Develop Reference

Read String from Arduino serial port with JAVA and jssc lib

String Serial_Input must contain a serial number card RFID (MIFARE) like this A45F45A7 (8 byte). sometimes when I approach the card to the RFID reader of arduino the string is like this A45F45 (truncated) , miss any char. there is a solution better that while loop ? (more elegant and efficient) Using Arduino IDE Serial Monitor the card's serial number is correct.
public static void connectionToCom(SerialPort serialPort, ComboBox<String> cbxComPort, TextArea txaMessages) throws SerialPortException
{
int baudrate = 9600; int databits = 8; int stopbits = 1; int parity = 0;
serialPort.openPort() ;
serialPort.setParams(baudrate, databits, stopbits, parity) ;
String Serial_Input = null;
try {
while (true)
{
if (serialPort.readString() != null)
{
Serial_Input = serialPort.readString(8);
System.out.println("Card Serial: " + Serial_Input + "\n");
//serialPort.closePort();
}
}
}
catch (SerialPortException ex){
txaMessages.appendText(ex.toString());
}
}
Here the result image

You could use the method addEventListener(SerialPortEventListener listener, int mask). It call a callback method whenever you receive a byte via serialPort.
The problem with the incomplete string could be 2 problems
The code is executing before the whole string is received. To solve this, you must add a code to verify the length of string you are receiving.
You are using readString twice. You may lost some bytes of the string in first usage.

How to discover host in a WiFi network in Android (JAVA)

I'm developing an Android application, I have to discover each hosts in a WiFi network, I have implemented a function that "ping" all IP address between 1 and 255 of a certain network.
This solution it work perfectly, but there is a problem, the execution time.. Every time that i start my application I wait about 256 second, it too long, i can't wait this time.
This is my source code (i found this code on Stack, i modified the code to work in my condition):
public class ScanNetwork {
ArrayList < String > hosts;
int i;
boolean finish = false;
public ArrayList < String > ScanNetwork(String ipAddress) {
hosts = new ArrayList < String > ();
final String subnet = ipAddress.substring(0, ipAddress.lastIndexOf("."));
for (i = 0; i < 256; i++) {
String currentHost = subnet + "." + i;
Process p1 = null;
int returnVal = 0;
try {
p1 = Runtime.getRuntime().exec("ping -w 50 -c 1 " + currentHost);
returnVal = p1.waitFor();
} catch (IOException e) {
System.out.println("Log: " + e.toString());
} catch (InterruptedException e) {
System.out.println("Log: " + e.toString());
}
boolean reachable = (returnVal == 0);
if (reachable) {
if (!hosts.contains(currentHost)) {
hosts.add(currentHost);
System.out.println(currentHost);
}
}
}
return hosts;
}
}
This source code is perfect but the execution time is excessive, there are other way to obtain all the host in the network ?
How i can solve this problem ?

The problem I see is that you are doing all the pings sequentially - the loop is spending most of its time waiting for replies. Try starting up a few AsyncTasks, each of which has an assigned range of addresses to search, and let them work in parallel.
Note that for a typical 192.168.1.x network, ".0" (all 0 bits) ".255" (all 1 bits) will not correspond to a host and doesn't need checking.
Also don't forget that not everybody responds to a ping (this is more likely in a corporate network, less so at home)

