Part2 JNI数据转换成C数据 e.g. jstring -GetStringUTFChars(),NewStringUTF(),ReleaseStringUTFChars() 1 2 3 4 5 JNIEXPORT void JNICALL Java_JNISample_sampleFunction(JNIEnv* env, jobject obj, jstring name) { const char * pname = env-GetStringUT
Part2
JNI数据转换成C数据
e.g. jstring - GetStringUTFChars(), NewStringUTF(), ReleaseStringUTFChars()
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JNIEXPORT void JNICALL
Java_JNISample_sampleFunction(JNIEnv* env, jobject obj, jstring name)
{
const char*
pname = env->GetStringUTFChars(name, NULL);
env->ReleaseStringUTFChars(name,
pname);
}
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e.g. Array
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JNIEXPORT
jint JNICALL Java_IntArray_sumArray
(JNIEnv
*env, jobject obj, jintArray arr) {
jint
buf[10];
jint
i, sum = 0;
//
This line is necessary, since Java arrays are not guaranteed
//
to have a continuous memory layout like C arrays.
env->GetIntArrayRegion(arr,
0, 10, buf);
for (i
= 0; i
sum
+= buf[i];
}
return sum;
}
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http://ironurbane.iteye.com/blog/425513
JNI的数据定义
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//
In "win\jni_mh.h" - machine header which is machine dependent
typedef long jint;
typedef __int64 jlong;
typedef signed char jbyte;
//
In "jni.h"
typedef unsigned char jboolean;
typedef unsigned short jchar;
typedef short jshort;
typedef float jfloat;
typedef double jdouble;
typedef jint
jsize;
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C++ 调用Java方法
Read: http://stackoverflow.com/questions/819536/how-to-call-java-function-from-c
Windows http://public0821.iteye.com/blog/423941
Linux http://blog.sina.com.cn/s/blog_48eef8410100fjxr.html
JNI数据类型
| Java Type |
Native Type |
Description |
| boolean |
jboolean |
8 bits, unsigned |
| byte |
jbyte |
8 bits, signed |
| char |
jchar |
16 bits, unsigned |
| double |
jdouble |
64 bits |
| float |
jfloat |
32 bits |
| int |
jint |
32 bits, signed |
| long |
jlong |
64 bits, signed |
| short |
jshort |
16 bits, signed |
| void |
void |
N/A |
JNI的类型签名
| Java Type |
Signature |
| boolean |
Z |
| byte |
B |
| char |
C |
| double |
D |
| float |
F |
| int |
I |
| long |
J |
| void |
V |
| object |
Lfully-qualified-class;
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type[]
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[type
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| method signature |
( arg-types) ret-type |
e.g.
Java side
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class JNISample
{
public native void launchSample();
static
{
System.loadLibrary("Sample");
}
public static int add(int a,int b)
{
return a+b;
}
public boolean judge(boolean bool)
{
return !bool;
}
}
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C++side
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JNIEnv
*env = GetJNIEnv(); //Get
env from JNI
jclass
cls;
cls
= env->FindClass("JNISample");
if(cls
!=0)
{
printf("find
java class success\n");
//
constructor
mid
= env->GetMethodID(cls,"<init>"</init>,"()V");
if(mid
!=0)
{
jobj=env->NewObject(cls,mid);
}
//
static function
mid
= env->GetStaticMethodID( cls, "add", "(II)I");
if(mid
!=0)
{
square
= env->CallStaticIntMethod( cls, mid, 5,5);
}
//
function returns boolean
mid
= env->GetMethodID( cls, "judge","(Z)Z");
if(mid
!=0){
jnot
= env->CallBooleanMethod(jobj, mid, 1);
}
}
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查看属性和方法的签名
Java版本 "java -version"
反编译工具 javap:
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javap
-s -p -classpath R:\test.Demo
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Check JNI version
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#ifdef
JNI_VERSION_1_4
printf("Version
is 1.4 \n");
#endif
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使用API
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jint
GetVersion(JNIEnv *env);
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返回值需要转换, Need convert the result from DEC to HEX;
JNI实现过程中的Issue
x86 or x64 "Can't load load IA 32-bit dll on a amd 64 bit platform"
确定本机上的默认JVM的版本和动态库的版本一致(x86或x64), Make sure JAVA's default path; check with "java -version" in command line.
3rdParty can't find dependent libraries 保证所依赖的动态库都能被找到;
1) copy the dll into executable file's folder 2) System.load() the dlls by dependecy orders
JNI_CreateJavaVM failed
C++创建JVM调用Java方法
http://docs.oracle.com/javase/1.4.2/docs/guide/jni/jni-12.html#JNI_CreateJavaVM & http://blog.csdn.net/louka/article/details/7318656
[我机器上装了多个版本的Java, 测试的时候没有成功]
jvm.dll(C:\Program Files (x86)\Java\jdk1.7.0_17\jre\bin\client; C:\Program Files (x86)\Java\jdk1.7.0_17\jre\bin\server; need check); jvm.lib(C:\Program Files (x86)\Java\jdk1.7.0_17\lib)
http://home.pacifier.com/~mmead/jni/cs510ajp/ & http://www.ntu.edu.sg/home/ehchua/programming/java/JavaNativeInterface.html
Sample http://chnic.iteye.com/category/20179
JNI doc http://docs.oracle.com/javase/7/docs/technotes/guides/jni/
>JNA https://github.com/twall/jna/ XstartOnFirstThread
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