Object Serialization

From Rosetta Code

Jump to: navigation, search

Programming Task
This is a programming task. It lays out a problem which Rosetta Code users are encouraged to solve, using languages they know.

Code examples should be formatted along the lines of one of the existing prototypes.

Create a set of data types based upon inheritance. Each data type or class should have a print command that displays the contents of an instance of that class to standard output. Create instances of each class in your inheritance hierarchy and display them to standard output. Write each of the objects to a file named objects.dat in binary form using serialization or marshalling. Read the file objects.dat and print the contents of each serialized object.

Contents

[edit] Ada

This file contains the package specification containing the public definitions of the inheritance tree rooted at the type Message. Each type in the inheritance tree has its own print procedure. 

with Ada.Calendar; use Ada.Calendar;
 
package Messages is
   type Message is tagged record
      Timestamp : Time;
   end record;
 
   procedure Print(Item : Message);
   procedure Display(Item : Message'Class);
 
   type Sensor_Message is new Message with record
      Sensor_Id : Integer;
      Reading : Float;
   end record;
 
   procedure Print(Item : Sensor_Message);
 
   type Control_Message is new Message with record
      Actuator_Id : Integer;
      Command     : Float;
   end record;
 
   procedure Print(Item : Control_Message);
 
end Messages;

The next portion contains the implementation of the procedures defined in the package specification. 

with Ada.Text_Io; use Ada.Text_Io;
with Ada.Integer_Text_Io; use Ada.Integer_Text_Io;
with Ada.Float_Text_IO; use Ada.Float_Text_IO;
 
package body Messages is
 
   -----------
   -- Print --
   -----------
 
   procedure Print (Item : Message) is
      The_Year : Year_Number;
      The_Month : Month_Number;
      The_Day   : Day_Number;
      Seconds   : Day_Duration;
   begin
      Split(Date => Item.Timestamp, Year => The_Year,
         Month => The_Month, Day => The_Day, Seconds => Seconds);
 
      Put("Time Stamp:");
      Put(Item => The_Year, Width => 4);
      Put("-");
      Put(Item => The_Month, Width => 1);
      Put("-");
      Put(Item => The_Day, Width => 1);
      New_Line;
   end Print; 
 
   -----------
   -- Print --
   -----------
 
   procedure Print (Item : Sensor_Message) is
   begin
      Print(Message(Item));
      Put("Sensor Id: ");
      Put(Item => Item.Sensor_Id, Width => 1);
      New_Line;
      Put("Reading: ");
      Put(Item => Item.Reading, Fore => 1, Aft => 4, Exp => 0);
      New_Line;
   end Print;
 
   -----------
   -- Print --
   -----------
 
   procedure Print (Item : Control_Message) is
   begin
      Print(Message(Item));
      Put("Actuator Id: ");
      Put(Item => Item.Actuator_Id, Width => 1);
      New_Line;
      Put("Command: ");
      Put(Item => Item.Command, Fore => 1, Aft => 4, Exp => 0);
      New_Line;
   end Print; 
 
   -------------
   ---Display --
   -------------
 
   procedure Display(Item : Message'Class) is
   begin
      Print(Item);
   end Display;
 
end Messages;

The final section of code creates objects of the three message types and performs the printing, writing, and reading. The Ada attributes 'Class'Output serialize the object and write it to the specified stream. The 'Class'Input attributes call a function automatically provided by the compiler which reads from the specified stream file and returns the object read. The Display procedure takes an object in the inheritance tree rooted at Message and dispatches the correct print procedure. 

