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HiLo uses
a hi/lo algorithm to efficiently generate
identifiers of type long, short or
int, given a table and column (by
default hibernate_unique_key and next_hi
respectively) as a source of hi values.
The hi/lo algorithm generates identifiers
that are unique only for a particular
database.
- This generator is database independent
- for the first record, the id value will be inserted as 1
- for the second record the id value will be inserted as 32768
- for the next records the id value will be incremented by 32768 and will stores into the database (i mean adds to the previous)
- actually this hibernate stores the count of id values generated in a column of separated table, with name “hibernate_unique_key” by default with the column name “next_hi”
- if we want to modify the table and column names theen wee need to pass 2 parameter’s for the hilo generators
Hilo (high and low) algorithm:
This algorithm generates identifiers of type long, short, int by using given table and its column as the source of ‘high’ values. The class name of this algorithm is “org.hibernate.id.TableHiLoGenerator”
This algorithm requires 3 mandatory parameters. Table, column, Max_lo
The column in the special table keeps track of the number of records that are inserted using this HiLo algorithm.
When multiple identity values are generated using this Hilo algorithm, the difference between each two values is (“Max_lo value+1”). This algorithm works with all database software.
Example: SQL> select * from mytable;
Mycol
400 —-> you can insert any value
<id name=”sno” column=”eid”>
<generator class=”hilo”>
<param name=”table”>mytable</param>
<param name=”column”>mycol</param>
<param name=”max_lo”>10</param>
</id>
Note: The first id value that has come through this algorithm is dynamic and random value. For this algorithm table must be empty.
Here is the example code to test HiLo functionality :
This is hibernate.cfg.xml file for connecting the postgreSQL database.
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<!-- <session-factory> <property name="hibernate.connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
hibernate word is optional <property name="connection.url">jdbc:oracle:thin:@localhost:1521:ORCL</property>
<property name="hibernate.connection.username">kcv</property> <property name="hibernate.connection.password">kcv</property>
<property name="hibernate.dialect">org.hibernate.dialect.Oracle10gDialect</property>
<property name="show_sql">true</property> <mapping resource="Employee.hbm.xml"/>
</session-factory> -->
<session-factory>
<property name="hibernate.current_session_context_class">thread</property>
<property name="hbm2ddl.auto">create</property>
<property name="dialect">org.hibernate.dialect.PostgreSQLDialect</property>
<property name="connection.url">jdbc:postgresql://localhost:5432/hibernate</property>
<property name="connection.username">postgres</property>
<property name="connection.password">password</property>
<property name="connection.driver_class">org.postgresql.Driver</property>
<property name="show_sql">true</property>
<property name="format_sql">true</property>
<property name="use_sql_comments">true</property>
<mapping resource="EmployeeBean.hbm.xml" />
</session-factory>
</hibernate-configuration>
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This is EmployeeBean.hbm.xml mapping file for map the Entity(POJO) class to columns.
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="com.cv.hibernate.algorithm.model.EmployeeBean"
table="EMPLOYEE_HILO">
<id name="id" type="java.lang.Long">
<column name="EID" precision="10" scale="0" />
<generator class="hilo">
<!-- Comment below lines if you need the actual HiLo algorithm implementation -->
<param name="table">EMPLOYEE_HILO</param>
<param name="column">EID</param>
<param name="max_lo">5</param>
</generator>
</id>
<property name="firstName" type="java.lang.String">
<column name="FIRSTNAME" length="29" not-null="true" />
</property>
<property name="lastName" type="java.lang.String">
<column name="LASTNAME" length="29" not-null="true" />
</property>
<property name="email" type="java.lang.String">
<column name="EMAIL" length="39" not-null="true" />
</property>
</class>
</hibernate-mapping>
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This is HiLo.java main class having the application business logic.
package com.cv.hibernate.algorithm;
import org.apache.log4j.Logger;
import org.hibernate.Session;
import com.cv.hibernate.algorithm.model.EmployeeBean;
import com.cv.hibernate.algorithm.util.HibernateUtil;
/**
* @author Chandra Vardhan
*/
public class HiLo {
private final static Logger logger = Logger.getLogger(HiLo.class);
public static void main(String args[]) throws Exception {
HibernateUtil.saveOrUpdate();
Session ses = HibernateUtil.getSession();
EmployeeBean eb = new EmployeeBean();
eb.setFirstName("chandra");
eb.setLastName("vardhan");
eb.setEmail("meetkodam@gmail.com");
ses.beginTransaction();
ses.saveOrUpdate(eb);
logger.info("Saved successful...");
ses.getTransaction().commit();
HibernateUtil.closeSession();
}
} |
This is EmployeeBean.java Entity(POJO) class having the fields needs to be configured in mapping file.
package com.cv.hibernate.algorithm.model;
/**
* @author Chandra Vardhan
*/
public class EmployeeBean {
private Long id;
private String firstName;
private String lastName;
private String email;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
} |
This is HibernateUtil.java utility class for getting the database connection.
package com.cv.hibernate.algorithm.util;
import java.util.List;
import org.apache.log4j.Logger;
import org.hibernate.HibernateException;
import org.hibernate.Query;
import org.hibernate.SQLQuery;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;
import com.cv.hibernate.algorithm.model.EmployeeBean;
/**
* Configures and provides access to Hibernate sessions, tied to the current
* thread of execution. Follows the Thread Local Session pattern, see
* {@link http://hibernate.org/42.html }.
