【 tulaoshi.com - 编程语言 】
提到串口编程,就不得不提到JNI,不得不提到JavaAPI中的文件描述符类:FileDescriptor。下面我分别对JNI、FileDescriptor以及串口的一些知识点和实现的源码进行分析说明。这里主要是参考了开源项目android-serialport-api。
串口编程需要了解的基本知识点:对于串口编程,我们只需对串口进行一系列的设置,然后打开串口,这些操作我们可以参考串口调试助手的源码进行学习。在Java中如果要实现串口的读写功能只需操作文件设备类:FileDescriptor即可,其他的事都由驱动来完成不用多管!当然,你想了解,那就得看驱动代码了。这里并不打算对驱动进行说明,只初略阐述应用层的实现方式。
(一)JNI:
关于JNI的文章网上有很多,不再多做解释,想详细了解的朋友可以查看云中漫步的技术文章,写得很好,分析也很全面,那么在这篇拙文中我强调3点:
1、如何将编译好的SO文件打包到APK中?(方法很简单,直接在工程目录下新建文件夹 libs/armeabi,将SO文件Copy到此目录即可)
2、命名要注意的地方?(在编译好的SO文件中,将文件重命名为:libfilename.so即可。其中filename.so是编译好后生成的文件)
3、MakeFile文件的编写(不用多说,可以直接参考package/apps目录下用到JNI的相关项目写法)
这是关键的代码:
代码如下:
span style="font-size:18px;" 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;
}
}
/span
(二)FileDescritor:
文件描述符类的实例用作与基础机器有关的某种结构的不透明句柄,该结构表示开放文件、开放套接字或者字节的另一个源或接收者。文件描述符的主要实际用途是创建一个包含该结构的FileInputStream 或FileOutputStream。这是API的描述,不太好理解,其实可简单的理解为:FileDescritor就是对一个文件进行读写。
(三)实现串口通信细节 1) 建工程:SerialDemo包名:org.winplus.serial,并在工程目录下新建jni和libs两个文件夹和一个org.winplus.serial.utils,如下图:
2) 新建一个类:SerialPortFinder,添加如下代码:
代码如下:
span style="font-size:18px;"package org.winplus.serial.utils;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.io.LineNumberReader;
import java.util.Iterator;
import java.util.Vector;
import android.util.Log;
public class SerialPortFinder {
private static final String TAG = "SerialPort";
private VectorDriver mDrivers = null;
public class Driver {
public Driver(String name, String root) {
mDriverName = name;
mDeviceRoot = root;
}
private String mDriverName;
private String mDeviceRoot;
VectorFile mDevices = null;
public VectorFile getDevices() {
if (mDevices == null) {
mDevices = new VectorFile();
File dev = new File("/dev");
File[] files = dev.listFiles();
int i;
for (i = 0; i files.length; i++) {
if (files[i].getAbsolutePath().startsWith(mDeviceRoot)) {
Log.d(TAG, "Found new device: " + files[i]);
mDevices.add(files[i]);
}
}
}
return mDevices;
}
public String getName() {
return mDriverName;
}
}
VectorDriver getDrivers() throws IOException {
if (mDrivers == null) {
mDrivers = new VectorDriver();
LineNumberReader r = new LineNumberReader(new FileReader(
"/proc/tty/drivers"));
String l;
while ((l = r.readLine()) != null) {
// Issue 3:
// Since driver name may contain spaces, we do not extract
// driver name with split()
String drivername = l.substring(0, 0x15).trim();
String[] w = l.split(" +");
if ((w.length = 5) && (w[w.length - 1].equals("serial"))) {
Log.d(TAG, "Found new driver " + drivername + " on "
+ w[w.length - 4]);
mDrivers.add(new Driver(drivername, w[w.length - 4]));
}
}
r.close();
}
return mDrivers;
}
public String[] getAllDevices() {
VectorString devices = new VectorString();
// Parse each driver
IteratorDriver itdriv;
try {
itdriv = getDrivers().iterator();
while (itdriv.hasNext()) {
Driver driver = itdriv.next();
IteratorFile itdev = driver.getDevices().iterator();
while (itdev.hasNext()) {
String device = itdev.next().getName();
String value = String.format("%s (%s)", device,
driver.getName());
devices.add(value);
}
}
} catch (IOException e) {
e.printStackTrace();
}
return devices.toArray(new String[devices.size()]);
}
public String[] getAllDevicesPath() {
VectorString devices = new VectorString();
// Parse each driver
IteratorDriver itdriv;
try {
itdriv = getDrivers().iterator();
while (itdriv.hasNext()) {
Driver driver = itdriv.next();
IteratorFile itdev = driver.getDevices().iterator();
while (itdev.hasNext()) {
String device = itdev.next().getAbsolutePath();
devices.add(device);
}
}
} catch (IOException e) {
e.printStackTrace();
}
return devices.toArray(new String[devices.size()]);
}
}
/span
上面这个类在“android-serialport-api串口工具测试随笔”中有详细的说明,我就不多说了。
3)新建SerialPort类,这个类主要用来加载SO文件,通过JNI的方式打开关闭串口
代码如下:
span style="font-size:18px;"package org.winplus.serial.utils;
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;
import android.util.Log;
