1.CMakeList.txt 配置

add_library( # Sets the name of the library.
             native-lib

             # Sets the library as a shared library.
             SHARED

             # Provides a relative path to your source file(s).
             src/main/cpp/native-lib.cpp
             )

add_library( # Sets the name of the library.
             Hello

             # Sets the library as a shared library.
             SHARED

             # Provides a relative path to your source file(s).
             src/main/cpp/Hello.c
             )

find_library( # Sets the name of the path variable.
              log-lib

              # Specifies the name of the NDK library that
              # you want CMake to locate.
              log )


target_link_libraries( # Specifies the target library.
                       native-lib

                       # Links the target library to the log library
                       # included in the NDK.
                       ${log-lib} )

target_link_libraries( # Specifies the target library.
                       Hello

                       # Links the target library to the log library
                       # included in the NDK.
                       ${log-lib} )

2.gradle 添加依赖

android {
  defaultConfig{
        externalNativeBuild {
            cmake {
                cppFlags "-frtti -fexceptions"
            }
             ndk {
                abiFilters 'armeabi', 'armeabi-v7a', 'arm64-v8a',"x86" //添加cpu平台
            }

        }
    }
  
    externalNativeBuild {
        cmake {
            path "CMakeLists.txt"
        }
    }
}

3.新建一个类 JNI.java 添加本地方法

public class JNI {

    static {
        System.loadLibrary("Hello");
    }

    public native String getNameFromJni();

    public native int add(int x, int y);

    public native String connect(String str);

    public native String md5FromJni(String str);

}

4.在cpp 下创建c/c++文件 Hello.c

#include <jni.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "MD5Utils.h"
#include "MD5Utils.c"
#include <android/log.h>


#define  LOG_TAG    "Hello"
#define  LOGI(...)  __android_log_print(ANDROID_LOG_INFO, LOG_TAG, __VA_ARGS__)
#define LOGE(...)  __android_log_print(ANDROID_LOG_ERROR, LOG_TAG, __VA_ARGS__)
#define LOGI(...)  __android_log_print(ANDROID_LOG_INFO, LOG_TAG, __VA_ARGS__)

JNIEXPORT jstring JNICALL
Java_com_lixinxin_jnidemo1_jni_JNI_getNameFromJni(JNIEnv *env, jobject instance) {
    char *returnValue = "Hello";
    return (*env)->NewStringUTF(env, returnValue);
}

JNIEXPORT jint JNICALL
Java_com_lixinxin_jnidemo1_jni_JNI_add(JNIEnv *env, jobject instance, jint x, jint y) {
    int value = x + y;
    return value;
}

JNIEXPORT jstring JNICALL
Java_com_lixinxin_jnidemo1_jni_JNI_connect(JNIEnv *env, jobject instance, jstring str_) {
    const char *str = (*env)->GetStringUTFChars(env, str_, 0);
    char *value = strcat(str, " jni string");
    return (*env)->NewStringUTF(env, value);
}

JNIEXPORT jstring JNICALL
Java_com_lixinxin_jnidemo1_jni_JNI_md5FromJni(JNIEnv *env, jobject instance, jstring str_) {
    const char *str = (*env)->GetStringUTFChars(env, str_, 0);
    MD5_CTX md5;
    MD5Init(&md5);

    unsigned char decrypt[16];
    MD5Update(&md5, str, strlen(str));
    MD5Final(&md5, decrypt);
    unsigned char hexstr[32];
    for (int i = 0; i < 16; i++) {
        sprintf(&hexstr[i * 2], "%02x", decrypt[i]);
    }
    LOGE("name=%s", (char *) hexstr);
    return (*env)->NewStringUTF(env, (char *) hexstr);
}

5.调用

 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        TextView tv = (TextView) findViewById(R.id.sample_text);
        JNI jni = new JNI();
        tv.setText(jni.md5FromJni("111111"));
    }