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<meta name="keywords" content="java, logging, inject, automated"></meta>
== Summary ==
<meta name="description" content="A tool for automated injection of logging code into Java class files"></meta>
== Motivation ==


Have you ever wondered how much cleaner your code would look if it weren't littered with all that logging code? And, when you're hunting bugs in production environments, do you produce tons of logging output, but often find that the critical bit of information that you need is missing?
Have you ever wondered how much cleaner your code would look, if it weren't littered with all that logging code? And, when you're hunting bugs in production environments, do you produce tons of logging output, but often find that the critical bit of information that you need is missing?


If the answers are "no" and "no", then stop reading. Otherwise, LOGGIFIER may be the tool you need.
If the answers are "no" and "no", then stop reading. Otherwise, LOGGIFIER may be the tool you need.
== Overview ==
The concept of LOGGIFIER is as follows:
* Relevant class files are instrumented during the build process:<br />Code similar to
    <nowiki>if (MyClass.__logger123.isLoggable(Level.FINE)) {
        Helper.logp(
            MyClass.__logger123,      // logger
            Level.FINE,              // level
            "com.acme.MyClass",      // sourceClass
            "main(String[])",        // sourceMethod
            "MyClass.java",          // source
            120,                      // lineNumber
            "ENTRY  args=(args={0})", // message
            new Object[] { arg1 }    // parameters
        );
    }</nowiki>
: is inserted all over the place. (<code>Helper.logp()</code> eventually calls <code>java.util.logging.Logger.logp()</code>, after having done some pretty-printing on the message arguments.) Where exactly (in the example: At the top of 'MyClass.main()'), and at what log level (here: FINE) is controlled by the applicable [[#Loggification rules|loggification rules]]. In typical scenarios, the default rules should generate a reasonable amount of logging points.
* The instrumentation remains even in production. This is possible because the instrumentation is optimized for very low overhead (as you can see in the code above: The call to 'isLoggable()' is typically super fast).
* Alternatively you loggify the code only when you start debugging. This is often less practical, because it requires that you either have access to the .jar/.war/.ear files in the target environment., or restart the JVM with loggification activated. Also, the restart or the loggification may influence the problems that you want to track down.
* Then, when it comes to debugging, you enable logging at runtime, e.g. by editing the 'logging.properties' file, or by connecting to the running JVM through JMX. LOGGIFIER does not have one single Logger or one Logger per class, but separate loggers for all classes, methods and events. (Loggers are cheap, so the cost for having hundreds of them is low.) Hence you can enable the logging very selectively and thereby keep the amount of logging output reasonable.


== Getting started ==
== Getting started ==


Click [[Loggifier.unkrig.de / Getting Started|here]] to take the fast track to Loggifier.
I presume that you know what <code>java.util.logging</code> is and why you want to use logging at all (e.g. in favor of an interactive debugger).
 
== Tools ==
 
There are various tools to loggify your classes:
 
* At build time:
** The LOGGIFIER [[Loggifier.unkrig.de / Tools / Command line tool|command line tool]]
** The LOGGIFIER [[Loggifier.unkrig.de / Tools / Eclipse plug-in|ECLIPSE plug-in]]
** The <code><de.unkrig.loggifier></code> [[Loggifier.unkrig.de / Tools / Ant task|ANT task]]
* At runtime:
** The [[Loggifier.unkrig.de / Tools / LoggifyingClassLoader|LoggifyingClassLoader]]
** The LOGGIFIER [[Loggifier.unkrig.de / Tools / Java agent|Java agent]]
 
== Loggification ==
 
The LOGGIFIER loads a class file and analyzes the bytecode of the class's constructors and methods. Looking at the code, it identifies "interesting" points where logging code could be inserted. Each of the logging points is characterized by an [[#Logging actions|action]]. For each logging point, the relevant [[#Loggification rules|loggification rules]] are executed, and the first that matches determines at what level the logging event is to be logged (or if no logging code is injected for this logging point). Loggification rules optionally have a [[#Discriminator expression|discriminator expression]], which has a set of [[#Discriminator expression parameters|parameters]].
 
=== Logging actions ===
 
Each section of code is characterized by an 'Action'. For example, the JVM bytecodes <code>PUTFIELD</code> and <code>PUTSTATIC</code> are characterized by action '''PUT'''.
 
