Java – what’s the difference between service layer and domain model layer

business-objectsdomain-modeljavaservice-layer

for example, I have a user table, to be layer-ing, I create such POJOs:

UserEntity.java
UserDao.java
UserBO.java (business object, domain model?)
UserService.java (for service layer)

what's the difference between UserBO.java and UserService.java? why we seperate it to two objects?

Best Answer

The Domain Model contains information and functionality related to what it means to be a User. It should map conceptually onto something that exists physically in the real world or a clearly defined concept in the problem space.

The Service contains information and functionality related to performing atomic units of work. It should map conceptually onto tasks that are performed on or by members of the Domain model. A single atomic task performed by clicking a button in the application generally involves many members of the Domain working together, unless you app is just a CRUD-y electronic filing cabinet.

Related Solutions

Java – What are the differences between a HashMap and a Hashtable in Java

There are several differences between HashMap and Hashtable in Java:

Hashtable is synchronized, whereas HashMap is not. This makes HashMap better for non-threaded applications, as unsynchronized Objects typically perform better than synchronized ones.
Hashtable does not allow null keys or values. HashMap allows one null key and any number of null values.
One of HashMap's subclasses is LinkedHashMap, so in the event that you'd want predictable iteration order (which is insertion order by default), you could easily swap out the HashMap for a LinkedHashMap. This wouldn't be as easy if you were using Hashtable.

Since synchronization is not an issue for you, I'd recommend HashMap. If synchronization becomes an issue, you may also look at ConcurrentHashMap.

Java – the difference between public, protected, package-private and private in Java

The official tutorial may be of some use to you.

	Class	Package	Subclass (same pkg)	Subclass (diff pkg)	World
`public`	+	+	+	+	+
`protected`	+	+	+	+
no modifier	+	+	+
`private`	+

+ : accessible
blank : not accessible

Best Answer

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Java – What are the differences between a HashMap and a Hashtable in Java

Java – the difference between public, protected, package-private and private in Java

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