{"id":9638,"date":"2013-03-12T10:00:30","date_gmt":"2013-03-12T08:00:30","guid":{"rendered":"http:\/\/www.javacodegeeks.com\/?p=9638"},"modified":"2013-03-12T06:08:31","modified_gmt":"2013-03-12T04:08:31","slug":"serialization-in-java","status":"publish","type":"post","link":"https:\/\/www.javacodegeeks.com\/2013\/03\/serialization-in-java.html","title":{"rendered":"Serialization in java"},"content":{"rendered":"

Java provides mechanism called serialization to persists java objects in a form of ordered or sequence of bytes that includes the object’s data as well as information about the object’s type and the types of data stored in the object. So if we have serialize any object then it can be read and deserialize it using object’s type and other information so we can retrieve original object.<\/p>\n

Classes ObjectInputStream and ObjectOutputStream are high-level streams that contain the methods for serializing and deserializing an object. ObjectOutputStream has many method for serializing object but commonly used method is:
\n 
\n <\/p>\n

    private void writeObject(ObjectOutputStream os) throws IOException\r\n    { \r\n\r\n    }<\/pre>\n
Similarly ObjectInputStream has<\/p>\n
    private void readObject(ObjectInputStream is) throws IOException, ClassNotFoundException\r\n    {\r\n\r\n    }<\/pre>\n
 Need of Serialization?<\/h2>\n
Serialization is usually used When the need arises to send your data over network or stored in files. By data I mean objects and not text. Now the problem is your Network infrastructure and your Hard disk are hardware components that understand bits and bytes but not Java objects. Serialization is the translation of your Java object’s values\/states to bytes to send it over network or save it.On other hand,Deserialization is conversion of byte code to corresponding java objects.<\/p>\n
 Concept of serialVersionUID : <\/h2>\n
SerialVersionUID is used to ensure that same object(That was used during Serialization) is loaded during Deserialization.serialVersionUID is used for version control of object.You can read more at serialVersionUID in java serialization<\/a><\/p>\n
For Serialization:<\/h2>\n
Steps are :<\/p>\n
\"\"<\/a><\/p>\n
Lets take an example: Create Employee.java in src->org.arpit.javapostsforlearning:<\/p>\n
1.Employee.java <\/h4>\n
package org.arpit.javapostsforlearning;\r\nimport java.io.Serializable;\r\npublic class Employee implements Serializable{\r\n\r\n    int employeeId;\r\n    String employeeName;\r\n    String department;\r\n\r\n    public int getEmployeeId() {\r\n        return employeeId;\r\n    }\r\n    public void setEmployeeId(int employeeId) {\r\n        this.employeeId = employeeId;\r\n    }\r\n    public String getEmployeeName() {\r\n        return employeeName;\r\n    }\r\n    public void setEmployeeName(String employeeName) {\r\n        this.employeeName = employeeName;\r\n    }\r\n    public String getDepartment() {\r\n        return department;\r\n    }\r\n    public void setDepartment(String department) {\r\n        this.department = department;\r\n    }\r\n}<\/pre>\n
As you can see above,if you want to serialize any class then it must implement Serializable interface which is marker interface. <\/b><\/p>\n
Marker interface in Java is interfaces with no field or methods or in simple word empty interface in java is called marker interface. Create SerializeMain.java in src->org.arpit.javapostsforlearning<\/p>\n
2.SerializeMain.java<\/h4>\n
package org.arpit.javapostsforlearning;\r\nimport java.io.FileOutputStream;\r\nimport java.io.IOException;\r\nimport java.io.ObjectOutputStream;\r\n public class SerializeMain {\r\n\r\n \/**\r\n  * @author Arpit Mandliya\r\n  *\/\r\n public static void main(String[] args) {\r\n\r\n  Employee emp = new Employee();\r\n  emp.setEmployeeId(101);\r\n  emp.setEmployeeName('Arpit');\r\n  emp.setDepartment('CS');\r\n  try\r\n  {\r\n   FileOutputStream fileOut = new FileOutputStream('employee.ser');\r\n   ObjectOutputStream outStream = new ObjectOutputStream(fileOut);\r\n   outStream.writeObject(emp);\r\n   outStream.close();\r\n   fileOut.close();\r\n  }catch(IOException i)\r\n  {\r\n   i.printStackTrace();\r\n  }\r\n }\r\n}<\/pre>\n
