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在这里，先简单介绍一下Android NDK和jni
NDK：可以参照~
http://baike.baidu.com/view/5236494.htm
简单来说，NDK就是提供了一个在Android平台上使用c/c++的一个平台，结合IDE，可以轻松快捷的将c/c++源码编译成so文件，并打包进android应用程序的apk里，并提供一堆Android程序特有的库。
JNI：可以参照~
http://baike.baidu.com/view/1272329.htm
简单来说，JNI就是允许java代码与其他语言写的代码交互，尤其是为C和C++而设计的。
开始步骤：可以参照~
ANDROID: NDK编程入门笔记
http://www.cnblogs.com/hibraincol/archive/2011/05/30/2063847.html
搭建好开发环境，并完成hello world之后，就可以开发自己需要的jni应用程序了
注：搭建ndk编译环境，有一些问题
Windows平台: 需要安装通过cygwin来模拟linux环境，并且通过linux的gcc来编译
Linux平台：在官网下载好android ndk安装包后，根据帮助一步步安装即可
Mac平台：mac os x虽然是基于unix的，但是默认情况下是不提供开发工具的，也木有gcc 之类的编译工具，开发人员需要先安装xcode以后，才能使用android ndk
下面我们说说java和c/c++之间调用的问题
Java调用c/c++
先看例子
public class Sample1
{
public native int intMethod(int n);
public native boolean booleanMethod(boolean bool);
public native String stringMethod(String text);
public native int intArrayMethod(int[] intArray);
public static void main(String[] args)
{
System.loadLibrary("Sample1");
Sample1 sample = new Sample1();
int square = sample.intMethod(5);
boolean bool = sample.booleanMethod(true);
String text = sample.stringMethod("JAVA");
int sum = sample.intArrayMethod(
new int[]{1,1,2,3,5,8,13} );
System.out.println("intMethod: " + square);
System.out.println("booleanMethod: " + bool);
System.out.println("stringMethod: " + text);
System.out.println("intArrayMethod: " + sum);
}
}
然后编译，编译完成以后，可以通过javah 工具所生成的 C/C++ 头文件
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class Sample1 */
#ifndef _Included_Sample1
#define _Included_Sample1
#ifdef __cplusplus
extern "C" {
#endif
JNIEXPORT jint JNICALL Java_Sample1_intMethod
(JNIEnv *, jobject, jint);
JNIEXPORT jboolean JNICALL Java_Sample1_booleanMethod
(JNIEnv *, jobject, jboolean);
JNIEXPORT jstring JNICALL Java_Sample1_stringMethod
(JNIEnv *, jobject, jstring);
JNIEXPORT jint JNICALL Java_Sample1_intArrayMethod
(JNIEnv *, jobject, jintArray);
#ifdef __cplusplus
}
#endif
#endif
C 函数实现
#include "Sample1.h"
#include <string.h>
JNIEXPORT jint JNICALL Java_Sample1_intMethod
(JNIEnv *env, jobject obj, jint num) {
return num * num;
}
JNIEXPORT jboolean JNICALL Java_Sample1_booleanMethod
(JNIEnv *env, jobject obj, jboolean boolean) {
return !boolean;
}
JNIEXPORT jstring JNICALL Java_Sample1_stringMethod
(JNIEnv *env, jobject obj, jstring string) {
const char *str = (*env)->GetStringUTFChars(env, string, 0);
char cap[128];
strcpy(cap, str);
(*env)->ReleaseStringUTFChars(env, string, str);
return (*env)->NewStringUTF(env, strupr(cap));
}
JNIEXPORT jint JNICALL Java_Sample1_intArrayMethod
(JNIEnv *env, jobject obj, jintArray array) {
int i, sum = 0;
jsize len = (*env)->GetArrayLength(env, array);
jint *body = (*env)->GetIntArrayElements(env, array, 0);
for (i=0; i<len; i++)
{ sum += body[i];
}
(*env)->ReleaseIntArrayElements(env, array, body, 0);
return sum;
}
void main(){}
c++函数实现
#include "Sample1.h"
#include <string.h>
JNIEXPORT jint JNICALL Java_Sample1_intMethod
(JNIEnv *env, jobject obj, jint num) {
return num * num;
}
JNIEXPORT jboolean JNICALL Java_Sample1_booleanMethod
