JNI--Java调用C语言

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————————————这篇笔记不去介绍如何配置jni开发环境了，上一篇有说明——————————————

activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools"android:orientation="vertical"android:layout_width="match_parent"android:layout_height="match_parent"android:paddingBottom="@dimen/activity_vertical_margin"android:paddingLeft="@dimen/activity_horizontal_margin"android:paddingRight="@dimen/activity_horizontal_margin"android:paddingTop="@dimen/activity_vertical_margin"tools:context=".MainActivity" ><Buttonandroid:onClick="javaCallCForAdd"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="java调用C代码加法运算" /><Buttonandroid:onClick="javaCallCForString"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="java调用C代码字符串运算" /><Buttonandroid:onClick="javaCallCForArray"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="java调用C代码数组运算" /></LinearLayout>

MainActivity.java

package com.atguigu.javacallc;import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;public class MainActivity extends Activity {private JNI jni;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);jni = new JNI();}//点击事件-Java代码调用C代码执行加法运算public void javaCallCForAdd(View view){int result  = jni.add(99, 1);Log.e("TAG","result=="+result );}public void javaCallCForString(View view){String result  = jni.sayHelloInC("I am from java");Log.e("TAG","result=="+result );}public void javaCallCForArray(View view){int iArray[] = {1,2,3,4,5,6};jni.arrElementsIncrease(iArray);for(int i=0;i<iArray.length;i++){Log.e("TAG","result=="+iArray[i] );}}
}

JNI.java

package com.atguigu.javacallc;public class JNI {{//加载动态链接库System.loadLibrary("atguigu");}/*** 让C语言实现加法运算，并且把结果返回给java代码*/public native int add(int x, int y);/***  让C语言实现字符串运算，并且把结果返回给java代码*/public native String sayHelloInC(String s);/*** 传入int类型的数组，让C语言把每个元素都加上10* 应用场景：图片处理，像素矩阵。*/public native int[] arrElementsIncrease(int[] intArray); 
}

下面是jni目录下的文件

Android.mk

LOCAL_PATH := $(call my-dir)include $(CLEAR_VARS)LOCAL_MODULE    := atguigu
LOCAL_SRC_FILES := atguigu.cLOCAL_LDLIBS += -llog
#1.liblog.so   lloginclude $(BUILD_SHARED_LIBRARY)

com_atguigu_javacallc_JNI.h（这个是javah生成拖拽过来的）

atguigu.c

#include "com_atguigu_javacallc_JNI.h"
#include<stdio.h>
#include<stdlib.h>#include <android/log.h>
#define LOG_TAG "atguigu"
#define LOGD(...) __android_log_print(ANDROID_LOG_ERROR, LOG_TAG, __VA_ARGS__)
#define LOGI(...) __android_log_print(ANDROID_LOG_INFO, LOG_TAG, __VA_ARGS__)/*** 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;
}/*** 做加法运算，把结果返回Java中的JNI.java类中的int add(int x, int y)*/
JNIEXPORT jint JNICALL Java_com_atguigu_javacallc_JNI_add(JNIEnv * env, jobject jobj, jint ji, jint jy){int result = ji + jy;//在Android平台上，失效了LOGD("LOGD --result==%d\n",result);return result;}
/*** 把Java代码传入进来的I am from java 后面加上add I am from C*/
JNIEXPORT jstring JNICALL Java_com_atguigu_javacallc_JNI_sayHelloInC(JNIEnv * env, jobject jobj, jstring jstr){//c 语言有字符串吗 jstring -->char*char* text1 = _JString2CStr(env,jstr);//I am from javachar* text2 = " add I am from C";//拼接函数-把拼接的结果放在第一个参数里面strcat(text1,text2);//jstring     (*NewStringUTF)(JNIEnv*, const char*);return (*env)->NewStringUTF(env,text1);}/*** 让C语言代码把传入的数组，每个元素都加上10*/
JNIEXPORT jintArray JNICALL Java_com_atguigu_javacallc_JNI_arrElementsIncrease(JNIEnv *env, jobject jobj, jintArray jarray){//1.得到数组的长度// jsize       (*GetArrayLength)(JNIEnv*, jarray);jsize jsizes = (*env)->GetArrayLength(env,jarray);//2.遍历数组// jint*       (*GetIntArrayElements)(JNIEnv*, jintArray, jboolean*);jint* jarrays = (*env)->GetIntArrayElements(env,jarray,JNI_FALSE);int i;for(i=0;i<jsizes;i++){//3.给每一个数组的元素加上10*(jarrays+i) += 10;}return jarray;}

————————————————Java调用C语言     第二个案例——————————————

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="match_parent"android:paddingBottom="@dimen/activity_vertical_margin"android:paddingLeft="@dimen/activity_horizontal_margin"android:paddingRight="@dimen/activity_horizontal_margin"android:paddingTop="@dimen/activity_vertical_margin"tools:context=".MainActivity" ><TextViewandroid:id="@+id/tv_status"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="登录状态" /><EditTextandroid:id="@+id/et_password"android:layout_width="match_parent"android:layout_height="wrap_content"android:layout_below="@id/tv_status"android:hint="请输入登录密码" /><Buttonandroid:id="@+id/btn_login"android:layout_width="match_parent"android:layout_height="wrap_content"android:layout_below="@id/et_password"android:text="登录" /></RelativeLayout>

MainActivity.java

package com.atguigu.checkpassword;import android.app.Activity;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;public class MainActivity extends Activity {{System.loadLibrary("CheckPassword");}private TextView tv_status;private EditText et_password;private Button btn_login;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);tv_status = (TextView) findViewById(R.id.tv_status);et_password = (EditText) findViewById(R.id.et_password);btn_login = (Button) findViewById(R.id.btn_login);// 设置点击事件btn_login.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {// 1.得到密码String password = et_password.getText().toString().trim();// 2.判断密码是否为空if (TextUtils.isEmpty(password)) {Toast.makeText(MainActivity.this, "密码不能空", 1).show();return;}// 3.传入密码给C语言int coder = login(password);// 4.根据返回的状态码设置是否登录成功if(coder ==200){tv_status.setText("登录成功");}else{tv_status.setText("登录失败");}}});}/*** 判断密码是否正确，如果正确返回200 错误返回400* * @param password* @return*/public native int login(String password);}

以下是src同级目录jni文件夹下的文件

Android.mk

LOCAL_PATH := $(call my-dir)include $(CLEAR_VARS)LOCAL_MODULE    := CheckPassword
LOCAL_SRC_FILES := CheckPassword.cinclude $(BUILD_SHARED_LIBRARY)

CheckPassword.c

#include "com_atguigu_checkpassword_MainActivity.h"
#include<stdlib.h>
#include<stdio.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;
}/**
判断密码是否正确，如果正确返回200
错误返回400
*/
int login(char* password){//判断密码//原始密码char* originPassword  = "atguigu123";int coder = strcmp(password,originPassword);if(coder==0){return 200;} else{return 400;}}JNIEXPORT jint JNICALL Java_com_atguigu_checkpassword_MainActivity_login(JNIEnv * env, jobject jobj, jstring jstr){//jstring-->char*char* text = _JString2CStr(env,jstr);int result = login(text);return result;}

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