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"
+ "exitn";
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");
}
}
/span
4) 新建一个MyApplication 继承android.app.Application,用来对串口进行初始化和关闭串口
代码如下:
span style="font-size:18px;"package org.winplus.serial;
import java.io.File;
import java.io.IOException;
import java.security.InvalidParameterException;
import org.winplus.serial.utils.SerialPort;
import org.winplus.serial.utils.SerialPortFinder;
import android.content.SharedPreferences;
public class MyApplication extends android.app.Application {
public SerialPortFinder mSerialPortFinder = new SerialPortFinder();
private SerialPort mSerialPort = null;
public SerialPort getSerialPort() throws SecurityException, IOException, InvalidParameterException {
if (mSerialPort == null) {
/* Read serial port parameters */
SharedPreferences sp = getSharedPreferences("android_serialport_api.sample_preferences", MODE_PRIVATE);
String path = sp.getString("DEVICE", "");
int baudrate = Integer.decode(sp.getString("BAUDRATE", "-1"));
/* Check parameters */
if ( (path.length() == 0) || (baudrate == -1)) {
throw new InvalidParameterException();
}
/* Open the serial port */
mSerialPort = new SerialPort(new File(path), baudrate, 0);
}
return mSerialPort;
}
public void closeSerialPort() {
if (mSerialPort != null) {
mSerialPort.close();
mSerialPort = null;
}
}
}
/span
5) 新建一个继承抽象的Activity类,主要用于读取串口的信息
代码如下:
span style="font-size:18px;"package org.winplus.serial;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.security.InvalidParameterException;
import org.winplus.serial.utils.SerialPort;
import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.content.DialogInterface.OnClickListener;
import android.os.Bundle;
public abstract class SerialPortActivity extends Activity {
protected MyApplication mApplication;
protected SerialPort mSerialPort;
protected OutputStream mOutputStream;
private InputStream mInputStream;
private ReadThread mReadThread;
private class ReadThread extends Thread {
@Override
public void run() {
super.run();
while (!isInterrupted()) {
int size;
try {
byte[] buffer = new byte[64];
if (mInputStream == null)
return;
/**
* 这里的read要尤其注意,它会一直等待数据,等到天荒地老,海枯石烂。如果要判断是否接受完成,只有设置结束标识,或作其他特殊的处理。
*/
size = mInputStream.read(buffer);
if (size 0) {
onDataReceived(buffer, size);
}
} catch (IOException e) {
e.printStackTrace();
return;
}
}
}
}
private void DisplayError(int resourceId) {
AlertDialog.Builder b = new AlertDialog.Builder(this);
b.setTitle("Error");
b.setMessage(resourceId);
b.setPositiveButton("OK", new OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
SerialPortActivity.this.finish();
}
});
b.show();
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mApplication = (MyApplication) getApplication();
try {
mSerialPort = mApplication.getSerialPort();
mOutputStream = mSerialPort.getOutputStream();
mInputStream = mSerialPort.getInputStream();
/* Create a receiving thread */
mReadThread = new ReadThread();
mReadThread.start();
} catch (SecurityException e) {
DisplayError(R.string.error_security);
} catch (IOException e) {
DisplayError(R.string.error_unknown);
} catch (InvalidParameterException e) {
DisplayError(R.string.error_configuration);
}
}
protected abstract void onDataReceived(final byte[] buffer, final int size);
@Override
protected void onDestroy() {
if (mReadThread != null)
mReadThread.interrupt();
mApplication.closeSerialPort();
mSerialPort = null;
super.onDestroy();
}
}
/span
6)编写string.xml 以及baudrates.xml文件
在string.xml文件中添加:
代码如下:
span style="font-size:18px;" string name="error_configuration"Please configure your serial port first./string
string name="error_security"You do not have read/write permission to the serial port./string
string name="error_unknown"The serial port can not be opened for an unknown reason./string
/span
在baudrates.xml文件中添加
代码如下:
span style="font-size:18px;"?xml version="1.0" encoding="utf-8"?
