2017-07-25 JNI (Java Native Interface) & singleton

工作日记

build

1. package into a assigned path[1](jobject vs jclass)and build a .jar file[2]
2. use cmake build a .dylib or .so file.[3]
3. assign[4] or set the java.lib.path [5][6], and put the .dylib or .so in.
4. use singleton[7] when load lib.

5. edit CmakeList.txt add .h & .cpp as entrance

   ADD_LIBRARY(projectName SHARED include/jni/com_****_JNI.h src/jni/****JNI.cpp)

   @Q: when using on the linux service, the third method doesn't work, also the other[8], we should notice the difference between osx and linux[9].

   @Q: while cmake the project

   /export/home/aiusr/env/image/bin/ld:src/jni/libJNI.a(IdcardRecognizerController.cpp.o): relocation R_X86_64_32 against '.bss' can not be used when making a shared object; recompile with -fPIC
   

   error occured

   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
   

   need to be modified to

   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -fPIC ")
   

   It seems like linux enviroment is the main reason.

public class JNIService {
    private static final JNIService instance = new JNIService();
    private JNIService(){
        try{
            System.out.println("----start-----");
            System.out.println(System.getProperty("java.library.path"));
            System.out.println("----end-----");
            System.loadLibrary("cppLib");
        }catch(Throwable e)
        {
            System.out.println("The cppLib don't load correctly");
        }
    }
    public static JNIService getInstance(){
        return instance;
    }
    //define a native function
    public native String function(int type, String filePath);
    public String callCpp(Map<String, Object> paramMap) throws Exception {
        String res = function(type, filePath);
        System.out.print("res is ------->>>>>>" + res);
        return res;
    }
}

test

1. because using of singleton, new the service will be illegal, so I used the JNIService.getInstance().

public class TestJNI {
    private JNIService jNIService = JNIService.getInstance();
    @Test
    public void test(){
        Map<String,Object> paramMap = new HashMap<String,Object>();
        paramMap.put("type","front");
        paramMap.put("imgFilePath","/Users/saber/Downloads/test_img/51152119960731792x_1.jpeg");
        try {
            String res = JNIService.callCpp(paramMap);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}