Optimize CharSource.wrap(CharSequence) for when the CharSequence is a String

lukesandberg · cpovirk · commit d6c6d253d22b · 2017-07-13T12:32:03.000-07:00
StringReader should be faster than CharSequenceReader in this case since it can use the String.getChars() method. ------------- Created by MOE: https://github.com/google/moe MOE_MIGRATED_REVID=161843629
diff --git a/android/guava/src/com/google/common/io/CharSource.java b/android/guava/src/com/google/common/io/CharSource.java
@@ -29,6 +29,7 @@
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.Reader;
+import java.io.StringReader;
 import java.io.Writer;
 import java.nio.charset.Charset;
 import java.util.Iterator;
@@ -408,7 +409,9 @@ public static CharSource concat(CharSource... sources) {
    * @since 15.0 (since 14.0 as {@code CharStreams.asCharSource(String)})
    */
   public static CharSource wrap(CharSequence charSequence) {
-    return new CharSequenceCharSource(charSequence);
+    return charSequence instanceof String
+        ? new StringCharSource((String) charSequence)
+        : new CharSequenceCharSource(charSequence);
   }
 
   /**
@@ -454,7 +457,7 @@ private static class CharSequenceCharSource extends CharSource {
 
     private static final Splitter LINE_SPLITTER = Splitter.onPattern("\r\n|\n|\r");
 
-    private final CharSequence seq;
+    protected final CharSequence seq;
 
     protected CharSequenceCharSource(CharSequence seq) {
       this.seq = checkNotNull(seq);
@@ -535,7 +538,54 @@ public String toString() {
     }
   }
 
-  private static final class EmptyCharSource extends CharSequenceCharSource {
+  /**
+   * Subclass specialized for string instances.
+   *
+   * <p>Since Strings are immutable and built into the jdk we can optimize some operations
+   *
+   * <ul>
+   *   <li>use {@link StringReader} instead of {@link CharSequenceReader}. It is faster since it can
+   *       use {@link String#getChars(int, int, char[], int)} instead of copying characters one by
+   *       one with {@link CharSequence#charAt(int)}.
+   *   <li>use {@link Appendable#append(CharSequence)} in {@link #copyTo(Appendable)} and {@link
+   *       #copyTo(CharSink)}. We know this is correct since strings are immutable and so the length
+   *       can't change, and it is faster because many writers and appendables are optimized for
+   *       appending string instances.
+   * </ul>
+   */
+  private static class StringCharSource extends CharSequenceCharSource {
+    protected StringCharSource(String seq) {
+      super(seq);
+    }
+
+    @Override
+    public Reader openStream() {
+      return new StringReader((String) seq);
+    }
+
+    @Override
+    public long copyTo(Appendable appendable) throws IOException {
+      appendable.append(seq);
+      return seq.length();
+    }
+
+    @Override
+    public long copyTo(CharSink sink) throws IOException {
+      checkNotNull(sink);
+      Closer closer = Closer.create();
+      try {
+        Writer writer = closer.register(sink.openStream());
+        writer.write((String) seq);
+        return seq.length();
+      } catch (Throwable e) {
+        throw closer.rethrow(e);
+      } finally {
+        closer.close();
+      }
+    }
+  }
+
+  private static final class EmptyCharSource extends StringCharSource {
 
     private static final EmptyCharSource INSTANCE = new EmptyCharSource();
 
diff --git a/guava/src/com/google/common/io/CharSource.java b/guava/src/com/google/common/io/CharSource.java
@@ -31,6 +31,7 @@
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.Reader;
+import java.io.StringReader;
 import java.io.UncheckedIOException;
 import java.io.Writer;
 import java.nio.charset.Charset;
@@ -475,7 +476,9 @@ public static CharSource concat(CharSource... sources) {
    * @since 15.0 (since 14.0 as {@code CharStreams.asCharSource(String)})
    */
   public static CharSource wrap(CharSequence charSequence) {
-    return new CharSequenceCharSource(charSequence);
+    return charSequence instanceof String
+        ? new StringCharSource((String) charSequence)
+        : new CharSequenceCharSource(charSequence);
   }
 
   /**
@@ -521,7 +524,7 @@ private static class CharSequenceCharSource extends CharSource {
 
     private static final Splitter LINE_SPLITTER = Splitter.onPattern("\r\n|\n|\r");
 
-    private final CharSequence seq;
+    protected final CharSequence seq;
 
     protected CharSequenceCharSource(CharSequence seq) {
       this.seq = checkNotNull(seq);
@@ -607,7 +610,54 @@ public String toString() {
     }
   }
 
-  private static final class EmptyCharSource extends CharSequenceCharSource {
+  /**
+   * Subclass specialized for string instances.
+   *
+   * <p>Since Strings are immutable and built into the jdk we can optimize some operations
+   *
+   * <ul>
+   *   <li>use {@link StringReader} instead of {@link CharSequenceReader}. It is faster since it can
+   *       use {@link String#getChars(int, int, char[], int)} instead of copying characters one by
+   *       one with {@link CharSequence#charAt(int)}.
+   *   <li>use {@link Appendable#append(CharSequence)} in {@link #copyTo(Appendable)} and {@link
+   *       #copyTo(CharSink)}. We know this is correct since strings are immutable and so the length
+   *       can't change, and it is faster because many writers and appendables are optimized for
+   *       appending string instances.
+   * </ul>
+   */
+  private static class StringCharSource extends CharSequenceCharSource {
+    protected StringCharSource(String seq) {
+      super(seq);
+    }
+
+    @Override
+    public Reader openStream() {
+      return new StringReader((String) seq);
+    }
+
+    @Override
+    public long copyTo(Appendable appendable) throws IOException {
+      appendable.append(seq);
+      return seq.length();
+    }
+
+    @Override
+    public long copyTo(CharSink sink) throws IOException {
+      checkNotNull(sink);
+      Closer closer = Closer.create();
+      try {
+        Writer writer = closer.register(sink.openStream());
+        writer.write((String) seq);
+        return seq.length();
+      } catch (Throwable e) {
+        throw closer.rethrow(e);
+      } finally {
+        closer.close();
+      }
+    }
+  }
+
+  private static final class EmptyCharSource extends StringCharSource {
 
     private static final EmptyCharSource INSTANCE = new EmptyCharSource();
 
