Why does the code execution never enter the catch block (java)?

Question

I am trying to throw a (custom) ImportException from the method importUsers in class UserHelper. I can see in the debugger that the throw clause is executed, but the method, from which the importUsers method is called, never catches the exception.

Here is the method, where the exception is thrown:

public static AccessorValidator importUsers(List<String> data, WebUser actor) throws ImportException {

    //(irrelevant code removed)

    try {
        isSuccess = insertUserData(st, blocks, db, actor);
    } catch (Exception e) {
        throw new ImportException("Could not insert user on line " + rowCounter);
    }

}

Here I try unsuccessfully to catch the thrown exception from execute method in AccessorValidator class:

    public ActionForward execute(ActionMapping mapping, ActionForm form, HttpServletRequest request,
        HttpServletResponse response) throws Exception {
    //(irrelevant code removed)
    try{
        av = UserHelper.importUsers(data, admin);
        System.out.print("test2");
    } catch (ImportException ie) {
        System.out.print("testE");
        returnMessageValue = ie.getMessage();
    } catch (Exception e) {
        System.out.print("testE2");
    }

The output is "test2", and the code execution never gets to either of the catch blocks. What do I do wrong?

Answer 1

try changing your method to

try {
    isSuccess = insertUserData(st, blocks, db, actor);
    system.out.print("after insertUserData");
} catch (Exception e) {
    System.out.print("before throwing");
    throw new ImportException("Could not insert user on line " + rowCounter);
}

so that you can make sure that what you see in debug is what actually being executed (by checking your console), and whether insertUserData actually throws an exception or not.

Answer 2

If "test2" is printed, then there is no exception at all being thrown by importUsers().

The line information in the debugger can be inaccurate. Try putting a breakpoint in the constructor of the Exception to see if it's really being created.

Answer 3

perhaps insertUserData() doesn't throw any exception in your test setup? It would help if that method was included in your question as well...

Answer 4

Are you sure that insertUserData actually throws an exception, and not only returns a true/false boolean? Seeing the debugger step to a line with a "throw" does not mean that something is thrown, as the line information is not always completely accurate.

Answer 5

Check the following, by order:

1. check that your breakpoints are synchronized with the source code
2. insertUserData() is not throwing an exception at all, verify if, at all, it should be throwing an exception or not. Looks like you are expecting something that never comes.
3. Check that ImportException is indeed the same object in both cases you refer to it

Answer 6

If the output is "test2" then certainly the exception was not thrown.

Just guessing ...

Sometimes your IDE may not be synchronized with the source code that is actually executing, specially if your code is part of an external library... If you change the library's code and don't update the actual classpath, or if that change happens while debugging, the lines of code may change and you may be seeing the exception to be thrown although that isn't really happening.

Answer 7

Problem solved. It appears that the try-catch block in method importUsers was surrounded by another try-catch block, which did not throw the ImportException. So the first catch block was working correctly, I just missed the second one.

Answer 8

try to catch a Throwable, the root of Exception and Error, with:

try{
        av = UserHelper.importUsers(data, admin);
        System.out.print("test2");
    } catch (ImportException ie) {
        System.out.print("testE");
        returnMessageValue = ie.getMessage();
    } catch (Exception e) {
        System.out.print("testE2");
    } catch (Throwable t) {
        // Here you'll catch *anything* else
        System.out.print("testTE");
    }