with Messages; use Messages;
with Ada.Streams.Stream_Io; use Ada.Streams.Stream_Io;
with Ada.Calendar; use Ada.Calendar;
with Ada.Text_Io;
 
procedure Streams_Example is
   S1 : Sensor_Message;
   M1 : Message;
   C1 : Control_Message;
   Now : Time := Clock;
   The_File : Ada.Streams.Stream_Io.File_Type;
   The_Stream : Ada.Streams.Stream_IO.Stream_Access;
begin
   S1 := (Now, 1234, 0.025);
   M1.Timestamp := Now;
   C1 := (Now, 15, 0.334);
   Display(S1);
   Display(M1);
   Display(C1);
   begin
      Open(File => The_File, Mode => Out_File,
         Name => "Messages.dat");
   exception
      when others =>
         Create(File => The_File, Name => "Messages.dat");
   end;
   The_Stream := Stream(The_File);
   Sensor_Message'Class'Output(The_Stream, S1);
   Message'Class'Output(The_Stream, M1);
   Control_Message'Class'Output(The_Stream, C1);
   Close(The_File);
   Open(File => The_File, Mode => In_File,
      Name => "Messages.dat");
   The_Stream := Stream(The_File);
   Ada.Text_Io.New_Line(2);
   while not End_Of_File(The_File) loop
      Display(Message'Class'Input(The_Stream));
   end loop;
   Close(The_File);
end Streams_Example;

Output results: 

Time Stamp:2007-3-9
Sensor Id: 1234
Reading: 0.0250
Time Stamp:2007-3-9
Time Stamp:2007-3-9
Actuator Id: 15
Command: 0.3340
 

Time Stamp:2007-3-9
Sensor Id: 1234
Reading: 0.0250
Time Stamp:2007-3-9
Time Stamp:2007-3-9
Actuator Id: 15
Command: 0.3340

[edit] ALGOL 68

Serialization in ALGOL 68 is achieved through a method called rowing. 

MODE ENTITY = STRUCT([6]CHAR name, INT creation);
FORMAT entity repr = $"Name: "g", Created:"g$;
MODE PERSON = STRUCT(ENTITY entity, STRING email);
FORMAT person repr = $f(entity repr)", Email: "g$;
 
PERSON instance1 := PERSON(ENTITY("Cletus", 20080808), "test+1@localhost.localdomain");
print((name OF entity OF instance1, new line));
 
ENTITY instance2 := ENTITY("Entity",20111111);
print((name OF instance2, new line));
 
FILE target;
INT errno := open(target, "rows.dat", stand back channel); # open file #
 
#  Serialize #
put(target,(instance1, new line, instance2, new line));
printf(($"Serialized..."l$));

close(target); # flush file stream #
errno := open(target, "rows.dat", stand back channel); # load again #

# Unserialize #
PERSON i1;
ENTITY i2;
get(target,(i1, new line, i2, new line));
printf(($"Unserialized..."l$));
 
printf((person repr, i1, $l$));
printf((entity repr, i2, $l$))

FLEXible length arrays (including STRINGs), and tagged-UNION types are problematic as the lengths of the arrays, and the tag of the union is not stored. Sometimes a FORMAT can be manually created to handle these lengths and tags. Also note that ALGOL 68 is strongly types and the type (mode) of the objectis note stored, but compiled into the code itself.

Output:
Cletus
Entity
Serialized...
Unserialized...
Name: Cletus, Created:  +20080808, Email: test+1@localhost.localdomain
Name: Entity, Created:  +20111111

[edit] E

(Inheritance, while supported by various features and patterns, is not a preferred design component in E; nor are simple record data structures.) 

def makeEvent(time :int) {
    return def event {
        to __printOn(out) { out.print(`@@$time`) }
        to __optUncall() { return [makeEvent, "run", [time]] }
        to getTime() { return time }
    }
}

def makeArrival(time :int, what :any, position :int) {
    return def arrival extends makeEvent(time) {
        to __printOn(out) { 
            out.print(`$what to $position $super`)
        }
        to __optUncall() { 
            return [makeArrival, "run", [time, what, position]]
        }
      
        to getWhat() { return what }
        to getPosition() { return position }
    }
}

After defining our data types, we can prepare to serialize them. 

