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    Hibernate

    Hibernate – Interceptors

    As you have learnt that in Hibernate, an object will be created and persisted. Once the object has been changed, it must be saved back to the database. This process continues until the next time the object is needed, and it will be loaded from the persistent store.

    Thus an object passes through different stages in its life cycle and Interceptor Interface provides methods, which can be called at different stages to perform some required tasks. These methods are callbacks from the session to the application, allowing the application to inspect and/or manipulate properties of a persistent object before it is saved, updated, deleted or loaded. Following is the list of all the methods available within the Interceptor interface −

    Sr.No. Method & Description
    1
    findDirty()

    This method is be called when the flush() method is called on a Session object.

    2
    instantiate()

    This method is called when a persisted class is instantiated.

    3
    isUnsaved()

    This method is called when an object is passed to the saveOrUpdate() method/

    4
    onDelete()

    This method is called before an object is deleted.

    5
    onFlushDirty()

    This method is called when Hibernate detects that an object is dirty (i.e. have been changed) during a flush i.e. update operation.

    6
    onLoad()

    This method is called before an object is initialized.

    7
    onSave()

    This method is called before an object is saved.

    8
    postFlush()

    This method is called after a flush has occurred and an object has been updated in memory.

    9
    preFlush()

    This method is called before a flush.

    Hibernate Interceptor gives us total control over how an object will look to both the application and the database.

    How to Use Interceptors?

    To build an interceptor, you can either implement Interceptor class directly or extend EmptyInterceptor class. Following will be the simple steps to use Hibernate Interceptor functionality.

    Create Interceptors

    We will extend EmptyInterceptor in our example where Interceptor’s method will be called automatically when Employee object is created and updated. You can implement more methods as per your requirements.

    importjava.io.Serializable;
    importjava.util.Date;
    importjava.util.Iterator;
    
    importorg.hibernate.EmptyInterceptor;
    importorg.hibernate.Transaction;
    importorg.hibernate.type.Type;
    
    publicclassMyInterceptorextendsEmptyInterceptor{
    privateint updates;
    privateint creates;
    privateint loads;
    
    publicvoidonDelete(Object entity,Serializable id,
    Object[] state,String[]propertyNames,Type[] types){
    // do nothing
    }
    
    // This method is called when Employee object gets updated.
    publicbooleanonFlushDirty(Object entity,Serializable id,
    Object[]currentState,Object[]previousState,String[]propertyNames,
    Type[] types){
    if( entity instanceofEmployee){
    System.out.println("Update Operation");
    returntrue;
    }
    returnfalse;
    }
    	
    publicbooleanonLoad(Object entity,Serializable id,
    Object[] state,String[]propertyNames,Type[] types){
    // do nothing
    returntrue;
    }
    
    // This method is called when Employee object gets created.
    publicbooleanonSave(Object entity,Serializable id,
    Object[] state,String[]propertyNames,Type[] types){
    if( entity instanceofEmployee){
    System.out.println("Create Operation");
    returntrue;
    }
    returnfalse;
    }
    
    //called before commit into database
    publicvoidpreFlush(Iterator iterator){
    System.out.println("preFlush");
    }
    
    //called after committed into database
    publicvoidpostFlush(Iterator iterator){
    System.out.println("postFlush");
    }
    }
    

    Create POJO Classes

    Now, let us modify a little bit our first example where we used EMPLOYEE table and Employee class to play with −

    publicclassEmployee{
    privateint id;
    privateStringfirstName;
    privateStringlastName;
    privateint salary;
    
    publicEmployee(){}
    
    publicEmployee(Stringfname,Stringlname,int salary){
    this.firstName=fname;
    this.lastName=lname;
    this.salary= salary;
    }
    
    publicintgetId(){
    return id;
    }
    
    publicvoidsetId(int id ){
    this.id = id;
    }
    
    publicStringgetFirstName(){
    returnfirstName;
    }
    
    publicvoidsetFirstName(Stringfirst_name){
    this.firstName=first_name;
    }
    
    publicStringgetLastName(){
    returnlastName;
    }
    
    publicvoidsetLastName(Stringlast_name){
    this.lastName=last_name;
    }
    
    publicintgetSalary(){
    return salary;
    }
    
    publicvoidsetSalary(int salary ){
    this.salary= salary;
    }
    }
    

    Create Database Tables

    Second step would be creating tables in your database. There would be one table corresponding to each object, you are willing to provide persistence. Consider the objects explained above, need to be stored and retrieved into the following RDBMS table −

    create table EMPLOYEE (
    id INT NOT NULL auto_increment,
    first_name VARCHAR(20)default NULL,
    last_name  VARCHAR(20)default NULL,
    salary     INT  default NULL,
       PRIMARY KEY (id)
    );
    

    Create Mapping Configuration File

    This step is to create a mapping file that instructs Hibernate — how to map the defined class or classes to the database tables.

