Injection Dependency in Spring

[Mason Bailey]

I'm writing an app that talks to one database, obtains credentials for other databases, and connects to the others. It does this using a DataSource and EntityManagerFactory constructed at runtime.

If I want to use Spring Data Repositories, I think I'd need to Autowire them, and therefore they must be Spring Beans.

How can I use Spring Data if I don't have a constructed DataSource until after I run a query against the first database?

[Tim Nachreiner]

All your datasources will be created when the app first loads, via component scan.  You just won't be able to 'open' the secondary datasource until you get the credentials from the first datasource.

[Himai Minh]

Hi, Mason,
Would you mind to post your example code so that we can see what you are working on?
In Spring Data JPA, you can simply create something like this:

public interface PersonRespository extends JpaRepository<Person, Integer> { }

Suppose you have a table called Person and the table primary key is an integer.

In your service layer, you can autowire the PersonRepository like this:

@Autowired
private Person personRepository;

In your resources folder, create a data.sql file and put something like this:

insert into person(id, name, birthday) values (1, "john smith", "1989-09-01");

In your pom.xml, include the following dependencies. The second one indicate that you want to your embedded H2 database.

<dependency>
   <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
   <groupId>com.h2database</groupId>
   <artifactId>h2</artifactId>
</dependency>

If you want to use MySQL database, you may want to include this instead of h2database:

<dependency>
   <groupId>mysql</groupId>
   <artifactId>mysql-connector-java</artifactId>
   <scope>runtime</scope>
</dependency>

And also specify the url of the MySQL database in application.properties in resources folder:

spring.datasource.rul = jdbc:mysql://localhost:3306/myTestdb?useSSL=false
spring.datasource.username =root
spring.datasource.password = secret
spring.jpa.generate-ddl = true
spring.jpa.hibernate.ddl-auto=create-drop
spring.datasource.initialization-mode=always