def surgeon := <import:org.erights.e.elib.serial.makeSurgeon>().diverge()
surgeon.addExit(makeEvent, "makeEvent")
surgeon.addExit(makeArrival, "makeArrival")

The 'exits' of the surgeon (so called because it cuts and joins object subgraphs) specify the points at which serialization should stop, instead replacing references to the objects with the specified names. On unserialization, the names are looked up and replaced with the corresponding objects. (The surgeon provides default exits for such things as false, true, null, and the list constructor.) 

def objs := [makeEvent(timer.now()),
             makeArrival(timer.now(), "Smith", 7)]

stdout.println(objs)
<file:objects.dat>.setBytes(surgeon.serialize(objs))
stdout.println(surgeon.unserialize(<file:objects.dat>.getBytes()))

[edit] Java

import java.io.*;
 
// classes must implement java.io.Serializable in order to be serializable
class Entity implements Serializable {
    // it is recommended to hard-code serialVersionUID so changes to class
    // will not invalidate previously serialized objects
    static final long serialVersionUID = 3504465751164822571L;
    String name = "Entity";
    public String toString() { return name; }
}
 
class Person extends Entity implements Serializable {
    static final long serialVersionUID = -9170445713373959735L;
    Person() { name = "Cletus"; }
}
 
public class SerializationTest {
    public static void main(String[] args) {
        Person instance1 = new Person();
        System.out.println(instance1);
 
        Entity instance2 = new Entity();
        System.out.println(instance2);
 
        // Serialize
        try {
            ObjectOutput out = new ObjectOutputStream(new FileOutputStream("objects.dat")); // open ObjectOutputStream
 
            out.writeObject(instance1); // serialize "instance1" and "instance2" to "out"
            out.writeObject(instance2);
            out.close();
            System.out.println("Serialized...");
        } catch (IOException e) {
            System.err.println("Something screwed up while serializing");
            e.printStackTrace();
            System.exit(1);
        }
 
        // Deserialize
        try {
            ObjectInput in = new ObjectInputStream(new FileInputStream("objects.dat")); // open ObjectInputStream
 
            Object readObject1 = in.readObject(); // read two objects from "in"
            Object readObject2 = in.readObject(); // you may want to cast them to the appropriate types
            in.close();
            System.out.println("Deserialized...");
 
            System.out.println(readObject1);
            System.out.println(readObject2);
        } catch (IOException e) {
            System.err.println("Something screwed up while deserializing");
            e.printStackTrace();
            System.exit(1);
        } catch (ClassNotFoundException e) {
            System.err.println("Unknown class for deserialized object");
            e.printStackTrace();
            System.exit(1);
        }
    }
}

[edit] OCaml

Objects which contain methods are difficult to serialize because it will want to serialize those methods too, but functions usually cannot be serialized. Instead, here we perform the task on non-object datatypes, with an outside function to print them. 

type entity = { name : string }
 
let create_entity () = { name = "Entity" }
let print_entity x = print_endline x.name
let create_person () = { name = "Cletus" }
 
let instance1 = create_person ()
let instance2 = create_entity ()
 
(* Serialize *)
let out_chan = open_out_bin "objects.dat";;
output_value out_chan instance1;;
output_value out_chan instance2;;
close_out out_chan;;
 
(* Deserialize *)
let in_chan = open_in_bin "objects.dat";;
let result1 : entity = input_value in_chan;;
let result2 : entity = input_value in_chan;;
close_in in_chan;;
 
print_entity result1;;
print_entity result2;;

[edit] Perl

Library: Storable 

{
    package Greeting;
    sub new {
        my $v = 'Hello world!'; 
        bless \$v, shift;
    };
    sub stringify {
        ${shift()};
    };
};
{
    package Son::of::Greeting;
    use base qw(Greeting); # inherit methods
    sub new { # overwrite method of super class
        my $v = 'Hello world from Junior!'; 
        bless \$v, shift;
    };
};
{
    use Storable qw(store retrieve);
    package main;
    my $g1 = Greeting->new;
    my $s1 = Son::of::Greeting->new;
    print $g1->stringify;
    print $s1->stringify;
 
    store $g1, 'objects.dat';
    my $g2 = retrieve 'objects.dat';
 
    store $s1, 'objects.dat';
    my $s2 = retrieve 'objects.dat';
 
    print $g2->stringify;
    print $s2->stringify;
};

[edit] PHP

Serialization in PHP is straightforward. The built-in function serialize() handles it in a single statement. 

