Difference between DTO VO POJO JavaBeans

Question

Have seen some similar questions    What is the difference between a JavaBean and a POJO  What is the Difference Between POJO  Plain Old Java Object  and DTO  Data Transfer Object     Can you also please tell me the contexts in which they are used  Or the purpose of them

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First Talk About  Normal Class - that s mean any class define that s a normally in java it s means you create different type of method properties etc  Bean - Bean is nothing it s only a object of that particular class using this bean you can access your java class same as object    and after that talk about last one POJO  POJO - POJO is that class which have no any services it s have only a default constructor and private property and those property for setting a value corresponding setter and getter methods  It s short form of Plain Java Object

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Value Object   Use when need to measure the objects  equality based on the objects  value  Data Transfer Object    Pass data with multiple attributes in one shot from client to server across layer  to avoid multiple calls to remote server  Plain Old Java Object   It s like simple class which properties  public no-arg constructor  As we declare for JPA entity    difference-between-value-object-pattern-and-data-transfer-pattern

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DTO vs VO  DTO - Data transfer objects are just data containers which are used to transport data between layers and tiers     It mainly contains attributes  You can even use public attributes without getters and setters   Data transfer objects do not contain any business logic       Analogy  Simple Registration form with attributes username    password  and email id           When this form is submitted in RegistrationServlet file you will get all the attributes from view layer to business layer where you pass   the attributes to java beans and then to the DAO or the persistence layer     DTO s helps in transporting the attributes from view layer to business layer and finally to the persistence layer       DTO was mainly used to get data transported across the network efficiently  it may be even from JVM to another JVM   DTOs are often java io Serializable - in order to transfer data across JVM   VO - A Value Object  1  2  represents itself a fixed set of data and is similar to a Java enum  A Value Object s identity is based on their state rather than on their object identity and is immutable  A real world example would be Color RED  Color BLUE  SEX FEMALE etc   POJO vs JavaBeans   1   The Java-Beanness of a POJO is that its private attributes are all accessed via public getters and setters that conform to the JavaBeans conventions  e g       private String foo      public String getFoo            public void setFoo String foo            2   JavaBeans must implement Serializable and have a no-argument constructor  whereas in POJO does not have these restrictions

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Java Beans are not the same thing as EJBs   The JavaBeans specification in Java 1 0 was Sun s attempt to allow Java objects to be manipulated in an IDE that looked like VB   There were rules laid down for objects that qualified as  Java Beans     Default constructor Getters and setters for private data members that followed the proper naming convention Serializable Maybe others that I m forgetting    EJBs came later   They combine distributed components and a transactional model  running in a container that manages threads  pooling  life cycle  and provides services   They are a far cry from Java Beans   DTOs came about in the Java context because people found out that the EJB 1 0 spec was too  chatty  with the database   Rather than make a roundtrip for every data element  people would package them into Java Beans in bulk and ship them around   POJOs were a reaction against EJBs

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Basically   DTO   Data transfer objects   can travel between seperate layers in software architecture   VO   Value objects   hold a object such as Integer Money etc   POJO  Plain Old Java Object which is not a special object   Java Beans  requires a Java Class to be serializable  have a no-arg constructor and a getter and setter for each field

