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.MACOS_AND_LINUX;
   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;
@@ -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 +892,21 @@ public JsonWriter newJsonWriter(Writer writer) throws IOException {
     if (prettyPrinting) {
       jsonWriter.setIndent("  ");
     }
+    switch (newlineStyle) {
+      case CURRENT_OS:
+        jsonWriter.setNewline(System.lineSeparator());
+        break;
+      case WINDOWS:
+        jsonWriter.setNewline("\r\n");
+        break;
+      case OLD_MACOS:
+        jsonWriter.setNewline("\r");
+        break;
+      case MACOS_AND_LINUX: // intentional fallthrough
+      default:
+        jsonWriter.setNewline("\n");
+        break;
+    }
     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;
@@ -488,6 +492,17 @@ public GsonBuilder setPrettyPrinting() {
     return this;
   }
 
+  /**
+   * Configures Gson to output JSON that uses a certain kind of newline.
+   * This option only affects JSON serialization.
+   *
+   * @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 +776,7 @@ 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 +1,54 @@
+/*
+ * 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 CR+LF} ({@code 0D 0A}, {@code "\r\n"}).
+   */
+  WINDOWS,
+
+  /**
+   * Using this style will result in the same newline convention that macOS, Linux, and UNIX-like
+   * systems use. This is {@code LF} ({@code 0A}, {@code "\n"}).
+   */
+  MACOS_AND_LINUX,
+
+  /**
+   * Using this style will result in the same newline convention that classic Mac OS used.
+   * Rarely needed. This is {@code CR} ({@code 0D}, {@code "\r"}).
+   */
+  OLD_MACOS;
+}

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 +230,22 @@ public final void setIndent(String indent) {
     }
   }
 
+  /**
+   * Sets the newline string to be used in the encoded document.
+   *
+   * @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 +670,7 @@ 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

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2016 The Gson Authors
+ * Copyright (C) 2022 The Gson Authors
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -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.MACOS_AND_LINUX, 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.MACOS_AND_LINUX, 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,

gson/src/test/java/com/google/gson/functional/NewlineTest.java

@@ -0,0 +1,97 @@
+/*
+ * 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.functional;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+import com.google.gson.NewlineStyle;
+
+/**
+ * Functional tests for newline option.
+ *
+ * @author Mihai Nita
+ */
+@RunWith(JUnit4.class)
+public class NewlineTest {
+
+  private Map<String, Integer> map;
+  private static final String EXPECTED = "{<EOL>  \"abc\": 1,<EOL>  \"def\": 5<EOL>}";
+
+  @Before
+  public void setUp() {
+    map = new LinkedHashMap<>();
+    map.put("abc", 1);
+    map.put("def", 5);
+  }
+
+  @Test
+  public void testNewlineDefault() {
+    Gson gson = new GsonBuilder().setPrettyPrinting().create();
+    String json = gson.toJson(map);
+    assertEquals(EXPECTED.replace("<EOL>", "\n"), json);
+  }
+
+  @Test
+  public void testNewlineCrLf() {
+    Gson gson = new GsonBuilder()
+        .setPrettyPrinting()
+        .setNewlineStyle(NewlineStyle.WINDOWS)
+        .create();
+    String json = gson.toJson(map);
+    assertEquals(EXPECTED.replace("<EOL>", "\r\n"), json);
+  }
+
+  @Test
+  public void testNewlineLf() {
+    Gson gson = new GsonBuilder()
+        .setPrettyPrinting()
+        .setNewlineStyle(NewlineStyle.MACOS_AND_LINUX)
+        .create();
+    String json = gson.toJson(map);
+    assertEquals(EXPECTED.replace("<EOL>", "\n"), json);
+  }
+
+  @Test
+  public void testNewlineCr() {
+    Gson gson = new GsonBuilder()
+        .setPrettyPrinting()
+        .setNewlineStyle(NewlineStyle.OLD_MACOS)
+        .create();
+    String json = gson.toJson(map);
+    assertEquals(EXPECTED.replace("<EOL>", "\r"), json);
+  }
+
+  @Test
+  public void testNewlineOs() {
+    Gson gson = new GsonBuilder()
+        .setPrettyPrinting()
+        .setNewlineStyle(NewlineStyle.CURRENT_OS)
+        .create();
+    String json = gson.toJson(map);
+    assertEquals(EXPECTED.replace("<EOL>", System.lineSeparator()), json);
+  }
+
+}

gson/src/test/java/com/google/gson/internal/bind/JsonTreeWriterTest.java

@@ -256,8 +256,12 @@ public void testJsonValue() throws IOException {
    * methods of {@code JsonWriter} must be overridden.
    */
   public void testOverrides() {
-    List<String> ignoredMethods = Arrays.asList("setLenient(boolean)", "isLenient()", "setIndent(java.lang.String)",
-        "setHtmlSafe(boolean)", "isHtmlSafe()", "setSerializeNulls(boolean)", "getSerializeNulls()");
+    List<String> ignoredMethods = Arrays.asList(
+        "setLenient(boolean)", "isLenient()",
+        "setIndent(java.lang.String)",
+        "setHtmlSafe(boolean)", "isHtmlSafe()",
+        "setNewline(java.lang.String)", "getNewline()",
+        "setSerializeNulls(boolean)", "getSerializeNulls()");
     MoreAsserts.assertOverridesMethods(JsonWriter.class, JsonTreeWriter.class, ignoredMethods);
   }
 }