Serialization
Serialization
• Serialization is the process of converting an
object into an intermediate format that can be
stored (e.g. in a file or transmitted across a
network) and "resurrected" later in the same
or another computer.
• We will focus on machine to machine
communication.
– Can be used for persistence
Serialization
• Convert language defined types and user defined
types to standard intermediate form
– Primitive types: e.g. integer, short, long, double, float,
boolean, char, array
– Collections: ArrayList, Map, Sets, etc.
– User defined typed: Classes and enums
• Must solve the graph traversal problem for types
that are recursive
Data Interchange Format
• “Binary”
• XML
– The standard for web applications
– We will use this in our project
• JSON
– Can be used for inter-language communication
– Becoming popular and another standard for web
applications
Data Interchange Format
• “Binary” – Java Serialization
– Only works in Java to Java Communication
– Faster
– Not human readable
– Mechanism
• For user defined types extend “Serializable”
• ObjectInputStream
• ObjectOutputStream
Data Interchange Format
• JSON
– Text Based – “Human Readable”
– Supposedly simpler than XML
– All Objects can converted to a standard form by using a combination of the
following conversions and annotations
•
•
•
•
Number (double precision)
String (double-quoted Unicode, with backslash escaping)
Boolean (true or false)
Array (an ordered sequence of values, comma-separated and enclosed in square
brackets; the values do not need to be of the same type)
• Object (an unordered collection of key:value pairs with the ':' character separating the
key and the value, comma-separated and enclosed in curly braces; the keys must be
strings and should be distinct from each other)
• null (empty
• JSON code for Java
– GSON
– FLEXJSON
– XStream
Data Interchange Format
• XML
– Text based – “Human Readable”
– XML structures tend to mimic the data structures
of the encoding language
– Implemented techniques often only work when
the source language and destination language are
the same
– Encoding/Decoding takes time
XML Software
• There are many, here are two
– JAXB – built into java
• Not as easy as it could be
• Tutorials
– From Oracle
– Small and Simple
– http://jaxb.java.net/tutorial/
– Xstream
• Very simple – especially compared to others
• The one you might want to consider
• Xstream
– Easy Example
Get the Xstream Jar
• Download the most recent jar.
– Go to here.
– Click on the most recent version (as of this time it
is 1.4.3)
– Download the main jar in the directory (currently
it is xstream-1.4.3.jar)
– Install it in your build path
Use Xstream
Declarations
•
•
•
•
import com.thoughtworks.xstream.Xstream;
import com.toughtworks.xstream.io.xml.DomDriver
private Xstream xmlStream; //variable declaration
xmlStream = new Xstream(new DomDriver());
Use Xstream
Client Side
• Client Side
– Object result = xmlStream.fromXML(connection.getInputStream());
• Used when transforming the results of a GET request to an HTTP
Server
• The connection is of type HttpURLConnection returned from
executing “openConnection()” on an object of type URL. Used to
execute the GET request and getting the results.
– xmlStream.toXML(object, connection.getOutputStream());
• Used to send an object (usually a command) to an HTTP server
Use Xstream
Server Side
• Client Side
– SomeType type =
(SomeType)xmlStream.fromXML(exchange.getRequestBody());
• The exchange is of type HttpExchange which is an abstract
representation of an instance of communication from a client to
this server.
• The “getRequestBody()” returns the information as an
InputStream
– xmlStream.toXML(responseObject, exchange.getResponseBody());
• Used to return an answer to the client
• “getResponseBody()” returns an OutputStream
Use Xstream
To And From a File or
To A String
• Object object = xmlStream.fromXML(file)
• The file is of type File
• Converts the contents of an XML file to an object
• The object is usually type cast to the appropriate type.
• xmlStream.toXML(object, fileOutputStream);
• Used to convert an object to an XML representation and writes it
to a FileOutputStream (a file)
• String string = xmlStream.toXML(object);
• Converts an object to its XML representation