Android cannot recieve all characters via bluetooth

I'm creating an app that sends and receive data with an arduino via bluetooth. Sending works fine, however when receiving data I don't get the first few characters of the string sent. I always don't get the first character, the second I sometimes get it, the third I almost always get it, etc.
So for example if the arduino sends "OK 1" I receive "K 1" or " 1" or "1", but never the complete string. An easy fix would be to add a few dummy characters, but that's a shit fix.
Here's the method which listens to incoming connections, directly copy/pasted from Android sample bluetooth code to send a simple string via bluetooth (though with a few fixes):
void beginListenForData()
{
final Handler handler = new Handler();
final byte delimiter = 10; //This is the ASCII code for a newline character
final boolean stopWorker = false;
final int readBufferPosition = 0;
final byte[]readBuffer = new byte[1024];
Thread workerThread = new Thread(new Runnable()
{
public void run()
{
while(!Thread.currentThread().isInterrupted() && !stopWorker)
{
try
{
int bytesAvailable = inStream.available();
int readBufferPosition2 = readBufferPosition;
if(bytesAvailable > 0)
{
byte[] packetBytes = new byte[bytesAvailable];
inStream.read(packetBytes);
for(int i=0;i<bytesAvailable;i++)
{
byte b = packetBytes[i];
if(b == delimiter)
{
byte[] encodedBytes = new byte[readBufferPosition2];
System.arraycopy(readBuffer, 0, encodedBytes, 0, encodedBytes.length);
final String data = new String(encodedBytes);
readBufferPosition2 = 0;
handler.post(new Runnable()
{
public void run()
{
result.setText(data);
}
});
}
else
{
readBuffer[readBufferPosition2++] = b;
}
}
}
}
catch (IOException ex)
{
}
}
}
});
workerThread.start();
}
Here's all my code in case you want to test it (warning: lots of dummy and outdated code):
MainActivity.java http://pastebin.com/cdjW4Y1V
XML layout file http://pastebin.com/Ruf5euPP
Click on the first button to connect to the arduino and click on the second button to send a string and to begin receiving data.
So yep, I have absolutely no idea why it doesn't work. It works fine with TerminalBT so it's not a problem with the arduino, it's a problem with my app, but why do I receive characters randomly?

one thing i noticed is that you should not use 10 for the delimiter.
I have encountered this error before if you use 10 then some times it does not get recognized properly.
you should use standard Java Function to parse the delimiter.
System.getProperty("line.separator");
//OR
System.lineSeparator();

What is the least painful way to extract data at the protocol layer in Java?

I'm trying to implement an Android application to connect to the open source software Motion. The goal is to be able to check the status of the application and get the last image captured.
I do not program in Java very much, my background is principally in C and Python. I've not had any real issues with understanding the UI part of Android, but I've found it to be incredibly painful to work with any sort of byte buffer. The Motion software has an HTTP API that is very simple. Opening the URL connection is easy in Java. The response from the default page looks like this
Motion 3.2.12 Running [4] Threads
0
1
2
3
For my purposes the first thing the application needs to do it parse out the number of threads. At some point I can also retrieve the version number from the first line, but that's not really important presently.
Here's my code
package com.hydrogen18.motionsurveillanceviewer;
import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.List;
public class MotionHttpApi {
String host;
int port = 80;
boolean secure = false;
int numberOfThreads = -1;
String getBaseUrl()
{
StringBuilder sb = new StringBuilder();
sb.append(secure ? "https://" : "http://");
sb.append(host);
sb.append(':');
sb.append(port);
return sb.toString();
}
public int getNumberOfCameras() throws IOException
{
if(numberOfThreads == -1)
{
retrieveSplash();
}
if(numberOfThreads == 1)
{
return 1;
}
return numberOfThreads - 1;
}
void retrieveSplash () throws IOException
{
URL url = new URL(getBaseUrl());
HttpURLConnection conn = (HttpURLConnection)url.openConnection();
if(conn.getResponseCode()!=HttpURLConnection.HTTP_OK)
{
throw new IOException("Got response code" + conn.getResponseCode());
}
try{
Byte[] buffer = new Byte[512];
byte[] sbuf = new byte[128];
int offset = 0;
InputStream in = new BufferedInputStream(conn.getInputStream());
boolean foundInfoString= false;
while( ! foundInfoString)
{
//Check to make sure we have not run out of space
if(offset == buffer.length)
{
throw new IOException("Response too large");
}
//Read into the smaller buffer since InputStream
//can't write to a Byte[]
final int result = in.read(sbuf,0,sbuf.length);
//Copy the data into the larger buffer
for(int i = 0; i < result;++i)
{
buffer[offset+i] = sbuf[i];
}
//Add to the offset
offset+=result;
//Wrap the array as a list
List<Byte> list = java.util.Arrays.asList(buffer);
//Find newline character
final int index = list.indexOf((byte) '\n');
//If the newline is present, extract the number of threads
if (index != -1)
{
//Find the number of threads
//Thread number is in the first lin like "[X]"
final int start = list.indexOf((byte)'[');
final int end = list.indexOf((byte)']');
//Sanity check the bounds
if(! (end > start))
{
throw new IOException("Couldn't locate number of threads");
}
//Create a string from the Byte[] array subset
StringBuilder sb = new StringBuilder();
for(int i = start+1; i != end; ++i)
{
final char c = (char) buffer[i].byteValue();
sb.append(c);
}
String numThreadsStr = sb.toString();
//Try and parse the string into a number
try
{
this.numberOfThreads = Integer.valueOf(numThreadsStr);
}catch(NumberFormatException e)
{
throw new IOException("Number of threads is NaN",e);
}
//No more values to extract
foundInfoString = true;
}
//If the InputStream got EOF and the into string has not been found
//Then an error has occurred.
if(result == -1 && ! foundInfoString )
{
throw new IOException("Never got info string");
}
}
}finally
{
//Close the connection
conn.disconnect();
}
}
public MotionHttpApi(String host,int port)
{
this.host = host;
this.port = port;
}
}
The code works just fine when you call getNumberOfCameras(). But I think I must not be really understandings omething in terms of java, because the retrieveSplash method is far too complex. I could do the same thing in just 10 or so lines of C or 1 line of Python. Surely there must be a saner way to manipulate bytes in java?
I think there are some style issues, like I probably should not be throwing IOException whenever the integer fails to parse. But that's a separate issue.

