Android JNI JNINativeMethod register

http://marakana.com/s/post/1292/jni_reference_example

Android JNI  JNINativeMethod register

1. Andoird JNINativeMethod 定义如下：

typedef struct {
const char* fname;
const char* sg;
void* fn;
} JNINativeMethod;

fname -- function name in java

sg -- character string used in descripting parameters and return value of function

fn -- function pointer;

2. parameter and return value

as far as sg in JNINativeMethod, followings are some examples

"()V"  -- void func();

"(II)V"   -- void func(int, int);

"(Ljava/lang/string; Ljava/lang/string)V" -- void func(string, string)

"(Ljava/lang/object; Ljava/lang/object; Ljava/lang/object)V"  -- void func(class, class, class);

 

3. Map Relatoin between java and C/C++

Character   Java Type    C/C++ Type

V                  void            void
Z                  boolean      jboolean
I                   int               jint
J                  long            jlong
D                 double         jdouble
F                 float            jfloat
B                 byte            jbyte
C                char            jchar
S                short           jshort

[I                int[]                   jintArray
[F              float[]               jfloatArray
[B              byte[]                jbyteArray
[C             char[]              jcharArray
[S             short[]             jshortArray
[D            double[]          jdoubleArray
[J             long[]              jlongArray
[Z             boolean[]      jbooleanArray

Ljava/lang/String  String   jstring

Ljava/net/Socket  Socket  jobject

 

4. example

method descripition                  Java Method

// Notes:  ";" is a must

"()Ljava/lang/String;"    -------     string func();

"(ILjava/lang/String;)J" -------      long func(int, string);

 

5 sample

5.1. java end

class ResourceService {
    public SyncMode sync_mode;
    public FileSystemType filesystem_type;
    public String service_ip;
    public int service_port;
    public String login_username;
    public String login_passwd;
    public String resource_path;
    public String resource_name;
    public String resource_ext;
   
    public ResourceService() {
     
    }
    public SyncMode getSyncMode() {
     return sync_mode;
    }
    public void setSyncMode(SyncMode mode) {
     sync_mode = mode;
    }
    public FileSystemType getFileSystemType() {
     return filesystem_type;
    }
    public void setFileSystemType(FileSystemType type) {
     filesystem_type = type;
    }
    public String getServiceIp() {
     return service_ip;
    }
    public void setServiceIp(String ip) {
        service_ip = ip;
    }
    public int getServicePort() {
     return service_port;
    }
    public void setServicePort(int port) {
     service_port = port;
    }
    public String getLoginUserName() {
     return login_username;
    }
    public void setLoginUserName(String name) {
     login_username = name;
    }
    public String getLoginPasswd() {
     return login_passwd;
    }
    public void setLoginPasswd(String passwd) {
     login_passwd = passwd;
    }
    public String getResourcePath() {
        return resource_path;
    }
    public void setResourcePath(String path) {
     resource_path = path;
    }
    public String getResourceName() {
     return resource_name;
    }
    public void setResourceName(String name) {
     resource_name = name;
    }
    public String getResourceExt() {
        return resource_ext;
    }
    public void setResourceExt(String ext) {
        resource_ext = ext;
    }
}

 

ResourceService rss = new ResourceService();

rss.setSyncMode(1);

.........................................

rss.setResourcePath("/");

 

LiveStream = LiveStream(rss);

class LiveStream {

    ResourceService rss;

    public LiveStream(ResourceService rss) {
        this.rss = rss;
       downStream();
  }

    public void downStream() {
      (new Thread() {
       @Override
       public void run() {
   
          native_down_stream(rss);
     }
     }).start();   
  }
 
  static {
      System.loadLibrary("liveclient");
  }

}

 

5.2. c/c++ end

5.2.1 register

static JNINativeMethod methods[] = {
    {"native_livestream", "(Ljava/lang/object)V", (void*) native_livestream},

or

    {"native_livestream", "(Lcom/live/ResourceService)V", (void*) native_livestream},

    {"native_live_getchannel", "()Ljava/lang/String;", (void*) native_live_getchannel},
};

 

5.2.2 declaration

#include <jni.h>

#include <android/log.h>

#define LOG_TAG "LiveClient"
#define LOGI(...) __android_log_print(ANDROID_LOG_INFO, LOG_TAG, __VA_ARGS__)

void native_livestream(JNIEnv *env UNUSED, jclass clazz UNUSED, jobject obj)；

5.2.3 define and implementation

void native_livestream(JNIEnv *env UNUSED, jclass clazz UNUSED, jobject obj)
{
    // ResourceService *rss = (ResourceService *)obj;
    ResourceService *rss = NULL;
    Sco_NET_RC rc;
    int fd = -1;
    jclass cls;
    jfieldID jmode_fid, jtype_fid, juser_fid, jpwd_fid;
    jfieldID jip_fid, jport_fid, jpath_fid, jname_fid, jext_fid;
    jint jmode, jtype, jport;
    jstring juser, jpwd, jip, jpath, jname, jext;

    int mode, type, port;
    char *user, *pwd, *ip, *path, *name, *ext;

    if(obj == NULL) {
        LOGI("Null Pointer in parameters in [%s].\n", __FUNCTION__);
        return;
    }

    rss = new ResourceService();

    if(!rss) {
        LOGI("Fail to alloc memory.\n");
        return;
    }

    // cls = env->FindClass("com/uw/ResourceService");
    cls = env->GetObjectClass(obj);
    if(cls == NULL) {
        LOGI("Fail to find class com.uw.ResourceService.\n");
        return;
    }

    jmode_fid = env->GetFieldID(cls, "sync_mode", "I");
    jtype_fid = env->GetFieldID(cls, "filesystem_type", "I");
    juser_fid = env->GetFieldID(cls, "login_username", "Ljava/lang/String");
    jpwd_fid = env->GetFieldID(cls, "login_passwd", "Ljava/lang/String");
    jip_fid  = env->GetFieldID(cls, "service_ip", "Ljava/lang/String");
    jport_fid = env->GetFieldID(cls, "service_port", "I");

 

    jpath_fid = env->GetFieldID(cls, "resource_path", "Ljava/lang/String");
    jname_fid = env->GetFieldID(cls, "resource_name", "Ljava/lang/String");
    jext_fid = env->GetFieldID(cls, "resource_ext", "Ljava/lang/String");

    jmode = env->GetIntField(obj, jmode_fid);
    jtype = env->GetIntField(obj, jtype_fid);
    jport = env->GetIntField(obj, jport_fid);
    jip = (jstring )env->GetObjectField(obj, jip_fid);
    juser = (jstring) env->GetObjectField(obj, juser_fid);
    jpwd = (jstring)env->GetObjectField(obj, jpwd_fid);
    jpath = (jstring)env->GetObjectField(obj, jpath_fid);
    jname = (jstring)env->GetObjectField(obj, jname_fid);
    jext = (jstring)env->GetObjectField(obj, jext_fid);

 

    rss->sync_mode = jmode;
    rss->filesystem_type = jtype;
    rss->service_port = jport;
    rss->service_ip = (uint8_t *)env->GetStringUTFChars(jip, NULL);
    rss->login_username = (uint8_t *)env->GetStringUTFChars(juser, NULL);
    rss->login_passwd = (uint8_t *)env->GetStringUTFChars(jpwd, NULL);
    rss->resource_path = (uint8_t *)env->GetStringUTFChars(jpath, NULL);
    rss->resource_name = (uint8_t *)env->GetStringUTFChars(jname, NULL);
    rss->resource_ext = (uint8_t *)env->GetStringUTFChars(jext, NULL);

................................................................................................................................

}

 

 

 

java end