Android JNI (implement your own jni_onload function)

You can register local functions in JNI in two ways:
(1) use the default local function registration process.
(2) rewrite the jni_onload () function by yourself. (This article introduces) (this is used in Android)

Java code:

package com.jni;public class JavaHello {public static native String hello();static {// load library: libtest.sotry {System.loadLibrary("test");} catch (UnsatisfiedLinkError ule) {System.err.println("WARNING: Could not load library!");}}public static void main(String[] args) {String s = new JavaHello().hello();System.out.println(s);}}

Local C language code:

# Include <stdlib. h> # include <string. h> # include <stdio. h> # include <JNI. h> # include <assert. h> jniexport jstring jnicall native_hello (jnienv * ENV, jclass clazz) {printf ("hello in C native code. /n "); Return (* env)-> newstringutf (ENV," Hello World returned. ") ;}# define jnireg_class" com/JNI/javahello "// specify the class to be registered/*** table of methods associated with a single class. */static jninativemethod gmethods [] = {"Hello "," () Ljava/lang/string; ", (void *) native_hello}, // bind};/** register several native methods for one class. */static int evaluate (jnienv * ENV, const char * classname, jninativemethod * gmethods, int nummethods) {jclass clazz; clazz = (* env)-> findclass (ENV, classname); If (clazz = NULL) {return jni_false;} If (* env)-> registernatives (ENV, clazz, gmethods, nummethods) <0) {return jni_false;} re Turn jni_true;}/** register native methods for all classes we know about. */static int registernatives (jnienv * env) {If (! Registernativemethods (ENV, jnireg_class, gmethods,
Sizeof (gmethods)/sizeof (gmethods [0]) return jni_false; return jni_true;}/** set some test stuff up. ** returns the JNI version on success,-1 on failure. */jniexport jint jnicall jni_onload (JavaVM * Vm, void * Reserved) {jnienv * Env = NULL; jint result =-1; if (* VM)-> getenv (Vm, (void **) & ENV, jni_version_1_4 )! = Jni_ OK) {return-1;} assert (ENV! = NULL); If (! Registernatives (ENV) {// register return-1;}/* success -- Return valid version number */result = jni_version_1_4; return result ;}

Compilation and running process:

1. Set three environment variables:
Export java_home: =/usr/lib/JVM/Java-6-sun-1.6.0.15
Export java_src_path: =/home/kortide/jackey/JNI/jni_onload/COM/jfo
Export native_src_path: =/home/kortide/jackey/JNI/jni_onload/JNI

2. Compile javahello. Java:
Javac $ java_src_path/javahello. Java

3. Compile nativehello. C to generate a shared library.
Gcc-I $ java_home/include/Linux-c-o $ native_src_path/nativehello. o $ native_src_path/nativehello. c

Gcc-FPIC-I $ java_home/include/Linux-shared-o $ native_src_path/libtest. So $ native_src_path/nativehello. o

4. Run
Java COM/JNI/javahello