- 1. Programmer's Survival Kit:Code Injection for Troubleshooting
Jakub Hol, Iterate AS http://bit.ly/codeinject
2. Learn code injection it can save your day! 3. The power of
code injection Code injectionaspect-oriented programming
(AOP*):
- Modify existingbinaryclasses at build/load time
4. Inject the same code into one or multiple places (DRY) 5.
Lifecycle: Write aspect > weave > run (For AOP check
Wikipedia or Spring docs.) * I will use AOP and Code Injection
interchangeably, however inaccurate that is 6. 3 tools, 2 (3)
examples 7. 1. The omnipresent Java Proxy
- In JRE java.lang.reflect.*
8. Not true AOP, applied manually 9. Can only proxy interfaces
10. Verbose 11. Client JDBC code: PreparedStatement rawStmt =
c.prepareStatement( "INSERT ..." ); PreparedStatement loggingStmt
=(PreparedStatement)
Proxy.newProxyInstance(...,newBatchLogger(rawStmt)); for( inti = 0;
i < data. length ; i++) { loggingStmt.setString(1, data[i]);
loggingStmt.addBatch(); // end a row, start a new one
if(isMultipleOfBatchSize(i)) loggingStmt.executeBatch(); // Logs
st. on failure } Ex.: Log data of a failed batch (0) 12.
classBatchLoggerimplements InvocationHandler{ publicObjectinvoke
(Object proxy , Method method , Object[] args)throwsThrowable {
try{ return method.invoke ( this . target ,
args);}catch(BatchUpdateException e) { } } ... Ex.: Log data of a
failed batch (1) 13. classBatchLoggerimplements InvocationHandler{
publicObjectinvoke (Object proxy , Method method , Object[]
args)throwsThrowable { if(isSetSomething(method)) { /* rememberargs
=column */ } if(isAddBatch(method)) { /*adda new row */ } try{
return method.invoke ( this . target ,
args);}catch(BatchUpdateException e) { /*logrememberedrows in the
batch*/ throwe; } finally{ if(isExecuteBatch(method)) { /*reset
rememberedrows */ } } } ... Ex.: Log data of a failed batch (2)
14.
15. Build-time weaving 16. Somehow low-level 17. Limited power
18. Weaving manually / custom Ant task For an example, see the
accompanying source code project and blog post. For an alternative
w/o most cons see GluonJ. 2. The independent Javassist 19. 3. The
almighty AspectJ
20. Build-time/load-time weaving 21. Weaving with Ant or Java
agentlib 22. Depends on AspectJ libraries at the run-time 23.
@Aspect public classLoggingAspect { @Around ( "execution(private
void TooQuiet3rdPartyClass.failingMethod(Object))" ) publicObject
interceptAndLog(ProceedingJoinPoint invocation)throwsThrowable {
try{ returninvocation.proceed(); }catch(Exception e) { thrownew
RuntimeException( "Failed for: "+ invocation.getArgs()[0] , e); } }
} Ex.: Include argument in exception 24. What it can do
- Troubleshooting: Improved logging, ...
25. Cross-cutting concerns: Security, transactions, traits, ...
- see EJBs 26. Testing:code coverage, mutation testing, ... 27.
Code injection/AOP is great but don'toveruse it see Glassbox.sf.net
28. Thank you!
- Much more detailed explanation with more topics and a link to
full source codes:
29. http://bit.ly/codeinject 30. feedback via the blog post's
comments welcomed! 31. Bonus slides 32. // Advice
my.example.TargetClass.myMethod(..) with a before and afteradvices
finalClassPool pool = ClassPool. getDefault (); finalCtClass
compiledClass = pool.get( "my.example.TargetClass" ); finalCtMethod
method =compiledClass .getDeclaredMethod( "myMethod" );
method.addLocalVariable( "startMs" , CtClass. longType );
method.insertBefore( "startMs = System.currentTimeMillis();" );
method.insertAfter( "{final long endMs =
System.currentTimeMillis(); System.out.println("Executed in ms: " +
(endMs-startMs));}" ); compiledClass.writeFile(
"/tmp/javassist/modifiedClassesFolder" ); // Enjoy the new / tmp
/javassist/my/example/TargetClass.class Ex: Performance monitoring
withJavassist
