Easy Tricks for JPA, Spring and Hibernate

Java frameworks have evolved, making us write less code and ship faster! Here, I will discuss some neat tricks to address common concerns in Hibernate and Spring.

1. Auto Scan JPA entities. This is an old trick!

Listing entities (via <class> element)  in persistence.xml isn't needed any more. You may drop it all together and use Spring's packagesToScan feature. Sample spring configuration below.

<bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
 <property name="persistenceUnitName" value="HelloService" />
 <property name="packagesToScan" value="com.x.y.z" />
 <property name="dataSource" ref="dataSource" />
 <property name="jpaVendorAdapter">
  <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
   <property name="showSql" value="true" />
   <property name="databasePlatform" value="org.hibernate.dialect.MySQL5Dialect" />
  </bean>
 </property>
</bean>

2.Entities often have audit columns like the following: 

@Column(name = "created_by", updatable = false)
protected String createdBy;

@Column(name = "creation_date", updatable = false)
protected Date createdOn;

@Column(name = "last_updated_by")
protected String lastUpdatedBy;

@Column(name = "last_updated")
protected Date lastUpdatedOn;

And providing those values require either writing pre-insert/update Hibernate listeners or writing setters. How about sprinkling some annotations to get the job done? I mean ... 

@Column(name = "created_by", updatable = false)
@ModifiedBy
protected String createdBy;

@Column(name = "creation_date", updatable = false)
@CreationTimestamp
protected Date createdOn;

@Column(name = "last_updated_by")
@ModifiedBy
protected String lastUpdatedBy;

@Column(name = "last_updated")
@UpdateTimestamp
protected Date lastUpdatedOn; 

It is quite simple. Read this:http://docs.jboss.org/hibernate/orm/4.3/topical/html/generated/GeneratedValues.html

3. Applications are deployed in different environments and configuring those are often messy and by messy I mean repetitive. Spring property place holder has a neat trick by using property of property to dynamically create the property key for each environment.

Sample common properties file for all environments. 

# ec2.properties is a properties for all environment.  
awsAccountId=${${env}.awsAccountId}
availabilityZone=${${env}.availabilityZone}
keyName=${${env}.dev}
expiry=${${env}.expiry}
instanceType=${${env}.instanceType}

dev.awsAccountId = 11111111111
dev.availabilityZone = us-east-1a
dev.keyName = dev
dev.expiry = 360000
dev.instanceType = m1.small

beta.awsAccountId = 222222222222
beta.availabilityZone = us-east-1a
beta.keyName = beta
beta.expiry = 360000
beta.instanceType = m1.large

Here is how you will use this file in spring context configuration - 

<bean id="ec2Settings"  class="x.y.z.EC2Settings">  
 <property name="accountId" value="${awsAccountId}" />  
 <property name="zone" value="${availabilityZone}" />  
 <property name="key" value="${keyName}" />  
 <property name="expiry" value="${expiry}" />
 <property name="instanceType" value="${instanceType}" />  
</bean>