Download Android JNI and Jar Library

Android JNI and JAR Library
JNI Library
1. JNI *.c sources file must include jni header file jni.h
#include <jni.h>
2. In Make file CFLAGS must add -I $(NDK_INC)/ and android_evn.mak must have
It in Makefile_android
CFLAGS += -I $(NDK_INC)/
android_evn.mak
ifeq ($(VER40), $(VER))
NDK_INC = $(ANDROID_SRC)/prebuilt/ndk/android-ndk-r6/platforms/android-9/arch$(ARCH)/usr/include
NDK_LIB = $(ANDROID_SRC)/prebuilt/ndk/android-ndk-r6/platforms/android-9/arch$(ARCH)/usr/lib
Endif
( Android 4.0 ndk/android-ndk-r6/platforms/android-9/arch-x86/usr/include/jni.h )
( Android 2.2 ndk/android-ndk-r4/platforms/android-8/arch-x86/usr/include/jni.h )
3. How to implements C function method
JNIEXPORT jboolean JNICALL
Java_ com_Advantech_SUSI_SUSILIB_SusiDllInit(JNIEnv *, jobject)
{
return SusiDllInit(); // SusiDllInit SUSI C function and return boolean
}
All available types define as below.,
Java Language
Type Native Type
Description
boolean
jboolean
unsigned 8 bits
byte
jbyte
signed 8 bits
char
jchar
unsigned 16 bits
short
jshort
signed 16 bits
int
jint
signed 32 bits
long
jlong
signed 64 bits
float
jfloat
32 bits
double
jdouble
64 bits
com_Advantech_SUSI is packages name and SUSILIB is jar class library
Implements in java file as below.,
import com.Advantech.SUSI.SUSILIB; // For Android APP
JNIEXPORT and JNICALL are macros defined at jni.h
Ref The Java™ Native Interface Programmer’s Guide and Specification ( ISBN 0-20132577-2 )
JNI use Get/Release<Type>ArrayElements functions to let native library code to obtain a direct pointer to the elements of
primitive arrays ( In Java no pointer only array)
If use Get<Type>ArrayElements and must use Get<Type>ArrayElements to release memory in Virtual Machine
JNIEXPORT jboolean JNICALL Java_com_Advantech_SUISI_SUSILIB_SusiHWMGetFanSpeed
(JNIEnv* env, jobject obj, jshort fanType, jshortArray retval, jshortArray typeSupport )
{
jboolean
jbool;
jshortArray jretval;
jshortArray jtypeSupport;
if( retval != NULL )
jretval = (*env)->GetShortArrayElements(env, retval, NULL); // If use C++ change to env->GetShortArrayElements
// Use Get<Type>ArrayElements to pointer to allow the native code to obtain a direct pointer to the elements of primitive
//arrays.
if( typeSupport != NULL )
jtypeSupport = (*env)->GetShortArrayElements(env, typeSupport, NULL); // To obtain a direct pointer to the elements of
primitive arrays
if( typeSupport != NULL ) {
jbool = SusiHWMGetFanSpeed ( (WORD) fanType, (WORD *) 0, (WORD *) jtypeSupport ); // Can’t pass NULL instead use
(void *) 0 or (WORD *) 0
} else {
jbool = SusiHWMGetFanSpeed ( (WORD) fanType, (WORD *) jretval, (WORD *) 0 );
}
if( retval != NULL )
(*env)->ReleaseShortArrayElements(env, retval, jretval, 0);
if( typeSupport != NULL )
(*env)->ReleaseShortArrayElements(env, typeSupport, jtypeSupport, 0);
return jbool;
}
JAR Library
1. Ceate a new Java class with Eclipse for Android APP call SUSI Methods
package com.Advantech.SUSI;
import android.util.Log;
public class SUSILIB
{
public static native boolean SusiHWMGetFanSpeed(short fanType, short[] retval, short[] typeSupport);
static
{
try {
Log.i("JAVA", "System.load(/system/lib/libSUSI-JNI.so)");
System.loadLibrary("SUSI-JNI");
// Load SUSI JNI library libSUSI-JNI.so from /system/lib
}
catch (UnsatisfiedLinkError use)
{
String msg = use.getMessage();
Log.e("JAVA", msg);
Log.e("JAVA", "WARNING: Could not load libSUSI-JNI.so");
}
}
}
2. Use Eclipse to build it and export a jar file for SUSI Demo APP
In Package Explorer first to select Export then select export destination
Select resource files to be created as JAR file and output JAR file, Press finish.