serialization in java

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Serialization in Java
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. Serialization in Java  Java Serialization is
the mechanism in which the state of an object is
converted to a byte stream so that the byte
stream can be reverted back into the copy of the
object written into a file or stored into a
database. It includes information about objects
type and types of data stored in the object. Once
the object is serialized into written into a
file, it can be read from the file and
deserialized which means that the type of
information and bytes that represent the object
can be utilized to create object in the memory
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Lets understand streams in computer systems
before proceeding further. A stream is simply a
sequence of data elements. Data in the form of
streams is generated from a source and consumed
at a destination. Different data streams in the
computer systems are 1. Byte Stream  It is a
low level I/O operation and does not have any
encoding scheme. The Java program should have a
buffered approach for I/O operations to process
Byte Stream.
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2. Data Stream  Data Stream allows to read-write
primitive data types and used to perform binary
I/O operations on primitive data types. I/O
operations can be performed for byte, char,
boolean, short, int, long, float, double and
strings efficiently and conveniently. 3. Character
Stream  The character stream can easily
translate to and from local character set unlike
byte stream. It has a proper encoding scheme such
as UNICODE, ASCII and is composed of streams of
characters. In Java UNICODE system is followed to
store characters as character stream.
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4. Object Stream  Object stream can covert the
state of an object into a byte stream so that it
can be stored into a database, file or
transported to any location (Serialization) and
used at a later point of time for retrieving the
stored values and restoring the old state of the
object. The process of serialization is instance
independent which means an object can be
serialized on one platform and deserialized on an
entirely different platform. To make an object
serializable we use java.io.Serializable
interface.
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Both the classes Object Input Stream and Object
Output Stream are high-level streams and extend
java.io.InputStream and java.io.OutputStream. The
ObjectOutputStream has many write methods for
writing different data types. One of the popular
write method in ObjectOutputStream is This
method serializes an object and converts it into
stream of bytes and sends it to output stream.
The popular method to read an object in
ObjectInputStream is
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This method reads the stream of bytes and
converts it back to an object which is called
deserialization. Java Serialization API contains
methods for serialization and deserialization. A
class must implement java.io.Serializable
interface to serialize an object. Lets
understand the concept of Serialization with the
help of an example.
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package com.serializationimport java.io.BufferedInputStreamimport java.io.BufferedOutputStreamimport java.io.FileInputStreamimport java.io.FileOutputStreamimport java.io.IOExceptionimport java.io.ObjectInputStreamimport java.io.ObjectOutputStreampublic class SerializationDemoExample / The method will read data from file for deSerialization. _at_param file _at_return _at_throws IOException _at_throws ClassNotFoundException/public static Object deSerialize(String file) throws IOException, ClassNotFoundException FileInputStream fileInputStream new FileInputStream(file)BufferedInputStream bufferedInputStream new BufferedInputStream(fileInputStream)ObjectInputStream objectInputStream new ObjectInputStream(bufferedInputStream)Object object objectInputStream.readObject()objectInputStream.close()return object/ The method writes data to file for Serialization. _at_param file _at_param object _at_throws IOException/public static void serialize(String file, Object object) throws IOException FileOutputStream fileOutputStream new FileOutputStream(file)BufferedOutputStream bufferedOutputStream new BufferedOutputStream(fileOutputStream)ObjectOutputStream objectOutputStream new ObjectOutputStream(bufferedOutputStream)objectOutputStream.writeObject(object)objectOutputStream.close()
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This class defines two methods deserialize and
serialize. In the deSerialize method the path and
file name of the file is called. This file
contains the byte stream of objects state. Once
the file name and path are called the deSerialize
method returns the object that can be down casted
to the corresponding serialized class object.
During deSerialize method we open the file in
read mode using FileInputStream class and pass
the object to BufferedInputStream class
constructor. The object is then passed to the
constructor class ObjectInputStream while
instantiating. In ObjectInputStream class we call
the readObject() method which will carry out the
actual deserialization.
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In the serialize method there are two parameters
i.e., file path name and data object which is
required to be serialized. In this method we
first open the file in write mode using
FileOutputStream class and pass the object to
BufferedOutputStream class constructor. Then the
object is passed to ObjectOutputStream class
while instantiating and writeObject() method is
called to serialize the data object and write
byte stream into opened file.
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There are certain fields in the class of an
object which you may not want to serialize such
as sensitive information (keys, password, etc.).
We protect those fields from getting saved during
the process of serialization. Using the keyword
transient before any field of an object wont get
serialized since transient objects are not
eligible for serialization. When deserialized the
value of these transient fields will have the
default value.
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package com.serialization import java.io.IOException public class SerializationImplDemo public static void main(String args) DataObject dataObject new DataObject()dataObject.setClient(Yolanda)dataObject.setStore(Programming store)dataObject.setId(hhhhh)dataObject.setPasswordKeys(MyG0tt!!) try SerializationDemoExample.serialize(file.txt, dataObject)DataObject object (DataObject) SerializationDemoExample.deSerialize(file.txt)System.out.println(object.toString()) catch (IOException exp) exp.printStackTrace() catch (ClassNotFoundException exp) exp.printStackTrace()
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Serialization in Java Example 3 DataObject.java
package com.serialization import java.io.Serializable public class DataObject implements Serializable private static final long serialVersionUID 1Lprivate String clientprivate String storetransient private String idtransient private String passwordKeys public String getClient() return clientpublic void setClient(String client) this.client clientpublic String getStore() return storepublic void setStore(String store) this.store storepublic String getId() return idpublic void setId(String id) this.id idpublic String getPasswordKeys() return passwordKeyspublic void setPasswordKeys(String passwordKeys) this.passwordKeys passwordKeys_at_Overridepublic String toString() String result client client \nstore store \nID id \npasswordKeys passwordKeysreturn result
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Now its time to implement our class to test the
process of serialization and deserialization. To
test serialization, well first populate the
fields of the data value object. Now well call
serialization method by passing the file name and
path as the first parameter file.txt and
dataObject as the second parameter. The
serialization of the object will write state of
data value object to the byte stream into
file.txt.
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In the last step deserialize method is called by
passing file path and name as the first
parameter. This method will deserialize the
object and read its state which is down casted
to data value object class. In order to get our
output we will print toString() method of data
value object class. When we run our Serialization
in Java program we can now observe the following
output
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client Yolandastore Programming ConceptsID
nullpasswordKeys null From the above output
we also observe that ID and passwordKeys fields
are null since we declared them as transient
fields and therefore they were not stored in the
file while saving objects state in the byte
stream.
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In this article you learned about how to
serialize and deserialize an object. However,
there are different serialization methods to
serialize an object such as Serialization with
Inheritance, Serialization with Aggregation,
Serialization with static data number,
Serialization with array or collection etc. which
well be covering in our next article.
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