一种特殊的Channel实现----EmbeddedChannel，它是Netty专门为改进针对ChannelHandler的单元测试而提供的。

名称	职责
writeInbound	将入站消息写到EmbeddedChannel中。如果可以通过readInbound方法从EmbeddedChannel中读取数据，则返回true
readInbound	从EmbeddedChannel中读取入站消息。任何返回东西都经过整个ChannelPipeline。如果没有任何可供读取的，则返回null
writeOutbound	将出站消息写到EmbeddedChannel中，如果现在可以通过readOutbound从EmbeddedChannel中读取到东西，则返回true
readOutbound	从EmbeddedChannel中读取出站消息。任何返回东西都经过整个ChannelPipeline。如果没有任何可供读取的，则返回null
finish	将EmbeddedChannel标记为完成，如果有可读取的入站或出站数据，则返回true。这个方法还将会调用EmbeddedChannel上的close方法

测试入站消息

public class FixedLengthFrameDecoder extends ByteToMessageDecoder {
    private final int frameLength;

    public FixedLengthFrameDecoder(int frameLength) {
        if (frameLength <= 0) {
            throw new IllegalArgumentException("frameLength must be positive integer: " + frameLength);
        }
        this.frameLength = frameLength;
    }

    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
        while (in.readableBytes() >= frameLength) {
            ByteBuf buf = in.readBytes(frameLength);
            out.add(buf);
        }
    }
}

public class FixedLengthFrameDecoderTest {
    @Test
    public void testFramesDecoded() {
        ByteBuf buf = Unpooled.buffer();
        for (int i = 0; i < 9; i++) {
            buf.writeByte(i);
        }
        ByteBuf input = buf.duplicate();
        EmbeddedChannel channel = new EmbeddedChannel(new FixedLengthFrameDecoder(3));
        Assert.assertTrue(channel.writeInbound(input.retain()));
        Assert.assertTrue(channel.finish());

        ByteBuf read = channel.readInbound();
        Assert.assertEquals(buf.readSlice(3), read);
        read.release();

        read = channel.readInbound();
        Assert.assertEquals(buf.readSlice(3), read);
        read.release();

        read = channel.readInbound();
        Assert.assertEquals(buf.readSlice(3), read);
        read.release();

        Assert.assertNull(channel.readInbound());
        buf.release();
    }

    @Test
    public void testFramesDecoded2() {
        ByteBuf buf = Unpooled.buffer();
        for (int i = 0; i < 9; i++) {
            buf.writeByte(i);
        }
        ByteBuf input = buf.duplicate();
        EmbeddedChannel channel = new EmbeddedChannel(new FixedLengthFrameDecoder(3));
        Assert.assertFalse(channel.writeInbound(input.readBytes(2)));
        Assert.assertTrue(channel.writeInbound(input.readBytes(7)));
        Assert.assertTrue(channel.finish());
        ByteBuf read = channel.readInbound();
        Assert.assertEquals(buf.readSlice(3), read);
        read.release();

        read = channel.readInbound();
        Assert.assertEquals(buf.readSlice(3), read);
        read.release();

        read = channel.readInbound();
        Assert.assertEquals(buf.readSlice(3), read);
        read.release();

        Assert.assertNull(channel.readInbound());
        buf.release();
    }
}

测试出站消息

public class AbsIntegerEncoder extends MessageToMessageEncoder<ByteBuf> {
    @Override
    protected void encode(ChannelHandlerContext channelHandlerContext, ByteBuf in, List<Object> out) throws Exception {
        while (in.readableBytes() >= 4) {
            int value = Math.abs(in.readInt());
            out.add(value);
        }
    }
}

public class AbsIntegerEncoderTest {
    @Test
    public void testEncoded() {
        ByteBuf buf = Unpooled.buffer();
        for (int i = 0; i < 10; i++) {
            buf.writeInt(i * -1);
        }
        EmbeddedChannel channel = new EmbeddedChannel(new AbsIntegerEncoder());
        Assert.assertTrue(channel.writeOutbound(buf));
        Assert.assertTrue(channel.finish());

        for (int i = 0; i < 10; i++) {
            Assert.assertEquals(Integer.valueOf(i), channel.readOutbound());
        }
        Assert.assertNull(channel.readOutbound());
    }
}

测试异常处理

public class FrameChunkDecoder extends ByteToMessageDecoder {
    private final int maxFrameSize;

    public FrameChunkDecoder(int maxFrameSize) {
        this.maxFrameSize = maxFrameSize;
    }

    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
        int readableBytes = in.readableBytes();
        if (readableBytes > maxFrameSize) {
            in.clear();
            throw new TooLongFrameException();
        }
        ByteBuf buf = in.readBytes(readableBytes);
        out.add(buf);
    }
}

public class FrameChunkDecoderTest {
    @Test
    public void testFramesDecoded() {
        ByteBuf buf = Unpooled.buffer();
        for (int i = 0; i < 9; i++) {
            buf.writeByte(i);
        }
        ByteBuf input = buf.duplicate();
        EmbeddedChannel channel = new EmbeddedChannel(new FrameChunkDecoder(3));
        Assert.assertTrue(channel.writeInbound(input.readBytes(2)));
        try {
            channel.writeInbound(input.readBytes(4));
            Assert.fail();
        } catch (TooLongFrameException e) {

        }
        Assert.assertTrue(channel.writeInbound(input.readBytes(3)));
        Assert.assertTrue(channel.finish());

        ByteBuf read = channel.readInbound();
        Assert.assertEquals(buf.readSlice(2), read);
        read.release();

        read = channel.readInbound();
        Assert.assertEquals(buf.skipBytes(4).readSlice(3), read);
        read.release();
        buf.release();
    }
}