我正在使用Java工具和Javassist将print语句插入到方法中。这主要是没有错误的,但是对于某些类方法(例如java.util.TimeZone.getSystemTimeZoneID
),我得到以下异常:
javassist.CannotCompileException: no method body
at javassist.CtBehavior.insertBefore(CtBehavior.java:695)
at javassist.CtBehavior.insertBefore(CtBehavior.java:685)
我的代码尝试通过检查CtBehaviour.isEmpty()
来避免此问题,但这没有任何区别。关于如何避免这种情况的任何建议?
这是一个最小的例子:
public class ExceptionExample implements ClassFileTransformer {
private static final ClassPool pool = ClassPool.getDefault();
public static void premain(String agentArgument,
Instrumentation instrumentation) {
instrumentation.addTransformer(new ExceptionExample());
}
@Override
public byte[] transform(final ClassLoader loader, final String className,
final Class<?> classBeingRedefined,
final ProtectionDomain protectionDomain, final byte[] classfileBuffer)
throws IllegalClassFormatException {
String dottedClassName = className.replace('/', '.');
if (dottedClassName.startsWith("java.lang")
|| dottedClassName.startsWith("java.util")) {
try {
System.out.println("Instrumenting: " + dottedClassName);
return adjustClass(dottedClassName, classBeingRedefined,
classfileBuffer);
} catch (Exception e) {
e.printStackTrace();
}
}
return classfileBuffer;
}
private byte[] adjustClass(final String className,
final Class<?> classBeingRedefined, final byte[] classfileBuffer)
throws IOException, RuntimeException, CannotCompileException {
CtClass cl = null;
try {
cl = pool.makeClass(new java.io.ByteArrayInputStream(classfileBuffer));
if (!cl.isInterface()) {
CtBehavior[] methods = cl.getDeclaredBehaviors();
for (CtBehavior method : methods) {
if (!method.isEmpty()) {
try {
method
.insertBefore(String.format(
"System.out.println(\"CALLING: %s\");",
method.getLongName()));
} catch (Throwable t) {
System.out.println("Error instrumenting " + className + "."
+ method.getName());
t.printStackTrace();
}
}
}
return cl.toBytecode();
}
} finally {
if (cl != null) {
cl.detach();
}
}
return classfileBuffer;
}
}
这是我正在测试的一个小班:
public class Main {
public static void main(String[] args) throws Exception {
Calendar c = Calendar.getInstance();
System.out.println(c.get(Calendar.YEAR));
}
}
示例输出(缩写):
Instrumenting: java.util.Calendar
CALLING: java.util.Calendar.<clinit>()
CALLING: java.util.Calendar.getInstance()
Instrumenting: java.util.TimeZone
Error instrumenting java.util.TimeZone.getSystemTimeZoneID
javassist.CannotCompileException: no method body
at javassist.CtBehavior.insertBefore(CtBehavior.java:695)
at javassist.CtBehavior.insertBefore(CtBehavior.java:685)
at com.cryptomathic.test.instrument.ExceptionExample.adjustClass(ExceptionExample.java:56)
at com.cryptomathic.test.instrument.ExceptionExample.transform(ExceptionExample.java:34)
at sun.instrument.TransformerManager.transform(Unknown Source)
at sun.instrument.InstrumentationImpl.transform(Unknown Source)
at java.util.Calendar.getInstance(Unknown Source)
at test.Main.main(Main.java:8)
Error instrumenting java.util.TimeZone.getSystemGMTOffsetID
javassist.CannotCompileException: no method body
at javassist.CtBehavior.insertBefore(CtBehavior.java:695)
at javassist.CtBehavior.insertBefore(CtBehavior.java:685)
at com.cryptomathic.test.instrument.ExceptionExample.adjustClass(ExceptionExample.java:56)
at com.cryptomathic.test.instrument.ExceptionExample.transform(ExceptionExample.java:34)
at sun.instrument.TransformerManager.transform(Unknown Source)
at sun.instrument.InstrumentationImpl.transform(Unknown Source)
at java.util.Calendar.getInstance(Unknown Source)
at test.Main.main(Main.java:8)
CALLING: java.util.TimeZone.<clinit>()
CALLING: java.util.TimeZone.getDefaultRef()
CALLING: java.util.TimeZone.getDefaultInAppContext()
CALLING: java.util.TimeZone.setDefaultZone()
CALLING: java.util.TimeZone.getTimeZone(java.lang.String,boolean)
CALLING: java.util.TimeZone.setID(java.lang.String)
...
答案 0 :(得分:4)
您需要首先检查它是否是本机方法,因为本机方法不支持这些方法(insertBefore(),insertAfter()..)。我写了一个小方法来检测CtMethod是否是原生的:
public static boolean isNative(CtMethod method) {
return Modifier.isNative(method.getModifiers());
}
我测试了它,它可以解决你的问题。
注意:无法检测本机方法,因为它们没有字节码。但是,如果支持本机方法前缀(Transformer.isNativeMethodPrefixSupported()),则可以使用Transformer.setNativeMethodPrefix()将本机方法调用包装在非本机调用中,然后可以对其进行检测。
答案 1 :(得分:2)
TimeZone.getSystemTimeZoneID()
是一种原生方法,我并不感到惊讶,这不起作用(我认为你根本无法做到这一点,但我还没有找到这个信息在Javassist doc中。)
要跳过本机方法,请使用Modifier.isNative()