org.apache.openjpa.enhance.ClassRedefiner Maven / Gradle / Ivy
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* to you under the Apache License, Version 2.0 (the
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* http://www.apache.org/licenses/LICENSE-2.0
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package org.apache.openjpa.enhance;
import java.lang.instrument.ClassDefinition;
import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.Instrumentation;
import java.lang.reflect.Method;
import java.security.ProtectionDomain;
import java.util.Map;
import org.apache.openjpa.conf.OpenJPAConfiguration;
import org.apache.openjpa.lib.log.Log;
import org.apache.openjpa.lib.util.JavaVersions;
import org.apache.openjpa.lib.util.Localizer;
import org.apache.openjpa.util.InternalException;
/**
* Redefines the method bodies of existing classes. Supports Java 5 VMs that
* have a java agent installed on the command line as well as newer VMs without
* any -javaagent flag.
*
* @since 1.0.0
*/
public class ClassRedefiner {
private static final Localizer _loc = Localizer.forPackage(ClassRedefiner.class);
private static Boolean _canRedefine = null;
/**
* For each element in classes, this method will redefine
* all the element's methods such that field accesses are intercepted
* in-line. If {@link #canRedefineClasses()} returns false,
* this method is a no-op.
*/
public static void redefineClasses(OpenJPAConfiguration conf,
final Map,byte[]> classes) {
Log log = conf.getLog(OpenJPAConfiguration.LOG_ENHANCE);
if (classes == null || classes.size() == 0 || !canRedefineClasses(log))
return;
Instrumentation inst = null;
ClassFileTransformer t = null;
try {
inst = InstrumentationFactory.getInstrumentation(log);
Class[] array = classes.keySet().toArray(new Class[classes.size()]);
if (JavaVersions.VERSION >= 6) {
log.trace(_loc.get("retransform-types", classes.keySet()));
t = new ClassFileTransformer() {
public byte[] transform(ClassLoader loader, String clsName,
Class classBeingRedefined, ProtectionDomain pd,
byte[] classfileBuffer) {
return classes.get(classBeingRedefined);
}
};
// these are Java 6 methods, and we don't have a Java 6 build
// module yet. The cost of reflection here is negligible
// compared to the redefinition / enhancement costs in total,
// so this should not be a big problem.
Method meth = inst.getClass().getMethod("addTransformer",
new Class[] { ClassFileTransformer.class, boolean.class });
meth.invoke(inst, new Object[] { t, true });
meth = inst.getClass().getMethod("retransformClasses",
new Class[] { array.getClass() });
meth.invoke(inst, new Object[] { array });
} else {
log.trace(_loc.get("redefine-types", classes.keySet()));
// in a Java 5 context, we can use class redefinition instead
ClassDefinition[] defs = new ClassDefinition[array.length];
for (int i = 0; i < defs.length; i++)
defs[i] = new ClassDefinition(array[i],
classes.get(array[i]));
inst.redefineClasses(defs);
}
} catch (Exception e) {
throw new InternalException(e);
} finally {
if (inst != null && t != null)
inst.removeTransformer(t);
}
}
/**
* @return whether or not this VM has an instrumentation installed that
* permits redefinition of classes. This assumes that all the arguments
* will be modifiable classes according to
* {@link java.lang.instrument.Instrumentation#isModifiableClass}, and
* only checks whether or not an instrumentation is available and
* if retransformation is possible.
*/
public static boolean canRedefineClasses(Log log) {
if (_canRedefine == null) {
try {
Instrumentation inst = InstrumentationFactory.getInstrumentation(log);
if (inst == null) {
_canRedefine = Boolean.FALSE;
} else if (JavaVersions.VERSION == 5) {
// if instrumentation is non-null and we're using Java 5,
// isRetransformClassesSupported isn't available,
// so we use the more basic class redefinition instead.
_canRedefine = Boolean.TRUE;
} else {
_canRedefine = (Boolean) Instrumentation.class.getMethod(
"isRetransformClassesSupported").invoke(inst);
}
} catch (Exception e) {
_canRedefine = Boolean.FALSE;
}
}
return _canRedefine.booleanValue();
}
}