{| class="wikitable"
|-
|'''ALOAD'''    ||Log array type, array value, index and element value read from an array
|-
|'''ARITH'''    ||Log operands, operator (+, -, ...) and result of an arithmetic operation
|-
|'''ASTORE'''    ||Log the array, the index and the value being stored in an array
|-
|'''CAST'''      ||Log the type to which the operand is casted
|-
|'''CATCH'''    ||Log the declared catch type and the actually caught exception
|-
|'''CLINIT'''    ||Log the name of a class that is initialized
|-
|'''CONST'''    ||Log the value of a constant being pushed on the operand stack
|-
|'''CONVERT'''  ||Log a value that is arithmetically converted and the conversion result
|-
|'''ENTRY'''    ||Log the target object (if non-static) and the arguments as a method begins execution
|-
|'''GET'''      ||Log declaring class of, name of, source instance of (if non-static) and value read from a field
|-
|'''INVOKE'''    ||Log signature, target object (if non-static) and arguments right before a method is invoked
|-
|'''INSTANCEOF'''||Log the type to which the operand type is compared
|-
|'''LENGTH'''    ||Log the array who's length is determined
|-
|'''LOAD'''      ||Log type of, name of and value read from a local variable
|-
|'''NEW'''      ||Log the type of a new object being instantiated
|-
|'''PUT'''      ||Log declaring class of, name of, target instance of (if non-static) and value assigned to field
|-
|'''RESULT'''    ||Log method signature and invocation result (if not 'void')
|-
|'''RETURN'''    ||Log the value that is being returned by a method (if not 'void')
|-
|'''STORE'''    ||Log value assigned to, type of and name of a local variable
|-
|'''SWITCH'''    ||Log the integer value that a switch is being executed on
|-
|'''THROW'''    ||Log an exception right before it is thrown
|}
 
=== Loggification rule syntax ===
 
A rule triggers if and only if
* It applies to the action of the loggification point (ENTRY, EXIT, THROW, ...)
* Its discriminator expression (if any) evaluates to TRUE for the actual point (who's properties are availables as variables in the discriminator expression, see above)
 
The syntax of all loggification rules is:


loggification-rule :=
So let's start with a very simple program:
    ( action { ',' action } | 'ALL' ) '=' level [ ':' discriminator-expression ]
action :=
    (One of the actions documented above)
level :=
    'SEVERE' | 'WARNING' | 'INFO' | 'CONFIG' | 'FINE' | 'FINER' | 'FINEST'
discriminator-expression :=
    (Syntax defined below)


Examples of valid loggification rules are:
  '''import''' java.util.logging.Logger;
   
  '''public class''' Main {
   
      '''private static final''' Logger LOGGER = Logger.getLogger("Main.USER");
   
      '''public static void''' main(String[] args) {
          System.out.println("HELLO WORLD");
          LOGGER.fine("About to terminate");
      }
  }


ALL=FINE
By default, java.util.logging is disabled, so we don't get any logging output:
ENTRY=FINE
ARITH=FINE
LOAD,CONVERT,ARITH,STORE=FINE
ALL=FINE:class =* "de.*"


(<code>=*</code> is the 'glob matching operator', e.g. "hello" matches "he*".)
  '''$ javac Main.java'''
  '''$ java Main'''
  HELLO WORLD
  '''$'''


=== Loggification rule precedence ===
To enable logging, we need to create one more file


The sequence of checked rules for each logging point is as follows:
  # File 'my_logging.properties'.
  handlers = java.util.logging.ConsoleHandler
  java.util.logging.ConsoleHandler.formatter = java.util.logging.SimpleFormatter
  java.util.logging.ConsoleHandler.level    = FINEST
  java.util.logging.SimpleFormatter.format  = [%2$20s] %4$s: %5$s%n
  .level = FINEST


;If the constructor or method being instrumented has a '@Loggify' annotation (not for action CLINIT)
, and run our program with the <code>java.util.logging.config.file</code> system property set:
:Its values in reverse order (i.e. the last value/rule takes the highest precedence).


;If a field 'static final String $$loggifierRules = "xyz"' was declared before the contructor or method being instrumented
  '''$ java -Djava.util.logging.config.file=my_logging.properties Main'''
:Its value, split at '\n', in reverse order (i.e. the last fragment/rule takes the highest precedence).
  HELLO WORLD
  <span style="color:red;">[          Main main] FINE: About to terminate</span>
  '''$'''


;If the class or interface being instrumented has a '@Loggify' annotation
So now let's loggify the 'Main' class! Get 'de.unkrig.loggifier.jar' and 'de.unkrig.loggifier-runtime.jar' from [http://loggifier.unkrig.de/download/] and run:
:Its values of in reverse order (i.e. the last value/rule takes the highest precedence).


