JNI笔记
- 背景
- Demo代码
- JNI.java
- MainActivity.java
- Android.mk
- Application.mk
- com_stone_javacallc_JNI.h
- javacallc.c
- build.gradle
背景
Demo代码
代码结构
JNI.java
package com.stone.javacallc;
/**
* Created by stoneWang
* Created on 2024/1/16
* java调用C
*/
public class JNI {
{
System.loadLibrary("javacallc");
}
/**
* 让C代码做加法运算,把结果返回
*
* @param x
* @param y
* @return
*/
public native int add(int x, int y);
/**
* 从Java传入字符串,C代码进行拼接
*
* @param s I am from java
* @return I am from java add I am from C
*/
public native String sayHello(String s);
/**
* 让C代码给每个元素加上10
*
* @param intArray
* @return
*/
public native int[] increaseArrayEles(int[] intArray);
}
MainActivity.java
package com.stone.javacallc;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
public class MainActivity extends AppCompatActivity {
private JNI jni;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
jni = new JNI();
}
public void add(View view) {
int result = jni.add(99, 1);
Log.e(MainActivity.class.getSimpleName(), "result:" + result);
}
public void string(View view) {
String result = jni.sayHello("I am from java ");
Log.e(MainActivity.class.getSimpleName(), "result:" + result);
}
public void array(View view) {
}
public void checkpw(View view) {
}
}
Android.mk
LOCAL_PATH :=$(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE :=javacallc
LOCAL_SRC_FILES :=javacallc.c
include $(BUILD_SHARED_LIBRARY)
Application.mk
App_ABI:=all
com_stone_javacallc_JNI.h
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_stone_javacallc_JNI */
#ifndef _Included_com_stone_javacallc_JNI
#define _Included_com_stone_javacallc_JNI
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class: com_stone_javacallc_JNI
* Method: add
* Signature: (II)I
*/
JNIEXPORT jint JNICALL Java_com_stone_javacallc_JNI_add
(JNIEnv *, jobject, jint, jint);
/*
* Class: com_stone_javacallc_JNI
* Method: sayHello
* Signature: (Ljava/lang/String;)I
*/
JNIEXPORT jstring JNICALL Java_com_stone_javacallc_JNI_sayHello
(JNIEnv *, jobject, jstring);
/*
* Class: com_stone_javacallc_JNI
* Method: increaseArrayEles
* Signature: ([I)[I
*/
JNIEXPORT jintArray JNICALL Java_com_stone_javacallc_JNI_increaseArrayEles
(JNIEnv *, jobject, jintArray);
#ifdef __cplusplus
}
#endif
#endif
javacallc.c
//
// Created by wanglei on 2024/1/16.
//
# include "com_stone_javacallc_JNI.h"
# include "string.h"
/**
* 把一个jstring转换成一个c语言的char* 类型.
*/
char* _JString2CStr(JNIEnv* env, jstring jstr) {
char* rtn = NULL;
jclass clsstring = (*env)->FindClass(env, "java/lang/String");
jstring strencode = (*env)->NewStringUTF(env,"GB2312");
jmethodID mid = (*env)->GetMethodID(env, clsstring, "getBytes", "(Ljava/lang/String;)[B");
jbyteArray barr = (jbyteArray)(*env)->CallObjectMethod(env, jstr, mid, strencode); // String .getByte("GB2312");
jsize alen = (*env)->GetArrayLength(env, barr);
jbyte* ba = (*env)->GetByteArrayElements(env, barr, JNI_FALSE);
if(alen > 0) {
rtn = (char*)malloc(alen+1); //"\0"
memcpy(rtn, ba, alen);
rtn[alen]=0;
}
(*env)->ReleaseByteArrayElements(env, barr, ba,0);
return rtn;
}
/**
*
* @param env
* @param jobj
* @param ji
* @param jj
* @return
*/
jint Java_com_stone_javacallc_JNI_add
(JNIEnv *env, jobject jobj, jint ji, jint jj){
int result = ji + jj;
return result;
};
jstring Java_com_stone_javacallc_JNI_sayHello
(JNIEnv *env, jobject jobj, jstring jstr){
char* fromJava = _JString2CStr(env, jstr);
char* fromc = "add I am from C";
// 拼接函数strcat
strcat(fromJava, fromc); // 把拼接的结果放在第一参数里面
// 将char转为jstring
return (*env)->NewStringUTF(env, fromJava);
};
build.gradle
apply plugin: 'com.android.application'
android {
compileSdkVersion 30
buildToolsVersion "30.0.2"
defaultConfig {
applicationId "com.stone.javacallc"
minSdkVersion 26
targetSdkVersion 30
versionCode 1
versionName "1.0"
testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
ndk{
moduleName "javacallc"
abiFilters "armeabi", "armeabi-v7a", "arm64-v8a" // cpu类型
}
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
}
}
externalNativeBuild {
ndkBuild {
path "src/main/jni/Android.mk"
}
}
}
dependencies {
implementation fileTree(dir: "libs", include: ["*.jar"])
implementation 'androidx.appcompat:appcompat:1.2.0'
implementation 'androidx.constraintlayout:constraintlayout:2.0.1'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'androidx.test.ext:junit:1.1.2'
androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'
}