HowToDoInJava

Hibernate Tutorial

Hibernate is an open source Java persistence framework project. It performs powerful object-relational mapping and query databases using HQL and SQL. Hibernate is a great tool for ORM mappings in Java. It can cut down a lot of complexity and thus defects as well from your application, which may otherwise find a way to exist. This is specially boon for developers with limited knowledge of SQL.

Initially started as an ORM framework, Hibernate has spun off into many projects, such as Hibernate Search, Hibernate Validator, Hibernate OGM (for NoSQL databases), and so on.

Hibernate Architecture

The following diagram summarizes the main building blocks in hibernate architecture.

Hibernate Architecture
Hibernate Architecture

Let’s understand what each block represents.

  1. Configuration : Generally written in hibernate.properties or hibernate.cfg.xml files. For Java configuration, you may find class annotated with @Configuration. It is used by Session Factory to work with Java Application and the Database. It represents an entire set of mappings of an application Java Types to an SQL database.
  2. Session Factory : Any user application requests Session Factory for a session object. Session Factory uses configuration information from above listed files, to instantiates the session object appropriately.
  3. Session : This represents the interaction between the application and the database at any point of time. This is represented by the org.hibernate.Session class. The instance of a session can be retrieved from the SessionFactory bean.
  4. Query : It allows applications to query the database for one or more stored objects. Hibernate provides different techniques to query database, including NamedQuery and Criteria API.
  5. First-level cache : It represents the default cache used by Hibernate Session object while interacting with the database. It is also called as session cache and caches objects within the current session. All requests from the Session object to the database must pass through the first-level cache or session cache. One must note that the first-level cache is available with the session object until the Session object is live.
  6. Transaction : enables you to achieve data consistency, and rollback incase something goes unexpected.
  7. Persistent objects : These are plain old Java objects (POJOs), which get persisted as one of the rows in the related table in the database by hibernate.They can be configured in configurations files (hibernate.cfg.xml or hibernate.properties) or annotated with @Entity annotation.
  8. Second-level cache : It is used to store objects across sessions. This needs to be explicitly enabled and one would be required to provide the cache provider for a second-level cache. One of the common second-level cache providers is EhCache.

Salient features of the Hibernate framework

  • Object/Relational Mapping

    Hibernate, as an ORM framework, allows the mapping of the Java domain object with database tables and vice versa. As a result, business logic is able to access and manipulate database entities via Java objects. It helps to speed up the overall development process by taking care of aspects such as transaction management, automatic primary key generation, managing database connections and related implementations, and so on.

  • JPA provider

    Hibernate does support the Java Persistence API (JPA) specification. JPA is a set of specifications for accessing, persisting, and managing data between Java objects and relational database entities.

  • Idiomatic persistence

    Any class that follows object-oriented principles such as inheritance, polymorphism, and so on, can be used as a persistent class.

  • High performance and scalability

    Hibernate supports techniques such as different fetching strategies, lazy initialization, optimistic locking, and so on, to achieve high performance, and it scales well in any environment.

  • Easy to maintain

    Hibernate is easier to maintain as it requires no special database tables or fields. It generates SQL at system initialization time. It is much quicker and easier to maintain compared to JDBC.

In this page, I have categorized all available hibernate examples in this blog. This page will be updated every time, a new hibernate tutorial is published in this blog. Stay Tuned !!

Feel free to suggest topics you want to read more on.

Basic concepts

How to build SessionFactory in Hibernate

If you have been watching previous hibernate releases then you must have noticed that they have deprecated a lot of classes in quick succession. Deprecated classes are AnnotationConfiguration, ServiceRegistryBuilder and so on.

In this hibernate tutorial, I am giving an example of building hibernate SessionFactory without using deprecated classes mentioned above. I am using the latest hibernate version i.e. Hibernate 4.3.6.Final, so you can make sure that you are using the latest approach for building session factory.

Entities Equality and Identity Concepts

Many times in our application, we face a situation where we have to compare two objects to check their equality for satisfying some business rules. In core java, we have already much knowledge about checking equality of objects, but in hibernate, we need to take care of a few extra things as well. Let’s learn what are those extra concepts.