;If using the four-parameter [[Loggifier.unkrig.de / Tools / LoggifyingClassLoader|LoggifyingClassLoader]] constructor
  '''$ ls -l'''
:The 'logLevelCalculator' argument.
  -rwx------+ 1 aunkrig users 969 Aug 26 11:23 Main.class
  '''$ java -cp de.unkrig.loggifier.jar de.unkrig.loggifier.Main Main.class'''
  '''$ ls -l'''
  -rwx------+ 1 aunkrig users 2314 Aug 26 11:23 Main.class
  '''$'''


;If using the [[Loggifier.unkrig.de / Tools / Ant task|ANT task]]
Not only can you pass class files to LOGGIFER, but also directories, files in ZIP format that contain '.class' files
:<code><rule></code> subelements, in reverse order (i.e. the last <code><rule></code> takes the highest precedence).
(e.g. JAR and WAR files), and even ZIP files that contain nested ZIP files with '.class' files (e.g. EAR files). In
any case, LOGGIFIER will modify the contained '.class' "in-place".


;If using the [[Loggifier.unkrig.de / Tools / Command line tool|LOGGIFIER command line tool]]
Now what logging do we get now?
:The '-rule' options, in reverse order (i.e. the last '-rule' option takes the highest precedence).


;If using the [[Loggifier.unkrig.de / Tools / Eclipse plug-in|ECLIPSE plug-in]]
  '''$ java -Djava.util.logging.config.file=my_logging.properties -cp de.unkrig.loggifier-runtime.jar\;. Main'''
:The levels on the "Loggifier" property page of each project. (This rule ALWAYS applies, hence the following rules are never executed).
  <span style="color:red;">[     Main <clinit>()] FINER: (Main.java:6) ENTRY  args=()</span>
  <span style="color:red;">[     Main <clinit>()] FINER: (Main.java:6) RETURN</span>
  <span style="color:red;">[ Main main(String[])] FINER: (Main.java:9) ENTRY  args=(args=String[0])</span>
  HELLO WORLD
  <span style="color:red;">[          Main main] FINE: About to terminate</span>
  <span style="color:red;">[ Main main(String[])] FINER: (Main.java:12) RETURN</span>
  '''$'''


;If using the [[Loggifier.unkrig.de / Tools / Java agent|Java agent]]
Notice that you now need to have the (very small) 'de.unkrig.loggifier-runtime.jar' on the class path, because the
:Its argument string passed to the agent, split at '\n', in reverse order (i.e. the last fragment/rule takes the highest precedence).
injected logging code needs that.


;If the action is LOAD or STORE, and the local variable's name ends with '__'
By default, LOGGIFIER injects a 'reasonable' amount of logging: You can see how the class initializer of the 'Main' class is executed, then the 'main()' method. Notice how the hand-written logging seamlessly mixes with the automatically injected logging.
:FINER


;If the action is GET or PUT, and the field's name ends with '__'
Effectively, we can now remove the hand-written logging code from our class, because the automatically injected logging
:FINER
code now does the job:


;If the action is NEW, CAST or INSTANCEOF, and the target class's name ends with '__'
  '''public class''' Main {
:FINER
   
      '''public static void''' main(String[] args) {
          System.out.println("HELLO WORLD");
      }
  }


;If the action is ENTRY, RETURN or THROW
Now let's compile, loggify and run again:
:FINER


;Last resort (when none of the above rules triggered)
  '''$ java -Djava.util.logging.config.file=my_logging.properties -cp de.unkrig.loggifier-runtime.jar\;. Main'''
:OFF
  <span style="color:red;">[    Main <clinit>()] FINER: (Main.java:6) ENTRY  args=()</span>
  <span style="color:red;">[    Main <clinit>()] FINER: (Main.java:6) RETURN</span>
  <span style="color:red;">[ Main main(String[])] FINER: (Main.java:9) ENTRY  args=(args=String[0])</span>
  HELLO WORLD
  <span style="color:red;">[ Main main(String[])] FINER: (Main.java:12) RETURN</span>
  '''$'''


Notice that non-static fields (a.k.a. 'instance variables') are initialized by the class's constructors. Static fields ('class variables') are initialized by the synthetic <code><clinit>()</code> method, which cannot be annotated in source code.
For demonstration, we now set the amount of logging to the highest possible level. There are several ways to configure
the injection of logging code: We can pass a 'loggification rule' to the LOGGIFER like '-rule ALL=FINE', or through a '@Loggify'
annotation to any class or method declaration:


=== Discriminator expression ===
  import de.unkrig.loggifier.runtime.annotation.Loggify;
   
  @Loggify("ALL=FINE")
  public class Main {
      // ...


