ISP in Spring Boot — Repository interfaces and service interfaces

Direct Answer

In Spring applications, apply ISP by giving each consumer the smallest useful contract. A read-only controller can depend on a query interface, while an administration use case can depend on a command interface. With Spring Data, choose or define repository interfaces deliberately; do not expose every persistence operation to code that only needs one query.

Code Example

interface CustomerQueries {
    Optional<CustomerView> findById(long id);
    List<CustomerView> findActive();
}

interface CustomerCommands {
    CustomerView create(CreateCustomer command);
    void deactivate(long id);
}

@RestController
final class CustomerReportController {
    private final CustomerQueries queries;

    CustomerReportController(CustomerQueries queries) {
        this.queries = queries;
    }

    @GetMapping("/customers/active")
    List<CustomerView> active() {
        return queries.findActive();
    }
}

The controller's Java contract contains no write operation. Authorization is still required because type shape alone cannot protect an HTTP endpoint.

Common Mistakes & Pitfalls

• Extending the largest repository by habit: choose capabilities deliberately or hide persistence behind an application-owned port.
• Assuming one Spring Data hierarchy for every version and store: verify the current module's official API.
• Treating a read-only Java type as authorization: enforce access at the web or service boundary.
• Injecting a narrow interface and later downcasting to the implementation: that restores the dependency ISP was meant to remove.