(JNIEnv *env, jobject obj, jboolean boolean) {
return !boolean;
}
JNIEXPORT jstring JNICALL Java_Sample1_stringMethod
(JNIEnv *env, jobject obj, jstring string) {
const char *str = env->GetStringUTFChars(string, 0);
char cap[128];
strcpy(cap, str);
env->ReleaseStringUTFChars(string, str);
return env->NewStringUTF(strupr(cap));
}
JNIEXPORT jint JNICALL Java_Sample1_intArrayMethod
(JNIEnv *env, jobject obj, jintArray array) {
int i, sum = 0;
jsize len = env->GetArrayLength(array);
jint *body = env->GetIntArrayElements(array, 0);
for (i=0; i<len; i++)
{ sum += body[i];
}
env->ReleaseIntArrayElements(array, body, 0);
return sum;
}
void main(){}
注：c和c++实现的方式略微不同
C 语法： jsize len = (*env)->GetArrayLength(env,array);
C++ 语法： jsize len =env->GetArrayLength(array);
c/c++调用Java
public class Sample2
{
public static int intMethod(int n) {
return n*n;
}
public static boolean booleanMethod(boolean bool) {
return !bool;
}
}
再看c的调用方式
#include <jni.h>
#ifdef _WIN32
#define PATH_SEPARATOR ';'
#else
#define PATH_SEPARATOR ':'
#endif
int main()
{
JavaVMOption options[1];
JNIEnv *env;
JavaVM *jvm;
JavaVMInitArgs vm_args;
long status;
jclass cls;
jmethodID mid;
jint square;
jboolean not;
options[0].optionString = "-Djava.class.path=.";
memset(&vm_args, 0, sizeof(vm_args));
vm_args.version = JNI_VERSION_1_2;
vm_args.nOptions = 1;
vm_args.options = options;
status = JNI_CreateJavaVM(&jvm, (void**)&env, &vm_args);
if (status != JNI_ERR)
{
cls = (*env)->FindClass(env, "Sample2");
if(cls !=0)
{ mid = (*env)->GetStaticMethodID(env, cls, "intMethod", "(I)I");
if(mid !=0)
{ square = (*env)->CallStaticIntMethod(env, cls, mid, 5);
printf("Result of intMethod: %d\n", square);
}
mid = (*env)->GetStaticMethodID(env, cls, "booleanMethod", "(Z)Z");
if(mid !=0)
{ not = (*env)->CallStaticBooleanMethod(env, cls, mid, 1);
printf("Result of booleanMethod: %d\n", not);
}
}
(*jvm)->DestroyJavaVM(jvm);
return 0;
}
else
return -1;
}
再看c++的调用例子
#include <jni.h>
#ifdef _WIN32
#define PATH_SEPARATOR ';'
#else
#define PATH_SEPARATOR ':'
#endif
int main()
{
JavaVMOption options[1];
JNIEnv *env;
JavaVM *jvm;
JavaVMInitArgs vm_args;
long status;
jclass cls;
jmethodID mid;
jint square;
jboolean not;
options[0].optionString = "-Djava.class.path=.";
memset(&vm_args, 0, sizeof(vm_args));
vm_args.version = JNI_VERSION_1_2;
vm_args.nOptions = 1;
vm_args.options = options;
status = JNI_CreateJavaVM(&jvm, (void**)&env, &vm_args);
if (status != JNI_ERR)
{
cls = (*env)->FindClass(env, "Sample2");
if(cls !=0)
{ mid = (*env)->GetStaticMethodID(env, cls, "intMethod", "(I)I");
if(mid !=0)
{ square = (*env)->CallStaticIntMethod(env, cls, mid, 5);
printf("Result of intMethod: %d\n", square);
}
mid = (*env)->GetStaticMethodID(env, cls, "booleanMethod", "(Z)Z");
if(mid !=0)
{ not = (*env)->CallStaticBooleanMethod(env, cls, mid, 1);
printf("Result of booleanMethod: %d\n", not);
}
}
(*jvm)->DestroyJavaVM(jvm);
return 0;
}
else
return -1;
}
C 语法： cls = (*env)->FindClass(env, "Sample2");
C++ 语法： cls = env->FindClass("Sample2");
先简单介绍到这里，下次再说