Android Studio : 使用 jni 实现串口通讯

添加 SerialPort 类

在网上找到 SerialPort 的 java 类，添加到项目中。

package com.xd.serialport;

import android.util.Log;

import java.io.File;
import java.io.FileDescriptor;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

public class SerialPort {
	private static final String TAG = "SerialPort";  
	  
	/* 
	 * Do not remove or rename the field mFd: it is used by native method close(); 
	 */  
	private FileDescriptor mFd;  
	private FileInputStream mFileInputStream;  
	private FileOutputStream mFileOutputStream;  
	  
	public SerialPort(File device, int baudrate, int flags) throws SecurityException, IOException {  
	  
	    /* Check access permission */  
	    if (!device.canRead() || !device.canWrite()) {  
	        try {  
	            /* Missing read/write permission, trying to chmod the file */  
	            Process su;  
	            su = Runtime.getRuntime().exec("/system/bin/su");  
	            String cmd = "chmod 666 " + device.getAbsolutePath() + "\n"  
	                    + "exit\n";  
	            su.getOutputStream().write(cmd.getBytes());  
	            if ((su.waitFor() != 0) || !device.canRead()  
	                    || !device.canWrite()) {  
	                throw new SecurityException();  
	            }  
	        } catch (Exception e) {  
	            e.printStackTrace();  
	            throw new SecurityException();  
	        }  
	    }  
	  
	    mFd = open(device.getAbsolutePath(), baudrate, flags);  
	    if (mFd == null) {  
	        Log.e(TAG, "native open returns null");  
	        throw new IOException();  
	    }  
	    mFileInputStream = new FileInputStream(mFd);  
	    mFileOutputStream = new FileOutputStream(mFd);  
	}  
	  
	// Getters and setters  
	public InputStream getInputStream() {  
	    return mFileInputStream;  
	}  
	  
	public OutputStream getOutputStream() {  
	    return mFileOutputStream;  
	}  
	  
	// JNI  
	private native static FileDescriptor open(String path, int baudrate, int flags);  
	public native void close();  
	static {  
	    System.loadLibrary("serial_port");  
	}  
}

项目结构如下：

---

生成 c 语言头文件

• 打开 Terminal（View -> Tool Windows -> Terminal）

  

• 输入cd app\src\main\java进入源码所在目录

  

• 输入javah -jni com.xd.serialport.SerialPort生成头文件

  

  

---

创建 jni 文件夹，添加 .c 文件

• 右键 Moudle，右键菜单中选择 New -> Folder -> JNI Folder，弹出的对话框，直接点击完成。

  

• 将前面生成的 .h 文件移入 jni 文件夹中。

• 右键 jni 文件夹，右键菜单中选择New -> C/C++ Source File创建与 .h 文件同名的 .c 文件。

  

• 为 .c 文件添加如下内容（来源于网络）。

  注意：需要将include头文件、open、close方法中的包名修改为自己的包名。

  #include <com_xd_serialport_SerialPort.h>  
  #include <termios.h>  
  #include <unistd.h>  
  #include <sys/types.h>  
  #include <sys/stat.h>  
  #include <fcntl.h>  
  #include <string.h>  
  #include <jni.h>  
      
  #include "android/log.h"  
  static const char *TAG="serial_port";  
  #define LOGI(fmt, args...) __android_log_print(ANDROID_LOG_INFO, TAG, fmt, ##args)  
  #define LOGD(fmt, args...) __android_log_print(ANDROID_LOG_DEBUG, TAG, fmt, ##args)  
  #define LOGE(fmt, args...) __android_log_print(ANDROID_LOG_ERROR, TAG, fmt, ##args)  
    
  /* 
  * Class: android_serialport_SerialPort 
  * Method: open 
  * Signature: (Ljava/lang/String;II)Ljava/io/FileDescriptor; 
  */  
  static speed_t getBaudrate(jint baudrate)  
  {  
      switch(baudrate) {  
      case 0: return B0;  
      case 50: return B50;  
      case 75: return B75;  
      case 110: return B110;  
      case 134: return B134;  
      case 150: return B150;  
      case 200: return B200;  
      case 300: return B300;  
      case 600: return B600;  
      case 1200: return B1200;  
      case 1800: return B1800;  
      case 2400: return B2400;  
      case 4800: return B4800;  
      case 9600: return B9600;  
      case 19200: return B19200;  
      case 38400: return B38400;  
      case 57600: return B57600;  
      case 115200: return B115200;  
      case 230400: return B230400;  
      case 460800: return B460800;  
      case 500000: return B500000;  
      case 576000: return B576000;  
      case 921600: return B921600;  
      case 1000000: return B1000000;  
      case 1152000: return B1152000;  
      case 1500000: return B1500000;  
      case 2000000: return B2000000;  
      case 2500000: return B2500000;  
      case 3000000: return B3000000;  
      case 3500000: return B3500000;  
      case 4000000: return B4000000;  
      default: return -1;  
      }  
  }  
    
