapKeySerialization, boolean generateNonExecutableGson, boolean htmlSafe,
-      boolean prettyPrinting, boolean lenient, boolean serializeSpecialFloatingPointValues,
-      boolean useJdkUnsafe,
+      boolean prettyPrinting, NewlineStyle newlineStyle, boolean lenient,
+      boolean serializeSpecialFloatingPointValues, boolean useJdkUnsafe,
       LongSerializationPolicy longSerializationPolicy, String datePattern, int dateStyle,
       int timeStyle, List<TypeAdapterFactory> builderFactories,
       List<TypeAdapterFactory> builderHierarchyFactories,
@@ -258,6 +262,7 @@ public Gson() {
     this.generateNonExecutableJson = generateNonExecutableGson;
     this.htmlSafe = htmlSafe;
     this.prettyPrinting = prettyPrinting;
+    this.newlineStyle = newlineStyle;
     this.lenient = lenient;
     this.serializeSpecialFloatingPointValues = serializeSpecialFloatingPointValues;
     this.useJdkUnsafe = useJdkUnsafe;
@@ -685,7 +690,7 @@ public JsonElement toJsonTree(Object src) {
    * <pre>
    * Type typeOfSrc = new TypeToken&lt;Collection&lt;Foo&gt;&gt;(){}.getType();
    * </pre>
-   * @return Json representation of {@code src}
+   * @return JSON representation of {@code src}.
    * @since 1.4
    *
    * @see #toJsonTree(Object)
@@ -707,7 +712,7 @@ public JsonElement toJsonTree(Object src, Type typeOfSrc) {
    * {@link Writer}, use {@link #toJson(Object, Appendable)} instead.
    *
    * @param src the object for which JSON representation is to be created
-   * @return Json representation of {@code src}.
+   * @return JSON representation of {@code src}.
    *
    * @see #toJson(Object, Appendable)
    * @see #toJson(Object, Type)
@@ -732,7 +737,7 @@ public String toJson(Object src) {
    * <pre>
    * Type typeOfSrc = new TypeToken&lt;Collection&lt;Foo&gt;&gt;(){}.getType();
    * </pre>
-   * @return JSON representation of {@code src}
+   * @return JSON representation of {@code src}.
    *
    * @see #toJson(Object, Type, Appendable)
    * @see #toJson(Object)
@@ -840,7 +845,7 @@ public void toJson(Object src, Type typeOfSrc, JsonWriter writer) throws JsonIOE
    * Converts a tree of {@link JsonElement}s into its equivalent JSON representation.
    *
    * @param jsonElement root of a tree of {@link JsonElement}s
-   * @return JSON String representation of the tree
+   * @return JSON String representation of the tree.
    * @since 1.4
    */
   public String toJson(JsonElement jsonElement) {
@@ -876,6 +881,7 @@ public void toJson(JsonElement jsonElement, Appendable writer) throws JsonIOExce
    *   <li>{@link GsonBuilder#serializeNulls()}</li>
    *   <li>{@link GsonBuilder#setLenient()}</li>
    *   <li>{@link GsonBuilder#setPrettyPrinting()}</li>
+   *   <li>{@link GsonBuilder#setNewlineStyle(NewlineStyle)}</li>
    * </ul>
    */
   public JsonWriter newJsonWriter(Writer writer) throws IOException {
@@ -886,6 +892,11 @@ public JsonWriter newJsonWriter(Writer writer) throws IOException {
     if (prettyPrinting) {
       jsonWriter.setIndent("  ");
     }
+    if (newlineStyle == NewlineStyle.CURRENT_OS) {
+      jsonWriter.setNewline(System.lineSeparator());
+    } else {
+      jsonWriter.setNewline(newlineStyle.getValue());
+    }
     jsonWriter.setHtmlSafe(htmlSafe);
     jsonWriter.setLenient(lenient);
     jsonWriter.setSerializeNulls(serializeNulls);

