To the best of my (current) understanding, Android has no console to send the messages to so the System.out.println messages get lost. Instead, Log.x (outputing to LogCat) should be used.
Yet, in the acclaimed Pro Android 2 book, listing 8-1 does just that:
in = new BufferedReader(new InputStreamReader(response.getEntity().getContent()));
StringBuffer sb = new StringBuffer("");
String line = "";
String NL = System.getProperty("line.separator");
while ((line = in.readLine()) != null) {
sb.append(line + NL);
}
in.close();
String page = sb.toString();
System.out.println(page);
Does System.out.println really work in Android or is it only a typo?
If the former (i.e. not a typo), what does it really do and where should I expect to find the output?
System.out.println prints to whatever is currently defined as the "standard" output PrintStream. It is possible to hook this up to point to the log stream, but really there is no good reason to use it. Use Log.x.
This is probably just a typo in the book. Nothing in that code snippet is Android specific.
That System.out.println code does work (despite what the android documentation says). I've tried it on my on my Android development set up (without changing the settings as they describe in the documentation). I've had tried on the set ups of my Android programming students, both on their Windows and Macs. And it always comes out the same way:
The following line does output to logcat by default.
System.out.println("blah blah");
Now of course, it's probably best to stick to Log.x() anyway. It's probably never a good idea to rely on undocumented features, especially in a book. This feature could be here today, and be just as well gone the next time the tools get updated.
From the android docs:
By default, the Android system sends stdout and stderr (System.out and System.err) output to /dev/null.
It also explains how to use System.out and System.err properly.
If you're using Eclipse, System.out will be displayed on the LogCat tab not in the Console.
You can also try the Log.i("MyLog", "The message here...."); also displayed on the LogCat.
Enjoy!
Related
I have a Java SE Application that use
input = new Scanner(System.in);
to get Input parameters
and use System.out.println("..");
to print results
Since all Java APIs used in the original Java Project are also available in Android, I have tried to import all classes without any error, but now I don't know how replicate the behaviour of the classic Java console in Android.
I have seen that there are developers that have achieved this in some IDE-like apps, but I don't know how.
Could you help me?
Example:
assume that you want to port this dummy Java SE Application in Android mantaining the console-like approach of the original code
public static void main(String[] args) {
System.out.println("Please enter your choice");
System.out.println("A, B");
Scanner myScanner = new Scanner(System.in);
String choice = myScanner .nextLine();
if (choice.charAt(0) == 'A') {
...do something
}
else{
...do something
}
}
You can execute system commands with exec(). Here is how to do it:
Runtime r = Runtime.getRuntime();
Process p = r.exec("uname -a"); // here goes your input
p.waitFor();
BufferedReader b = new BufferedReader(new InputStreamReader(p.getInputStream()));
String line = "";
while ((line = b.readLine()) != null) {
System.out.println(line);
}
Update:
Ok, from what I understand, you would like to compile and run code written by user. I can see 3 options:
Most difficult I think. Get the source code of some Java compiler and include it in your project. So, user inputs a text. You compile it, run and give the output.
Using already built compiler. This requires root. Install javac on your device. Then, in your application you can call it with the above exec() code.
Easiest one. Using internet and for example, Ideone.com. In your app you send code to compile on Ideone. You get back the output and present it to the user.
I'm using the Android's log to supervise an application use, so I'm using logcat into the phone not in Eclipse.
Well, if I just write in the log and send me the information everything it's ok, but I receive information from previous executions.
I decided to clear the log every time that my application starts, but now I usually lose the first log messages. Maybe logcat needs some time to get cleared? because when I try to do into debug everything it's ok.
Example:
clear log, message 1, message 2, message 3, ...
Sometimes I don't receive message 1, sometimes don't receive 1 and 2...
I have checked all my code for possible accidental clears but I didn't find anything...
