JNI调用Java方法

package com.biumall.dynamic.one;
public class Hello {
    //1. load Hello.so
    static {
        System.loadLibrary("Hello");
    }
    // 2. define native computer()
    public static native int computer(String type, int a, int b);
    //add
    public int add(int x, int y) {
        return x + y;
    }
    //sub
    public int sub(int x, int y) {
        return x - y;
    }
}

#include <jni.h>
#include <android/log.h>
#include<stdio.h>
#include<string.h>
​
//LOG_TAG
#define LOG_TAG "from_dynamic_jni_+"
#define LOGD(...) __android_log_print(ANDROID_LOG_DEBUG, LOG_TAG, __VA_ARGS__)
#define LOGI(...) __android_log_print(ANDROID_LOG_INFO, LOG_TAG, __VA_ARGS__)
#define LOGE(...) __android_log_print(ANDROID_LOG_ERROR, LOG_TAG, __VA_ARGS__)
​
//获取数组大小
#define ARRAY_LENGTH(x) ((int)(sizeof(x) / sizeof((x)[0])))
//定义Hello.java类路径[包名+类名，只不过.换成了/]
//com.biumall.dynamic.one.Hello
#define DYNAMIC_CLASS "com/biumall/dynamic/one/Hello"
​
//声明方法
int c_add(JNIEnv *env, jclass jclazz, int x, int y);
int c_sub(JNIEnv *env, jclass jclazz, int x, int y);
​
//native 方法
JNIEXPORT jint JNICALL native_computer(JNIEnv *env, jclass jclazz, jstring type, jint a, jint b) {
    const char *charType = (*env)->GetStringUTFChars(env, type, 0);
    int count;
    if (!strcmp(charType, "-")) {
        count = c_sub(env, jclazz, a, b);
    } else if (!strcmp(charType, "+")) {
        count = c_add(env, jclazz, a, b);
    }
    return count;
}
​
//jni 调用 java add方法
int c_add(JNIEnv *env, jclass jclazz, int x, int y) {
    jmethodID methodID = (*env)->GetMethodID(env, jclazz, "add", "(II)I");
    jobject object = (*env)->AllocObject(env, jclazz);
    return (*env)->CallIntMethod(env, object, methodID, x, y);
}
//jni 调用 java sub方法
int c_sub(JNIEnv *env, jclass jclazz, int x, int y) {
    jmethodID methodID = (*env)->GetMethodID(env, jclazz, "sub", "(II)I");
    jobject object = (*env)->AllocObject(env, jclazz);
    return (*env)->CallIntMethod(env, object, methodID, x, y);
}
​
//定义Java和JNI函数的绑定表
// 方法数组，分别为：(方法名[java层定义的],方法签名,函数指针[c层对应替换的方法])
// 可以通过javac和javap 获取 方法签名
JNINativeMethod method_table[] = {
        {"computer", "(Ljava/lang/String;II)I", (void *) native_computer},
};
​
int registerNativeMethods(JNIEnv *env, const char *className, JNINativeMethod *methods,
                          int methods_size) {
    jclass clazz = NULL;
    //反射Java类
    clazz = (*env)->FindClass(env, className);
    if (NULL == clazz) {
        return JNI_ERR;
    }
    int result = (*env)->RegisterNatives(env, clazz, methods, methods_size);
    LOGD("registerNativeMethods result : %d", result);
    if (result < 0) {
        return JNI_ERR;
    }
    return JNI_OK;
}
​
JNIEXPORT jint JNI_OnLoad(JavaVM *vm, void *reserved ){
    JNIEnv *env = NULL;
    int result = (*vm)->GetEnv(vm, (void **) &env, JNI_VERSION_1_6);
    LOGD("JNI_OnLoad 1 result : %d", result);
    if(result != JNI_OK){
        return JNI_ERR;
    }
    result = registerNativeMethods(env, DYNAMIC_CLASS, method_table, ARRAY_LENGTH(method_table));
    LOGD("JNI_OnLoad 2 result : %d", result);
    if(result != JNI_OK){
        return JNI_ERR;
    }
    return JNI_VERSION_1_6;
}