How can we print line numbers to the log in java

Question

How to print line numbers to the log  Say when outputting some information to the log  I also want to print the line number where that output is in the source code  As we can see in the stack trace  it displays the line number where the exception has occurred  Stack trace is available on the exception object   Other alternative could be like manually including the line number when printing to the log  Is there any other way

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The stackLevel depends on depth you call this method  You can try from 0 to a large number to see what difference      If stackLevel is legal  you will get string like java lang Thread getStackTrace Thread java 1536   public static String getCodeLocationInfo int stackLevel            StackTraceElement   stackTraceElements   Thread currentThread   getStackTrace            if  stackLevel  lt  0    stackLevel  gt   stackTraceElements length                return  Stack Level Out Of StackTrace Bounds                     StackTraceElement stackTraceElement   stackTraceElements stackLevel           String fullClassName   stackTraceElement getClassName            String methodName   stackTraceElement getMethodName            String fileName   stackTraceElement getFileName            int lineNumber   stackTraceElement getLineNumber             return String format   s  s  s  s    fullClassName  methodName  fileName  lineNumber

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Below code is tested code for logging line no class name and method name from where logging method is called  public class Utils         debug variable enables disables all log messages to logcat    Useful to disable prior to app store submission     public static final boolean debug   true         l method used to log passed string and returns the    calling file as the tag  method and line number prior    to the string s message     public static void l String s        if  debug            String   msg   trace Thread currentThread   getStackTrace    3           Log i msg 0   msg 1    s         else           return                 l  tag  string     used to pass logging messages as normal but can be disabled    when debug    false     public static void l String t  String s        if  debug            Log i t  s         else           return                 trace    Gathers the calling file  method  and line from the stack    returns a string array with element 0 as file name and     element 1 as method line      public static String   trace final StackTraceElement e    final int level        if  e    null  amp  amp  e length  gt   level            final StackTraceElement s   e level           if  s    null    return new String                     e level  getFileName    e level  getMethodName           e level  getLineNumber                               return null

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We ended up using a custom class like this for our Android work   import android util Log      public class DebugLog    public final static boolean DEBUG   true       public static void log String message      if  DEBUG        String fullClassName   Thread currentThread   getStackTrace   2  getClassName        String className   fullClassName substring fullClassName lastIndexOf        1       String methodName   Thread currentThread   getStackTrace   2  getMethodName        int lineNumber   Thread currentThread   getStackTrace   2  getLineNumber         Log d className         methodName           lineNumber  message

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Look at this link  In that method you can jump to your line code  when you double click on LogCat s row   Also you can use this code to get line number   public static int getLineNumber         int lineNumber   0      StackTraceElement   stackTraceElement   Thread currentThread                getStackTrace        int currentIndex   -1      for  int i   0  i  lt  stackTraceElement length  i              if  stackTraceElement i  getMethodName   compareTo  getLineNumber      0                        currentIndex   i   1              break                       lineNumber   stackTraceElement currentIndex  getLineNumber         return lineNumber

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Here is the logger that we use     it wraps around Android Logger and display class name  method name and line number   http   www hautelooktech com 2011 08 15 android-logging

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From Angsuman Chakraborty  archived        Get the current line number      return int - Current line number      public static int getLineNumber         return Thread currentThread   getStackTrace   2  getLineNumber

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The code posted by  simon buchan will work     Thread currentThread   getStackTrace   2  getLineNumber     But if you call it in a method it will always return the line number of the line in the method so rather use the code snippet inline

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Quick and dirty way   System out println  I m in line           new Exception   getStackTrace   0  getLineNumber       With some more details   StackTraceElement l   new Exception   getStackTrace   0   System out println      l getClassName       l getMethodName       l getLineNumber       That will output something like this   com example mytest MyClass myMethod 103

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I am compelled to answer by not answering your question   I m assuming that you are looking for the line number solely to support debugging   There are better ways   There are hackish ways to get the current line   All I ve seen are slow   You are better off using a logging framework like that in java util logging package or log4j   Using these packages you can configure your logging information to include context down to the class name   Then each log message would be unique enough to know where it came from   As a result  your code will have a  logger  variable that you call via     logger debug  a really descriptive message     instead of      System out println  a really descriptive message

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I use this  little method that outputs the trace and line number of the method that called it     Log d TAG   Where did i put this debug code again        Utils lineOut       Double click the output to go to that source code line   You might need to adjust the level value depending on where you put your code   public static String lineOut         int level   3      StackTraceElement   traces      traces   Thread currentThread   getStackTrace        return    at      traces level

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This is exactly the feature I implemented in this lib  XDDLib   But  it s for android   Lg d  int array    intArrayOf 1  2  3    int list    listOf 4  5  6       One click on the underlined text to navigate to where the log command is  That StackTraceElement is determined by the first element outside this library  Thus  anywhere outside this lib will be legal  including lambda expression  static initialization block  etc

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My way it works for me  String str    select os name from os where os idos   nameid   try           PreparedStatement stmt   conn prepareStatement str           ResultSet rs   stmt executeQuery            if  rs next                  a   rs getString  os n1ame      lt  lt  lt ----Here is the ERROR                             stmt close        catch  SQLException e            System out println  error line       e getStackTrace   2  getLineNumber                         return a

