Hibernate Validator

Project Lead:	Emmanuel Bernard
Latest release:	3.0.0 GA (Changelog) (Road Map)
Release date:	20.03.2007
Requirements:	Hibernate Core 3.2, JDK 5.0

Following the DRY (Don't Repeat Yourself) principle, Hibernate Validator let's you express your domain constraints once (and only once) and ensure their compliance at various level of your system automatically.

Annotations are a very convenient and elegant way to specify invariant constraints on the domain model implementation, the persistent classes. Hibernate Validator comes bundled with a set of common validations (@NotNull, @Email, @Max, and so on), and you can build you own validation rules very easily.

This is an example of an annotated persistent class:

public class Address {

    @NotNull private String line1;

    private String line2;

    private String zip;

    private String state;

    @Length(max = 20)

    @NotNull

    private String country;

    @Range(min = -2, max = 50, message = "Floor out of range")

    public int floor;

        ...

}

Hibernate Validator integrates with Hibernate by applying the constraints on the database schema (DDL generation) and by checking entity validity before Hibernate inserts or updates instances. You can use Hibernate Validator with any Java Persistence provider, not only Hibernate, although you will not be able to use automatic DDL alteration for constraint generation outside of Hibernate EntityManager.

Hibernate Validator constraint checking can be triggered programmatically, for example by the business layer. JBoss Seam makes use of this capability and integrates it with JSF, providing end to end validation from the presentation level down to the database constraints with a unique definition and declaration of integrity rules. Hibernate Validator is fully internationalized.

The project lead of Hibernate Validator is an expert group member of JSR 303: Bean Validation.

32.What are the Collection types in Hibernate ?

Bag

Set

List

Array

Map

31.What is the advantage of Hibernate over jdbc?

Hibernate Vs. JDBC :-

JDBC	Hibernate
With JDBC, developer has to write code to map an object model's data representation to a relational data model and its corresponding database schema.	Hibernate is flexible and powerful ORM solution to map Java classes to database tables. Hibernate itself takes care of this mapping using XML files so developer does not need to write code for this.
With JDBC, the automatic mapping of Java objects with database tables and vice versa conversion is to be taken care of by the developer manually with lines of code.	Hibernate provides transparent persistence and developer does not need to write code explicitly to map database tables tuples to application objects during interaction with RDBMS.
JDBC supports only native Structured Query Language (SQL). Developer has to find out the efficient way to access database, i.e. to select effective query from a number of queries to perform same task.	Hibernate provides a powerful query language Hibernate Query Language (independent from type of database) that is expressed in a familiar SQL like syntax and includes full support for polymorphic queries. Hibernate also supports native SQL statements. It also selects an effective way to perform a database manipulation task for an application.
Application using JDBC to handle persistent data (database tables) having database specific code in large amount. The code written to map table data to application objects and vice versa is actually to map table fields to object properties. As table changed or database changed then it’s essential to change object structure as well as to change code written to map table-to-object/object-to-table.	Hibernate provides this mapping itself. The actual mapping between tables and application objects is done in XML files. If there is change in Database or in any table then the only need to change XML file properties.
With JDBC, it is developer’s responsibility to handle JDBC result set and convert it to Java objects through code to use this persistent data in application. So with JDBC, mapping between Java objects and database tables is done manually.	Hibernate reduces lines of code by maintaining object-table mapping itself and returns result to application in form of Java objects. It relieves programmer from manual handling of persistent data, hence reducing the development time and maintenance cost.
With JDBC, caching is maintained by hand-coding.	Hibernate, with Transparent Persistence, cache is set to application work space. Relational tuples are moved to this cache as a result of query. It improves performance if client application reads same data many times for same write. Automatic Transparent Persistence allows the developer to concentrate more on business logic rather than this application code.
In JDBC there is no check that always every user has updated data. This check has to be added by the developer.	Hibernate enables developer to define version type field to application, due to this defined field Hibernate updates version field of database table every time relational tuple is updated in form of Java class object to that table. So if two users retrieve same tuple and then modify it and one user save this modified tuple to database, version is automatically updated for this tuple by Hibernate. When other user tries to save updated tuple to database then it does not allow saving it because this user does not have updated data.

32.What are the Collection types in Hibernate ?

Bag

Set

List

Array

Map

33.What are the ways to express joins in HQL?

HQL provides four ways of expressing (inner and outer) joins:-

An implicit association join

An ordinary join in the FROM clause

A fetch join in the FROM clause.

A theta-style join in the WHERE clause.

34.Define cascade and inverse option in one-many mapping?

cascade - enable operations to cascade to child entities.
cascade="all|none|save-update|delete|all-delete-orphan"

inverse - mark this collection as the "inverse" end of a bidirectional association.
inverse="true|false"
Essentially "inverse" indicates which end of a relationship should be ignored, so when persisting a parent who has a collection of children, should you ask the parent for its list of children, or ask the children who the parents are?

37.How can a whole class be mapped as immutable?

Mark the class as mutable="false" (Default is true),. This specifies that instances of the class are (not) mutable. Immutable classes, may not be updated or deleted by the application.

44.What are the differences between EJB 3.0 & Hibernate

Hibernate Vs EJB 3.0 :-

Hibernate	EJB 3.0
Session–Cache or collection of loaded objects relating to a single unit of work	Persistence Context-Set of entities that can be managed by a given EntityManager is defined by a persistence unit
XDoclet Annotations used to support Attribute Oriented Programming	Java 5.0 Annotations used to support Attribute Oriented Programming
Defines HQL for expressing queries to the database	Defines EJB QL for expressing queries
Supports Entity Relationships through mapping files and annotations in JavaDoc	Support Entity Relationships through Java 5.0 annotations
Provides a Persistence Manager API exposed via the Session, Query, Criteria, and Transaction API	Provides and Entity Manager Interface for managing CRUD operations for an Entity
Provides callback support through lifecycle, interceptor, and validatable interfaces	Provides callback support through Entity Listener and Callback methods
Entity Relationships are unidirectional. Bidirectional relationships are implemented by two unidirectional relationships	Entity Relationships are bidirectional or unidirectional

45.What are the types of inheritance models in Hibernate?

There are three types of inheritance models in Hibernate:

Table per class hierarchy

Table per subclass

Table per concrete class