Add support to read classpath from the CLASSPATH environment variable

[andirady]

Some workflows doesn't use maven, gradle or bazel. This PR allows the user to declare the CLASSPATH environment variable.

[brown]

Setting an explicit Java classpath is currently supported via the java.classPath JSON initialization parameter. I too use the language server with Java source code that is not compiled using Maven, Gradle, or Bazel. When I do, I configure my editor to supply the language server with a classpath and documentation path using java.classPath and java.docPath. By using JSON to make these settings, I can work on more than one project at a time in my editor, with each running language server receiving the right classpath for the project it is handling.

[andirady]

Setting an explicit Java classpath is currently supported via the java.classPath JSON initialization parameter. I too use the language server with Java source code that is not compiled using Maven, Gradle, or Bazel. When I do, I configure my editor to supply the language server with a classpath and documentation path using java.classPath and java.docPath. By using JSON to make these settings, I can work on more than one project at a time in my editor, with each running language server receiving the right classpath for the project it is handling.

Sometimes I just want to write a single file which is to be run using java source launcher. Or I can have the classpath stored in a file and I can use it like so:

export CLASSPATH=`cat classpath.txt`
vim hello.java

and in the hello.java, I can have the following:

///usr/bin/env java -cp `cat classpath.txt` $0 $@; exit
class myScript {
   /* ... */
}

If the lang server have support for CLASSPATH environment variable, I don't have to create a separate file.

[georgewfraser]

Can you please add a test @andirady ?

[andirady]

Can you please add a test @andirady ?

Done.

The behavior is, when it's a simple project and CLASSPATH is specified, it'll read from that environment variable, if the project uses a build tool, it's up to the build tool to handle the CLASSPATH.