Long story short:
- I need to transform every class in my program (even the java
library that are loaded before my agent). - I have find a way to do it but is not completly working. I'm open to new ideas.
- My actual method act strange: it's supposed to print the same names in file and console but they are not. I'm sure that those classes reach my transform method because if I try to instrument them I get an error.
Complete story: I have created an agent in order to inject some custom code in every class that is loaded into my project. I add this agent at runtime using the option -javaagent and this work just fine.
The problem is that when my agent is attached to the JVM a lot of classes are already loaded (e.g. the java.io.* classes) and so my transformation miss an entire bunch of classes. So my question is: there is a way in which I can instrument all those class that I'm missing? Every suggestion is more then welcome.
For now I have tried like this:
public class MyTransformer implements ClassFileTransformer {
public static void premain(String agentArgs, Instrumentation inst) {
final MyTransformer t = MyTransformer .getInstance();
inst.addTransformer(t, true);
MyTransformer .log.info(t + " registered via JVM option -javaagent");
// TEST
// by the time we are attached, the classes to be
// dumped may have been loaded already. So, check
// for candidates in the loaded classes.
Class[] classes = inst.getAllLoadedClasses();
List<Class> candidates = new ArrayList<Class>();
for (Class c : classes) {
if (inst.isModifiableClass(c) && inst.isRetransformClassesSupported()){
candidates.add(c);
}
}
System.out.println("There are "+candidates.size()+" classes");
try {
// if we have matching candidates, then
// retransform those classes so that we
// will get callback to transform.
if (! candidates.isEmpty()) {
Iterator it = candidates.iterator();
while(it.hasNext()){
Class c = (Class)it.next();
if(!c.getName().startsWith("javassist")){
System.out.println(" ========================> In Progress:"+c.getName());
inst.retransformClasses(c);
}
}
}else{
System.out.println("candidates.isEmpty()");
}
} catch (Exception e) {
e.printStackTrace();
}
}
public byte[] transform(ClassLoader loader, String className,
Class<?> classBeingRedefined, ProtectionDomain protectionDomain,
byte[] classfileBuffer) throws IllegalClassFormatException {
byte[] byteCode = classfileBuffer;
final String dot_classname = className.replace('/', '.');
// log classes that are going throug the instrumentor
// just log if the java.io. is coming here
try {
PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter(path, true)));
out.println(dot_classname);
out.close();
} catch (IOException ex) {
Logger.getLogger(MyTransformer.class.getName()).log(Level.SEVERE, null, ex);
}
return byteCode;
}
}
So my first attempt is to take in the "premain" method every class already loaded and if it's possible reTransfrom it with the method "retransfromClasses".
Now in my transform method I have only a log that write into a file every class that is going to be transformed. Now my test results are:
There are 1486 classes
==> In Progress:com.sun.org.apache.xerces.internal.parsers.AbstractXMLDocumentParser
==> In Progress:java.lang.Enum
==> In Progress:java.lang.ThreadGroup
==> In Progress:java.nio.file.FileSystem
==> In Progress:java.util.regex.Pattern$Prolog
==> In Progress:com.sun.org.apache.xerces.internal.dom.AttributeMap
==> In Progress:java.util.regex.Matcher
==> In Progress:org.apache.commons.beanutils.converters.ShortConverter
==> In Progress:com.google.gson.JsonNull
==> In Progress:java.util.concurrent.CopyOnWriteArrayList$COWIterator
==> In Progress:java.util.concurrent.locks.ReentrantLock
==> In Progress:java.lang.NoSuchMethodError
==> In Progress:org.apache.commons.lang.BooleanUtils
==> In Progress:java.lang.reflect.WeakCache$CacheValue
==> In Progress:com.google.gson.internal.bind.TypeAdapters$33
==> In Progress:java.lang.reflect.Type
==> In Progress:sun.reflect.generics.scope.AbstractScope
==> In Progress:org.apache.log4j.helpers.DateTimeDateFormat
==> In Progress:sun.nio.cs.MS1252
==> In Progress:java.lang.Integer$IntegerCache
==> In Progress:com.sun.org.apache.xerces.internal.utils.SecuritySupport$3
==> In Progress:org.apache.commons.configuration.MapConfiguration
==> In Progress:org.apache.commons.beanutils.IntrospectionContext
==> In Progress:java.io.Reader
==> In Progress:java.util.WeakHashMap$Holder
==> In Progress:java.util.ServiceLoader$LazyIterator
==> In Progress:java.util.regex.Pattern$Branch
==> In Progress:java.lang.IllegalMonitorStateException
==> In Progress:java.util.regex.Pattern$Curly
==> In Progress:org.apache.commons.configuration.resolver.EntityRegistry
==> In Progress:java.io.IOException
==> In Progress:java.io.FilterOutputStream
==> In Progress:org.apache.log4j.LogManager
==> In Progress:sun.util.logging.PlatformLogger$Level
==> In Progress:java.nio.charset.CoderResult$1
==> In Progress:com.google.gson.FieldNamingPolicy$5
==> In Progress:com.google.gson.internal.ObjectConstructor
==> In Progress:sun.util.calendar.BaseCalendar$Date
So you can notice that I can find every class (even the java.io) in which I interested. Now if we take a look at the file that is supposed to contain every class that MyTransformer tried to transform we notice that there are no common entries and that's really strange.
org.apache.commons.beanutils.converters.ShortConverter
com.google.gson.JsonNull
org.apache.commons.lang.BooleanUtils
com.google.gson.internal.bind.TypeAdapters$33
org.apache.log4j.helpers.DateTimeDateFormat
org.apache.commons.configuration.MapConfiguration
org.apache.commons.beanutils.IntrospectionContext
org.apache.commons.configuration.resolver.EntityRegistry
org.apache.log4j.LogManager
com.google.gson.FieldNamingPolicy$5
com.google.gson.internal.ObjectConstructor
org.apache.log4j.Layout
com.google.gson.internal.bind.TypeAdapters
org.apache.log4j.PropertyConfigurator
com.sap.psr.vulas.java.JavaEnumId
org.apache.commons.collections.collection.AbstractSerializableCollectionDecorator
org.apache.commons.logging.impl.LogFactoryImpl
org.apache.commons.lang.text.StrTokenizer
Another problem that I found is that if I try to insert in Mytransformer.transform(..) method some tampering in the bytecode it will break my execution. I mean the transformation operation that I am using is perfectly fine as I use it on every class that is loaded after my agent is attached. But somehow if I try to use it one those "retransformed" classes I will rise this error:
==> In Progress:org.apache.commons.lang.text.StrMatcher$TrimMatcher java.lang.UnsupportedOperationException: class redefinition failed: attempted to change the schema (add/remove fields)
at sun.instrument.InstrumentationImpl.retransformClasses0(Native Method)
at sun.instrument.InstrumentationImpl.retransformClasses(InstrumentationImpl.java:144)
I know that there are limitations on the transformation of native classes but I don't thing that my transform operation is attempting to change the schema. I will investigate on this point and post updates.
