code: /*
   * Copyright 2014 Google Inc. All rights reserved.
   *
   * 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.flatbuffers;
  
  import java.nio.ByteBuffer;
  import java.nio.CharBuffer;
  import java.nio.charset.CharacterCodingException;
  import java.nio.charset.CharsetDecoder;
  import java.nio.charset.CharsetEncoder;
  import java.nio.charset.CoderResult;
  import java.nio.charset.StandardCharsets;
  
  /**
   * This class implements the Utf8 API using the Java Utf8 encoder. Use
   * Utf8.setDefault(new Utf8Old()); to use it.
   */
  public class Utf8Old extends Utf8 {
  
    private static class Cache {
      final CharsetEncoder encoder;
      final CharsetDecoder decoder;
      CharSequence lastInput = null;
      ByteBuffer lastOutput = null;
  
      Cache() {
        encoder = StandardCharsets.UTF_8.newEncoder();
        decoder = StandardCharsets.UTF_8.newDecoder();
      }
    }
  
    private static final ThreadLocal<Cache> CACHE =
        ThreadLocal.withInitial(() -> new Cache());
  
    // Play some games so that the old encoder doesn't pay twice for computing
    // the length of the encoded string.
  
    @Override
    public int encodedLength(CharSequence in) {
      final Cache cache = CACHE.get();
      int estimated = (int) (in.length() * cache.encoder.maxBytesPerChar());
      if (cache.lastOutput == null || cache.lastOutput.capacity() < estimated) {
        cache.lastOutput = ByteBuffer.allocate(Math.max(128, estimated));
      }
      cache.lastOutput.clear();
      cache.lastInput = in;
      CharBuffer wrap = (in instanceof CharBuffer) ?
                            (CharBuffer) in : CharBuffer.wrap(in);
      CoderResult result = cache.encoder.encode(wrap, cache.lastOutput, true);
      if (result.isError()) {
        try {
          result.throwException();
        } catch (CharacterCodingException e) {
          throw new IllegalArgumentException("bad character encoding", e);
        }
      }
      cache.lastOutput.flip();
      return cache.lastOutput.remaining();
    }
  
    @Override
    public void encodeUtf8(CharSequence in, ByteBuffer out) {
      final Cache cache = CACHE.get();
      if (cache.lastInput != in) {
        // Update the lastOutput to match our input, although flatbuffer should
        // never take this branch.
        encodedLength(in);
      }
      out.put(cache.lastOutput);
    }
  
    @Override
    public String decodeUtf8(ByteBuffer buffer, int offset, int length) {
      CharsetDecoder decoder = CACHE.get().decoder;
      decoder.reset();
      buffer = buffer.duplicate();
      buffer.position(offset);
      buffer.limit(offset + length);
      try {
        CharBuffer result = decoder.decode(buffer);
        return result.toString();
      } catch (CharacterCodingException e) {
        throw new IllegalArgumentException("Bad encoding", e);
      }
    }
  }
  