For Deserialization:<\/h4>\n
Steps are:<\/p>\n
\"\"<\/a><\/p>\n
Create DeserializeMain.java in src->org.arpit.javapostsforlearning<\/p>\n
3.DeserializeMain.java<\/h4>\n
package org.arpit.javapostsforlearning;\r\nimport java.io.IOException;\r\nimport java.io.ObjectInputStream;\r\n\r\npublic class DeserializeMain {\r\n \/**\r\n  * @author Arpit Mandliya\r\n  *\/\r\n public static void main(String[] args) {\r\n\r\n  Employee emp = null;\r\n       try\r\n       {\r\n          FileInputStream fileIn =new FileInputStream('employee.ser');\r\n          ObjectInputStream in = new ObjectInputStream(fileIn);\r\n          emp = (Employee) in.readObject();\r\n          in.close();\r\n          fileIn.close();\r\n       }catch(IOException i)\r\n       {\r\n          i.printStackTrace();\r\n          return;\r\n       }catch(ClassNotFoundException c)\r\n       {\r\n          System.out.println('Employee class not found');\r\n          c.printStackTrace();\r\n          return;\r\n       }\r\n       System.out.println('Deserialized Employee...');\r\n       System.out.println('Emp id: ' + emp.getEmployeeId());\r\n       System.out.println('Name: ' + emp.getEmployeeName());\r\n       System.out.println('Department: ' + emp.getDepartment());\r\n }\r\n}<\/pre>\n
 4.Run it:<\/h4>\n
First run SerializeMain.java then DeserializeMain.java and you will get following output:<\/p>\n
Deserialized Employee...\r\nEmp id: 101\r\nName: Arpit\r\nDepartment: CS<\/pre>\n
So we have serialize an employee object and then deserialized it.It seems very simple but it can be very complex when reference object,inheritance come into the picture.So we will see different cases one by one and how we can apply serialization in different scenarios.<\/p>\n
 Case 1-What if an object has a reference to other objects<\/h2>\n
We have seen very simple case of serialization,now what if it also a reference to other objects.How will it serialized then? will reference object will also get serialized?.Yes,You don’t have to explicitly serialize reference objects.When you serialize any object and if it contain any other object reference then Java serialization serialize that object’s entire object graph.<\/p>\n
For example:Lets say,Employee now has reference to address object and Address can have reference to some other object(e.g.Home) then when you serialize Employee object all other reference objects such as address and home will be automatically serialized. Lets create Address class and add object of Address as a reference to above employee class.<\/p>\n
Employee.java:<\/h4>\n
package org.arpit.javapostsforlearning;\r\nimport java.io.Serializable;\r\n\r\npublic class Employee implements Serializable{\r\n\r\n int employeeId;\r\n String employeeName;\r\n String department;\r\n Address address;\r\n\r\n public int getEmployeeId() {\r\n  return employeeId;\r\n }\r\n public void setEmployeeId(int employeeId) {\r\n  this.employeeId = employeeId;\r\n }\r\n public String getEmployeeName() {\r\n  return employeeName;\r\n }\r\n public void setEmployeeName(String employeeName) {\r\n  this.employeeName = employeeName;\r\n }\r\n public String getDepartment() {\r\n  return department;\r\n }\r\n public void setDepartment(String department) {\r\n  this.department = department;\r\n }\r\n public Address getAddress() {\r\n  return address;\r\n }\r\n public void setAddress(Address address) {\r\n  this.address = address;\r\n }\r\n}<\/pre>\n
Create Address.java in org.arpit.javapostsforlearning:
 
<\/div> <\/div><\/p>\n
Address.java:<\/h4>\n
package org.arpit.javapostsforlearning;\r\npublic class Address {\r\n\r\n int homeNo;\r\n String street;\r\n String city;\r\n public Address(int homeNo, String street, String city) {\r\n  super();\r\n  this.homeNo = homeNo;\r\n  this.street = street;\r\n  this.city = city;\r\n }\r\n public int getHomeNo() {\r\n  return homeNo;\r\n }\r\n public void setHomeNo(int homeNo) {\r\n  this.homeNo = homeNo;\r\n }\r\n public String getStreet() {\r\n  return street;\r\n }\r\n public void setStreet(String street) {\r\n  this.street = street;\r\n }\r\n public String getCity() {\r\n  return city;\r\n }\r\n public void setCity(String city) {\r\n  this.city = city;\r\n }\r\n}<\/pre>\n
