Common Alerting Protocol Library
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Common Alerting Protocol Library Build Status

Copyright 2014 Google Inc.

The CAP Library is a collection of code and tools to work with public alerting messages in the Common Alerting Protocol format.

Namely, a well-tested and easy-to-use Java library that supports

  • creation and parsing of feeds in the CAP format,
  • validating of feeds against common CAP profiles.

Moreover, it includes a simple web application to validate the correctness of CAP messages.


The CAP Library is designed to support CAP versions 1.0, 1.1, and 1.2. There are classes that can parse XML CAP messages as well as easily create new messages and write them to XML, JSON, (soon) ASN.1, and (soon) KML.

The main data structures are auto-generated from a Google protocol buffer implementation of the CAP spec in proto/cap.proto. Protocol buffers are Google's language-neutral, platform-neutral, extensible mechanism for serializing structured data - think XML, but smaller, faster, and simpler.

The generated classes offer a clean API for creating and manipulating alert objects. The alert data structures are immutable; they provide only getters. New alerts are constructed via Builder classes. See javatests/com/google/publicalerts/cap/, for an example.

javatests/com/google/publicalerts/cap/ provides a good overview of how to get started using the library.

To learn more about Google protocol buffers, see and


Install ant

You can download and install Apache Ant from

Run all tests

» APPENGINE_JAVA_SDK=/path/to/appengine-sdk ant test

Compile the library into a jar

» cd java
» ant jar

Compile and run the validator

» cd validator
» APPENGINE_JAVA_SDK=/path/to/appengine-sdk ant runserver