exceptions_test.rb

require 'java'
$CLASSPATH << "."

def foo
  foo
end

begin
 # These all work as expected:
 #
 # java.lang.Integer.decode('aaa')
 # Java::Thrower::throwError
 # Java::Thrower::throwOutOfMemoryError
 # Java::Thrower::throwStackOverflow
 # Java::Thrower::throwNPE

 # These don't work with rescue Exception:
 #
 # foo # this causes stack overflow and exits JRuby:
 # Error: Your application used more stack memory than the safety cap of 1024k.
 # Can be rescued with rescue java.lang.StackOverflowError though.
 #
 #
 # raise java.lang.NullPointerException.new("baaaa") # exits JRuby:
 #       NativeConstructorAccessorImpl.java:-2:in `newInstance0': java.lang.NullPointerException: baaaa
 #       from NativeConstructorAccessorImpl.java:39:in `newInstance'
 #       from DelegatingConstructorAccessorImpl.java:27:in `newInstance'
 #       from Constructor.java:513:in `newInstance'
 #
 #
 # a = ''; 1000000.times {a << String.new('a'*10000)} # produces OOME
 # Error: Your application used more memory than the safety cap of 500m.
rescue Exception => e
 puts "Caught in Ruby: #{e.class} -- #{e}"
end

Thrower.java

public class Thrower {

  public static void throwError() {
    System.err.println("About to throw Error");
    throw new UnknownError("Unknown Error");
  }
  
  public static void throwOutOfMemoryError () {
    System.err.println("About to throw OutOfMemoryError ");
    throw new OutOfMemoryError ("No Memory Error");
  }

  public static void throwNPE() {
    System.err.println("About to throw NPE");
    throw new NullPointerException("NPE");
  }
  
  public static void throwStackOverflow() {
    throwStackOverflow();
  }
}