*/
public class HibernateUtil {
private final static Logger logger = Logger.getLogger(HibernateUtil.class);
/**
* Location of hibernate.cfg.xml file. Location should be on the classpath
* as Hibernate uses #resourceAsStream style lookup for its configuration
* file. The default classpath location of the hibernate config file is in
* the default package. Use #setConfigFile() to update the location of the
* configuration file for the current session.
*/
private static String CONFIG_FILE_LOCATION = "hibernate.cfg.xml";
private static final ThreadLocal<Session> threadLocal = new ThreadLocal<Session>();
private static Configuration configuration = new Configuration();
private static SessionFactory sessionFactory;
static {
try {
configuration = configuration.configure(CONFIG_FILE_LOCATION);
StandardServiceRegistryBuilder builder = new StandardServiceRegistryBuilder()
.applySettings(configuration.getProperties());
sessionFactory = configuration.buildSessionFactory(builder.build());
logger.info("%%%% Connection successful %%%%");
} catch (Exception e) {
logger.error("%%%% Error Creating SessionFactory %%%%");
e.printStackTrace();
}
}
private HibernateUtil() {
}
/**
* Returns the ThreadLocal Session instance. Lazy initialize the
* <code>SessionFactory</code> if needed.
*
* @return Session
* @throws HibernateException
*/
public static Session getSession() throws HibernateException {
Session session = (Session) threadLocal.get();
if (session == null || !session.isOpen()) {
if (sessionFactory == null) {
rebuildSessionFactory();
}
session = (sessionFactory != null) ? sessionFactory.openSession()
: null;
threadLocal.set(session);
}
return session;
}
/**
* Rebuild hibernate session factory
*
*/
public static void rebuildSessionFactory() {
try {
configuration = configuration.configure(CONFIG_FILE_LOCATION);
StandardServiceRegistryBuilder builder = new StandardServiceRegistryBuilder()
.applySettings(configuration.getProperties());
sessionFactory = configuration.buildSessionFactory(builder.build());
logger.info("%%%% Connection successful %%%%");
} catch (Exception e) {
logger.error("%%%% Error Creating SessionFactory %%%%");
e.printStackTrace();
}
}
/**
* Close the single hibernate session instance.
*
* @throws HibernateException
*/
public static void closeSession() throws HibernateException {
Session session = (Session) threadLocal.get();
threadLocal.set(null);
if (session != null) {
session.close();
System.exit(0);
}
}
/**
* return session factory
*
*/
public static SessionFactory getSessionFactory() {
return sessionFactory;
}
/**
* return hibernate configuration
*
*/
public static Configuration getConfiguration() {
return configuration;
}
public static void saveOrUpdate() {
Session ses = getSession();
Query q = ses.createQuery("FROM EmployeeBean");
List list = q.list();
if (list != null && list.size() <= 0) {
SQLQuery query = ses
.createSQLQuery("insert into EMPLOYEE_HILO values(1,'chandra','vardhan','meetkodam@gmail.com')");
query.addEntity(EmployeeBean.class);
ses.beginTransaction();
int i = query.executeUpdate();
if (i > 0)
logger.info("Saved successful...");
ses.getTransaction().commit();
}
ses.close();
}
} |
This is log4j.properties file having the entries for logging the information into the console/file.
#By default enabling Console appender
# Root logger option
log4j.rootLogger=INFO, stdout
# Redirect log messages to console
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%-5p [%c]:%L -->> %m%n
# Redirect log messages to a log file
#log4j.appender.file=org.apache.log4j.RollingFileAppender
#log4j.appender.file.File=C:\\servlet-application.log
#log4j.appender.file.MaxFileSize=5MB
#log4j.appender.file.MaxBackupIndex=10
#log4j.appender.file.layout=org.apache.log4j.PatternLayout
#log4j.appender.file.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n
|
This is pom.xml file having the entries of dependency jars and information to build the application .
| <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.cv.hibernate.algorithm</groupId>
<artifactId>algorithms</artifactId>
<version>1.0</version>
<dependencies>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-entitymanager</artifactId>
<version>4.3.5.Final</version>
</dependency>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-c3p0</artifactId>
<version>4.3.5.Final</version>
</dependency>
<dependency>
<artifactId>hibernate-core</artifactId>
<groupId>org.hibernate</groupId>
<version>4.3.5.Final</version>
</dependency>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-validator</artifactId>
<version>4.2.0.Final</version>
</dependency>
<dependency>
<groupId>org.hibernate.common</groupId>
<artifactId>hibernate-commons-annotations</artifactId>
<version>4.0.4.Final</version>
</dependency>
<dependency>
<groupId>org.hibernate.javax.persistence</groupId>
<artifactId>hibernate-jpa-2.0-api</artifactId>
<version>1.0.1.Final</version>
</dependency>
<dependency>
<groupId>javax.validation</groupId>
<artifactId>validation-api</artifactId>
<version>1.0.0.GA</version>
provided
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.6.4</version>
</dependency>
<dependency>
<groupId>org.jboss.logging</groupId>
<artifactId>jboss-logging</artifactId>
<version>3.1.0.CR2</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
<version>1.6.4</version>
</dependency>
<dependency>
<groupId>postgresql</groupId>
<artifactId>postgresql</artifactId>
<version>9.1-901.jdbc4</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-simple</artifactId>
<version>1.7.5</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.3</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
</plugins>
</build>
</project> |
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