عرض عملي: تشخيص فشل بدء التشغيل بسبب Bean غامض

خطوة بخطوة

1. Add a second PaymentProvider implementation and start the app.
2. Read the report: it says expected single matching bean but found 2 and lists both names.
3. Planned mistake: "fix" it by deleting one implementation. Explain why that removes a needed feature.
4. Fix 1: @Primary on the default. Fix 2: @Qualifier("paypal") at the injection point.
5. Fix 3: inject Map<String, PaymentProvider> and choose by key at run time.
6. Run again and confirm the app starts.