The tool (in this repo) comprises 3 classes (given below). The problem is how to make my ParaTracer.Logger class visible in every class I instrument (such as java.util.Random shown below). The statement cp.importPackage( "ParaTracer.Logger"); doesn't seem to work and I am getting this error:
java.lang.NoClassDefFoundError: ParaTracer/Logger
at java.util.Random.nextLong(Random.java)
I tried dynamically loading the Logger class inside every instrumented class. But it seems I was using Class.getMethod() incorrectly, or the Javassist compiler is too primitive to compile dynamic class-loading code. I get this error:
javassist.CannotCompileException: [source error] getMethod(java.lang.String,java.lang.Class,java.lang.Class) not found in java.lang.Class
The following 3 classes are exported into a JAR file with MANIFEST.MF file defining the Premain-Class and is passed to the JVM when running any instrumented program using the switch:
-javaagent:/Path/To/ParaTracerAgent.jar
Here are the 3 classes.
package ParaTracer;
import java.lang.instrument.Instrumentation;
import javassist.CannotCompileException;
import javassist.ClassPool;
import javassist.CtClass;
import javassist.CtField;
import javassist.CtNewConstructor;
import javassist.CtNewMethod;
public class ParaTracer {
private static volatile Instrumentation instr;
public static void premain(String agentArgs, Instrumentation inst) {
instr = inst;
SimpleClassTransformer transformer = new SimpleClassTransformer();
inst.addTransformer( transformer, false );
}
}
The transformer class:
package ParaTracer;
import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.IllegalClassFormatException;
import java.security.ProtectionDomain;
import java.util.HashMap;
import java.util.HashSet;
import javassist.ClassPool;
import javassist.CtClass;
import javassist.CtMethod;
public class SimpleClassTransformer implements ClassFileTransformer {
public HashMap< String, HashSet< String > > mInstrumentedMethods;
public SimpleClassTransformer() {
mInstrumentedMethods = new HashMap< String, HashSet< String > >();
mInstrumentedMethods.put( "java.util.Random", new HashSet< String >() );
mInstrumentedMethods.get( "java.util.Random").add( "nextLong" );
}
@Override
public byte[] transform(
ClassLoader loader,
String className,
Class<?> classBeingRedefined,
ProtectionDomain protectionDomain,
byte[] classfileBuffer) throws IllegalClassFormatException {
System.err.println( "---- Instrumenting: " + className );
byte[] byteCode = classfileBuffer;
String normalizedClassName = className.replaceAll("/", ".");
if ( mInstrumentedMethods.containsKey( normalizedClassName ) ) {
try {
ClassPool cp = ClassPool.getDefault();
cp.importPackage( "ParaTracer.Logger");
CtClass cc = cp.get( normalizedClassName );
for( String method : mInstrumentedMethods.get( normalizedClassName ) ) {
CtMethod m = cc.getDeclaredMethod( method );
StringBuilder sbs = new StringBuilder();
sbs.append( "long tid = Thread.currentThread().getId();" );
sbs.append( "StringBuilder sbArgs = new StringBuilder();" );
sbs.append( "sbArgs.append( System.identityHashCode( $0 ) );" );
CtClass[] pTypes = m.getParameterTypes();
for( int i=0; i < pTypes.length; ++i ) {
CtClass pType = pTypes[i];
if ( pType.isPrimitive() ) {
sbs.append( "sbArgs.append( \", \" + $args[" + i + "] );" );
} else {
sbs.append( "sbArgs.append( \", \" + System.identityHashCode( $args[" + i + "] ) );" );
}
}
sbs.append( "ParaTracer.Logger.pushArgs( tid, sbArgs.toString() );" );
sbs.append( "StringBuilder sb = new StringBuilder();" );
sbs.append( "sb.append( tid + \" : " + m.getLongName() + ".<START>(\" );" );
sbs.append( "sb.append( sbArgs.toString() );" );
sbs.append( "sb.append( \")\" );" );
sbs.append( "ParaTracer.Logger.print( sb.toString() );" );
m.insertBefore("{" + sbs.toString() + "}");
StringBuilder sbe = new StringBuilder();
sbe.append( "long tid = Thread.currentThread().getId();" );
sbe.append( "String args = ParaTracer.Logger.popArgs( tid );" );
sbe.append( "StringBuilder sb = new StringBuilder();" );
sbe.append( "sb.append( tid + \" : " + m.getLongName() + ".<END>(\" );" );
sbe.append( "sb.append( args );" );
sbe.append( "sb.append( \")\" );" );
sbe.append( "ParaTracer.Logger.print( sb.toString() );" );
m.insertAfter("{" + sbe.toString() + "}");
}
byteCode = cc.toBytecode();
cc.detach();
} catch (Exception ex) {
ex.printStackTrace();
}
}
return byteCode;
}
}
The thread-safe logger class is given by:
package ParaTracer;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.HashMap;
import java.util.Stack;
public class Logger {
private static String loggerFilePath = "\"/some/fixed/path\"";
private static FileWriter fw;
private static PrintWriter out;
private static HashMap< Long, Stack<String> > callStacks;
public static synchronized void pushArgs( long tid, String args ) {
try {
init();
} catch (IOException e) {
e.printStackTrace();
}
if ( ! callStacks.containsKey( tid ) ) {
callStacks.put( tid, new Stack<String>() );
}
callStacks.get( tid ).push( args );
}
public static synchronized String popArgs( long tid ) {
assert( callStacks.containsKey( tid ) );
assert( ! callStacks.get( tid ).empty() );
return callStacks.get( tid ).pop();
}
public static synchronized void shutdown() {
if ( fw == null ) return;
try {
fw.close();
} catch (IOException e) {
e.printStackTrace();
}
}
public static synchronized void print( String str ) {
try {
init();
} catch (IOException e) {
e.printStackTrace();
}
out.print( str );
}
private static void init() throws IOException {
if ( fw != null ) return;
fw = new FileWriter( loggerFilePath );
out = new PrintWriter( fw );
callStacks = new HashMap< Long, Stack<String> >();
}
}
According to the documentation for Java agents the agent class is loaded by the system classloader. But if you want to instrument core Java classes and refer from those to a custom class of your own then that class would need to be available to the bootstrap classloader rather than the system one.