Read the first line as Gautam Tandon suggested and then use a regex.
You can then check if the regex matches and even easily extract the number.
Regex' can be created at http://txt2re.com. I've already done that for you.
The page even creates Java, Pyhton, C, etc. files for you to work with.
// URL that generated this code:
// http://txt2re.com/index-java.php3?s=Motion%203.2.12%20Running%20[4]%20Threads&-7&-19&-5&-20&-1&2&-22&-21&-62&-63&15
import java.util.regex.*;
class Main
{
public static void main(String[] args)
{
String txt="Motion 3.2.12 Running [4] Threads";
String re1="(Motion)"; // Word 1
String re2="( )"; // White Space 1
String re3="(3\\.2\\.12)"; // MMDDYY 1
String re4="( )"; // White Space 2
String re5="(Running)"; // Word 2
String re6="( )"; // White Space 3
String re7="(\\[)"; // Any Single Character 1
String re8="(\\d+)"; // Integer Number 1
String re9="(\\])"; // Any Single Character 2
String re10="( )"; // White Space 4
String re11="((?:[a-z][a-z]+))"; // Word 3
Pattern p = Pattern.compile(re1+re2+re3+re4+re5+re6+re7+re8+re9+re10+re11,Pattern.CASE_INSENSITIVE | Pattern.DOTALL);
Matcher m = p.matcher(txt);
if (m.find())
{
String word1=m.group(1);
String ws1=m.group(2);
String mmddyy1=m.group(3);
String ws2=m.group(4);
String word2=m.group(5);
String ws3=m.group(6);
String c1=m.group(7);
String int1=m.group(8);
String c2=m.group(9);
String ws4=m.group(10);
String word3=m.group(11);
System.out.print("("+word1.toString()+")"+"("+ws1.toString()+")"+"("+mmddyy1.toString()+")"+"("+ws2.toString()+")"+"("+word2.toString()+")"+"("+ws3.toString()+")"+"("+c1.toString()+")"+"("+int1.toString()+")"+"("+c2.toString()+")"+"("+ws4.toString()+")"+"("+word3.toString()+")"+"\n");
}
}
}
//-----
// This code is for use with Sun's Java VM - see http://java.sun.com/ for downloads.
//
// Paste the code into a new java application or a file called 'Main.java'
//
// Compile and run in Unix using:
// # javac Main.java
// # java Main
//
String int1=m.group(8); gives you the desired integer. Of course you can simplify the above code. It's way to verbose right now.

You can simplify the retrieveSplash method considerably by using BufferedReader. Here's a simpler version of your function:
void retrieveSplash_simpler() throws IOException {
URL url = new URL(getBaseUrl());
HttpURLConnection conn = (HttpURLConnection)url.openConnection();
// open the connection
conn.connect();
// create a buffered reader to read the input stream line by line
BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));
// find number of threads
String firstLine = reader.readLine();
int x = firstLine.indexOf("[");
int y = firstLine.indexOf("]");
if (x > 0 && y > 0 && x < y) {
try {
numberOfThreads = Integer.parseInt(firstLine.substring(x+1, y));
} catch (NumberFormatException nfe) {
// disconnect and throw exception
conn.disconnect();
throw new IOException("Couldn't locate number of threads");
}
} else {
// disconnect and throw exception
conn.disconnect();
throw new IOException("Couldn't locate number of threads");
}
// disconnect
conn.disconnect();
}
I'd further clean up the above method by using try/catch/finally blocks at the appropriate places so that I don't have to duplicate that "conn.disconnect()". But I didn't do that here to keep it simple (try/catch/finally do become tricky sometimes...).

