JNI调用so动态库

1、编写native接口

package org.demo;

public class JniDemo
{
    public static native int bmp2fea(byte[] bmp, byte[] fea, byte[] err);

    public static native int feaMatch(byte[] fea1, byte[] fea2, int level);

}

2、根据native接口生成声明文件（.h）

javah -classpath . -jni org.demo.JniDemo

3、编写接口代码调动so动态库（.c）

#include <stdlib.h>
#include <stadio.h>
#include <string.h>
#include 'org_demo_JniDemo.h'

extern int feaMatch(char *pRegAscii, char *pVerAscii, int level);
extern int bmp2fea(unsigned char* bmp, char* feature, char* errinfo);

JNIEXPORT jint JNICALL JAVA_org_demo_JniDemo_bmp2fea  (JNIEnv *env, jclass arg, jbyteArray bmp, jbyteArray fea, jbyteArray err) 
{
    char out[1024]  = { 0 };
    char errinfo[1024] = { 0 };
    jbyte* pbmp = (*env)->GetByteArrayElements(env, bmp, 0);
    jsize inSize = (*env)->GetArrayLength(env, bmp);
    //bmp大小平均150k,使用malloc
    char *tmp = (char*)malloc(inSize + 1);
    memset(tmp, 0, inSize+1);
    memcpy(tmp, pbmp, inSize);

    int ret = bmp2fea((unsigned char*)tmp, (char*)out, (char*)errinfo);
    if (ret == 0)
    {
        (*env)->SetByteArrayRegion(env, fea, 0, strlen(out), (jbyte*)out);
        if (strlen(errinfo) > 0)
             (*env)->SetByteArrayRegion(env, err, 0, strlen(errinfo), (jbyte*)out);
    } 
    else
    {
        if (strlen(errinfo) > 0)
             (*env)->SetByteArrayRegion(env, err, 0, strlen(errinfo), (jbyte*)out);
    }
    if (tmp != NULL) 
    {
        free(tmp);
    }
    (*env)->ReleaseByteArrayElements(env, bmp, pbmp, 0);
    return rt;
}

JNIEXPORT jint JNICALL Java_org_demo_JniDemo_feaMatch (JNIEnv *env, jclass arg, jbyteArray fea1, jbyteArray fea2, jint level)
{
    char tmp1[1024] = { 0 };
    char tmp2[1024] = { 0 };

    jbyte* pFea1 = (*env)->GetByteArrayElements(env, fea1, 0);
    jsize inSize1 = (*env)->GetArrayLength(env, fea1);
    memcpy(tmp1, pFea1, inSize1);
    jbyte* pFea2 = (*env)->GetByteArrayElements(env, fea2, 0);
    jsize inSize2 = (*env)->GetArrayLength(env, fea2);
    memcpy(tmp2, pFea2, inSize2);
   
    int ret = feaMatch(tmp1, tmp2, level);
    (*env)->ReleaseByteArrayElements(env, fea1, pFea1, 0);
    (*env)->ReleaseByteArrayElements(env, fea1, pFea2, 0);
    return ret;
}

4、根据.h、.c编译生成so，如下makefie文件make生成libengine.so

ODIR=.
EDIR=.
LDIR=.
INC_DIR=./

CC=g++
AR=ar -r
LD=ld
RM=rm -rf
cc=gcc
STRIP=strip
MKDIR=mkdir -p

INCLUDES=-I$(INC_DIR)
CCFLAGS=-g $(INCLUDES) -fPIC
LIBS=-lc -ldl -ldemo

SRC_DIR=./
ALL_DIR=-I$(SRC_DIR) -I/usr/java/jdk1.7.0_80/include/ -I/usr/java/jdk1.7.0_80/include/linux/

LIBAPI_SO=$(LDIR)/libengine.so
BIZD=$(EDIR)/test

PROGRAM=$(LIBAPI_SO)

####object files####
LIBAPI_OBJ=$(ODIR)/org_demo_JniDemo.o
####object files####
BIZ_OBJ=$(ODIR)/test.o
##############
all:$(PROGRAM)
force:
$(LIBAPI_SO)::$(LIBAPI_OBJ)
    @echo ----Linking...----
    $(LD) -share -o $(LIBAPI_SO) $(LIBAPI_OBJ) -L./ $(LIBS)
    @echo ----make $@ OK----
$(BIZD)::$(BIZ_OBJ)
    @echo ----Linking...----
    $(cc) -o $(BIZD) $(BIZD_OBJ) -L$(LDIR) $(LIBS) $(CCFLAGS)
    @echo ----make $@ OK----
clean::
    @$(RM) $(ODIR)/*.o $(PROGRAM)
cleanobj::
    @$(RM) $(BIZ_OBJ)
cleanbin::
    @$(RM) $(PROGRAM)

.SUFFIXES:.cpp .c .o .so .a
####common#####
$(ODIR)/%.o:$(SRC_DIR)/%.c
    $(cc) $(CCFLAGS) $< $(ALL_DIR) -c -o $@

5、java调用native接口

package org.demo;

import org.demo.JniDemo;

public class Demo
{
    static {
        // 动态库名： libdemo.so
        System.loadLibrary("demo");
        // libengine.so
        System.loadLibrary("engine");
    }

    public static int bmp2fea(byte[] bmp, byte[] fea, byte[] err)
    {
        return JniDemo.bmp2fea(bmp, fea, err);
    }

    public static int feaMatch(byte[] fea1, byte[] fea2, int level)
    {
         return JniDemo.feaMatch(fea1, fea2, level);
    } 
} 

6、配置动态库路径

方法一:
#linux用户环境变量配置：
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/demo/lib/

方法二：
#程序启动是配置JVM参数：
java -Djava.library.path=/demo/lib/ -server -cp $CLASSPATH org.demo.Test