keensoft / pdf-signature-position

PDF visual signatures without overlapping

pdf-signature-position

Obtains a new visible signature position in a PDF that ensures no overlapping with existing ones.

Originally developed to avoid visible signature overlapping when using @firma MiniApplet repeatedly on the same document.

Generation

It's a usual Maven project:

mvn clean package

Use

The artifact it's a Java 5 Library. The invocation it's as simple as creating an instance and calling getNextPosition with an InputStream to the PDF document and the desired position.

PdfSignaturePosition psp = new PdfSignaturePosition();
SignaturePosition nextPosition = psp.getNextPosition(fis, position);

If null position is informed it will use defaults in properties:

signature.pdf.position.default.page=1

signature.pdf.position.default.lowerLeftX=40
signature.pdf.position.default.lowerLeftY=100
signature.pdf.position.default.upperRightX=130
signature.pdf.position.default.upperRightY=200

signature.pdf.position.default.margin=10

Signature position

The origin of coordinates is the lower left corner of the document.

The signature rectangle is informed by two points coordinates:

• Lower left corner
• Upper right corner

Positioning algorithm

The positioning algorithm is simple:

1. Check for overlapping or out of margins with current position.
2. Until no overlapping or out of margins repeat update position: i. If collision move right. ii. If out of right margin move one line up. iii. If out of top margin move to bottom line.

To avoid infinite loops the process is limited to 50 iterations and rises a RuntimeException if reached.

Log

Log is managed by Simple Logging Facade for Java (SLF4J).

Extension

The positioning algorithm can be redefined overriding updatePosition method.

protected void updatePosition(Rectangle signatureRectangle, Rectangle collision, boolean outInRight, boolean outInTop, float margin)

Visual representation

To ease tracing calculated positions in development, the library creates a visual representation when launched with system property signature.pdf.position.visual (constant provided):

System.setProperty(Simulator.SYSTEM_PROPERTY_ENABLE_VISUAL, "");

After the process ends it launchs a window showing:

where color boxes are:

• Blue - Document
• Black - Current visible signatures in document
• Red - Initial position
• Orange - Intermediate position
• Green - Final position returned