$ curl -i -X PUT http://localhost:8080/api/products/42 \
     -H 'Content-Type: application/json' -H 'If-Match: "stale-etag-from-a-while-ago"' \
     -d '{"name":"Laptop Pro","price":1199}'

HTTP status: 412
Current ETag header returned: "4e47fa7e"
Body: {"currentEtag":"\"4e47fa7e\"","error":"Resource was modified since you last read it"}
