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Friday, September 26. 2008Hibernate Tutorial part 4 - annotations and mavenIn the last part of my hibernate tutorials I showed how to get a simple application inserting data into a database. This part doesn't expand on that in terms of features, in fact, this tutorial actually does less! However, the last tutorial required you to download a whole load of JAR files, and manage all dependencies. I did make this easy for you, by providing a single download and telling you exactly what you needed - but this time, I'm going to make it even easier! The purpose of this is to get you started with Hibernate annotations, and Maven. All you need is a text editor, a working Java 5 or higher install, and Maven. If you've never heard of Maven before, you might want to look at my getting started with spring and maven tutorial The first step we want to take is to create our project. We're going to use Maven to do this, by doing as follows: mvn archetype:generate --batch-mode \ -DarchetypeArtifactId=maven-archetype-quickstart \ -DgroupId=uk.co.pookey.hibernate \ -DartifactId=hibernate
If you want to know more about what those options mean, you should have a look at the Maven documentation. This command will create a skeleton project in the <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/maven-v4_0_0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>uk.co.pookey.hibernate</groupId> <artifactId>hibernate</artifactId> <packaging>jar</packaging> <version>1.0-SNAPSHOT</version> <name>hibernate</name> <url>http://maven.apache.org</url> <build> <plugins> <plugin> <artifactId>maven-compiler-plugin</artifactId> <version>2.0.2</version> <configuration> <source>1.5</source> <target>1.5</target> </configuration> </plugin> </plugins> </build> <dependencies> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>3.8.1</version> <scope>test</scope> </dependency> <dependency> <groupId>org.hibernate</groupId> <artifactId>hibernate</artifactId> <version>3.2.6.ga</version> </dependency> <dependency> <groupId>org.hibernate</groupId> <artifactId>hibernate-annotations</artifactId> <version>3.3.1.GA</version> </dependency> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>5.1.6</version> </dependency> </dependencies> </project> The important things to note here are that we've changed the config of maven-compiler-plugin to compile for java 1.5 - without doing this annotations would not work. Also, notice the dependencies we've added - we've told maven we need the hibernate, hibernate-annotations, and mysql connector libraries. Maven will take care of downloading them, and all of their dependencies when we build - you no longer need to worry about them!
Our next step is to configure our hibernate settings. As before, we do this in <?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="connection.url">jdbc:mysql://localhost/hibernate</property> <property name="connection.username">root</property> <property name="connection.password">"Schipiaf2</property> <property name="connection.driver_class">com.mysql.jdbc.Driver</property> <property name="dialect">org.hibernate.dialect.MySQLDialect</property> <property name="show_sql">true</property> <property name="format_sql">true</property> <property name="hbm2ddl.auto">create</property> <!-- JDBC connection pool (use the built-in) --> <property name="connection.pool_size">1</property> <property name="current_session_context_class">thread</property> </session-factory> </hibernate-configuration>
That's most of the configuration done - it's time to write some code! When we created our project, Maven created a class package uk.co.pookey.hibernate; import org.hibernate.Session; import org.hibernate.SessionFactory; import org.hibernate.Transaction; import org.hibernate.cfg.AnnotationConfiguration; public class App { public static void main( String[] args ) { SessionFactory sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory(); Session session = sessionFactory.getCurrentSession(); } } That's it! We have hibernate installed, configured, and running. We can test that it's all working now by asking maven to compile and run our project. There will be no useful output, but if this is the first time you're running Maven, you'll see it download all the required JAR files, and output a whole load of stuff as your application and hibernate start. Here's the command you need: mvn clean compile exec:java -Dexec.mainClass=uk.co.pookey.hibernate.App
Now it's time to add a model to our project. We're going to put models in the package uk.co.pookey.hibernate.model; import java.util.Date; import javax.persistence.Entity; import javax.persistence.Id; import javax.persistence.GeneratedValue; @Entity public class Blog { private Long id; private String subject; private String body; private Date createdAt; @Id @GeneratedValue public Long getId() { return id; } public void setId(Long id) { this.id = id; } public String getSubject() { return subject; } public void setSubject(String subject) { this.subject = subject; } public String getBody() { return body; } public void setBody(String body) { this.body = body; } public Date getCreatedAt() { return createdAt; } public void setCreatedAt(Date createdAt) { this.createdAt = createdAt; } }
Notice we've not annotated all of our properties, in fact - we only did the Id field. We need to do the Id field to inform hibernate this is our identifier column - hibernate will 'guess' the other fields magically, so that's really all we need to do here! Much easier then writing an XML file as we did before. One more thing we do need to do is modify our <hibernate-configuration> <session-factory> .... <mapping class="uk.co.pookey.hibernate.model.Blog" /> </session-factory> </hibernate-configuration>
We are nearly finished now - all that remains is to create a package uk.co.pookey.hibernate; import uk.co.pookey.hibernate.model.Blog; import org.hibernate.Session; import org.hibernate.SessionFactory; import org.hibernate.Transaction; import org.hibernate.cfg.AnnotationConfiguration; public class App { public static void main( String[] args ) { SessionFactory sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory(); Session session = sessionFactory.getCurrentSession(); Transaction tx = session.beginTransaction(); Blog b = new Blog(); session.save(b); tx.commit(); } } That's it! We're done. Here is the output when we run our application, trimmed to show only the exciting bits. $ mvn clean compile exec:java -Dexec.mainClass=uk.co.pookey.hibernate.App ... 26-Sep-2008 22:46:56 org.hibernate.tool.hbm2ddl.SchemaExport execute INFO: schema export complete Hibernate: insert into Blog (body, createdAt, subject) values (?, ?, ?) ... Here is the source code, should you want a copy: hibernate-part4.tar.gz. Notice this file is considerably smaller than the previous example - as it doesn't' need to contain the JAR files - Maven will sort that out for you! This of course is just an introduction to annotations and hibernate. Perhaps if I write part 5, I'll show more. Hopefully though this is enough to get you started and ready to experiment yourselves.
I'm only writing this article because of the positive feedback I got from previous parts - your feedback does mean a lot to me (sad isn't it? Trackbacks
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) - so if you found this useful please do leave a comment letting me know!