Hibernate (1) Hibernate introduction and simple examples to understand hibernate transaction rollback usage

1 Hibernate profileHibernate is an ORM (object relation mapping objects-relational mapping) framework that is in the project's Persistence Layer, also known as the Persistence layer framework (persistence layer framework and OJB, etc.). Hibernate is essentially a lightweight encapsulation of JDBC. 2 Benefits of using Hibernate

① introduces hibernate to refine worker roles, giving programmers more attention to business processes. Let database personnel pay more attention to the various operations related to the database.
② layering is clearer and less coupled
③ versatility: It's easier to move from one database platform to another
④: Programming Java objects with relational databases for easier operation
⑤ Performance Guarantee: Hibernate may be based on different databases, processing different operations is the most optimized SQL statements, without our thinking, for the sub-algorithm, in Hibernate will appear more simple and reliable.
⑥ Increased program Robustness 3 Some concepts and development methods

①:Three ways Hibernate is developed:
-by Domain object->mapping->db. (Official recommendation)
-Starting with DB, use tools to generate mapping and domain Object. (More use)
-Starts with the mapping file.
② data Persistence layer/Object Relational mapping File This file describes the relationship of tables and objects, and the corresponding relationship between the properties of the object and the fields of the table; naming convention : domain object name. Hbm.xml " 4 simple example

① Introducing Hibernate Development Kit (HTTP://PAN.BAIDU.COM/S/1QYWE6NY)
② Creating a data table, writing domain code
③ writing Employee.hbm.xml file (Object Relational mapping file)

<?xml version= "1.0" encoding= "Utf-8"?> <!--mapping file requires a DTD to specify format--<! DOCTYPE hibernate-mapping Public "-//hibernate/hibernate mapping DTD 3.0//en" "Http://hibernate.sourceforge.net/hi Bernate-mapping-3.0.dtd ">  
 ④ manual Configuration  hibernate.cfg.xml  file (Hibernate's core profile), which is used to configure the type of database connected, driver, user name, Password, etc. (HIBERNATE-DISTRIBUTION-3.3.1.GA-DIST\HIBERNATE-DISTRIBUTION-3.3.1.GA\PROJECT\ETC) 

<?xml version= ' 1.0 ' encoding= ' utf-8 '?> <! DOCTYPE hibernate-configuration Public "-//hibernate/hibernate configuration DTD 3.0//en" "Http://hibernat
        E.sourceforge.net/hibernate-configuration-3.0.dtd ">  
 ⑤ Write  testmain.java  file, test crud 
 

public static void Deleteemployee () {Session session = Mysessionfactory.getsessionfactory (). Opensession ();

    Transaction ts = session.begintransaction ();

    Session.delete (Session.load (Employee.class, 3));

    Ts.commit ();
Session.close ();

    } public static void UpdateEmployee () {Session session = Mysessionfactory.getsessionfactory (). Opensession ();

    Transaction ts = session.begintransaction ();

    Modify User Employee employee = (employee) session.load (Employee.class, 3);
    Employee.setname ("Hello");

    Ts.commit ();
Session.close (); } public static void AddEmployee () {///1 Creates a configuration that is used to read the Hibernate.cfg.xml file and complete initialization//configuration con
    figuration = new Configuration (). Configure ("Hibernate.cfg.xml"); Configuration configuration = new configuration (). Configure (); The default is Hibernate.cfg.xml//2 Create Sessionfactory "This is a session factory, is a heavyweight object" sessionfactory sessionfactory = Configuration.bu
    Ildsessionfactory (); 3 Create session, equivalent to JDBC ConneCtion "" Session session = Sessionfactory.opensession ();

    4 for Hibernate, a transaction is required to commit Transaction transcation = Session.begintransaction () When a crud operation is performed;
    Add an employee employee employees employee = new Employee ();
    Employee.setname ("Jiaozenglian");
    Employee.setemail ("jiao@sohu.com");

    Employee.sethiredate (New Date ()); Save Session.save (employee);
    ==> INSERT INTO ...//submit transcation.commit ();
Session.close (); }
 
Mysessionfactory.java file (set it as a singleton because the configuration object is resource-intensive)

Import org.hibernate.SessionFactory;
Import org.hibernate.cfg.Configuration;
Public final class Mysessionfactory {
    private static sessionfactory sessionfactory = null;
    static {
        sessionfactory = new Configuration (). Configure (). Buildsessionfactory ();
    }

    public static Sessionfactory Getsessionfactory () {
        return sessionfactory;
    }
}
 
5 Switching databases 
① First, reconfigure the hibernate.cfg.xml file

<?xml version= ' 1.0 ' encoding= ' utf-8 '?> <! DOCTYPE hibernate-configuration Public "-//hibernate/hibernate configuration DTD 3.0//en" "Http://hibernat
        E.sourceforge.net/hibernate-configuration-3.0.dtd ">  
 ② configuration  Employee.hbm.xml  file 
 

<?xml version= "1.0" encoding= "Utf-8"?> <!--mapping file requires a DTD to specify format--<! DOCTYPE hibernate-mapping Public "-//hibernate/hibernate mapping DTD 3.0//en" "Http://hibernate.sourceforge.net/hi Bernate-mapping-3.0.dtd ">  
6 Hibernate Fundamentals Diagram 

only the configuration is a class, the other three are interface interface. 
- Other libraries required by Hibernate :
7 Optimizing UpdateEmployee Adding a transaction rollback

public static void UpdateEmployee () {
    //ROLLBACK TRANSACTION
    Session session = Mysessionfactory.getsessionfactory (). Opensession ();

    Transaction ts = null;
    try {
        ts = session.begintransaction ();
        Modify User
        Employee employee = (employee) session.load (Employee.class, 3);

        Employee.setname ("Nihao");

        Ts.commit ();

    } catch (Exception e) {
        if (ts!=null) {
            ts.rollback ();
        }
        E.printstacktrace ();
        throw new RuntimeException (E.getmessage ());
    } Finally {
        if (session!=null && session.isopen ()) {
            session.close ();}}
}