Defining Association Mappings between Hibernate Entities

When we annotate the java classes with JPA annotations and make them persistent entities, we can face situations where two entities can be related and must be referenced from each other, in either uni-direction or in bi-direction. Let’s understand a few basic things before actually creating references between hibernate entities.

Entity / Persistence LifeCycle States Concepts

Given an instance of an object that is mapped to Hibernate, it can be in any one of four different states: transient, persistent, detached, or removed. We are going to learn about them today in this hibernate tutorial.

Using In-memory Database With Hibernate

In this example, I am using HSQLDB Database for creating and accessing in-memory database through our hibernate code.

Hibernate JPA Cascade Types

To enable cascade and inverse effect, we had used “CascadeType” attribute in entities. In this tutorial, we will learn about various type of available options for cascading via CascadeType.

Pros and Cons of Hibernate Annotations Vs Mappings

As you may know that prior to the inline annotations, the only way to create hibernate mappings was through XML files. Although various tools from Hibernate and third-party projects allowed part or all of these mappings to be generated from Java source code automatically. Today annotations are the newest way to define mappings but it is not automatically the best way to do so. Let’s discuss the drawbacks and benefits of hibernate (or I should say JPA) annotations before discussing when to apply them.

Hibernate Query Language [HQL]

HQL is an object-oriented query language, similar to SQL, but instead of operating on tables and columns, HQL works with persistent objects and their properties. It is a superset of the JPQL, the Java Persistence Query Language; a JPQL query is a valid HQL query, but not all HQL queries are valid JPQL queries. HQL is a language with its own syntax and grammar.

Let’s learn HQL using the following examples:

  1. Basic HQL Syntax
    • Update Operation
    • Delete Operation
    • Insert Operation
    • Select Operation
  2. The from Clause and Aliases
  3. The select Clause and Projection
  4. Using Named Parameters
  5. Paging Through the Result Set
  6. Obtaining a Unique Result
  7. Sorting Results with the order by Clause
  8. Associations
  9. Aggregate Methods
  10. Named Queries
  11. Using Native SQL
  12. Enable Logging and Commenting

Hibernate Criteria Queries

The Criteria Query API lets you build nested, structured query expressions in Java, providing a compile-time syntax checking that is not possible with a query language like HQL or SQL. The Criteria API also includes query by example (QBE) functionality. This lets you supply example objects that contain the properties you would like to retrieve instead of having to step-by-step spell out the components of the query. It also includes projection and aggregation methods, including count(). Let’s explore it’s different features in detail.

  1. Basic Usage Example
  2. Using Restrictions with Criteria
  3. Paging Through the Result Set
  4. Obtaining a Unique Result
  5. Obtaining Distinct Results
  6. Sorting the Query’s Results
  7. Performing Associations (Joins)
  8. Adding Projections
  9. Query By Example (QBE)
  10. Summary

Lazy Loading in Hibernate

In this this tutorial, I will be discussing a must-known feature in hibernate known as lazy loading. This is useful specially if you working in a very large application.

CRUD Operation Examples

Hello world insert data

In this tutorial, I am giving example of inserting data in a single table.

Hibernate named query tutorial

Named queries in hibernate is a technique to group the HQL statements in single location, and lately refer them by some name whenever need to use them. It helps largely in code cleanup because these HQL statements are no longer scattered in whole code.

Loading entity from database example

Examples of loading an hibernate entity using either load or get method.

Save() and saveOrUpdate() for Saving Entities

Please not that creating an instance of a class, you mapped with a hibernate annotations, does not automatically persist the object to the database. It must be save explicitly after attaching it to a valid hibernate session. Let’s learn how to do it.

Merging and Refreshing Entities

In this tutorial, I am discussing few thoughts around refresh() and merge() method present in hibernate session class.

Hibernate entity mappings

Hibernate one to one mapping using annotations

Let’s discuss variations of one-to-one mappings supported in hibernate:

  1. Using foreign key association
  2. Using a common join table
  3. Using shared primary key

Hibernate one to many mapping using annotations

Discuss variations of one-to-many mappings supported in hibernate:

  1. Using foreign key association
  2. Using a join table

Hibernate many to many mapping using annotations

Discuss variations of many-to-many mappings supported in hibernate.

