org.slf4j.instrumentation

Class LogTransformer

java.lang.Object

org.slf4j.instrumentation.LogTransformer

All Implemented Interfaces:

java.lang.instrument.ClassFileTransformer

public class LogTransformer
extends java.lang.Object
implements java.lang.instrument.ClassFileTransformer

LogTransformer does the work of analyzing each class, and if appropriate add log statements to each method to allow logging entry/exit.

This class is based on the article Add Logging at Class Load Time with Java Instrumentation.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	LogTransformer.Builder Builder provides a flexible way of configuring some of many options on the parent class instead of providing many constructors.

Field Summary

Fields

Modifier and Type	Field and Description
private boolean	addEntryExit
private java.lang.String[]	ignore
private java.lang.String	level
private java.lang.String	levelEnabled
private java.lang.String	loggerName
private boolean	verbose

Constructor Summary

Constructors

Modifier	Constructor and Description
private	LogTransformer(LogTransformer.Builder builder)

Method Summary

Modifier and Type	Method and Description
private byte[]	doClass(java.lang.String name, java.lang.Class<?> clazz, byte[] b) doClass() process a single class by first creates a class description from the byte codes.
private void	doMethod(javassist.CtBehavior method) process a single method - this means add entry/exit logging if requested.
byte[]	transform(java.lang.ClassLoader loader, java.lang.String className, java.lang.Class<?> clazz, java.security.ProtectionDomain domain, byte[] bytes)
private byte[]	transform0(java.lang.String className, java.lang.Class<?> clazz, java.security.ProtectionDomain domain, byte[] bytes) transform0 sees if the className starts with any of the namespaces to ignore, if so it is returned unchanged.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

level

private java.lang.String level

levelEnabled

private java.lang.String levelEnabled

addEntryExit

private boolean addEntryExit

verbose

private boolean verbose

ignore

private java.lang.String[] ignore

loggerName

private java.lang.String loggerName

Constructor Detail

LogTransformer

private LogTransformer(LogTransformer.Builder builder)

Method Detail

transform

public byte[] transform(java.lang.ClassLoader loader,
                        java.lang.String className,
                        java.lang.Class<?> clazz,
                        java.security.ProtectionDomain domain,
                        byte[] bytes)

Specified by:

transform in interface java.lang.instrument.ClassFileTransformer

transform0

private byte[] transform0(java.lang.String className,
                          java.lang.Class<?> clazz,
                          java.security.ProtectionDomain domain,
                          byte[] bytes)

transform0 sees if the className starts with any of the namespaces to ignore, if so it is returned unchanged. Otherwise it is processed by doClass(...)

Parameters:

className -

clazz -

domain -

bytes -

Returns:

doClass

private byte[] doClass(java.lang.String name,
                       java.lang.Class<?> clazz,
                       byte[] b)

doClass() process a single class by first creates a class description from the byte codes. If it is a class (i.e. not an interface) the methods defined have bodies, and a static final logger object is added with the name of this class as an argument, and each method then gets processed with doMethod(...) to have logger calls added.

Parameters:

name - class name (slashes separate, not dots)

clazz -

b -

Returns:

doMethod

private void doMethod(javassist.CtBehavior method)
               throws javassist.NotFoundException,
                      javassist.CannotCompileException

process a single method - this means add entry/exit logging if requested. It is only called for methods with a body.

Parameters:

method - method to work on

Throws:

javassist.NotFoundException

javassist.CannotCompileException