传递java.lang.Object作为参数

Question

I know that passing a an Object is not a good practise. But in this case it seems the best solution to me.

public void doSomething(final Object obj) {
    // some code
    ...
    if (obj instanceof InputStream) {
            document = PDDocument.load((InputStream) obj);
    } else if (obj instanceof File) {
        document = PDDocument.load((File) obj);
    } else {
        throw new IllegalArgumentException("Argument must be an instance of " + InputStream.class.getName() + " or " + " " + File.class.getName() + ".");
    // more code
    ...
    }
}

An alternative solution would have more duplicated code (all the line before and after PDDocument.load(obj); )

public void doSomething(final InputStream obj) {
    // some code
    ...
    document = PDDocument.load(obj);
    // more code
    ...
    }
}

public void doSomething(final File obj) {
    // some code
    ...
    document = PDDocument.load(obj);
    // more code
    ...
    }
}

Due to the duplicated code I prefer the first solution.

Do you know any better solution to solve this problem?

Answer 1

Pass in the result of

PDDocument.load(specificallyTypedVariable)

as a parameter to the method.

---

This assumes that // some code isn't doing some kind of setup for the load call. If that's the case, you could pass in a Function<? super T, PDDocument> Function<? super T, PDDocument> along with the T you're going to load it from:

public <T> void doSomething(final T obj, Function<? super T, PDDocument> loader) {
  // some code
  PDDocument document = loader.apply(obj);
  // other code.
}

and invoke like:

doSomething(someFile, PDDocument::load);
doSomething(someInputStream, PDDocument::load);

Answer 2

Since PDDocument can load from an InputStream and you can obtain an InputStream from a File anyway, I'd suggest:

public void doSomething(final InputStream in)
{
    // some code
    document = PDDocument.load(in);
    // more code
}

public void doSomething(final File file)
{
    try (
        final InputStream in = new FileInputStream(file);
    ) {
        doSomething(in);
    } catch (IOException e) {
        throw new RuntimeException(e);
    }
}

Of course, handle errors accordingly!

---

Also, I don't understand why you don't return the document and put that processing in a method returning void ?

Answer 3

Move

// some code
...
document = PDDocument.load(obj);
// more code

to a separate private method which can only be called by the two above methods