Drawing arrows in JavaFX

byRafal Rusin
March 7, 2011
1 minute read

Some time in the past, I was wondering what’s the easiest solution for drawing arrowconnections between shapes. The problem boils down to computing boundary point for given shape, which intersects with connecting line.
The solution is not so difficult when we consider polygon shapes. But it becomes more difficult considering curves and far more difficult for generic SVG shapes.
In this article, I show a simple way to find such boundary points for generic SVG shapes, utilizing JavaFX “contains” method and simple bisection algorithm.
Following application does the job: Launch JNLP,Browse on GitHub.
Application allows to drag shapes to track shape boundaries.

So, “contains” method in JavaFX allows us to poll any 2D point for intersection with SVG shape. Next, we need to assume, that we know a point inside a shape, from which every ray has exactly one intersection. This includes star-like shapes and ellipses. Next, we can use simple bisection algorithm to find such boundary point. We cut off once length between two points is too small. Following snippet does the job:

Next, we need to draw arrows on the ends. In order to do that, we can use JavaFX Affine Transform, which is matrix transformation for SVG path. We need to compute transformation vectors for the matrix. This sounds scarry, but in fact is relatively easy. First vector in matrix is (targetPoint – sourcePoint) / length. Second one is perpendicular to it. Following code applies transformation:

Tags:
java

Rafal Rusin

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DDevelopment & Design

Spring Security by example: securing methods

byJakub Nabrdalik
March 30, 2011

This is a part of a simple Spring Security tutorial:

1. Set up and form authentication
2. User in the backend (getting logged user, authentication, testing)
3. Securing web resources
4. Securing methods
5. OpenID (login via gmail)
6. OAuth2 (login via Facebook)
7. Writing on Facebook wall with Spring Social

Securing web resources is all nice and cool, but in a well designed application it's more natural to secure methods (for example on backend facade or even domain objects). While we may get away with role-based authorization in many intranet business applications, nobody will ever handle assigning roles to users in a public, free to use Internet service. We need authorization based on rules described in our domain.

For example: there is a service AlterStory, that allows cooperative writing of stories, where one user is a director (like a movie director), deciding which chapter proposed by other authors should make it to the final story.

The method for accepting chapters, looks like this:

DDevelopment & Design

Simple trick to DRY your Grails controller

byTomasz Kalkosiński
June 5, 2013

Grails controllers are not very DRY. It's easy to find duplicated code fragments in default generated controller. Take a look at code sample below. It is duplicated four times in show, edit, update and delete actions:

class BookController {
def show() {
def bookInstance = Book.get(params.id)
if (!bookInstance) {
flash.message = message(code: 'default.not.found.message', args: [message(code: 'book.label', default: 'Book'), params.id])
redirect(action: "list")
return
        }
        [bookInstance: bookInstance]
    }
}

Why is it duplicated?

There is a reason for that duplication, though. If you move this snippet to a method, it can redirect to "list" action, but it can't prevent controller from further execution. After you call redirect, response status changes to 302, but after method exits, controller still runs subsequent code.

Solution

At TouK we've implemented a simple trick to resolve that situation:

wrap everything with a simple withStoppingOnRender method,
whenever you want to render or redirect AND stop controller execution - throw EndRenderingException.

We call it Big Return - return from a method and return from a controller at once. Here is how it works:

class BookController {
def show(Long id) {
withStoppingOnRender {
Book bookInstance = Book.get(id)
validateInstanceExists(bookInstance)
            [bookInstance: bookInstance]
        }
    }

protected Object withStoppingOnRender(Closure closure) {
try {
return closure.call()
        } catch (EndRenderingException e) {}
    }

private void validateInstanceExists(Book instance) {
if (!instance) {
flash.message = message(code: 'default.not.found.message', args: [message(code: 'book.label', default: 'Book'), params.id])
redirect(action: "list")
throw new EndRenderingException()
        }
    }
}

class EndRenderingException extends RuntimeException {}

Example usage

For simple CRUD controllers, you can use this solution and create some BaseController class for your controllers. We use withStoppingOnRender in every controller so code doesn't look like a spaghetti, we follow DRY principle and code is self-documented. Win-win-win! Here is a more complex example:

class DealerController {
@Transactional
def update() {
withStoppingOnRender {
Dealer dealerInstance = Dealer.get(params.id)
validateInstanceExists(dealerInstance)
validateAccountInExternalService(dealerInstance)
checkIfInstanceWasConcurrentlyModified(dealerInstance, params.version)
            dealerInstance.properties = params
saveUpdatedInstance(dealerInstance)
redirectToAfterUpdate(dealerInstance)
        }
    }
}