Hibernate Connection Pooling and Caching

C3P0 Connection Pool Configuration Tutorial

By default, Hibernate uses JDBC connections in order to interact with a database. Creating these connections is expensive—probably the most expensive single operation Hibernate will execute in a typical-use case. Since JDBC connection management is so expensive that possibly you will advise to use a pool of connections, which can open connections ahead of time (and close them only when needed, as opposed to “when they’re no longer used”).

C3P0 is an example of an external connection pool. In this tutorial, we will learn to use it with hibernate.

Hibernate EhCache configuration

Caching is facility provided by ORM frameworks which help users to get fast running web application, while help framework itself to reduce the number of queries made to the database in a single transaction. Hibernate also provide this caching functionality at first level and second level.

In this tutorial, I am giving an example using ehcache configuration as second level cache in hibernate.

Hibernate first level cache with example

Fist level cache in hibernate is enabled by default and you do not need to do anything to get this functionality working. Let’s learn more about it.

Hibernate second level cache with example

In this tutorial, I am giving concepts around hibernate second level cache and give example using code snippets.

Hibernate best practices

Hibernate @NaturalId usage and example

Hibernate 4 has bring lots of improvements and @NaturalId is one of such nice improvements. As you know @Id annotation is used as meta data for specifying the primary key of an entity. But sometimes, entity is usually used in DAO layer code with id which not not primary key but its logical or natural id. In such cases, @NaturalId annotation will prove good replacement of named queries in hibernate.

Get entity reference for lazy loading

Lazy loading is a design pattern commonly used in computer programming to defer initialization of an object until the point at which it is needed. Hibernate lazy loading can be done by specifying “fetch= FetchType.LAZY” in hibernate mapping annotations.

Integration with other frameworks

Integrate Hibernate with Spring framework

This hibernate tutorial is focused on usage of Hibernate with Spring 3 framework. I will show that how a basic end to end application flow looks like as a result of this integration.

Exceptions you might face

[Solved] Initial SessionFactory creation failed.org.hibernate.HibernateException: Errors in named queries

Hibernate tutorial references

Hibernate docs

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Feedback, Discussion and Comments

  1. venkat

    Hi Lokesh, I have doubt on 2nd level cache.
    1) How does the 2nd level cache mechanism works?
    2) If the hibernate application database is updated by some other session, how the 2nd level cache know it? how it’s going to update the cache?

    Reply

  2. Mehdi Afifi

    Hi, it would be nice to write a page for inheritance in hibernate. Thanks.

    Reply

  3. janmaijay

    is hibernate and jpa are interconnected

    Reply

    • Lokesh Gupta

      JPA is specification and hibernate is implementation. Just like JAX-RS is specification and Jersey is implementation.

      Reply

  4. hari

    Is it returning the old data? How the new data is being updated in database? If possible send me code as well at my mail id.

    Reply

  5. Himansu

    Hi Lokesh,
    It will be great if you can move your sample code to online version control hosting services like github or bitbucket and link it to the page, Also can you explain about bootstrapping hibernate without persistence.xml

    Regards,
    Himansu

    Reply

  6. Fajruddin Sk

    How many away to solve (1+n)select query problem?

    Reply

  7. AnandRam

    Hello,

    I have doubt lazy loading of child objects. It might be other entity(OneToOne relationship, child entity fetch type is lazy) or a lazy collection. After closing the session when we try to access child object or lazy collection am getting “org.hibernate.LazyInitializationException: could not initialize proxy – no Session.

    1) without closing the session it is working fine.
    2)before session closed we should load the lazy objects, it’s working fine after closing the session also.

    3) I read in one article : After closing the session, By passing the proxy object to the below method, we can get the original object.
    I tried it but not success , Please suggest me will the code is proper or not.

    public static T initializeAndUnproxy(T entity) {
    if (entity == null) {
    throw new NullPointerException(
    “Entity passed for initialization is null”);
    }

    Hibernate.initialize(entity);
    if (entity instanceof HibernateProxy) {
    entity = (T) ((HibernateProxy) entity)
    .getHibernateLazyInitializer().getImplementation();
    }
    return entity;
    }

    Thanks,
    Ramanand

    Reply

    • Lokesh Gupta

      Code looks good to me. What problem do you face??

      Reply

      • Ramanand

        Hello Lokesh,

        I am using the above “initializeAndUnproxy” method out of session, it should work. But the lazy object is not getting loaded into hibernate persistence context, i am getting same exception “org.hibernate.LazyInitializationException: could not initialize proxy – no Session.” could you please provide full example.

