Example of Spring boot microservice with JPA and IBM i as datasource
This is basically an initial project created by spring.io, however I have added all the boilerplate for getting you up and running with Spring Boot and the IBM i as the datasource which will showcase access to a very old "file" on the IBM i.
This is a Gradle project so all required dependencies are being setup and ready in the build.gradle file.
You can also take a closer look at /resources/application.properties and see what it takes to configure your runtime environment.
In that Java source root you will find Application. Spring Boot is so kind to read all subdirectories and instantiate classes assisted by the annotations you will find in classes in the subdirectories.
Lets go through these classes - bottom up.
Here we have the mapping layer between Db2 and the JPA - The Java Persistence Architecture. You will find the old names, and the mapped names used in Java.
by purpose, I have used the old and ugly QCUSTCDT file, so you can see you can use my git project for transformation projects in the future.
In the repositories you find the I/O functionality - the queries. The basic repo inherits from a CRUD ( Create/Read/Update/Delete) - functionality, however you can extend with all kind of you own access. I have here showcased JPQL - which is almost SQL but using the entity model. That means - you can use all the nice names.
The controller is where you describe your endpoints - the URL you are referring to from your client code.
You have to set environment variables according to your system like this:
HOST=MYIBMI;USERID=MYNAME;PASSWORD=mysecret;PORT=8888;LIBL=QIWS
Then you can start the service. When you open your browser then you can refer to this URL and see if it works:
Now when you start the spring-boot application is listening on port 8888 on you local host.
So first step is to see if the application works:
http://localhost:8888/api/hello
If you get a "Hello world" then let's see if the database connections also works:
http://localhost:8888/api/customerList/
This will produce the complete list of "customers".
Now, getting one object as JSON - one customer by id:
http://localhost:8888/api/customer/839283
Finally, let's try the JPQL - Java Persistence Query Language defined i the controller :
http://localhost:8888/api/customerSearch?search=john
Notice that the logging is being set to a level so you can examine what real SQL statements running against the Db2 database. That ofcause can be changed if you open the /resources/application.properties and modify the SQL logging tag