Question

I understand these are necessary…of course to write proper code, but is there a design pattern that will help avoid having to repeat try…catch blocks repeatedly in a class? For instance, I wrote a particular class that throws 5 different exceptions.

public void iterateComparatorResults(ArrayList<ComparatorValue> results) throws IOException, IllegalArgumentException, IntrospectionException, IllegalAccessException, InvocationTargetException {
    Iterator<ComparatorValue> iterator = results.iterator();
    for(int i=0; i<results.size(); i++) {
        //Set data variables.
        setBeans(results.get(i).getClientBean(), results.get(i).getServerBean());
        setValues(results.get(i).getClientValue(), results.get(i).getServerValue());

        if(results.get(i).isMatch()) {
            //Data matches.
            runIteratorTrueAction();
        } else if(results.get(i).getInnerBeans() != null){
            //Value is a nested bean. Iterate again.
            ArrayList<ArrayList<ComparatorValue>> innerResults = results.get(i).getInnerBeans();
            for(int r=0; r<innerResults.size(); r++) {
                iterateComparatorResults(innerResults.get(r));
            }

        } else {
            //Data does not match.
            runIteratorFalseAction();
        }
    }
}

Everytime I reference this particular method is any other class, I have to use a try catch block that looks like this.

try {
    beanComparator.setIteratorFalseAction(falseAction);
                beanComparator.iterateComparatorResults(beanComparator.compareBeans(contact, compareContact));
} catch (IllegalArgumentException e) {
    e.printStackTrace();
} catch (IOException e) {
    e.printStackTrace();
} catch (IntrospectionException e) {
    e.printStackTrace();
} catch (IllegalAccessException e) {
    e.printStackTrace();
} catch (InvocationTargetException e) {
    e.printStackTrace();
}

I am hoping there is some design pattern I can implement so I can create a separate class or something and hide all the try blocks in one place then reference that class and use the try blocks without actually having to write them. Similar to the way that other frameworks like Spring do? I just need a little direction on how to do this as I have no idea even where to begin.

Answer 1

I’m not sure how real-world your example is, but there’s no need to a) catch each exception separately, if you don’t handle them differently, or b) catch them at all, in many cases.

What you’re doing in your example, just printing a stack trace, is a bad idea in almost all cases. You’re printing messy information to a place where no one’s likely paying attention.

I follow two general guidelines:

1. Handle the exception at the point at which it’s thrown, if you can (to close an open file on a file access exception, for instance, or retry a troublesome interface (stupid unreliable bespoke USB devices…)).
2. Allow the exception to bubble up to a point higher in your stack, where you can catch all exceptions you can’t otherwise handle. Log them, display them, or kill your application, whatever makes the most sense.

I’ll illustrate the second point with some code, stolen from inspired by the Java tutorials.

private String readFirstLineFromFile(String path) throws IOException
{
    try (BufferedReader br = new BufferedReader(new FileReader(path)))
    {
        return br.readLine();
    }
}

Here, we’ve defined a method that attempts to read from a file. Lots of things can go wrong here, but there’s nothing the code at this level is going to do about that. Instead, it’s going to pass the buck to the method that called it, with the throws clause. That calling method may handle the exception itself, or pass the buck to its caller, with the same clause:

private String readAllTheFiles() throws IOException
{
    for (...)
    {
        readFirstLineFromFile(...);
    }
}

Now, there’s lots of debate around why Java requires the throws in this case. Many other languages don’t use them, for better or worse. You’ll often see RuntimeExceptions – exceptions that don’t require a throws clause. If your method might throw an exception that extends from RuntimeException, you don’t need to declare that fact in a throws.