        AnandRam

        Reply

        • Lokesh Gupta

          I am out for 2 days. I will work on it on weekend.

          Reply

          • AnanRam

            Hello Lokesh,

            am waiting for your response.

            Thanks,
            AnandRam

            Reply

            • Lokesh Gupta

              I played around with code and found below configuration solve your problem :
              <property name="hibernate.enable_lazy_load_no_trans">true</property>

              Ref : SO Thread

              I will study more on this topic and post a dedicated tutorial with more information.

              Reply

  8. saurabh

    I have two databse d1 and d2 in first i have to insert 1 to 10000 and in d2 10000 to onwards using hibernate how i do???

    Reply

  9. Srikant

    Hi Lokesh, I have generated Hibernate Pojo’s Using Eclipse Jboss Plugin. It’s generated fine my problem is every pojo created bidirectionally. But I don’t want bi-direction . And we are using Hibernate XML not annotation One Transaction Code will there in different method in different class should i pass Hibernate session as parameter.

    Reply

    • Lokesh Gupta

      1) If you don’t want bi-directional then you should manually edit generated mappings.
      2) Hibernate transactions are applied at method level. Methods are a complete unit of any task. If task require calling two separate methods, the you should create a third method which will call first two methods inside it. Now apply transaction on this third method. No need to pass session as parameter.

      Reply

  10. Ranga Reddy

    Hi Lokesh, Hibernate4 supports multitency. Can you post articles related to this. And also provide some example.

    Reply

  11. Mohan Kumar

    sir,how to configure hibernate config file for sql server connection..

    Reply

  12. Ranjan

    Hi Lokesh,
    Have a doubt. I need to mention fetch strategy either lazy or eager.
    But I found somewhere it is mentioned as @OneToMany(fetch = FetchType.LAZY) also there is another annotaton
    @Fetch(FetchMode.SELECT).

    I am actually confused which one we should use…

    Could you please advice

    Ranjan

    Reply

  13. Beena Kumari

    Nice tutorial….Having unique imformation

    Reply

  14. venki

    Hi Lokesh Gupta
    i’m new to hibernate, already i was learnig hibernate without annotattions, but here some of code is developed with annotations, i can’t understatnd,what should i learn first can u help me please

    Reply

  15. ubk

    Many people who leave in the world is selfless and valueless but some people are born for meaning to give human like you….

    Reply

      • venkata

        Hi Lokesh,

        I want to hit database for every 5 seconds to retrieve changes occurred in database during that interval time and display same to the user using JSP.

        I have written the code like using spring controller. But not able to get the latest changes in database.
        Could you please look into my code and let me know which prevented not to display upto latest changes.

        MyController code:

        @RequestMapping(value = “/home”, method = RequestMethod.GET)
        public String home(Locale locale, Model model) {
        logger.info(“Welcome home! The client locale is {}.”, locale);

        Date date = new Date();
        DateFormat dateFormat = DateFormat.getDateTimeInstance(DateFormat.LONG, DateFormat.LONG, locale);

        String formattedDate = dateFormat.format(date);
        List list=homeService.demoServiceMethod();
        model.addAttribute(“serverTime”, formattedDate );
        model.addAttribute(“list”, list);
        return “home”;
        }

        MyService where I am calling the database using the scheduler

        @Service
        public class HomeService {

        List employees=new ArrayList();

        public List demoServiceMethod()
        {
        //System.out.println(“Method executed at every 5 seconds. Current time is : :”+new Date());
        demoServiceMethod1();

        return employees;
        }

        @Scheduled(cron=”*/10 * * * * ?”)
        public void demoServiceMethod1()
        {
        System.out.println(“Method executed at every 5 seconds. Current time is : :”+new Date());
        SessionFactory sf = HibernateUtil.getSessionFactory();
        Session session = sf.openSession();
        employees = session.createQuery(“from employee “).setCacheable(false).list();
        System.out.println(“list size==”+employees.size());
        session.close();
        }

        }

        Appreciate your hep.

        Reply

        • Lokesh Gupta

          Is it returning the old data? How the new data is being updated in database? If possible send me code as well at my mail id.

          Reply

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