Using Instrumentation to record unhandled exception

I think you should use ASM to manipulate bytecode directly. Here is algoritms:

1. Visit all try/catch blocks (see visitTryCatchBlock) and save all handler labels
2. Visit instructions until one of the handler labels met.

3. After handler label insert logging code

   GETSTATIC java/lang/System out
   LDC "exception X occured"
   INVOKEVIRTUAL java/io/PrintStream println (java/lang/String)V
   

And ensure that your javaagent works fine. Checkt that your MANIFEST.MF file contains proper premain declaration and enables class transformation.

---

About your current code. Here

 if (className.startsWith("com/alu/")) {
      return insertLog(className, classBeingRedefined, classfileBuffer);
 }

you transforming classes inside particular package. That classes contain code that, in particular, throw exceptions.

And here

 if(className.endsWith("Exception")){
     System.out.println("============= exception occured "+className);
 }

you log of class being retransfomed when it is first loaded by JVM, when its name ends with "Exception". Not when exception occured. But transforming exception is useless itself. So I guess you should proceed like this:

if (className.startsWith("com/alu/")) {
    System.out.println("============= class transformed "+ className);
    return insertLog(className, classBeingRedefined, classfileBuffer);
} 

So you could know that your agent at least works.

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You have to deal with code like this

    try {
        if(search.equals("Category")){
            //do operation
        }
    } catch (Exception e) {
    }

where exceptions are swallowed. You transform methods that they will be like this:

try {
    try {
        if(search.equals("Category")){
            //do operation
        }
    } catch (Exception e) {
    }
} catch (Exception e) {
    e.printStackTrace();
}

Of course, when exception was swallowed by the first catch, the second one never cathes it. Instead, you should transform existing catch blocks themself, to get the following code:

try {
    if(search.equals("Category")){
        //do operation
    }
} catch (Exception e) {
    e.printStackTrace();
}

Above I shown you how to achieve this with ASM.