1、编写native方法（java2c）和非native方法（c2java）:
package com.example.provider;public class CallbackJava {
// C调用java空方法
public void helloFromJava() {System.out.println("hello from java");
}// C调用java中的带两个int参数的方法
public int Add(int x, int y) {
int result = x + y;
System.out.println("java result=" + result);
return result;
}// C调用java中参数为string的方法
public void printString(String s) {
System.out.println("java " + s);
}//静态方法
public static void printStaticStr(String s) {
System.out.println("java static-> " + s);
}// 让c代码调用对应的java代码
public native void callHelloFromJava();public native void callAdd();
public native void callPrintString();
// 调用一个静态的c代码
public native void callPrintStaticStr();
}
2、通过javah命令生成签名，通过javap命令生产native方法签名：
3、c代码
FindClass：找到java中的类文件
GetMethodID：根据类和方法签名找到要调用的方法。
#include <stdio.h>
#include <jni.h>
#include <malloc.h>
#include "com_example_provider_CallbackJava.h";#include <android/log.h>
#define LOG_TAG "System.out.c"
#define LOGD(...) __android_log_print(ANDROID_LOG_DEBUG, LOG_TAG, __VA_ARGS__)
#define LOGI(...) __android_log_print(ANDROID_LOG_INFO, LOG_TAG, __VA_ARGS__)jmethodID getMethodId(JNIEnv * env, char* methodname, char* signname) {
jclass jclazz = (*env)->FindClass(env, "com/example/provider/CallbackJava");
if (jclazz == 0) {
LOGD("class not find ");
return;
}
//2、找class中方法的id,第三个参数方法名称，第四个参数该方法对应的签名
jmethodID methodid = (*env)->GetMethodID(env, jclazz, methodname, signname);
if (methodid == 0) {
LOGD("method not find ");
return;
}
return methodid;
}JNIEXPORT void JNICALL Java_com_example_provider_CallbackJava_callHelloFromJava
(JNIEnv * env, jobject obj) {
//1、 找java中的class文件
//第二个参数是类名的（包名）
jclass jclazz = (*env)->FindClass(env,"com/example/provider/CallbackJava");
if(jclazz==0) {
LOGD("class not find ");
return;
}
//2、找class中方法的id,第三个参数方法名称，第四个参数该方法对应的签名
jmethodID methodid = (*env)->GetMethodID(env, jclazz,"helloFromJava","()V");
if(methodid==0) {
LOGD("helloFromJava method not find ");
return;
}
//3、调用方法
//void (*CallVoidMethod)(JNIEnv*, jobject, jmethodID, ...);
(*env)->CallVoidMethod(env,obj,methodid);
}JNIEXPORT void JNICALL Java_com_example_provider_CallbackJava_callAdd
(JNIEnv *env, jobject obj) {
jmethodID mid = getMethodId(env,"Add","(II)I");
int result = (*env)->CallIntMethod(env, obj, mid,3,6);
LOGD("c to java add: d%",result);
}JNIEXPORT void JNICALL Java_com_example_provider_CallbackJava_callPrintString
(JNIEnv *env, jobject obj) {
LOGD("c to java callPrintString start ");
jmethodID mid = getMethodId(env,"printString","(Ljava/lang/String;)V");
(*env)->CallVoidMethod(env, obj, mid,(*env)->NewStringUTF(env," call printString finish"));
LOGD("c to java callPrintString finish ");
}JNIEXPORT void JNICALL Java_com_example_provider_CallbackJava_callPrintStaticStr
(JNIEnv *env, jobject obj) {
jclass jclazz = (*env)->FindClass(env, "com/example/provider/CallbackJava");
if (jclazz == 0) {
LOGD("class not find ");
return;
}
//静态方法调用GetStaticMethodID 和 CallStaticXXXMethod
jmethodID methodid = (*env)->GetStaticMethodID(env, jclazz, "printStaticStr", "(Ljava/lang/String;)V");
if (methodid == 0) {
LOGD("printStaticStr method not find ");
return;
}
(*env)->CallStaticVoidMethod(env, jclazz, methodid,(*env)->NewStringUTF(env,"static hello java"));}
Android学习笔记_JNI_c调用java代码