Easy Groovy Iteration

The problem

Let's say we want to check the correct mimetype and file extension of the file being uploaded. In a typical Java way I would write something like this:

boolean isRightType = "image/jpeg".equals(contentType)
    || "image/png".equals(contentType)
    || "image/x-png".equals(contentType);

boolean isRightFileExt = filename.endsWith(".png")
    || filename.endsWith(".jpg")
    || filename.endsWith(".jpeg");

Groovy solution

The Groovy way is much simpler and more elegant.

private static CONTENT_TYPES = ["image/jpeg", "image/png", "image/x-png"]
private static FILE_EXTENTIONS = [".png", ".jpg", ".jpeg"]
...
boolean isRightType = CONTENT_TYPES.any { it.equals(contentType) }
boolean isRightFileExt = FILE_EXTENTIONS.any { filename.endsWith(it) }

This was just a small example. What I really find useful are some of the following constructs that make my programming life really pleasant

Groovy Iteration

each

Simple collection iteration

def fibList = [1, 1, 2, 3, 5, 8, 13]
fibList.each { println it }  // prints all of the numbers in the list

any

If you need to find out if any element of the collection meets the condition.

def fibList = [1, 1, 2, 3, 5, 8, 13]
assert fibList.any { it == 3 }
assert fibList.any { it - 2 > 10 }

This is pretty much equivalent to a Java construct

boolean any(List list, Condition cond)
    for (E e : list) {
        if (cond.meets(e)) {
            return true;
        }
    }
    return false;
}

every

If you need to find out if any element of the collection meets the condition.

def fibList = [1, 1, 2, 3, 5, 8, 13]
assert fibList.every { it > 0 }

This is pretty much equivalent to a Java construct

boolean every(List list, Condition cond)
    for (E e : list) {
        if (!cond.meets(e)) {
            return false;
        }
    }
    return true;
}

collect

If you need to create a new collection that contains each element of the original collection transformed in some way.

def fibList = [1, 1, 2, 3, 5, 8, 13]
assert fibList.collect { it - 1 } == [0, 0, 1, 2, 4, 7, 12]

This is pretty much equivalent to a Java construct

List every(List list, Command command)
    List result = new ArrayList(list.size());
    for (E e : list) {
        result.add(command(e));
    }
    return result;
}

findAll

If you need to create a new collection that contains all elements that meet the condition.

def fibList = [1, 1, 2, 3, 5, 8, 13]
assert fibList.findAll { it > 1 && it < 5 } == [2, 3]

This is pretty much equivalent to a Java construct

List findAll(List list, Condition cond)
    List result = new ArrayList(list.size());
    for (E e : list) {
        if (!cond.meets(e)) {
            result.add(e);
        }
    }
    return result;
}

find

If you need to find first element that matches the condition.

def fibList = [1, 1, 2, 3, 5, 8, 13]
assert fibList.find { it > 1 } == 2

This is pretty much equivalent to a Java construct

E findAll(List list, Condition cond)
    for (E e : list) {
        if (!cond.meets(e)) {
            return e;
        }
    }
    return null;
}

References

• Groovy Makes Iteration Easy by Ted Naleid