How do I write outputs to the Log in Android?

Question

I want to write some debugging output to the log to review it with logcat.

If I write something to System.out this is already displayed in logcat.

What is the clean way to write to the log and add levels and tags to my output?

score 222 · Accepted Answer · edited Nov 14 '17 at 13:32

222

Look into android.util.Log. It lets you write to the log with various log levels, and you can specify different tags to group the output. For example

Log.w("myApp", "no network");

will output a warning with the tag myApp and the message no network.

edited Nov 14 '17 at 13:32

Mike Vella

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answered Mar 02 '10 at 16:37

Erich Douglass

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what would be the different by using `log.d` ? – Maduro Oct 24 '15 at 14:59
6

`w` in `Log.w(...)` stands for warning. There are [more](https://developer.android.com/reference/android/util/Log.html#pubmethods) versions: `d` - debug, `e` - error, `i` - info, `v` - verbose, [`wtf`](http://stackoverflow.com/questions/9524369/how-does-log-wtf-differ-from-log-e) - What a Terrible Failure. ;-) – patryk.beza May 19 '16 at 10:13

user1767754 · Answer 2 · 2016-03-14T06:11:47.217

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The Tag is just used to easily find your output, because the Output of LogCat can be sometimes very long. You can define somewhere in your class:

private static final String TAG = "myApp";

and use it when debugging

Log.v(TAG, "did something");

enter image description here

You can apply as well a Filter to only search for the tag.

edited Mar 14 '16 at 06:11

answered Sep 28 '14 at 12:53

user1767754

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score 17 · Answer 3 · answered Mar 02 '10 at 16:36

17

Use android.util.Log and the static methods defined there (e.g., e(), w()).

answered Mar 02 '10 at 16:36

CommonsWare

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score 10 · Answer 4 · edited Nov 17 '17 at 06:26

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import android.util.Log;

and then

Log.i("the your message will go here");

edited Nov 17 '17 at 06:26

Pang

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answered Feb 24 '17 at 13:04

Atreya Rath

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score 7 · Answer 5 · answered Apr 20 '18 at 04:22

7

Please see the logs as this way,

Log.e("ApiUrl = ", "MyApiUrl") (error)
Log.w("ApiUrl = ", "MyApiUrl") (warning)
Log.i("ApiUrl = ", "MyApiUrl") (information)
Log.d("ApiUrl = ", "MyApiUrl") (debug)
Log.v("ApiUrl = ", "MyApiUrl") (verbose)

answered Apr 20 '18 at 04:22

Dnyaneshwar Panchal

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score 1 · Answer 6 · answered Aug 09 '19 at 08:15

You can use my libary called RDALogger. Here is github link.

With this library, you can log your message with method name/class name/line number and anchor link. With this link, when you click log, screen goes to this line of code.

To use library, you must do implementations below.

in root level gradle

allprojects {
        repositories {
            ...
            maven { url 'https://jitpack.io' }
        }
    }

in app level gradle

dependencies {
            implementation 'com.github.ardakaplan:RDALogger:1.0.0'
    }

For initializing library, you should start like this (in Application.class or before first use)

RDALogger.start("TAG NAME").enableLogging(true);

And than you can log whatever you want;

    RDALogger.info("info");
    RDALogger.debug("debug");
    RDALogger.verbose("verbose");
    RDALogger.warn("warn");
    RDALogger.error("error");
    RDALogger.error(new Throwable());
    RDALogger.error("error", new Throwable());

And finally output shows you all you want (class name, method name, anchor link, message)

08-09 11:13:06.023 20025-20025/com.ardakaplan.application I/Application: IN CLASS : (ENApplication.java:29)   ///   IN METHOD : onCreate
    info

score 0 · Answer 7 · edited Feb 23 '18 at 19:53

0

String one = object.getdata();
Log.d(one,"");

edited Feb 23 '18 at 19:53

grg

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answered Nov 23 '17 at 06:09

Vickie Kangare

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Usually it's better to explain a solution instead of just posting some rows of anonymous code. You can read [How do I write a good answer](https://stackoverflow.com/help/how-to-answer), and also [Explaining entirely code-based answers](https://meta.stackexchange.com/questions/114762/explaining-entirely-%E2%80%8C%E2%80%8Bcode-based-answers) – Anh Pham Nov 23 '17 at 06:28

score 0 · Answer 8 · answered Apr 20 '18 at 04:12

Recently I found this approach to writing logs in android, which I think is super awesome.

public static final boolean FORCED_LOGGING = true;
private static final int CALLER_STACK_INDEX = 3;

public static void showLogs(String message) {
        if (FORCED_LOGGING) {
            StackTraceElement caller = Thread.currentThread().getStackTrace()[CALLER_STACK_INDEX];

            String fullClassName = caller.getClassName();
            String className = fullClassName.substring(fullClassName.lastIndexOf('.') + 1);
            String methodName = caller.getMethodName();
            int lineNumber = caller.getLineNumber();

            Log.i("*** " + className + "." + methodName + "():" + lineNumber + "\n" , message);
        }
    }

How do I write outputs to the Log in Android?

8 Answers8

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