如何提高序列化类的输出效率？

Question

I am serializing a class (save the contents of the class) so that i can restore it at a later time. so i implemented built-in serialization mechanism using ObjectOutputStream class, but the output size is quite large.

but i want to make the output more efficient, or smaller in size, than that generated by the built-in serialization method. How can i make the output more efficient ?

I know that,

Java supports serialization, which is the capability of taking an object and creating a byte representation that can be used to restore the object at a later time. By using an internal serialization mechanism, most of the setup to serialize objects is taken care of. Java will transform the properties of an object into a byte stream, which can then be saved to a file or transmitted over the wire.

but I am already doing that, and i need more efficient way. is it even possible ?

Answer 1

I'd recommend against Java built-in serialization. You'd better go with a serialization library, like Jackson , or any other you like.

Now, with regard to the output size, you could compress the output by decorating the ObjectOutputStream with Java's GZIPOutputStream :

OutputStream os = ...; // this is your ObjectOutputStream
GZIPOutputStream gzipOutputStream = new GZIPOutputStream(os);

and then work with gzipOutputStream instance as if it were your original ObjectOutputStream .

Keep in mind that you should also use Java's GZIPInputStream in order to read the serialized data:

InputStream is = ...; // this is your actual InputStream
GZIPInputStream gzipInputStream = new GZIPInputStream(is);

and then work with gzipInputStream instance as if it were your original InputStream .

Answer 2

If there are things in the class you don't require to save to file use the java keyword: transient and it won't be serialized.

eg private transient Logger logger = Logger.getLogger();

Answer 3

Why don't you try compressing the output file.. I found this article : http://www.devsumo.com/technotes/2014/03/java-compressed-serialization/

GZIPOutputStream is used to compress the output.

Answer 4

You can use a custom format to serialize your class. In this case I'd use a binary format to reduce the final size, avoiding textual representations such as XML and JSON.

An example implementation could be something like the following:

public class YourClass
{
  private int field1;
  private byte field2;
  // ...

  public void encode(DataOutput stream) throws IOException
  {
     stream.writeInt(field1);
     stream.writeByte(field2);
  }

  public static YourClass decode(DataInput stream) throws IOException
  {
    YourClass ret = new YourClass();
    ret.field1 = stream.readInt();
    ret.field2 = stream.readByte();
    return ret;
  }
}

The encode method is used to write the class to a stream, the decode method reads it back from it. The decode method is static so that it can also create the class instance without relying on the user to do it manually.

Also note that if your class has class instances as member fields and you want to preserve them you have to encode these too, so it's better if you include the encode and decode methods in all classes that are serializable or are part of a serializable class.

Of course this means quite a lot of work, as all fields have to be read and written by hand, but is probably the most space efficient solution.

Answer 5

You can use JSONReader and JsonWriter and convert the object into JSON format and you can store it somewhere for future use. In this case your class not needs to implement serializable interface. and for storing the json in database requires very less space. and it become lightweight