    < ?xml version ="1.0" encoding ="utf-8"?>
    < !DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
    
    < hibernate-mapping>
    < classname="Employee"table="EMPLOYEE">
    
    < metaattribute="class-description">
             This class contains the employee detail. 
    < /meta>
    
    < idname="id"type="int"column="id">
    < generatorclass="native"/>
    < /id>
    
    < propertyname="firstName"column="first_name"type="string"/>
    < propertyname="lastName"column="last_name"type="string"/>
    < propertyname="salary"column="salary"type="int"/>
    
    < /class>
    < /hibernate-mapping>
    

    Create Application Class

    Finally, we will create our application class with the main() method to run the application. Here, it should be noted that while creating session object, we used our Interceptor class as an argument.

    importjava.util.List;
    importjava.util.Date;
    importjava.util.Iterator;
    
    importorg.hibernate.HibernateException;
    importorg.hibernate.Session;
    importorg.hibernate.Transaction;
    importorg.hibernate.SessionFactory;
    importorg.hibernate.cfg.Configuration;
    
    publicclassManageEmployee{
    privatestaticSessionFactory factory;
    publicstaticvoid main(String[]args){
    
    try{
    factory=newConfiguration().configure().buildSessionFactory();
    }catch(Throwable ex){
    System.err.println("Failed to create sessionFactory object."+ex);
    thrownewExceptionInInitializerError(ex);
    }
    
    ManageEmployee ME =newManageEmployee();
    
    /* Add few employee records in database */
    Integer empID1 =ME.addEmployee("Zara","Ali",1000);
    Integer empID2 =ME.addEmployee("Daisy","Das",5000);
    Integer empID3 =ME.addEmployee("John","Paul",10000);
    
    /* List down all the employees */
    ME.listEmployees();
    
    /* Update employee's records */
    ME.updateEmployee(empID1,5000);
    
    /* Delete an employee from the database */
    ME.deleteEmployee(empID2);
    
    /* List down new list of the employees */
    ME.listEmployees();
    }
    
    /* Method to CREATE an employee in the database */
    publicIntegeraddEmployee(Stringfname,Stringlname,int salary){
    Sessionsession=factory.openSession(newMyInterceptor());
    Transactiontx=null;
    IntegeremployeeID=null;
    
    try{
    tx=session.beginTransaction();
    Employeeemployee=newEmployee(fname,lname, salary);
    employeeID=(Integer)session.save(employee);
    tx.commit();
    }catch(HibernateException e){
    if(tx!=null)tx.rollback();
    e.printStackTrace();
    }finally{
    session.close();
    }
    returnemployeeID;
    }
    
    /* Method to  READ all the employees */
    publicvoidlistEmployees(){
    Sessionsession=factory.openSession(newMyInterceptor());
    Transactiontx=null;
    
    try{
    tx=session.beginTransaction();
    List employees =session.createQuery("FROM Employee").list();
    for(Iteratoriterator=employees.iterator();iterator.hasNext();){
    Employeeemployee=(Employee)iterator.next();
    System.out.print("First Name: "+employee.getFirstName());
    System.out.print("  Last Name: "+employee.getLastName());
    System.out.println("  Salary: "+employee.getSalary());
    }
    tx.commit();
    }catch(HibernateException e){
    if(tx!=null)tx.rollback();
    e.printStackTrace();
    }finally{
    session.close();
    }
    }
    
    /* Method to UPDATE salary for an employee */
    publicvoidupdateEmployee(IntegerEmployeeID,int salary ){
    Sessionsession=factory.openSession(newMyInterceptor());
    Transactiontx=null;
    
    try{
    tx=session.beginTransaction();
    Employeeemployee=(Employee)session.get(Employee.class,EmployeeID);
    employee.setSalary( salary );
    		session.update(employee);
    tx.commit();
    }catch(HibernateException e){
    if(tx!=null)tx.rollback();
    e.printStackTrace();
    }finally{
    session.close();
    }
    }
    
    /* Method to DELETE an employee from the records */
    publicvoiddeleteEmployee(IntegerEmployeeID){
    Sessionsession=factory.openSession(newMyInterceptor());
    Transactiontx=null;
    
    try{
    tx=session.beginTransaction();
    Employeeemployee=(Employee)session.get(Employee.class,EmployeeID);
    session.delete(employee);
    tx.commit();
    }catch(HibernateException e){
    if(tx!=null)tx.rollback();
    e.printStackTrace();
    }finally{
    session.close();
    }
    }
    }
    

    Compilation and Execution

    Here are the steps to compile and run the above mentioned application. Make sure, you have set PATH and CLASSPATH appropriately before proceeding for the compilation and execution.

    • Create hibernate.cfg.xml configuration file as explained in configuration chapter.
    • Create Employee.hbm.xml mapping file as shown above.
    • Create Employee.java source file as shown above and compile it.
    • Create MyInterceptor.java source file as shown above and compile it.
    • Create ManageEmployee.java source file as shown above and compile it.
    • Execute ManageEmployee binary to run the program.


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