I'm doing some work using the JavaMail API, and I've run across encodings which Java doesn't support natively (by design), such as UTF7/unicode-1-1-utf-7. For that encoding in particular I found the JUTF7 implementation of a Java Charset and CharsetProvider for UTF7. However, having added the jutf7.jar to my classpath I still get UnsupportedEncodingExceptions, and unicode-1-1-utf-7 is definitely one of JUTF7's aliases.
Is there a way to manually load the Charset or ensure that the Charset is being loaded so that I can rule that out as a cause?
There's a bit more to using a new Charset, apart from putting the necessary classes into the classpath. To quote the Javadocs:
A charset provider identifies itself with a provider-configuration file named java.nio.charset.spi.CharsetProvider in the resource directory META-INF/services. The file should contain a list of fully-qualified concrete charset-provider class names, one per line. [...]
( http://download.oracle.com/javase/6/docs/api/java/nio/charset/spi/CharsetProvider.html )
Is this special file present in the JAR?
You should make sure the jar is loaded by the main classloader. You can achieve this by adding the jar to the JVM's jre/lib/ext extension directory, or by adding it to the classpath of the main program. For example if you are using Tomcat, add -cp /path/to/jutf7.jar to Tomcat's startup script.
Similarly, if you want to test jutf7 from the scala REPL, you need to start it as follows
env JAVA_OPTS="-cp /path/to/jutf7-1.0.0.jar" scala
Tested with Java HotSpot(TM) 64-Bit Server VM (build 20.8-b03-424, mixed mode)
来源：https://stackoverflow.com/questions/6308587/loading-a-java-charset-manually