Java FTP Download progress

I have looked at many examples and tried to understand what i`m doing wrong but with no success, maybe you can help me. It always stops at the second file, but the first one is just crated on c:\ with 0kb size.
files_server.get(i) is ArrayList with all files that i wish to download.
My code:
public FTPConnection() {
StartD std = new StartD();
std.start();
}
class StartD extends Thread{
#Override
public void run()
{
for (int i = 0; i < files_server.size(); i++) {
err = ftpDownload(files_server.get(i), "C:/"+ files_server.get(i));
if (!err)
{
System.out.println("Error in download, breaking");
break;
}
}
}
public boolean ftpDownload(String srcFilePath, String desFilePath)
{
try {
FileOutputStream desFileStream = new FileOutputStream(desFilePath);
InputStream input = mFTPClient.retrieveFileStream(srcFilePath);
byte[] data = new byte[1024];
int count;
while ((count = input.read(data)) != -1)
{
desFileStream.write(data, 0, count);
}
desFileStream.close();
} catch (Exception e) {
return false;
}
return true;
}}
If I use the finction:
public boolean ftpDownload(String srcFilePath, String desFilePath) {
boolean status = false;
try {
FileOutputStream desFileStream = new FileOutputStream(desFilePath);
status = mFTPClient.retrieveFile(srcFilePath, desFileStream);
desFileStream.close();
return status;
} catch (Exception e) {
}
return status;
}
instead, everything works just fine, but i can`t monitor file download progress.

I've only used it for file unzipping and not FTP, but in that case InputStream buffers can return zero, so I'd say it's worth trying changing your while loop to something like:
while ((count = input.read(data)) >= 0)
public int read(byte[] b) throws IOException
Reads some number of bytes from the input stream and stores them into the buffer array b.
The number of bytes actually read is returned as an integer. This
method blocks until input data is available, end of file is detected,
or an exception is thrown.
If the length of b is zero, then no bytes are read and 0 is returned;
It could also be that you're assigning count twice, which could chop the first byte off the data:
int count = input.read(data);
while ((count = input.read(data)) != -1)
So don't assign anything to count when you declare it.

Let's assume your library is the FTP client from the commons-net package. It's not easy to figure out what's wrong with your code, because we can't run it and because your description (the second file stops) is not sufficient (does it throw an exception? Does it hang forever? Does it complete without any side effect?). Anyway I have a couple of advices:
Use a CountingOutputStream (from Apache commons-io) to monitor progress
Use a ProtocolCommandListener to log what's going on
Also, note that the first 1024 bytes are always lost. Eventually, I don't know how safe it is to put a file in C:\ with the same name it has on the server. At the best, it could lead to permission troubles, at the worst it may originate a security flaw - anyway this doesn't hold if you have some degree of control over the filenames, but hey consider this advice.
This is a sample client
public class FTP {
public static void main(String[] args) throws SocketException, IOException {
FTPClient client = new FTPClient();
client.addProtocolCommandListener(new ProtocolCommandListener(){
#Override
public void protocolCommandSent(ProtocolCommandEvent evt) {
logger.debug(evt.getMessage());
}
#Override
public void protocolReplyReceived(ProtocolCommandEvent evt) {
logger.debug(evt.getMessage());
}
});
client.connect("ftp.mozilla.org");
client.login("anonymous", "");
client.enterLocalPassiveMode();
OutputStream out = new CountingOutputStream(new NullOutputStream()) {
#Override
public void beforeWrite(int count) {
super.beforeWrite(count);
logger.info("Downloaded " + getCount() + " bytes");
}
};
for (String filename: new String[] {"MD5SUMS", "SHA1SUMS"})
client.retrieveFile("pub/firefox/releases/15.0b4/" + filename, out);
out.close();
client.disconnect();
}
private static Logger logger;
static {
logger = Logger.getLogger(FTP.class.getCanonicalName());
}
}
Once configured, the logger will output all the raw socket conversation, and it may help you to better understand the problem, provided it's on the FTP side and not in application IO