gpakosz/UnicodeBOMInputStream

UnicodeBOMInputStream

A helper class to skip Unicode BOMs at the beginning of input streams.

I initially released this class as a Stack Overflow answer and it apparently got copy-pasted into several Java projects already. However, code put as answers on Stack Overflow is licensed under CC-BY-SA 3.0 which may not suit everybody.

Why?

Many years have passed since I wrote this class and today Java still doesn't properly deal with UTF-8 Unicode Byte Order Marks (BOMs) at the beginning of data.

In 2001, someone opened bug JDK-4508058 with the sound expectation that Java should detect and skip UTF-8 BOMs at the beginning of UTF-8 streams, the same way it does for e.g. UTF-16.

Bug JDK-4508058 remained open for a while, got fixed, and ultimately got reverted because existing Java code relied on UTF-8 BOMs not being skipped, see JDK-6378911:

the Java EE 5 RI and SJSAS 9.0 has been relying on detecting a BOM, setting the appropriate encoding, and discarding the BOM bytes before reading the input

The problem is that we cannot implement different behaviour depending on the JRE version we're running against.

In the end, instead of fixing JDK-4508058 and accept this would be an annoyance only for Java EE 5 RI and SJSAS 9.0 users, people in charge at Sun couldn't be bothered supporting 2 JDK versions and decided we're all living in a better world if JDK-4508058 gets closed as "won't fix".

In 2010, someone opened bug JDK-6959785 to reconsider the decision...

For more than 20 years now, every now and then, someone in the world edits an XML file with Notepad.exe which adds useless UTF-8 BOMs, and breaks their favorite Java XML parser.

Meanwhile, just skip the BOM yourself.

Usage

Wrap any InputStream with UnicodeBOMInputStream and use the getBOM() and/or skipBOM() methods. See UnicodeBOMInputStreamUsage.java.

If you find this library useful and decide to use it in your own projects please drop me a line @gpakosz.