I call this function at the beginning (in onCreate())
public static void clearLog(){
ArrayList<String> commandLine = new ArrayList<String>();
commandLine.add("logcat");
commandLine.add("-c");//CLEAR
Runtime process = Runtime.getRuntime();
process.exec(commandLine.toArray(new String[0]));
TAG = "";
}
Then I add logs
log.i(TAG, "message1");
..
log.i(TAG, "messageN");
And this is how I collect the log:
ArrayList<String> commandLine = new ArrayList<String>();
commandLine.add("logcat");
commandLine.add("-d");//dump and exit
commandLine.add("-v");//especify verbose mode
commandLine.add("raw");//raw show only the message, brief for show all
commandLine.add(TAG + ":V");//show TAG's log
commandLine.add("*:S");//hide others
Process process = Runtime.getRuntime().exec(
commandLine.toArray(new String[0]));
BufferedReader bufferedReader = new BufferedReader(
new InputStreamReader(process.getInputStream()));
String line, log = "";
while ((line = bufferedReader.readLine()) != null) {
log += line + LINE_SEPARATOR;
}
From the docs for exec():
Executes the specified command and its arguments in a separate native process.
So it's running in a separate process. There's not really a good way to tell if it has finished before you start logging.
Instead of clearing the log, you could change the log TAG on each run. Just use the regular tag an append some number that identifies the run, even just a random one. Then when you collect your logs, you can filter by that, and only collect the ones you want.
I feel like I am on crazy pills right now. A specific part of my application has been working just fine for several days, and today it just stopped working and I can not figure out why. This part of my code used to output the total data since boot that each specific app has sent and received. Now, the values always show up as 0.
A couple things that may or may not be affecting this:
1.) My Nexus 4 was just updated to Android 4.3 today, but I doubt this is an issue because this worked just fine right after I updated.
2.) With the Android API 18 update, some methods from the Traffic Stats API are now deprecated, but these are methods I am not even using, so this should have no effect.
http://developer.android.com/reference/android/net/TrafficStats.html
All help is greatly appreciated.
PackageManager packageManager=this.getPackageManager();
List<ApplicationInfo> appList=packageManager.getInstalledApplications(0);
for (ApplicationInfo appInfo : appList) {
String appLabel = (String) packageManager.getApplicationLabel(appInfo);
int uid = appInfo.uid;
Log.d("data", String.valueOf(TrafficStats.getUidRxBytes(uid) + TrafficStats.getUidTxBytes(uid)));
Update[January 23, 2014]: Testing the getUidRxBytes() and getUidTxBytes() on my Nexus 4 running Android 4.4.2 shows that the values are no longer 0, but are reporting the correct statistics.
I have reported the issue to the AOSP issue tracker: here
I have also created an alternate solution to the problem which I have pasted below:
private Long getTotalBytesManual(int localUid){
File dir = new File("/proc/uid_stat/");
String[] children = dir.list();
if(!Arrays.asList(children).contains(String.valueOf(localUid))){
return 0L;
}
File uidFileDir = new File("/proc/uid_stat/"+String.valueOf(localUid));
File uidActualFileReceived = new File(uidFileDir,"tcp_rcv");
File uidActualFileSent = new File(uidFileDir,"tcp_snd");
String textReceived = "0";
String textSent = "0";
try {
BufferedReader brReceived = new BufferedReader(new FileReader(uidActualFileReceived));
BufferedReader brSent = new BufferedReader(new FileReader(uidActualFileSent));
String receivedLine;
String sentLine;
if ((receivedLine = brReceived.readLine()) != null) {
textReceived = receivedLine;
}
if ((sentLine = brSent.readLine()) != null) {
textSent = sentLine;
}
}
catch (IOException e) {
}
return Long.valueOf(textReceived).longValue() + Long.valueOf(textReceived).longValue();
}
The TrafficStats class get the information about network traffic from the /proc/uid_stat/<uid> directory. This contains information about the tcp, udp bytes and packets sent and received. If the files are not present the TrafficStats class can't get the network stats. You can check if the files are present, If not you are out of luck and should look for other way.
If the files are present you can try to read it yourself.
Also the getUidTxBytes() and getUIDRxBytes() report only the TCP traffic and miss UDP traffic. So if your app is doing lots of UDP traffic (like voip) then you'll not get any info.
There is already a bug filed for this : https://code.google.com/p/android/issues/detail?id=32410
I have done some detailed research about this, and to clarify some details, since Android 4.3 the TrafficStats API has changed in the way it extracts details from the device.
Prior to Android 4.3 the UID traffic stats were available for TCP and UDP and included API for bytes and packets & sent and received. That data was extracted from the /proc/uid_stat/[pid]/* files.
In Android 4.3, the developers has decided to switch to a better and more safe API, using the xt_qtaguid UID statistics, which is part of the netfilter kernel module in Linux.
