04-2-B-Spring-Tools-Suite.adoc

Setting up a Spring-based Backend

You can download the Spring Tools Suite IDE from here.

Running the Backend Application from Eclipse

1. Import the EventRegistration-Backend Spring Boot project as a Gradle project from File > Import…​ > Gradle > Existing Gradle project using the default settings. Select the previously generated Spring project folder as the root of the project.
   

2. Ignore the bin folder.
   

3. Find the EventRegistrationApplication.java source file, then right click and select Run As > Spring Boot App. The application will fail to start, since the database is not yet configured, but this action will create an initial run configuration. Example console output (fragment):

   [...]
   ***************************
   APPLICATION FAILED TO START
   ***************************
   
   Description:
   
   Failed to configure a DataSource: 'url' attribute is not specified and no embedded datasource could be configured.
   
   Reason: Failed to determine a suitable driver class
   [...]

4. Obtain the database URL to access the database remotely, e.g., by opening up a terminal and running: heroku run echo \$JDBC_DATABASE_URL --app=<YOUR_BACKEND_APP_NAME>.

5. In Eclipse, open the EventRegistration-Backend - EventregistrationApplication run configuration page and add an environment variable called SPRING_DATASOURCE_URL with the value obtained in the previous step.
   

6. Add the spring.jpa.hibernate.ddl-auto=update to application.properties. The database content along with the tables this way will be deleted (as necessary) then re-created each time your application starts.
   

   Important

   In production, the value of this property should be none (instead of update). Possible values are none, create, validate, and update.

7. If needed: troubleshooting:

   • If you get an error message saying something similar to createClob() is not yet implemented, then you can try setting the spring.jpa.properties.hibernate.jdbc.lob.non_contextual_creation=true variable in your application.properties. It could be a workaround a workaround for an issue with Postgres.
     

   • Sometimes environment variables don’t work with Spring apps. In this case you can set the spring.datasource.url, the spring.datasource.username, and the spring.datasource.password variables in the application properties as an alternative to setting the SPRING_DATASOURCE_URL environment variable.
     

   • Make sure no other apps are running on localhost:8080. You can test it by opening the browser and entering localhost:8080 as the address.

Spring Transactions

1. Verify the contents of the EventRegistrationApplication class:

   package ca.mcgill.ecse321.eventregistration;
   
   import org.springframework.boot.autoconfigure.SpringBootApplication;
   import org.springframework.boot.SpringApplication;
   import org.springframework.web.bind.annotation.RestController;
   import org.springframework.web.bind.annotation.RequestMapping;
   
   @RestController
   @SpringBootApplication
   public class EventRegistrationApplication {
   
   	public static void main(String[] args) {
   		SpringApplication.run(EventRegistrationApplication.class, args);
   	}
   
   	@RequestMapping("/")
   	public String greeting() {
   		return "Hello world!";
   	}
   }

2. Create a new package in src/main/java and name it ca.mcgill.ecse321.eventregistration.dao.

3. Create the EventRegistrationRepository class within this new package

   package ca.mcgill.ecse321.eventregistration.dao;
   
   import java.sql.Date;
   import java.sql.Time;
   import java.util.List;
   
   import javax.persistence.EntityManager;
   import javax.persistence.TypedQuery;
   
   import org.springframework.beans.factory.annotation.Autowired;
   import org.springframework.stereotype.Repository;
   import org.springframework.transaction.annotation.Transactional;
   
   import ca.mcgill.ecse321.eventregistration.model.Person;
   import ca.mcgill.ecse321.eventregistration.model.Event;
   
   @Repository
   public class EventRegistrationRepository {
   
   	@Autowired
   	EntityManager entityManager;
   
   	@Transactional
   	public Person createPerson(String name) {
   		Person p = new Person();
   		p.setName(name);
   		entityManager.persist(p);
   		return p;
   	}
   
   	@Transactional
   	public Person getPerson(String name) {
   		Person p = entityManager.find(Person.class, name);
   		return p;
   	}
   
   	@Transactional
   	public Event createEvent(String name, Date date, Time startTime, Time endTime) {
   		Event e = new Event();
   		e.setName(name);
   		e.setDate(date);
   		e.setStartTime(startTime);
   		e.setEndTime(endTime);
   		entityManager.persist(e);
   		return e;
   	}
   
   	@Transactional
   	public Event getEvent(String name) {
   		Event e = entityManager.find(Event.class, name);
   		return e;
   	}
   
   }

4. Add a new method that gets all events before a specified date (deadline). Use a typed query created from an SQL command:

   @Transactional
   public List<Event> getEventsBeforeADeadline(Date deadline) {
   	TypedQuery<Event> q = entityManager.createQuery("select e from Event e where e.date < :deadline",Event.class);
   	q.setParameter("deadline", deadline);
   	List<Event> resultList = q.getResultList();
   	return resultList;
   }

Note

To try the methods, you can create a JUnit test under src/test/java. Currently the methods in EventRegistrationRepository directly access the objects stored in the database via the EntityManager instance and these methods should implement both database operations and service business logic (including input validation — which we omitted in this part). In later sections, however, we will see how we can easily separate the database access and the service business logic in Spring applications.

Debugging: connecting to the database using a client

There are cases when a developer wants to know the contents of the database. In this case, a database client program can be used to access the database schema and table contents. Here are the general steps to access the Postgres database provided by Heroku:

1. Obtain the database URL to access the database remotely, e.g., by opening up a terminal and running: heroku run echo \$JDBC_DATABASE_URL --app=<YOUR_BACKEND_APP_NAME>.

2. The returned value follows the format that holds all main important parameters that are needed for accessing the database server:

   jdbc:postgresql://<HOST>:<PORT>/<DATABASE_NAME>?user=<USERNAME>&password=<PASSWORD>&sslmode=require

   These parameters are:

   • Database host: the URL for the server

   • Port: the por on which the DB server is listening

   • Database name: the first section after the URL

   • Username: the first parameter value in the provided URL

   • Password: the second parameter value in the provided URL

3. With these parameters you can use any Postgres client you prefer to connect to the database. Here is an example for such a connection from Linux using postgres-client:

   $> psql postgresql://ec2-54-243-223-245.compute-1.amazonaws.com:5432/d4412g60aaboa7?user=hdjnflfirvkmmr
   Password:
   psql (10.6 (Ubuntu 10.6-0ubuntu0.18.04.1))
   SSL connection (protocol: TLSv1.2, cipher: ECDHE-RSA-AES256-GCM-SHA384, bits: 256, compression: off)
   Type "help" for help.
   
   d4412g60aaboa7=> \dt
                             List of relations
    Schema |                Name                | Type  |     Owner
   --------+------------------------------------+-------+----------------
    public | event                              | table | hdjnflfirvkmmr
    public | person                             | table | hdjnflfirvkmmr
    public | registration                       | table | hdjnflfirvkmmr
    public | registration_manager               | table | hdjnflfirvkmmr
    public | registration_manager_events        | table | hdjnflfirvkmmr
    public | registration_manager_persons       | table | hdjnflfirvkmmr
    public | registration_manager_registrations | table | hdjnflfirvkmmr
   (7 rows)
   
   d4412g60aaboa7=> select * from event ;
    name |    date    | end_time | start_time
   ------+------------+----------+------------
    e1   | 3899-10-09 | 12:00:00 | 10:00:00
   (1 row)
   
   d4412g60aaboa7=> \q
   $>