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

@@ -24,6 +24,7 @@
 import static com.google.gson.Gson.DEFAULT_NUMBER_TO_NUMBER_STRATEGY;
 import static com.google.gson.Gson.DEFAULT_OBJECT_TO_NUMBER_STRATEGY;
 import static com.google.gson.Gson.DEFAULT_PRETTY_PRINT;
+import static com.google.gson.Gson.DEFAULT_NEWLINE_STYLE;
 import static com.google.gson.Gson.DEFAULT_SERIALIZE_NULLS;
 import static com.google.gson.Gson.DEFAULT_SPECIALIZE_FLOAT_VALUES;
 import static com.google.gson.Gson.DEFAULT_USE_JDK_UNSAFE;
@@ -67,6 +68,7 @@
  *     .setDateFormat(DateFormat.LONG)
  *     .setFieldNamingPolicy(FieldNamingPolicy.UPPER_CAMEL_CASE)
  *     .setPrettyPrinting()
+ *     .setNewlineStyle(NewlineStyle.CURRENT_OS)
  *     .setVersion(1.0)
  *     .create();
  * </pre>
@@ -99,6 +101,7 @@ public final class GsonBuilder {
   private boolean serializeSpecialFloatingPointValues = DEFAULT_SPECIALIZE_FLOAT_VALUES;
   private boolean escapeHtmlChars = DEFAULT_ESCAPE_HTML;
   private boolean prettyPrinting = DEFAULT_PRETTY_PRINT;
+  private NewlineStyle newlineStyle = DEFAULT_NEWLINE_STYLE;
   private boolean generateNonExecutableJson = DEFAULT_JSON_NON_EXECUTABLE;
   private boolean lenient = DEFAULT_LENIENT;
   private boolean useJdkUnsafe = DEFAULT_USE_JDK_UNSAFE;
@@ -130,6 +133,7 @@ public GsonBuilder() {
     this.generateNonExecutableJson = gson.generateNonExecutableJson;
     this.escapeHtmlChars = gson.htmlSafe;
     this.prettyPrinting = gson.prettyPrinting;
+    this.newlineStyle = gson.newlineStyle;
     this.lenient = gson.lenient;
     this.serializeSpecialFloatingPointValues = gson.serializeSpecialFloatingPointValues;
     this.longSerializationPolicy = gson.longSerializationPolicy;
@@ -478,8 +482,8 @@ public GsonBuilder addDeserializationExclusionStrategy(ExclusionStrategy strateg
   }
 
   /**
-   * Configures Gson to output Json that fits in a page for pretty printing. This option only
-   * affects Json serialization.
+   * Configures Gson to output JSON that fits in a page for pretty printing. This option only
+   * affects JSON serialization.
    *
    * @return a reference to this {@code GsonBuilder} object to fulfill the "Builder" pattern
    */
@@ -488,6 +492,19 @@ public GsonBuilder setPrettyPrinting() {
     return this;
   }
 
+  /**
+   * Configures Gson to output JSON that uses a certain kind of newline.
+   * This option only affects JSON serialization.
+   *
+   * <p>Has no effect if the serialized format is a single line.</p>
+   *
+   * @return a reference to this {@code GsonBuilder} object to fulfill the "Builder" pattern
+   */
+  public GsonBuilder setNewlineStyle(NewlineStyle newlineStyle) {
+    this.newlineStyle = Objects.requireNonNull(newlineStyle);
+    return this;
+  }
+
   /**
    * Configures Gson to allow JSON data which does not strictly comply with the JSON specification.
    *
@@ -761,7 +778,7 @@ public Gson create() {
 
     return new Gson(excluder, fieldNamingPolicy, new HashMap<>(instanceCreators),
         serializeNulls, complexMapKeySerialization,
-        generateNonExecutableJson, escapeHtmlChars, prettyPrinting, lenient,
+        generateNonExecutableJson, escapeHtmlChars, prettyPrinting, newlineStyle, lenient,
         serializeSpecialFloatingPointValues, useJdkUnsafe, longSerializationPolicy,
         datePattern, dateStyle, timeStyle, new ArrayList<>(this.factories),
         new ArrayList<>(this.hierarchyFactories), factories,

