问题
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?
回答1:
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?
回答2:
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