I generally avoid having the class know how to serialize itself, for a couple of reasons. First, if you want to (de)serialize to/from a different format, you now need to pollute the model with that extra logic. If the model is accessed via an interface, then you also pollute the contract.
public class Image
{
public void toJPG(String filePath) { ... }
public Image fromJPG(String filePath) { ... }
}
But what if you want to serialize it to/from a PNG, and GIF? Now the class becomes
public class Image
{
public void toJPG(String filePath) { ... }
public Image fromJPG(String filePath) { ... }
public void toPNG(String filePath) { ... }
public Image fromPNG(String filePath) { ... }
public void toGIF(String filePath) { ... }
public Image fromGIF(String filePath) { ... }
}
Instead, I typically like to use a pattern similar to the following:
public interface ImageSerializer
{
void serialize(Image src, Stream outputStream);
Image deserialize(Stream inputStream);
}
public class JPGImageSerializer : ImageSerializer
{
public void serialize(Image src, Stream outputStream) { ... }
public Image deserialize(Stream inputStream) { ... }
}
public class PNGImageSerializer : ImageSerializer
{
public void serialize(Image src, Stream outputStream) { ... }
public Image deserialize(Stream inputStream) { ... }
}
public class GIFImageSerializer : ImageSerializer
{
public void serialize(Image src, Stream outputStream) { ... }
public Image deserialize(Stream inputStream) { ... }
}
Now, at this point, one of the caveats with this design is that the serializers need to know the identity of the object it's serializing. Some would say that this is bad design, as the implementation leaks outside of the class. The risk/reward of this is really up to you, but you could slightly tweak the classes to do something like
public class Image
{
public void serializeTo(ImageSerializer serializer, Stream outputStream)
{
serializer.serialize(this.pixelData, outputStream);
}
public void deserializeFrom(ImageSerializer serializer, Stream inputStream)
{
this.pixelData = serializer.deserialize(inputStream);
}
}
This is more of a general example, as images usually have metadata that goes along with it; things like compression level, colorspace, etc. which may complicate the process.
