About this Tutorial
This tutorial shows two things:
- You don't need to write DAOs if you just need generic CRUD functionality.
- How to write DAOs when you need custom functionality.
If you're new to Hibernate, you might want to read the Hibernate Reference Guide before starting this tutorial.
Table of Contents
- Register a personDao bean definition
- Create a DAO Test to test finder functionality
- Create a DAO Interface and implementation
- Run the DAO Test
The code for this tutorial is located in the "tutorial-hibernate" module of the appfuse-demos project on Google Code. Use the following command to check it out from Subversion:
Register a personDao bean definition
AppFuse 2.x doesn't require you to write a DAO to persist a POJO. You can use one of the pre-existing classes if all you need is CRUD on an object:
- GenericDaoHibernate: A generics-based class that requires you to create a Spring bean definition.
- UniversalDaoHibernate: A class that requires you to cast to the specific object type.
UniversalDaoHibernate class is already registered as a "universalDao" bean, so you can easily use it without any additional configuration. However, many developers prefer the generics-based DAO because it provides type safety. To register a personDao bean, open src/main/webapp/WEB-INF/applicationContext.xml (or core/src/main/resources/applicationContext.xml for a modular archetype) and add the following to it:
After doing this, you can use this bean as a dependency of an object by adding the following setter method (and the appropriate wiring in Spring):
If you need more than just CRUD functionality, you'll want to continue reading below. If not, you can continue to Creating new Managers. This is a tutorial for creating Business Facades, which are similar to Session Facades, but don't use EJBs. These facades are used to provide communication from the front-end to the DAO layer.
Create a DAO Test to test finder functionality
Now you'll create a DaoTest to test that your DAO works. "Wait a minute," you say, "I haven't created a DAO!" You are correct. However, I've found that Test-Driven Development breeds higher quality software. For years, I thought write your test before your class was hogwash. It just seemed stupid. Then I tried it and I found that it works great. The only reason I do test-driven stuff now is because I've found it rapidly speeds up the process of software development.
To start, create a
PersonDaoTest.java class in your src/test/java/**/dao directory (or core/src/test/java/**/dao directory for a modular archetype). This class should extend
org.appfuse.dao.BaseDaoTestCase, a subclass of Spring's AbstractTransactionalDataSourceSpringContextTests. This parent class is used to load Spring's ApplicationContext (since Spring binds interfaces to implementations), and for (optionally) loading a .properties file that has the same name as your
*Test.class. In this example, if you put a
PersonDaoTest.properties file in src/test/resources/org/appfuse/tutorial/dao, this file's properties will be available via an "rb" variable.
The code you see above is what you need for a basic Spring integration test that initializes and configures an implementation of PersonDao. Spring will use autowiring by name to call the
setPersonDao() method and set the "personDao" bean as a dependency of this class.
Now you need test that the finder method works in your DAO. To do this, create a method that begin with "test" (all lower case). As long as this method is public, has a
void return type and take no arguments, it invoked and run by JUnit. Add the following method to your
You'll notice that this method relies on pre-existing data in order to pass. The DbUnit Maven Plugin is used to populate the database with test data before the tests are run, so you can simply add the new table/record to the src/test/resources/sample-data.xml file (or core/src/test/resources/sample-data.xml for a modular archetype).
If you reformat the XML in sample-data.xml, make sure no line breaks are added inside the tag values. I was surprised when <password>xxxxxxx</password> was broken into three lines. Since the password was no longer decryptable with extra tabs and newline characters, I could no longer log in under any name. This is a feature of DBUnit that allows adding any characters to the database content.
Since the PersonDao you're about to write includes CRUD functionality, you can also write a test to verify CRUD works properly.
In the above example, you can see that person.set*(value) is being called to populate the Person object before saving it. This is easy in this example, but it could get quite cumbersome if you're persisting an object with 10 required fields. This is why a ResourceBundle exists in
BaseDaoTestCase. Simply create a
PersonDaoTest.properties file in the same directory as
PersonDaoTest.java and define your property values inside it:
The personDao.save() method seems to call the hibernateTemplate.merge method which doesn't connect the person object to the session. As such the person.getId() returns null as it's auto-generated. It worked if i called hibernateTemplate.saveOrUpdate().
I tend to just hard-code test values into Java code - but the .properties file is an option that works great for large objects.
Then, rather than calling person.set* to populate your objects, you can use the
At this point, the
PersonDaoTest class won't compile yet because there is no
PersonDao.class in your classpath, you need to create it.
Create a DAO Interface and implementation
PersonDao.java interface in the src/main/java/**/dao (or core/src/main/java/**/dao for a modular archetype) directory and specify the finder method for any implementation classes.
Notice in the class above there is no exception on the method signature. This is due to the power of Spring and how it wraps Exceptions with RuntimeExceptions. At this point, you should be able to compile all your code using your IDE or mvn test-compile. However, if you try to run mvn test -Dtest=PersonDaoTest, you will get an error:
Unfortunately, this doesn't tell you much about what went wrong. To find the real problem, you need to open target/surefire-reports/org.appfuse.tutorial.dao.PersonDaoTest.txt (or core/target/surefire-reports/org.appfuse.tutorial.dao.PersonDaoTest.txt for a modular archetype). In this file, the real problem is shown:
|Showing errors in your console|
To show testing errors in your console, append -Dsurefire.useFile=false to your mvn test command.
This is an error message from Spring - indicating that you need to specify a bean named "personDao" in a Spring context file. Before you do that, you need to create the
PersonDaoHibernate class that implements the finder method in
PersonDao. To do this, create a new class in src/main/java/**/dao/hibernate (or core/src/main/java/**/dao/hibernate for the modular archetype) and name it
PersonDaoHibernate.java. It should extend
GenericDaoHibernate and implement
PersonDao. Javadocs eliminated for brevity.
Now, if you try to run mvn test -Dtest=PersonDaoTest, you will get the same error. You need to configure Spring so it knows that
PersonDaoHibernate is the implementation of
applicationContext.xml file in src/main/webapp/WEB-INF (or core/src/main/resources for a modular archetype) and add the following XML to it:
Run the DAO Test
Save all your edited files and try running mvn test -Dtest=PersonDaoTest one more time.
Yeah Baby, Yeah:
Total time: 9 seconds
|Open Session In View Filter|
If you want to use Hibernate's lazy-loading feature in your application, you'll need to uncomment the lazyLoadingFilter (and its mapping) in web.xml.
Next Up: Part II: Creating new Managers - A HowTo for creating Business Facades, which are similar to Session Facades, but don't use EJBs. These facades are used to provide communication from the front-end to the DAO layer.