始终在Java中设置file.encoding系统属性是一个好主意吗？

Question

I think it is a good idea to always set file.encoding system property in Java application.

Suppose I do not set file.encoding . It means that Java will use a platform-dependent default charset (eg in String.getBytes ), which makes the whole application platform-dependent.

If we set -Dfile.encoding=UTF-8 , for example, we guarantee that such calls as String.getBytes work the same in any platform.

Does it make sense?

Answer 1

No, it doesn't necessarily make sense. If you want to read files that have not been created by your own application, on any platform, you'd better leave the file encoding as it is by default, because that's what you'll need to be able to read these files.

And if you read files created by your own applications, or by applications which use a well-known and specified file encoding, then you should simply use this encoding when instantiating your IO readers and writers.

For methods such as String.getBytes() just don't use them, and use String.getBytes(Charset) instead if you want to use a specific encoding instead of the platform's default one.

Answer 2

Conditionally yes. As JB mentioned, using the "platform default" may occasionally help when reading files generated by other local applications (or other remote ones on the same platform if you have a homogeneous server farm).

So, take the choice with care, but in general I'd say do it. The advice to always create your own readers isn't always possible. I believe in general that most things generating files that use extended characters end up using UTF-8 for it.

In the end, because many files are dependent on the choices made outside your control, it's going to come down to testing and customization, but I feel far more comfortable suggesting that you start with UTF-8 and downgrade as necessary than the inverse.

Answer 3

It is not generally a good idea to set the file.encoding System-Property, because this is not a supported configuration option in Java.

That means it may or may not work. Not working can mean Exceptions . To be precise problems of the sort "It works on Java 1.6, it works on Java 1.7 on Windows, BUT it does not work on Java 1.7 on Linux anymore."

The reason behind that is given here :

The "file.encoding" property is not required by the J2SE platform specification; it's an internal detail of Sun's implementations and should not be examined or modified by user code. It's also intended to be read-only; it's technically impossible to support the setting of this property to arbitrary values on the command line or at any other time during program execution.

The preferred way to change the default encoding used by the VM and the runtime system is to change the locale of the underlying platform before starting your Java program.