将 lib 添加到 jni 应用程序的 makefile

Question

我不明白如何使用 JNI 运行在 java 中编写 C++ 代码。我认为 makefile 中有一些错误，我认为缺少一些库。

我在 java class:

中有这个代码

private native void getCanny(long mat);
getCanny(mat.getNativeObjAddr());

和 Mat2Image.h 生成：

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class Mat2Image */

#ifndef _Included_Mat2Image
#define _Included_Mat2Image
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     Mat2Image
 * Method:    getCanny
 * Signature: (J)V
 */
JNIEXPORT void JNICALL Java_Mat2Image_getCanny
  (JNIEnv *, jobject, jlong);

#ifdef __cplusplus
}
#endif
#endif

这是我制作的 .cpp：

#include "Mat2Image.h"
#include <iostream>
#include <opencv2/core/core.hpp>
#include <opencv2/imgproc.hpp>


JNIEXPORT void JNICALL Java_Mat2Image_getCanny
   (JNIEnv * env, jobject obj, jlong matr){


       cv::Mat* frame=(cv::Mat*)matr;
            cv::cvtColor(*frame, *frame, CV_BGR2GRAY);
            cv::GaussianBlur(*frame, *frame, cv::Size(7,7), 1.5, 1.5);
            cv::Canny(*frame, *frame, 0, 30, 3);


}

这是我的生成文件：

# Define a variable for classpath
CLASS_PATH = ../bin

# Debug: -g3=compile with extra debugg infos. -ggdbg3=include things like macro defenitions. -O0=turn off optimizations.
DEBUGFLAGS = -g3 -ggdb3 -O0
CFLAGS = $(DEBUGFLAGS)

# Define a virtual path for .class in the bin directory
vpath %.class $(CLASS_PATH)

all : libMat.so

# $@ matches the target, $< matches the first dependancy
libMat.so : libMat.o
    g++ $(CFLAGS) -W -shared -o $@ $<

# $@ matches the target, $< matches the first dependancy
libMat.o : Mat2Image.cpp Mat2Image.h
    g++ $(CFLAGS) -fPIC -I/usr/lib/jvm/jdk1.8.0_111/include -I/usr/lib/jvm/jdk1.8.0_111/include/linux -c $< -o $@

# $* matches the target filename without the extension
# manually this would be: javah -classpath ../bin HelloJNI
HelloJNI.h : Mat2Image.class
    javah -classpath $(CLASS_PATH) $*

clean :
    rm -f Mat2Image.h libMat.o libMat.so

但是当我尝试运行方法时出现此错误：

/usr/lib/jvm/jdk1.8.0_111/bin/java: symbol lookup error: /home/buzzo/Downloads/helloJni-master/jni/libMat.so: undefined symbol: _ZN2cv8cvtColorERKNS_11_InputArrayERKNS_12_OutputArrayEii

我认为问题出在 makefile 上，我该如何编辑它？

Answer 1

您的代码似乎使用了未 linked 的符号。

我建议 link 你与 opencv 的共享库？

如果您想查看从 JNI 使用共享库的示例代码，请查看此处：

https://github.com/mkowsiak/jnicookbook/tree/master/recipes/recipeNo023

在您的情况下，opencv 库似乎不在 LD_LIBRARY_PATH。

Answer 2

我通过修改makefile解决了：

我改

libMat.so : libMat.o
    g++ $(CFLAGS) -W -shared -o $@ $<

和

libMat.so : libMat.o
    g++ $(CFLAGS) -W -shared -o $@ $< -lopencv_imgproc

这是最终的 makefile：

# Define a variable for classpath
CLASS_PATH = ../bin
# Debug: -g3=compile with extra debugg infos. -ggdbg3=include things like macro defenitions. -O0=turn off optimizations.
DEBUGFLAGS = -g3 -ggdb3 -O0
CFLAGS = $(DEBUGFLAGS)

# Define a virtual path for .class in the bin directory
vpath %.class $(CLASS_PATH)

all : libMat.so

# $@ matches the target, $< matches the first dependancy
libMat.so : libMat.o
    g++ $(CFLAGS) -W -shared -o $@ $< -lopencv_imgproc

# $@ matches the target, $< matches the first dependancy
libMat.o : Mat2Image.cpp Mat2Image.h
    g++ $(CFLAGS) -fPIC -I/usr/lib/jvm/jdk1.8.0_111/include -I/usr/lib/jvm/jdk1.8.0_111/include/linux -c $< -o $@ 

# $* matches the target filename without the extension
# manually this would be: javah -classpath ../bin HelloJNI
HelloJNI.h : Mat2Image.class
    javah -classpath $(CLASS_PATH) $*

clean :
    rm -f libMat.o libMat.so

将 lib 添加到 jni 应用程序的 makefile

Add lib to makefile for jni app

java

c++

makefile

java-native-interface

lib