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

@@ -0,0 +1,69 @@
+/*
+ * Copyright (C) 2022 Google Inc.
+ *
+ * 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.google.gson;
+
+/**
+ * An enumeration that defines the kind of newline to use for serialization.
+ *
+ * @see <a href="https://en.wikipedia.org/wiki/Newline">Wikipedia Newline article</a>
+ *
+ * @since $next-version$
+ */
+public enum NewlineStyle {
+  /**
+   * Using this style will result in the same kind of newline that the current environment uses.
+   *
+   * <p>So it will produce {@code "\r\n"} when running on Windows, and {@code "\n"} when running
+   * on macOS &amp; Linux.</p>
+   *
+   * @see System#lineSeparator()
+   */
+  CURRENT_OS(""),
+
+  /**
+   * Using this style will result in the same newline convention that Windows uses
+   * and MS-DOS used. This is {@code "\r\n"} ({@code U+000D U+000A}).
+   */
+  CRLF("\r\n"),
+
+  /**
+   * Using this style will result in the same newline convention that macOS, Linux, and UNIX-like
+   * systems use. This is {@code "\n"} ({@code U+000A}).
+   */
+  LF("\n"),
+
+  /**
+   * Using this style will result in the same newline convention that classic Mac OS used.
+   * Rarely needed. This is {@code "\r"} ({@code U+000D}).
+   */
+  CR("\r");
+
+  private final String value;
+
+  private NewlineStyle(String value) {
+    this.value = value;
+  }
+
+  /**
+   * The string value that will be used as newline, not the name of the constant.
+   *
+   * @return the string value of the enum constant.
+  */
+  public String getValue() {
+    return this.value;
+  }
+}

gson/src/main/java/com/google/gson/stream/JsonWriter.java

@@ -185,6 +185,11 @@ public class JsonWriter implements Closeable, Flushable {
    */
   private String indent;
 
+  /**
+   * A string to be used as newline.
+   */
+  private String newline = "\n";
+
   /**
    * The name/value separator; either ":" or ": ".
    */
@@ -225,6 +230,24 @@ public final void setIndent(String indent) {
     }
   }
 
+  /**
+   * Sets the newline string to be used in the encoded document.
+   *
+   * <p>Has no effect if the serialized format is a single line.</p>
+   *
+   * @param newline the string that will be used for newline.
+   */
+  public final void setNewline(String newline) {
+    this.newline = Objects.requireNonNull(newline, "newline == null");
+  }
+
+  /**
+   * Returns the newline string used by this writer.
+   */
+  public final String getNewline() {
+    return newline;
+  }
+
   /**
    * Configure this writer to relax its syntax rules. By default, this writer
    * only emits well-formed JSON as specified by <a
@@ -649,7 +672,7 @@ private void newline() throws IOException {
       return;
     }
 
-    out.write('\n');
+    out.write(newline);
     for (int i = 1, size = stackSize; i < size; i++) {
       out.write(indent);
     }

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

@@ -57,7 +57,7 @@ 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, true, LongSerializationPolicy.DEFAULT, null, DateFormat.DEFAULT,
+        true, NewlineStyle.LF, true, false, true, LongSerializationPolicy.DEFAULT, null, DateFormat.DEFAULT,
         DateFormat.DEFAULT, new ArrayList<TypeAdapterFactory>(),
         new ArrayList<TypeAdapterFactory>(), new ArrayList<TypeAdapterFactory>(),
         CUSTOM_OBJECT_TO_NUMBER_STRATEGY, CUSTOM_NUMBER_TO_NUMBER_STRATEGY,
@@ -72,7 +72,7 @@ public void testOverridesDefaultExcluder() {
   public void testClonedTypeAdapterFactoryListsAreIndependent() {
     Gson original = new Gson(CUSTOM_EXCLUDER, CUSTOM_FIELD_NAMING_STRATEGY,
         new HashMap<Type, InstanceCreator<?>>(), true, false, true, false,
-        true, true, false, true, LongSerializationPolicy.DEFAULT, null, DateFormat.DEFAULT,
+        true, NewlineStyle.LF, true, false, true, LongSerializationPolicy.DEFAULT, null, DateFormat.DEFAULT,
         DateFormat.DEFAULT, new ArrayList<TypeAdapterFactory>(),
         new ArrayList<TypeAdapterFactory>(), new ArrayList<TypeAdapterFactory>(),
         CUSTOM_OBJECT_TO_NUMBER_STRATEGY, CUSTOM_NUMBER_TO_NUMBER_STRATEGY,