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   /*
    * Copyright 2012 The Netty Project
    *
    * The Netty Project licenses this file to you 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:
    *
    *   https://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 io.netty.handler.codec.string;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.ByteBufUtil;
  import io.netty.channel.ChannelHandler.Sharable;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.ChannelPipeline;
  import io.netty.handler.codec.LineBasedFrameDecoder;
  import io.netty.handler.codec.MessageToMessageEncoder;
  import io.netty.util.internal.ObjectUtil;
  
  import java.nio.CharBuffer;
  import java.nio.charset.Charset;
  import java.util.List;
  
  /**
   * Encodes the requested {@link String} into a {@link ByteBuf}.
   * A typical setup for a text-based line protocol in a TCP/IP socket would be:
   * <pre>
   * {@link ChannelPipeline} pipeline = ...;
   *
   * // Decoders
   * pipeline.addLast("frameDecoder", new {@link LineBasedFrameDecoder}(80));
   * pipeline.addLast("stringDecoder", new {@link StringDecoder}(CharsetUtil.UTF_8));
   *
   * // Encoder
   * pipeline.addLast("stringEncoder", new {@link StringEncoder}(CharsetUtil.UTF_8));
   * </pre>
   * and then you can use a {@link String} instead of a {@link ByteBuf}
   * as a message:
   * <pre>
   * void channelRead({@link ChannelHandlerContext} ctx, {@link String} msg) {
   *     ch.write("Did you say '" + msg + "'?\n");
   * }
   * </pre>
   */
  @Sharable
  public class StringEncoder extends MessageToMessageEncoder<CharSequence> {
  
      private final Charset charset;
  
      /**
       * Creates a new instance with the current system character set.
       */
      public StringEncoder() {
          this(Charset.defaultCharset());
      }
  
      /**
       * Creates a new instance with the specified character set.
       */
      public StringEncoder(Charset charset) {
          this.charset = ObjectUtil.checkNotNull(charset, "charset");
      }
  
      @Override
      protected void encode(ChannelHandlerContext ctx, CharSequence msg, List<Object> out) throws Exception {
          if (msg.length() == 0) {
              return;
          }
  
          out.add(ByteBufUtil.encodeString(ctx.alloc(), CharBuffer.wrap(msg), charset));
      }
  }