Android - JNI guidelines

Question

I want to incorporate small, lean and mean C-based parser into my Android project. I've done JNI programming in the past but not any type of native (C) development on Android. My plan is to compile C lib into SO and create JNI wrapper around it which I'm going to use in my app. Is this how it can/should be done? Second and most important question - how can I include .so into my APK? Where would it go?

Answer 1

use Android NDK
Download n docs Android NDK 1.6

This will save you from writing JNI layer for lib and also will install the app in the lib folder of your app data folder.

Answer 2

Someone said that JNI in android sucks : http://www.koushikdutta.com/2009/01/jni-in-android-and-foreword-of-why-jni.html

Answer 3

Depending on how much data you pass and how often I seriously doubt a Java/JNI/C would perform faster than a native java implementation.

Passing anything other than a "Java Int" to a "C long" invokes the JNI data conversion routines which are anything but lean and mean.

So unless your JNI routine fits the pattern:

• Pass small amount of data.
• Do lots and lots of work in C.
• Pass small result set back.

You will be considerably slower than a native java implementation. If you stick with the basic "C" like java operations (+,-,*,==,>) using the "native" data types (int, char, String) and avoid the fancy libraries Java will perform nearly as fast as C.

The remaining bug-bear of java performance is the time taken to fire up the JVM and get everything going, but as you are starting off from a Java program this is a non issue.

The other reason for "slow" java performance is people insist on unnecessary factories, containers, xml beans etc. etc. where plain, simple methods would do the job better.