Android中JNI如何使用，很多新手对此不是很清楚，为了帮助大家解决这个难题，下面小编将为大家详细讲解，有这方面需求的人可以来学习下，希望你能有所收获。
1.导入C语言的类
首先我们需要把C语言写的功能类放入我们的项目中。这里我直接从资料中找了一个，毕竟我不会写。路径在src/main/jni中
find_name.cpp
#include <jni.h>#include <string.h> #include <stdio.h>#include <stdlib.h>#include <string.h>#include <netdb.h>#include <sys/stat.h>#include <sys/types.h>#include <sys/select.h>#include <sys/socket.h>#include <netinet/in.h>#include <arpa/inet.h> #define send_MAXSIZE 50#define recv_MAXSIZE 1024 struct NETBIOSNS {unsigned short int tid; //unsigned short int 占2字节unsigned short int flags;unsigned short int questions;unsigned short int answerRRS;unsigned short int authorityRRS;unsigned short int additionalRRS;unsigned char name[34];unsigned short int type;unsigned short int classe;}; char *getNameFromIp(const char *ip); extern "C" jstring Java_com_hao_cmake_MainActivity_cpuFromJNI(JNIEnv* env, jobject thiz, jstring ip) {const char* str_ip;str_ip = env->GetStringUTFChars(ip, 0);return env->NewStringUTF(getNameFromIp(str_ip));} char *getNameFromIp(const char *ip) {char str_info[1024] = { 0 };struct sockaddr_in toAddr; //sendto中使用的对方地址struct sockaddr_in fromAddr; //在recvfrom中使用的对方主机地址char send_buff[send_MAXSIZE];char recv_buff[recv_MAXSIZE];memset(send_buff, 0, sizeof(send_buff));memset(recv_buff, 0, sizeof(recv_buff));int sockfd; //socketunsigned int udp_port = 137;int inetat;if ((inetat = inet_aton(ip, &toAddr.sin_addr)) == 0) {sprintf(str_info, "[%s] is not a valid IP address\n", ip);return str_info;}if ((sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0) {sprintf(str_info, "%s socket error sockfd=%d, inetat=%d\n", ip, sockfd, inetat);return str_info;}bzero((char*) &toAddr, sizeof(toAddr));toAddr.sin_family = AF_INET;toAddr.sin_addr.s_addr = inet_addr(ip);toAddr.sin_port = htons(udp_port); //构造netbios结构包struct NETBIOSNS nbns;nbns.tid = 0x0000;nbns.flags = 0x0000;nbns.questions = 0x0100;nbns.answerRRS = 0x0000;nbns.authorityRRS = 0x0000;nbns.additionalRRS = 0x0000;nbns.name[0] = 0x20;nbns.name[1] = 0x43;nbns.name[2] = 0x4b;int j = 0;for (j = 3; j < 34; j++) {nbns.name[j] = 0x41;}nbns.name[33] = 0x00;nbns.type = 0x2100;nbns.classe = 0x0100;memcpy(send_buff, &nbns, sizeof(nbns));int send_num = 0;send_num = sendto(sockfd, send_buff, sizeof(send_buff), 0,(struct sockaddr *) &toAddr, sizeof(toAddr));if (send_num != sizeof(send_buff)) {sprintf(str_info,"%s sendto() error sockfd=%d, send_num=%d, sizeof(send_buff)=%d\n",ip, sockfd, send_num, sizeof(send_buff));shutdown(sockfd, 2);return str_info;}int recv_num = recvfrom(sockfd, recv_buff, sizeof(recv_buff), 0,(struct sockaddr *) NULL, (socklen_t*) NULL);if (recv_num < 56) {sprintf(str_info, "%s recvfrom() error sockfd=%d, recv_num=%d\n", ip,sockfd, recv_num);shutdown(sockfd, 2);return str_info;}//这里要初始化。因为发现linux和模拟器都没问题，真机上该变量若不初始化，其值就不可预知unsigned short int NumberOfNames = 0;memcpy(&NumberOfNames, recv_buff + 56, 1);char str_name[1024] = { 0 };unsigned short int mac[6] = { 0 };int i = 0;for (i = 0; i < NumberOfNames; i++) {char NetbiosName[16];memcpy(NetbiosName, recv_buff + 57 + i * 18, 16);//依次读取netbios nameif (i == 0) {sprintf(str_name, "%s", NetbiosName);}}sprintf(str_info, "%s|%s|", ip, str_name);for (i = 0; i < 6; i++) {memcpy(&mac[i], recv_buff + 57 + NumberOfNames * 18 + i, 1);sprintf(str_info, "%s%02X", str_info, mac[i]);if (i != 5) {sprintf(str_info, "%s-", str_info);}}return str_info;}这里要注意一点，jstring Java_com_hao_cmake_MainActivity_cpuFromJNI方法中，com_hao_cmake是我们的包名，MainActivity是调用JNI的Activity名称，cpuFromJNI是对应方法的名字。
2.接着导入Android.mk文件
这个文件也是放在jni文件夹中
LOCAL_PATH := $(call my-dir)include $(CLEAR_VARS) # 指定so库文件的名称LOCAL_MODULE := jni_mix# 指定需要编译的源文件列表LOCAL_SRC_FILES := find_name.cpp# 指定C++的编译标志LOCAL_CPPFLAGS += -fexceptions# 指定要加载的静态库#LOCAL_WHOLE_STATIC_LIBRARIES += android_support# 指定需要链接的库LOCAL_LDLIBS := -llog include $(BUILD_SHARED_LIBRARY)$(call import-module, android/support)3.我们配置一下build.gradle文件
android -> defaultConfig 下添加
externalNativeBuild{ ndkBuild{ abiFilters "arm64-v8a","armeabi-v7a" }}android 下添加
externalNativeBuild { ndkBuild { path file('src/main/jni/Android.mk') }}packagingOptions{ pickFirst 'lib/arm64-v8a/libjni_mix.so' pickFirst 'lib/armeabi-v7a/libjni_mix.so'}4.好了，此时可以编译一下项目了
5.此时我们可以找一下我们生成的so包了
在build → intermediates → ndkBuild → debug → obj → local下，我们可以找到我们生成的相关配置平台的so文件
6.将生成的so文件拷入src/main/jniLibs中
这个样子的
7.调用C语言方法的Activity如下
public class MainActivity extends AppCompatActivity { public native String cpuFromJNI(String ip); static { System.loadLibrary("jni_mix"); } @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); String str = cpuFromJNI("192.168.0.163"); Toast.makeText(this,str,Toast.LENGTH_SHORT).show(); }}这样我们就完成了用C语言类生成so包，并使用JNI进行调用的全流程。
注意：在使用JNI进行调用的时候，我们的环境一定要有NDK，这个我这里就不说了，大家如果没有搭建需要上网找找搭建一下。
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