DllNotFoundException from example project in Unity Manual

Hello,

I am currently in progress of trying to use Pocketsphinx library in Unity 5.4.

The library is written in java, and it is my first time trying to use external java library into unity.

So, I thought the great place to learn how to do this, would be to look at Unity manual of using java plugin.

I downloaded the example project from this page

https://docs.unity3d.com/Manual/PluginsForAndroid.html

the example project that I downloaded was

https://docs.unity3d.com/uploads/Examples/AndroidJavaPlugin.zip

However, when I run the example project above, I get this error.

DllNotFoundException: javabridge
CallJavaCode.OnGUI () (at Assets/CallJavaCode.cs:16)

there is a file called libjavabridge.so under the Plugin/Android so I don't know why Unity is not detecting this library.

Any help will be appreciated!