Optimistic Locking on Inventory Updates with @Version and a Retrying Conflict Handler in Spring Boot

package com.shop.inventory;

import org.springframework.orm.ObjectOptimisticLockingFailureException;
import org.springframework.retry.annotation.Backoff;
import org.springframework.retry.annotation.Recover;
import org.springframework.retry.annotation.Retryable;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

@Service
public class InventoryService {

    private final InventoryItemRepository repository;

    public InventoryService(InventoryItemRepository repository) {
        this.repository = repository;
    }

    @Retryable(
        retryFor = ObjectOptimisticLockingFailureException.class,
        maxAttempts = 4,
        backoff = @Backoff(delay = 25, multiplier = 2.0, random = true)
    )
    @Transactional
    public InventoryItem adjustStock(String sku, int delta) {
        InventoryItem item = repository.findBySku(sku)
                .orElseThrow(() -> new UnknownSkuException(sku));

        if (delta < 0) {
            item.decrement(-delta);
        } else {
            item.increment(delta);
        }
        // Commit issues UPDATE ... WHERE id = ? AND version = ?
        return repository.save(item);
    }

    @Recover
    public InventoryItem recoverFromConflict(ObjectOptimisticLockingFailureException ex,
                                             String sku, int delta) {
        throw new StockConflictException(sku, ex);
    }
}

package com.shop.inventory;

import org.springframework.http.HttpStatus;
import org.springframework.web.bind.annotation.*;

@RestController
@RequestMapping("/api/inventory")
public class InventoryController {

    private final InventoryService service;

    public InventoryController(InventoryService service) {
        this.service = service;
    }

    @PostMapping("/{sku}/adjust")
    public StockView adjust(@PathVariable String sku, @RequestParam int delta) {
        InventoryItem item = service.adjustStock(sku, delta);
        return new StockView(item.getSku(), item.getAvailable(), item.getVersion());
    }

    @ExceptionHandler(StockConflictException.class)
    @ResponseStatus(HttpStatus.CONFLICT)
    public ApiError onConflict(StockConflictException ex) {
        return new ApiError("stock_conflict",
                "Concurrent update lost the race for sku " + ex.getSku());
    }

    @ExceptionHandler(IllegalStateException.class)
    @ResponseStatus(HttpStatus.UNPROCESSABLE_ENTITY)
    public ApiError onInvariant(IllegalStateException ex) {
        return new ApiError("invalid_stock_state", ex.getMessage());
    }

    @ExceptionHandler(UnknownSkuException.class)
    @ResponseStatus(HttpStatus.NOT_FOUND)
    public ApiError onUnknown(UnknownSkuException ex) {
        return new ApiError("unknown_sku", ex.getMessage());
    }

    public record StockView(String sku, int available, long version) {
    }

    public record ApiError(String code, String message) {
    }
}