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" >    <Button        android:onClick="javaCallCForAdd"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="java调用C代码加法运算" />         <Button        android: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" />           <Button        android: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    := atguiguLOCAL_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" >    <TextView        android:id="@+id/tv_status"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="登录状态" />    <EditText        android: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" />    <Button        android: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    := CheckPasswordLOCAL_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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