This API (procfs) allows access based on process UID, and this is why when you try to access to TrafficStats API in Android=>4.3 you will get zero information for not-own UID.
btw, the commit that caused the issue is the following:
https://github.com/android/platform_frameworks_base/commit/92be93a94edafb5906e8bc48e6fee9dd07f5049e
*Improve TrafficStats UID APIs.
Deprecate transport layer statistics, leaving only the summarized
network layer statistics.
Improve documentation to be clear about layers where measurements
occur, and their behavior since boot. Under the hood, move to using
xt_qtaguid UID statistics.
Bug: 6818637, 7013662
Change-Id: I9f26992e5fcdebd88c671e5765bd91229e7b0016*
I'm developing a multi-tab application. In one of the tab I want to show the logcat but I have a lot of problem running it correctly.
Right now I'm using the following command but I don't get anything in my TextView. :
Process process = Runtime.getRuntime().exec("/system/bin/logcat -s com.vittorio:I");
But when I run the same command into Terminal it works flawlessy.
I've also tryed this other command :
Process process = Runtime.getRuntime().exec("/system/bin/logcat *:I");
but for some reason it prints also Debug level messages ...
EDIT (1):
I've by-passed the problem by adding an high-level filter (java) to the whole log.. so I only print in my textview what I need. It's a very dirty solution but for now is the only one I managed to come with.
I would like to point out that I'me experiencing different behaviours on my phones :
Galaxy S Plus (rooted) : I can see the log.
Galaxy Y (rooted) : No log
Nexus One (not-rooted) : No log
EDIT (2) - SOLVED (NEED ROOTED PHONE):
After some struggling I managed to solve my problem. Actually navigating through the init.rc system file I saw that the permissions for /dev/log/main and /dev/log/system where setted to 620.. that's why I couldn't open the log on some of my phones. So I rooted also my Nexus One and added this commands into my activity before calling the logcat command :
Process process_su = Runtime.getRuntime().exec("su");
Process process_ch = Runtime.getRuntime().exec("chmod 777 /dev/log/main");
Done! :D
Hope this info will help anyone who will face my same issue.
You have to use this permission :
<uses-permission android:name="android.permission.READ_LOGS" />
and then you can use that snippet i found
try {
Process process = Runtime.getRuntime().exec("logcat -v");
BufferedReader bufferedReader = new BufferedReader(
new InputStreamReader(process.getInputStream()));
StringBuilder logString=new StringBuilder();
String line;
while ((line = bufferedReader.readLine()) != null) {
logString.append(line);
}
TextView tv = (TextView)findViewById(R.id.logTextView);
tv.setText(logString.toString());
} catch (IOException e) {
}
I didn't try it but it seems correct
I am trying to write an app which reads the logs created by adb logcat. Following the code on link1 and link2, I have the following code:
try {
Process process = Runtime.getRuntime().exec("logcat");
System.out.println("Process : " + process); // shows process id
BufferedReader bufferedReader = new BufferedReader(
new InputStreamReader(process.getInputStream()));
System.out.println("Buffered reader : " + bufferedReader.readLine());
StringBuilder log = new StringBuilder();
String line;
while ((line = bufferedReader.readLine()) != null) {
log.append(line);
}
TextView tv = (TextView) findViewById(R.id.textView1);
tv.setText(log.toString());
} catch (IOException e) {
}
To test what the buffered reader is reading, I put a println, but I get a message "cannot bind tcp:5038". The above code does not read any logs. I also tried using "logcat *:V" but I did not get logs of even lowest priority.
I gave my app the permission: android.permission.READ_LOGS.
I am testing my code on Android emulator.
Can someone please point out what am I doing wrong.
Thanks for helping.
EDIT:
I tried "logcat -d" and I got one line of log. In the code, it can be observed that a try/catch block has been provided; when I remove the permission READ_LOGS from the app, no exception is raised and the bufferReader simply prints null (Usually when an app does not find a permission it requires, it raises an exception). What is the reason for this behavior ?
EDIT2:
I tried Log.d(TAG, log.toString()) and got more than one line of text. Can someone please explain the last question from the previous edit: when I remove the required permission, why is an exception not raised by the app ?
You are likely getting the message "cannot bind tcp:5038" due to not having
<uses-permission android:name="android.permission.INTERNET" />
in your manifest
You can never get the permission to read logs through Runtime.getRuntime().
The android dev team decided to stop granting these permissions to third-party apps. Only system apps can now get them.
More details:https://code.google.com/p/acra/issues/detail?id=100