Why Groovy file write with UTF-16LE produce BOM char? - encoding

Question

Do you have idea why first and secod lines below do not produce BOM to the file and third line does? I thought UTF-16LE is correct encoding name and that encoding does no create BOM automatically to beginning of the file.
new File("foo-wo-bom.txt").withPrintWriter("utf-16le") {it << "test"}
new File("foo-bom1.txt").withPrintWriter("UnicodeLittleUnmarked") {it << "test"}
new File("foo-bom.txt").withPrintWriter("UTF-16LE") {it << "test"}
Another samples
new File("foo-bom.txt").withPrintWriter("UTF-16LE") {it << "test"}
new File("foo-bom.txt").getBytes().each {System.out.format("%02x ", it)}
prints
ff fe 74 00 65 00 73 00 74 00
and with java
PrintWriter w = new PrintWriter("foo.txt","UTF-16LE");
w.print("test");
w.close();
FileInputStream r = new FileInputStream("foo.txt");
int c;
while ((c = r.read()) != -1) {
System.out.format("%02x ",c);
}
r.close();
prints
74 00 65 00 73 00 74 00
With Java is does not produce BOM and with Groovy there is BOM.

Answer 1

There appears to be a difference in behavior with withPrintWriter. Try this out in your GroovyConsole
File file = new File("tmp.txt")
try {
String text = " "
String charset = "UTF-16LE"
file.withPrintWriter(charset) { it << text }
println "withPrintWriter"
file.getBytes().each { System.out.format("%02x ", it) }
PrintWriter w = new PrintWriter(file, charset)
w.print(text)
w.close()
println "\n\nnew PrintWriter"
file.getBytes().each { System.out.format("%02x ", it) }
} finally {
file.delete()
}
It outputs
withPrintWriter
ff fe 20 00
new PrintWriter
20 00
This is because calling new PrintWriter calls the Java constructor, but calling withPrintWriter eventually calls org.codehaus.groovy.runtime.ResourceGroovyMethods.writeUTF16BomIfRequired(), which writes the BOM.
I'm uncertain whether this difference in behavior is intentional. I was curious about this, so I asked on the mailing list. Someone there should know the history behind the design.
Edit: GROOVY-7465 was created out of the aforementioned discussion.