JNI和Qt通信(Part2)

来源：好走旅游网

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()

JNIEXPORT void JNICALL Java_JNISample_sampleFunction(JNIEnv* env, jobject obj, jstring name)

{

const char* pname = env->GetStringUTFChars(name, NULL);

env->ReleaseStringUTFChars(name, pname);

}

e.g. Array

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 < 10; i++) {

sum += buf[i];

}

return sum;

}

http://ironurbane.iteye.com/blog/425513

JNI的数据定义

// In "win\jni_mh.h" - machine header which is machine dependent

typedef long jint;

typedef __int 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;

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	bits
float	jfloat	32 bits
int	jint	32 bits, signed
long	jlong	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;
type[]	[type
method signature	( arg-types) ret-type

e.g.

Java side

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;

}

C++side

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,"","()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);

}

查看属性和方法的签名

Java版本 "java -version"

反编译工具 javap:

1	`javap -s -p -classpath R:\test.Demo`

Check JNI version

#ifdef JNI_VERSION_1_4

printf("Version is 1.4 \n");

#endif

使用API

1	`jint GetVersion(JNIEnv *env);`

返回È需要转换, Need convert the result from DEC to HEX;

JNI实现过程中的Issue

x86 or x "Can't load load IA 32-bit dll on a amd 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x), 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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