Discriminator expressions are implemented by means of <code>de.unkrig.commons.text.expression.ExpressionEvaluator</code>; find the expression syntax documented [http://commons.unkrig.de/javadoc/de/unkrig/commons/text/expression/Parser.html here].
Then compile, loggify and run again:


=== Discriminator expression parameters ===
  '''$ javac Main.java -cp de.unkrig.loggifier-runtime.jar'''
  '''$ java -cp de.unkrig.loggifier.jar de.unkrig.loggifier.Main Main.class'''
  '''$ java -Djava.util.logging.config.file=my_logging.properties -cp de.unkrig.loggifier-runtime.jar\;. Main'''
  <span style="color:red;">[    Main <clinit>()] FINE: (Main.java:1) CLINIT Main</span>
  <span style="color:red;">[    Main <clinit>()] FINE: (Main.java:9) ENTRY  args=()</span>
  <span style="color:red;">[    Main <clinit>()] FINE: (Main.java:9) CONST  "Main.USER"</span>
  <span style="color:red;">[    Main <clinit>()] FINE: (Main.java:9) INVOKE Logger.getLogger(String): args=("Main.USER")</span>
  <span style="color:red;">[    Main <clinit>()] FINE: (Main.java:9) RESULT Logger.getLogger(String) => java.util.logging.Logger@53c60f74</span>
  <span style="color:red;">[    Main <clinit>()] FINE: (Main.java:9) PUT    java.util.logging.Logger@53c60f74 => Main.LOGGER</span>
  <span style="color:red;">[    Main <clinit>()] FINE: (Main.java:9) RETURN</span>
  <span style="color:red;">[ Main main(String[])] FINE: (Main.java:12) ENTRY  args=(args=String[0])</span>
  <span style="color:red;">[ Main main(String[])] FINE: (Main.java:12) GET    System.out => java.io.PrintStream@7020b3a3</span>
  <span style="color:red;">[ Main main(String[])] FINE: (Main.java:12) CONST  "HELLO WORLD"</span>
  <span style="color:red;">[ Main main(String[])] FINE: (Main.java:12) INVOKE PrintStream.println(String): target=java.io.PrintStream@7020b3a3, args=("HELLO WORLD")</span>
  HELLO WORLD
  <span style="color:red;">[ Main main(String[])] FINE: (Main.java:12) RESULT PrintStream.println(String)</span>
  <span style="color:red;">[ Main main(String[])] FINE: (Main.java:14) GET    Main.LOGGER => java.util.logging.Logger@53c60f74</span>
  <span style="color:red;">[ Main main(String[])] FINE: (Main.java:14) CONST  "About to terminate"</span>
  <span style="color:red;">[ Main main(String[])] FINE: (Main.java:14) INVOKE Logger.fine(String): target=java.util.logging.Logger@53c60f74, args=("About to terminate")</span>
  <span style="color:red;">[          Main main] FINE: About to terminate</span>
  <span style="color:red;">[ Main main(String[])] FINE: (Main.java:14) RESULT Logger.fine(String)</span>
  <span style="color:red;">[ Main main(String[])] FINE: (Main.java:15) RETURN</span>
  '''$'''


To provide fine-grained control over loggification, the properties of each loggification point are provided as parameters to the discriminator expression:
(Notice that JAVAC now needs "de.unkrig.loggifier-runtime.jar" on the class path, because "@de.unkrig.loggifier.runtime.annotation.Loggify" lives there.)


;action
Now you can watch how the <code>System.out</code> field is read and the string constant <code>"HELLO WORLD"</code> is used - if you're interested.
:One of the [[#Logging actions|documented logging actions]]
;source
:The name of the Java source file that JAVAC stores in each <code>.class</code> file if enabled by <code>-g:source</code>.
;classAccess
:The accessibility of the class being instrumented (<code>public</code>, <code>protected</code> or <code>private</code>)
;class
:The fully qualified name of the class being instrumented, e.g. <code>pkg.MyClass</code>
;methodAccess
:The accessibility of the method being instrumented (<code>public</code>, <code>protected</code> or <code>private</code>)
;method
:The enhanced, dequalified name of the method being instrumented, e.g. <code>meth(String, MyClass)</code> or <code><T extends IOException>meth(T, MyClass, List<T>)</code>
;line
:The line number related to the code point being instrumented that JAVAC stores in each .class file if enabled by <code>-g:lines</code>
;type
:The relevant type for the operation, e.g. <code>pkg.Class</code>, <code>pkg.Class[][]</code>, <code>int[][]</code> (only for actions '''CAST''', '''INSTANCEOF''' and '''NEW''')
;classAndField
:The subject class and field, e.g. <code>pkg.Class.field</code> (only for actions '''GET''' and '''PUT''')
;variable
:The name of the subject local variable (only for actions '''LOAD''' and '''STORE''')


At each loggification point, the LOGGIFIER determines if logging code is to be inserted or not ('discrimination') and
LOGGIFIER is not only available as a command-line tool, but also as an ECLIPSE plug-in and an ANT task.
on which level the event will be logged at runtime ('level'). This is achieved by checking the 'loggification
rules'.


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