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Log4J allows you to include the line number as part of its output pattern   See http   logging apache org log4j 1 2 apidocs org apache log4j PatternLayout html for details on how to do this  the key element in the conversion pattern is  L     However  the Javadoc does include the following      WARNING Generating caller location   information is extremely slow  It s   use should be avoided unless execution   speed is not an issue

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You can t guarantee line number consistency with code  especially if it is compiled for release  I would not recommend using line numbers for that purpose anyway  it would be better to give a payload of the place where the exception was raised  the trivial method being to set the message to include the details of the method call    You might like to look at exception enrichment as a technique to improve exception handling  http   tutorials jenkov com java-exception-handling exception-enrichment html

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For anyone wondering  the index in the getStackTrace   3  method signals the amount of threads the triggering line travels until the actual  getStackTrace   method excluding the executing line  This means that if the Thread currentThread   getStackTrace   X  getLineNumber    line is executed from 3 nested methods above  the index number must be 3  Example  First layer private static String message String TAG  String msg         int lineNumber   Thread currentThread   getStackTrace   3  getLineNumber         return  quot    quot    TAG    quot  java  quot   lineNumber   quot   quot     quot   quot    msg     Second Layer private static void print String s            System out println s      Third Layer public static void normal          String TAG          String message         print              message                      TAG                      message                         Executing Line      Print normal TAG   quot StatelessDispatcher quot     As someone that has not received any formal education on IT  this has been mind opening on how compilers work

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private static final int CLIENT CODE STACK INDEX   static          Finds out the index of  this code  in the returned stack Trace - funny but it differs in JDK 1 5 and 1 6     int i   0      for  StackTraceElement ste   Thread currentThread   getStackTrace              i            if  ste getClassName   equals Trace class getName                   break                      CLIENT CODE STACK INDEX   i     private String methodName         StackTraceElement ste Thread currentThread   getStackTrace   CLIENT CODE STACK INDEX 1       return ste getMethodName       ste getLineNumber

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you can use -  Reporter log

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I would recommend using a logging toolkit such as log4j  Logging is configurable via properties files at runtime  and you can turn on   off features such as line number   filename logging   Looking at the javadoc for the PatternLayout gives you the full list of options - what you re after is  L

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If it s been compiled for release this isn t possible  You might want to look into something like Log4J which will automatically give you enough information to determine pretty closely where the logged code occurred

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These all get you the line numbers of your current thread and method which work great if you use a try catch where you are expecting an exception  But if you want to catch any unhandled exception then you are using the default uncaught exception handler and current thread will return the line number of the handler function  not the class method that threw the exception  Instead of using Thread currentThread   simply use the Throwable passed in by the exception handler   Thread setDefaultUncaughtExceptionHandler new Thread UncaughtExceptionHandler                 public void uncaughtException Thread t  Throwable e                                  if fShowUncaughtMessage e t                                      System exit 1                               In the above use e getStackTrace   0  in your handler function  fShowUncaughtMessage  to get the offender

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first the general method  in an utility class  in plain old java1 4 code though  you may have to rewrite it for java1 5 and more          Returns the first   class method line      of the first class not equal to  StackTraceUtils  and aclass   lt br   gt     Allows to get past a certain class      param aclass class to get pass in the stack trace  If null  only try to get past StackTraceUtils       return   class method line       never empty  because if aclass is not found  returns first class past StackTraceUtils      public static String getClassMethodLine final Class aclass         final StackTraceElement st   getCallingStackTraceElement aclass       final String amsg         st getClassName           st getMethodName           st getLineNumber             lt     Thread currentThread   getName       gt          return amsg      Then the specific utility method to get the right stackElement            Returns the first stack trace element of the first class not equal to  StackTraceUtils  or  LogUtils  and aClass   lt br   gt       Stored in array of the callstack   lt br   gt       Allows to get past a certain class        param aclass class to get pass in the stack trace  If null  only try to get past StackTraceUtils         return stackTraceElement  never null  because if aClass is not found  returns first class past StackTraceUtils        throws AssertionFailedException if resulting statckTrace is null  RuntimeException          public static StackTraceElement getCallingStackTraceElement final Class aclass        final Throwable           t           new Throwable        final StackTraceElement   ste         t getStackTrace        int index   1      final int limit   ste length      StackTraceElement   st          ste index       String              className   st getClassName        boolean aclassfound   false      if aclass    null            aclassfound   true            StackTraceElement   resst   null      while index  lt  limit            if shouldExamine className  aclass     true                if resst    null                    resst   st                            if aclassfound    true                    final StackTraceElement ast   onClassfound aclass  className  st                   if ast    null                        resst   ast                      break                                              else                               if aclass    null  amp  amp  aclass getName   equals className     true                        aclassfound   true                                                    index   index   1          st          ste index           className   st getClassName              if isNull resst              throw new AssertionFailedException StackTraceUtils getClassMethodLine       null argument      stack trace should null       NON-NLS-1            return resst         static private boolean shouldExamine String className  Class aclass          final boolean res   StackTraceUtils class getName   equals className     false  amp  amp   className endsWith LOG UTILS              false     aclass   null  amp  amp  aclass getName   endsWith LOG UTILS           return res         static private StackTraceElement onClassfound Class aclass  String className  StackTraceElement st          StackTraceElement   resst   null        if aclass    null  amp  amp  aclass getName   equals className     false                    resst   st                if aclass    null                    resst   st                return resst

[java] How can we print line numbers to the log in java

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