$myObj = new Object();
$serializedObj = serialize($myObj);

In order to un-serialize the object, use the unserialize() function. Note that the class of object must be defined in the script where un-serialization takes place, or the class' methods will be lost.

[edit] Python

# Object Serialization in Python
# serialization in python is accomplished via the Pickle module.
# Alternatively, one can use the cPickle module if speed is the key,
# everything else in this example remains the same.
 
import pickle
 
class Entity:
	def __init__(self):
		self.name = "Entity"
	def printName(self):
		print self.name
 
class Person(Entity): #OldMan inherits from Entity
	def __init__(self): #override constructor
		self.name = "Cletus" 
 
instance1 = Person()
instance1.printName()
 
instance2 = Entity()
instance2.printName()
 
target = file("objects.dat", "w") # open file
 
#  Serialize
pickle.dump((instance1, instance2), target) # serialize `instance1` and `instance2`to `target`
target.close() # flush file stream
print "Serialized..."
 
# Unserialize
target = file("objects.dat") # load again
i1, i2 = pickle.load(target)
print "Unserialized..."
 
i1.printName()
i2.printName()

[edit] Ruby

class Being
  def initialize(specialty=nil)
    @specialty=specialty
  end
  def to_s
    "(object_id = #{object_id})\n"+"(#{self.class}):".ljust(12)+to_s4Being+(@specialty ? "\n"+" "*12+@specialty : "")
  end
  def to_s4Being
    "I am a collection of cooperative molecules with a talent for self-preservation."
  end
end
 
class Earthling < Being
  def to_s4Being
    "I originate from a blue planet.\n"+" "*12+to_s4Earthling
  end
end
 
class Mammal < Earthling
  def initialize(type)
    @type=type
  end
  def to_s4Earthling
    "I am champion in taking care of my offspring and eating everything I can find, except mammals of type #{@type}."
  end
end
 
class Fish < Earthling
  def initialize(iq)
    @iq=(iq>1 ? :instrustableValue : iq)
  end
  def to_s4Earthling
    "Although I think I can think, I can't resist biting in hooks."
  end
end
 
class Moonling < Being
  def to_s4Being
    "My name is Janneke Maan, and apparently some Earthlings will pay me a visit."
  end
end
 
diverseCollection=[]
diverseCollection << (marsian=Being.new("I come from Mars and like playing hide and seek."))
diverseCollection << (me=Mammal.new(:human))
diverseCollection << (nemo=Fish.new(0.99))
diverseCollection << (jannakeMaan=Moonling.new)
 
puts "BEGIN ORIGINAL DIVERSE COLLECTION"
diverseCollection.each do |being|
  puts "",being.to_s
end
puts "END ORIGINAL DIVERSE COLLECTION"
puts "\n"+"*"*50+"\n\n"
 
#Marshal the diverse Array of beings
File.open('diverseCollection.bin','w') do |fo|
  fo << Marshal.dump(diverseCollection)
end
 
#load the Array of diverse beings
sameDiverseCollection=Marshal.load(File.read('diverseCollection.bin'))
 
puts "BEGIN LOADED DIVERSE COLLECTION"
puts(
     sameDiverseCollection.collect do |being|
       being.to_s
     end.join("\n\n")
     )
puts "END LOADED DIVERSE COLLECTION"
Retrieved from "http://www.rosettacode.org/wiki/Object_Serialization"
Personal tools