Java Bean VS Spring Bean

A Java object can be a JavaBean, a POJO and a Spring bean all at the same time.

POJO

POJO is an acronym for Plain Old Java Object. The term was coined by Martin Fowler et. al., as a ‘fancy’ way to describe ordinary Java Objects that do not require a framework to use, nor need to be run in an application server environment. It is often used to distinguish simpler, lightweight Java objects from ‘heavyweight’ code like EJBs. The use of these kinds of lightweight objects in programming is described in books such as “POJOs in Action” and advocated by frameworks like Spring.

Java Bean

The concept of JavaBeans was originally devised for Swing to facilitate the development of standalone GUI components, but the pattern has been repurposed for the land of Spring beans and back-end persistence with Hibernate.

JavaBeans are classes that encapsulate many objects into a single object (the bean). The name “Bean” was given to encompass the following standards, which aims to create reusable software components for Java.

Must implement Serializable.
It should have a public no-arg constructor.
All properties in java bean must be private with public getters and setter methods.

JavaBean conventions

The class should be serializable.
Have a public default constructor.
class properties are private, accessed by getter and setter.

Advantages

properties, events, and methods can be reused in other applications
register events
can be saved to persistent storage and restored

Disadvantages

public no-arg constructor cannot guarantee a proper initialization
Java Beans are mutable in nature.
Boilerplate code, like getter and setter.

Java Bean VS POJO

An object in Java may be a POJO but not a JavaBean. For instance, it may implement an interface or extend specified classes, but because it refers to objects that are stateful and/or exist outside the scope of the Java Virtual Machine (JVM)—for example, HTTP or database connections —it cannot reasonably be serialized to disk and then restored.

Spring Bean

Spring beans are just object instances that are managed by the Spring IOC container. They’re created based on BeanDefinition.

Bean Definition

BeanDefinition describe the properties of a bean. It contains the following metadata:

A package-qualified class name
Bean behavioral configuration: scope, lifecycle callbacks, and so forth
collaborators or dependencies
Other configuration settings

BeanDefinition properties

class
name
scope
constructor arguments
properties
autowiring mode
lazy-initialization mode
initialization method
destruction method

three ways of defining a Spring bean

Using stereotype @Component annotation
using @Bean annotation in a custom Java configuration class
XML configuration