resources
string-array name="baudrates_name"
item50/item
item75/item
item110/item
item134/item
item150/item
item200/item
item300/item
item600/item
item1200/item
item1800/item
item2400/item
item4800/item
item9600/item
item19200/item
item38400/item
item57600/item
item115200/item
item230400/item
item460800/item
item500000/item
item576000/item
item921600/item
item1000000/item
item1152000/item
item1500000/item
item2000000/item
item2500000/item
item3000000/item
item3500000/item
item4000000/item
/string-array
string-array name="baudrates_value"
item50/item
item75/item
item110/item
item134/item
item150/item
item200/item
item300/item
item600/item
item1200/item
item1800/item
item2400/item
item4800/item
item9600/item
item19200/item
item38400/item
item57600/item
item115200/item
item230400/item
item460800/item
item500000/item
item576000/item
item921600/item
item1000000/item
item1152000/item
item1500000/item
item2000000/item
item2500000/item
item3000000/item
item3500000/item
item4000000/item
/string-array
/resources
/span
7)开始编写界面了:在main.xml布局文件中添加两个编辑框,一个用来发送命令,一个用来接收命令:
代码如下:
span style="font-size:18px;"?xml version="1.0" encoding="utf-8"?
LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical"
EditText
android:id="@+id/EditTextReception"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_weight="1"
android:gravity="top"
android:hint="Reception"
android:isScrollContainer="true"
android:scrollbarStyle="insideOverlay"
/EditText
EditText
android:id="@+id/EditTextEmission"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:hint="Emission"
android:lines="1"
/EditText
/LinearLayout
/span
8) SerialDemoActivity类的实现:
代码如下:
span style="font-size:18px;"package org.winplus.serial;
import java.io.IOException;
import android.os.Bundle;
import android.view.KeyEvent;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.TextView.OnEditorActionListener;
public class SerialDemoActivity extends SerialPortActivity{
EditText mReception;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
// setTitle("Loopback test");
mReception = (EditText) findViewById(R.id.EditTextReception);
EditText Emission = (EditText) findViewById(R.id.EditTextEmission);
Emission.setOnEditorActionListener(new OnEditorActionListener() {
public boolean onEditorAction(TextView v, int actionId, KeyEvent event) {
int i;
CharSequence t = v.getText();
char[] text = new char[t.length()];
for (i=0; it.length(); i++) {
text[i] = t.charAt(i);
}
try {
mOutputStream.write(new String(text).getBytes());
mOutputStream.write('n');
} catch (IOException e) {
e.printStackTrace();
}
return false;
}
});
}
@Override
protected void onDataReceived(final byte[] buffer, final int size) {
runOnUiThread(new Runnable() {
public void run() {
if (mReception != null) {
mReception.append(new String(buffer, 0, size));
}
}
});
}
}
/span
写到这里,代码基本上写完了。下面就是要实现JNI层的功能了,要实现JNI,必须首先生成头文件,头文件的生成方式也很简单, 我们编译工程,在终端输入 javah org.winplus.serial.utils.SerialPort 则会生成头文件:org_winplus_serial_utils_SerialPort.h,这个头文件的名字可以随意命名。我们将它命名为:SerialPort.h拷贝到新建的目录jni中,新建SerialPort.c 文件,这两个文件的代码就不贴出来了。直接到上传的代码中看吧。
(四)串口的应用,可实现扫描头,指纹识别等外围USB转串口的特色应用 还蛮繁琐的,以上只是对开源项目android-serialport-api 进行精简想了解此项目请点击此处!就这样吧,晚了准备见周公去!