Android(安卓)JNI(实现自己的JNI_OnLoad函数)
16lz
2021-01-25
实现JNI中本地函数注册可以两种方式:
(1)采用默认的本地函数注册流程。
(2)自己重写JNI_OnLoad()函数。(本文介绍)(Android中采用这种)
Java端代码:
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);}}
本地C语言代码:
#include#include #include #include #include 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"//指定要注册的类/*** Table of methods associated with a single class.*/static JNINativeMethod gMethods[] = {{ "hello", "()Ljava/lang/String;", (void*)native_hello },//绑定};/** Register several native methods for one class.*/static int registerNativeMethods(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;}return 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)) {//注册return -1;}/* success -- return valid version number */result = JNI_VERSION_1_4;return result;}
编译及运行流程:
1 设置三个环境变量:
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 编译JavaHello.java:
javac $JAVA_SRC_PATH/JavaHello.java
3. 编译NativeHello.c,生成共享库
gcc -I $JAVA_HOME/include -I $JAVA_HOME/include/linux -c -o $NATIVE_SRC_PATH/NativeHello.o $NATIVE_SRC_PATH/NativeHello.c
gcc -fPIC -I $JAVA_HOME/include -I $JAVA_HOME/include/linux -shared -o $NATIVE_SRC_PATH/libtest.so $NATIVE_SRC_PATH/NativeHello.o
4. 运行
java com/jni/JavaHello
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