Move your Logger class into a separate JAR file, and list that file in the Boot-Class-Path attribute of the agent JAR's manifest:
Boot-Class-Path: ParaTracerLogger.jar
Now the logger class is visible on the bootstrap loader and can be seen by the instrumented java.lang classes.
I ended up having the ClassFileTransformer.tranform method as follows:
Basically, the code inserted by Javassist reopens the same log file every time there is a message to be written out and appends that message to the output file. Having a separate log file was important because redirecting standard output/error will result in contaminated log files if those streams are already used by the instrumented application (as is usually the case).
@Override
public byte[] transform(
ClassLoader loader,
String className,
Class<?> classBeingRedefined,
ProtectionDomain protectionDomain,
byte[] classfileBuffer)
throws IllegalClassFormatException {
byte[] byteCode = classfileBuffer;
String normalizedClassName = className.replaceAll("/", ".");
System.out.println( "\tNormalized: " + normalizedClassName );
ClassMonitorSet classMonitorSet = monitorClass( normalizedClassName );
if ( classMonitorSet != null ) {
System.out.println( "\tMonitoring: " + normalizedClassName );
try {
ClassPool cp = ClassPool.getDefault();
CtClass cc = cp.get( normalizedClassName );
for( String methodName : classMonitorSet.monitorSet ) {
CtMethod[] methods = cc.getDeclaredMethods( methodName );
for( CtMethod method : methods ) {
StringBuilder sbs = new StringBuilder();
sbs.append( "long tid = Thread.currentThread().getId();" );
sbs.append( "StringBuilder sbArgs = new StringBuilder();" );
sbs.append( "sbArgs.append( System.identityHashCode( $0 ) );" );
CtClass[] pTypes = method.getParameterTypes();
for( int i=0; i < pTypes.length; ++i ) {
CtClass pType = pTypes[i];
if ( pType.isPrimitive() ) {
sbs.append( "sbArgs.append( \", \" + $args[" + i + "] );" );
} else {
sbs.append( "sbArgs.append( \", \" + System.identityHashCode( $args[" + i + "] ) );" );
}
}
sbs.append( "StringBuilder sb = new StringBuilder();" );
sbs.append( "sb.append( tid + \" : " + method.getLongName() + ".<START>(\" );" );
sbs.append( "sb.append( sbArgs.toString() );" );
sbs.append( "sb.append( \")\" );" );
sbs.append( "String fPath = \"/path/to/log.out\";" );
sbs.append( "try {" );
sbs.append( " java.io.FileWriter fw = new java.io.FileWriter( fPath, true );" );
sbs.append( " java.io.PrintWriter out = new java.io.PrintWriter( fw, true );" );
sbs.append( " out.println( sb.toString() );" );
sbs.append( " fw.close();" );
sbs.append( "} catch (java.io.IOException e) {" );
sbs.append( " e.printStackTrace();" );
sbs.append( "}" );
method.insertBefore("{" + sbs.toString() + "}");
StringBuilder sbe = new StringBuilder();
sbe.append( "long tid = Thread.currentThread().getId();" );
sbe.append( "StringBuilder sb = new StringBuilder();" );
sbe.append( "sb.append( tid + \" : " + method.getLongName() + ".<END>(*)\" );" );
sbe.append( "String fPath = \"/path/to/log.out\";" );
sbe.append( "try {" );
sbe.append( " java.io.FileWriter fw = new java.io.FileWriter( fPath, true );" );
sbe.append( " java.io.PrintWriter out = new java.io.PrintWriter( fw, true );" );
sbe.append( " out.println( sb.toString() );" );
sbe.append( " fw.close();" );
sbe.append( "} catch (java.io.IOException e) {" );
sbe.append( " e.printStackTrace();" );
sbe.append( "}" );
method.insertAfter("{" + sbe.toString() + "}");
}
}
byteCode = cc.toBytecode();
cc.detach();
} catch (Exception ex) {
ex.printStackTrace();
}
}
return byteCode;
}
来源：https://stackoverflow.com/questions/29451704/using-javassist-to-log-method-calls-and-argument-values-how-to-make-a-logger-cl