Create SerializeDeserializeMain.java in org.arpit.javapostsforlearning:<\/p>\n
SerializeDeserializeMain.java:<\/h4b>\n
package org.arpit.javapostsforlearning;\r\nimport java.io.FileInputStream;\r\nimport java.io.FileOutputStream;\r\nimport java.io.IOException;\r\nimport java.io.ObjectInputStream;\r\nimport java.io.ObjectOutputStream;\r\n\r\npublic class SerializeDeserializeMain {\r\n \/**\r\n  * @author Arpit Mandliya\r\n  *\/\r\n public static void main(String[] args) {\r\n\r\n  Employee emp = new Employee();\r\n  emp.setEmployeeId(101);\r\n  emp.setEmployeeName('Arpit');\r\n  emp.setDepartment('CS');\r\n  Address address=new Address(88,'MG road','Pune');\r\n  emp.setAddress(address);\r\n  \/\/Serialize\r\n  try\r\n  {\r\n   FileOutputStream fileOut = new FileOutputStream('employee.ser');\r\n   ObjectOutputStream outStream = new ObjectOutputStream(fileOut);\r\n   outStream.writeObject(emp);\r\n   outStream.close();\r\n   fileOut.close();\r\n  }catch(IOException i)\r\n  {\r\n   i.printStackTrace();\r\n  }\r\n\r\n  \/\/Deserialize\r\n  emp = null;\r\n  try\r\n  {\r\n   FileInputStream fileIn =new FileInputStream('employee.ser');\r\n   ObjectInputStream in = new ObjectInputStream(fileIn);\r\n   emp = (Employee) in.readObject();\r\n   in.close();\r\n   fileIn.close();\r\n  }catch(IOException i)\r\n  {\r\n   i.printStackTrace();\r\n   return;\r\n  }catch(ClassNotFoundException c)\r\n  {\r\n   System.out.println('Employee class not found');\r\n   c.printStackTrace();\r\n   return;\r\n  }\r\n  System.out.println('Deserialized Employee...');\r\n  System.out.println('Emp id: ' + emp.getEmployeeId());\r\n  System.out.println('Name: ' + emp.getEmployeeName());\r\n  System.out.println('Department: ' + emp.getDepartment());\r\n  address=emp.getAddress();\r\n  System.out.println('City :'+address.getCity());\r\n }\r\n}<\/pre>\n
Run it :<\/h4>\n
When you run SerializeDeserializeMain.java.You will get following output:<\/p>\n
java.io.NotSerializableException: org.arpit.javapostsforlearning.Address\r\n    at java.io.ObjectOutputStream.writeObject0(Unknown Source)\r\n    at java.io.ObjectOutputStream.defaultWriteFields(Unknown Source)\r\n    at java.io.ObjectOutputStream.writeSerialData(Unknown Source)\r\n    at java.io.ObjectOutputStream.writeOrdinaryObject(Unknown Source)\r\n    at java.io.ObjectOutputStream.writeObject0(Unknown Source)\r\n    at java.io.ObjectOutputStream.writeObject(Unknown Source)<\/pre>\n
We got exception what went wrong.I forgot to mention,Address class must also be serializable.So you have to make Address serializable by implement serialzable interface.<\/p>\n
Address.java:<\/h4>\n
import java.io.Serializable;\r\n\r\npublic class Address implements Serializable{\r\n\r\n int homeNo;\r\n String street;\r\n String city;\r\n public Address(int homeNo, String street, String city) {\r\n  super();\r\n  this.homeNo = homeNo;\r\n  this.street = street;\r\n  this.city = city;\r\n } \r\n public int getHomeNo() {\r\n  return homeNo;\r\n }\r\n public void setHomeNo(int homeNo) {\r\n  this.homeNo = homeNo;\r\n }\r\n public String getStreet() {\r\n  return street;\r\n }\r\n public void setStreet(String street) {\r\n  this.street = street;\r\n }\r\n public String getCity() {\r\n  return city;\r\n }\r\n public void setCity(String city) {\r\n  this.city = city;\r\n }\r\n}<\/pre>\n
Run again:<\/h4>\n
When you run again SerializeDeserializeMain.java.You will get following output:<\/p>\n
Deserialized Employee...  \r\nEmp id: 101  \r\nName: Arpit  \r\nDepartment: CS  \r\nCity: Pune<\/pre>\n
Case 2:What if you don’t have access to reference object’s source code(e.g you don’t have access to above Address class)<\/h2>\n
If you don’t have access to address class then how will you implement serializable interface in Address class.Is there any alternative to that? yes there is,You can create another class which extends address and make it serialzable but It can fails in many cases:<\/p>\n