Spring Boot Data Fetching — Field Injection

This project demonstrates field injection: Spring supplies a Data implementation to FetchData, and the app calls that implementation to print a result.

What I built

• pom.xml — Maven configuration for the Spring Boot project and Java 17.
• SpringBootDependencyDataFetchProjectApplication.java — starts Spring Boot, retrieves FetchData, and calls show().
• Data.java — interface defining the getData() operation.
• Oracle.java — Data implementation marked @Primary; prints Fetching data from oracle.
• MYSQL.java — alternate Data implementation; prints fetch data from sql.
• FetchData.java — uses @Autowired private Data d; and calls d.getData() inside show().

How @Primary is used

Both Oracle and MYSQL implement Data. When Spring injects a Data bean into FetchData, @Primary marks Oracle as the default choice. That is why the app prints the Oracle message.

Compared with my Paradise Restaurant Spring project

In the Paradise project, Billcounter.java uses constructor injection through Billcounter(PaymentMode p). In this project, FetchData.java uses field injection through @Autowired on Data d.

Console output

Fetching data from oracle
get the data