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Sathya7032
Sathya7032

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Why http://10.0.2.2 Works Instead of localhost in Android Emulator (React Native + Spring Boot)

#reactnative #react #springboot #mobile

When I was connecting my React Native app (running in the Android emulator) to my Spring Boot backend on my computer, using:

fetch("http://localhost:8080/api")
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…didn’t work. ❌
But when I changed it to:

fetch("http://10.0.2.2:8080/api")
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…it worked perfectly. ✅

Why?

  • localhost inside the emulator points to the emulator itself — not your computer.
  • Your Spring Boot server is running on your computer, not inside the emulator.
  • 10.0.2.2 is a special IP address in the Android emulator that acts like “localhost of your computer”.

Think of it like this:

localhost → talks to the emulator
10.0.2.2 → talks to your computer

When to Use It

  • Use 10.0.2.2 only for Android emulator.
  • For iOS simulator, you can still use localhost.
  • For real devices, use your computer’s local IP (e.g., 192.168.x.x).

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