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JavaBeans  A JavaBean is a class that follows the JavaBeans conventions as defined by Sun  Wikipedia has a pretty good summary of what JavaBeans are      JavaBeans are reusable software components for Java that can be manipulated visually in a builder tool  Practically  they are classes written in the Java programming language conforming to a particular convention  They are used to encapsulate many objects into a single object  the bean   so that they can be passed around as a single bean object instead of as multiple individual objects  A JavaBean is a Java Object that is serializable  has a nullary constructor  and allows access to properties using getter and setter methods       In order to function as a JavaBean class  an object class must obey certain conventions about method naming  construction  and behavior  These conventions make it possible to have tools that can use  reuse  replace  and connect JavaBeans       The required conventions are          The class must have a public default constructor  This allows easy instantiation within editing and activation frameworks    The class properties must be accessible using get  set  and other methods  so-called accessor methods and mutator methods   following a standard naming convention  This allows easy automated inspection and updating of bean state within frameworks  many of which include custom editors for various types of properties    The class should be serializable  This allows applications and frameworks to reliably save  store  and restore the bean s state in a fashion that is independent of the VM and platform          Because these requirements are largely expressed as conventions rather than by implementing interfaces  some developers view JavaBeans as Plain Old Java Objects that follow specific naming conventions    POJO  A Plain Old Java Object or POJO is a term initially introduced to designate a simple lightweight Java object  not implementing any javax ejb interface  as opposed to heavyweight EJB 2 x  especially Entity Beans  Stateless Session Beans are not that bad IMO   Today  the term is used for any simple object with no extra stuff  Again  Wikipedia does a good job at defining POJO      POJO is an acronym for Plain Old Java   Object  The name is used to emphasize   that the object in question is an   ordinary Java Object  not a special   object  and in particular not an   Enterprise JavaBean  especially before   EJB 3   The term was coined by Martin   Fowler  Rebecca Parsons and Josh   MacKenzie in September 2000             We wondered why people were so against using regular objects in their     systems and concluded that it was     because simple objects lacked a fancy     name  So we gave them one  and it s     caught on very nicely           The term continues the pattern of   older terms for technologies that do   not use fancy new features  such as   POTS  Plain Old Telephone Service  in   telephony  and PODS  Plain Old Data   Structures  that are defined in C     but use only C language features  and   POD  Plain Old Documentation  in Perl       The term has most likely gained   widespread acceptance because of the   need for a common and easily   understood term that contrasts with   complicated object frameworks  A   JavaBean is a POJO that is   serializable  has a no-argument   constructor  and allows access to   properties using getter and setter   methods  An Enterprise JavaBean is not   a single class but an entire component   model  again  EJB 3 reduces the   complexity of Enterprise JavaBeans        As designs using POJOs have become   more commonly-used  systems have   arisen that give POJOs some of the   functionality used in frameworks and   more choice about which areas of   functionality are actually needed    Hibernate and Spring are examples    Value Object  A Value Object or VO is an object such as java lang Integer that hold values  hence value objects   For a more formal definition  I often refer to Martin Fowler s description of Value Object      In Patterns of Enterprise Application Architecture I described Value Object as a small object such as a Money or date range object  Their key property is that they follow value semantics rather than reference semantics       You can usually tell them because their notion of equality isn t based on identity  instead two value objects are equal if all their fields are equal  Although all fields are equal  you don t need to compare all fields if a subset is unique - for example currency codes for currency objects are enough to test equality       A general heuristic is that value objects should be entirely immutable  If you want to change a value object you should replace the object with a new one and not be allowed to update the values of the value object itself - updatable value objects lead to aliasing problems       Early J2EE literature used the term value object to describe a different notion  what I call a Data Transfer Object  They have since changed their usage and use the term Transfer Object instead       You can find some more good material on value objects on the wiki  and by Dirk Riehle    Data Transfer Object  Data Transfer Object or DTO is a  anti  pattern introduced with EJB  Instead of performing many remote calls on EJBs  the idea was to encapsulate data in a value object that could be transfered over the network  a Data Transfer Object  Wikipedia has a decent definition of Data Transfer Object      Data transfer object  DTO   formerly known as value objects or VO  is a design pattern used to transfer data between software application subsystems  DTOs are often used in conjunction with data access objects to retrieve data from a database       The difference between data transfer objects and business objects or data access objects is that a DTO does not have any behaviour except for storage and retrieval of its own data  accessors and mutators        In a traditional EJB architecture  DTOs serve dual purposes  first  they work around the problem that entity beans are not serializable  second  they implicitly define an assembly phase where all data to be used by the view is fetched and marshalled into the DTOs before returning control to the presentation tier      So  for many people  DTOs and VOs are the same thing  but Fowler uses VOs to mean something else as we saw   Most of time  they follow the JavaBeans conventions and are thus JavaBeans too  And all are POJOs

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POJO   It is a java file class  which doesn t extend or implement any other java file class    Bean   It is a java file class  in which all variables are private  methods are public and appropriate getters and setters are used for accessing variables   Normal class   It is a java file class  which may consist of public private default protected variables and which may or may not extend or implement another java file class

[java] Difference between DTO, VO, POJO, JavaBeans?

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