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The Netty project is an effort to provide an asynchronous event-driven network application framework and tools for rapid development of maintainable high performance and high scalability protocol servers and clients. In other words, Netty is a NIO client server framework which enables quick and easy development of network applications such as protocol servers and clients. It greatly simplifies and streamlines network programming such as TCP and UDP socket server.

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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:
 *
 *   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 org.jboss.netty.handler.codec.string;

import java.nio.charset.Charset;

import org.jboss.netty.buffer.ChannelBuffer;
import org.jboss.netty.channel.Channel;
import org.jboss.netty.channel.ChannelHandler.Sharable;
import org.jboss.netty.channel.ChannelHandlerContext;
import org.jboss.netty.channel.ChannelPipeline;
import org.jboss.netty.channel.MessageEvent;
import org.jboss.netty.handler.codec.frame.DelimiterBasedFrameDecoder;
import org.jboss.netty.handler.codec.frame.Delimiters;
import org.jboss.netty.handler.codec.frame.FrameDecoder;
import org.jboss.netty.handler.codec.oneone.OneToOneDecoder;

/**
 * Decodes a received {@link ChannelBuffer} into a {@link String}.  Please
 * note that this decoder must be used with a proper {@link FrameDecoder}
 * such as {@link DelimiterBasedFrameDecoder} if you are using a stream-based
 * transport such as TCP/IP.  A typical setup for a text-based line protocol
 * in a TCP/IP socket would be:
 *  * {@link ChannelPipeline} pipeline = ...;
 *
 * // Decoders
 * pipeline.addLast("frameDecoder", new {@link DelimiterBasedFrameDecoder}(80, {@link Delimiters#lineDelimiter()}));
 * pipeline.addLast("stringDecoder", new {@link StringDecoder}(CharsetUtil.UTF_8));
 *
 * // Encoder
 * pipeline.addLast("stringEncoder", new {@link StringEncoder}(CharsetUtil.UTF_8));
 * 
 * and then you can use a {@link String} instead of a {@link ChannelBuffer}
 * as a message:
 *  * void messageReceived({@link ChannelHandlerContext} ctx, {@link MessageEvent} e) {
 *     String msg = (String) e.getMessage();
 *     ch.write("Did you say '" + msg + "'?\n");
 * }
 * 
 *
 * @apiviz.landmark
 */
@Sharable
public class StringDecoder extends OneToOneDecoder {

    // TODO Use CharsetDecoder instead.
    private final Charset charset;

    /**
     * Creates a new instance with the current system character set.
     */
    public StringDecoder() {
        this(Charset.defaultCharset());
    }

    /**
     * Creates a new instance with the specified character set.
     */
    public StringDecoder(Charset charset) {
        if (charset == null) {
            throw new NullPointerException("charset");
        }
        this.charset = charset;
    }

    /**
     * @deprecated Use {@link #StringDecoder(Charset)} instead.
     */
    @Deprecated
    public StringDecoder(String charsetName) {
        this(Charset.forName(charsetName));
    }

    @Override
    protected Object decode(
            ChannelHandlerContext ctx, Channel channel, Object msg) throws Exception {
        if (!(msg instanceof ChannelBuffer)) {
            return msg;
        }
        return ((ChannelBuffer) msg).toString(charset);
    }
}