refactor: replace local StringWriter with StringBuilder (#2852)

Author: MukjepScarlet

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

@@ -45,7 +45,6 @@
 import java.io.IOException;
 import java.io.Reader;
 import java.io.StringReader;
-import java.io.StringWriter;
 import java.io.Writer;
 import java.lang.reflect.Type;
 import java.math.BigDecimal;
@@ -844,7 +843,7 @@ public String toJson(Object src) {
    * @see #toJson(Object)
    */
   public String toJson(Object src, Type typeOfSrc) {
-    StringWriter writer = new StringWriter();
+    StringBuilder writer = new StringBuilder();
     toJson(src, typeOfSrc, writer);
     return writer.toString();
   }
@@ -962,7 +961,7 @@ public void toJson(Object src, Type typeOfSrc, JsonWriter writer) throws JsonIOE
    * @since 1.4
    */
   public String toJson(JsonElement jsonElement) {
-    StringWriter writer = new StringWriter();
+    StringBuilder writer = new StringBuilder();
     toJson(jsonElement, writer);
     return writer.toString();
   }

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

@@ -21,7 +21,6 @@
 import com.google.gson.stream.JsonWriter;
 import java.io.IOException;
 import java.io.Reader;
-import java.io.StringWriter;
 import java.math.BigDecimal;
 import java.math.BigInteger;
 
@@ -422,13 +421,13 @@ public short getAsShort() {
   @Override
   public String toString() {
     try {
-      StringWriter stringWriter = new StringWriter();
-      JsonWriter jsonWriter = new JsonWriter(stringWriter);
+      StringBuilder stringBuilder = new StringBuilder();
+      JsonWriter jsonWriter = new JsonWriter(Streams.writerForAppendable(stringBuilder));
       // Make writer lenient because toString() must not fail, even if for example JsonPrimitive
       // contains NaN
       jsonWriter.setStrictness(Strictness.LENIENT);
       Streams.write(this, jsonWriter);
-      return stringWriter.toString();
+      return stringBuilder.toString();
     } catch (IOException e) {
       throw new AssertionError(e);
     }

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

@@ -16,6 +16,7 @@
 
 package com.google.gson;
 
+import com.google.gson.internal.Streams;
 import com.google.gson.internal.bind.JsonTreeReader;
 import com.google.gson.internal.bind.JsonTreeWriter;
 import com.google.gson.stream.JsonReader;
@@ -24,7 +25,6 @@
 import java.io.IOException;
 import java.io.Reader;
 import java.io.StringReader;
-import java.io.StringWriter;
 import java.io.Writer;
 
 /**
@@ -157,13 +157,13 @@ public final void toJson(Writer out, T value) throws IOException {
    * @since 2.2
    */
   public final String toJson(T value) {
-    StringWriter stringWriter = new StringWriter();
+    StringBuilder stringBuilder = new StringBuilder();
     try {
-      toJson(stringWriter, value);
+      toJson(Streams.writerForAppendable(stringBuilder), value);
     } catch (IOException e) {
       throw new JsonIOException(e);
     }
-    return stringWriter.toString();
+    return stringBuilder.toString();
   }
 
   /**