  /* 
   * Class:     android_serialport_SerialPort 
   * Method:    open 
   * Signature: (Ljava/lang/String;II)Ljava/io/FileDescriptor; 
   */  
  JNIEXPORT jobject JNICALL Java_com_xd_serialport_SerialPort_open  
    (JNIEnv *env, jclass thiz, jstring path, jint baudrate, jint flags)  
  {  
      int fd;  
      speed_t speed;  
      jobject mFileDescriptor;  
    
      /* Check arguments */  
      {  
          speed = getBaudrate(baudrate);  
          if (speed == -1) {  
              /* TODO: throw an exception */  
              LOGE("Invalid baudrate");  
              return NULL;  
          }  
      }  
    
      /* Opening device */  
      {  
          jboolean iscopy;  
          const char *path_utf = (*env)->GetStringUTFChars(env, path, &iscopy);  
          LOGD("Opening serial port %s with flags 0x%x", path_utf, O_RDWR | flags);  
          fd = open(path_utf, O_RDWR | flags);  
          LOGD("open() fd = %d", fd);  
          (*env)->ReleaseStringUTFChars(env, path, path_utf);  
          if (fd == -1)  
          {  
              /* Throw an exception */  
              LOGE("Cannot open port");  
              /* TODO: throw an exception */  
              return NULL;  
          }  
      }  
    
      /* Configure device */  
      {  
          struct termios cfg;  
          LOGD("Configuring serial port");  
          if (tcgetattr(fd, &cfg))  
          {  
              LOGE("tcgetattr() failed");  
              close(fd);  
              /* TODO: throw an exception */  
              return NULL;  
          }  
    
          cfmakeraw(&cfg);  
          cfsetispeed(&cfg, speed);  
          cfsetospeed(&cfg, speed);  
    
          if (tcsetattr(fd, TCSANOW, &cfg))  
          {  
              LOGE("tcsetattr() failed");  
              close(fd);  
              /* TODO: throw an exception */  
              return NULL;  
          }  
      }  
    
      /* Create a corresponding file descriptor */  
      {  
          jclass cFileDescriptor = (*env)->FindClass(env, "java/io/FileDescriptor");  
          jmethodID iFileDescriptor = (*env)->GetMethodID(env, cFileDescriptor, "<init>", "()V");  
          jfieldID descriptorID = (*env)->GetFieldID(env, cFileDescriptor, "descriptor", "I");  
          mFileDescriptor = (*env)->NewObject(env, cFileDescriptor, iFileDescriptor);  
          (*env)->SetIntField(env, mFileDescriptor, descriptorID, (jint)fd);  
      }  
    
      return mFileDescriptor;  
  }  
    
  /* 
   * Class:     cedric_serial_SerialPort 
   * Method:    close 
   * Signature: ()V 
   */  
  JNIEXPORT void JNICALL Java_com_xd_serialport_SerialPort_close  
    (JNIEnv *env, jobject thiz)  
  {  
      jclass SerialPortClass = (*env)->GetObjectClass(env, thiz);  
      jclass FileDescriptorClass = (*env)->FindClass(env, "java/io/FileDescriptor");  
    
      jfieldID mFdID = (*env)->GetFieldID(env, SerialPortClass, "mFd", "Ljava/io/FileDescriptor;");  
      jfieldID descriptorID = (*env)->GetFieldID(env, FileDescriptorClass, "descriptor", "I");  
    
      jobject mFd = (*env)->GetObjectField(env, thiz, mFdID);  
      jint descriptor = (*env)->GetIntField(env, mFd, descriptorID);  
    
      LOGD("close(fd = %d)", descriptor);  
      close(descriptor);  
  }
  

  

---

配置NDK，生成 .so 文件

• 在 local.properties 添加 ndk 路径

  

  android-ndk的版本至少要 r9d 以上的版本，如果等于或低于该版本，运行时会提示No rule to make target的错误。我使用的是 r10e 的版本。

• 在 module 的 build.gradle 中添加 ndk 配置

  在 defaultConfig 节点下添加：

  ndk{  
  	abiFilter "armeabi"  
  	moduleName "serial_port"  // 生成so的名称
  	ldLibs "log", "z", "m", "jnigraphics", "android"  
  }
  

• 在 gradle.properties 中添加android.useDeprecatedNdk=true，否则 sync 时会提示错误NDK integration is deprecated in the current plugin.

• Sync Project with Gradle Files

• 运行项目，将在目录\build\intermediates\ndk\debug\lib\armeabi下生成libserial_port.so文件。

  

• 将 so 文件拷贝到\src\main\jniLibs\armeabi目录下。

  

至此，串口通讯可以正常使用了。

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参考资料

• android 串口编程

• android studio下的jni应用

• android studio jni开发 串口通信

• android studio 串口jni开发