Apache Jena - Is it possible to write to output the BASE directive? - serialization

Question

I just started using Jena Apache, on their introduction they explain how to write out the created model. As input I'm using a Turtle syntax file containing some data about some OWL ontologies, and I'm using the #base directive to use relative URI's on the syntax:
#base <https://valbuena.com/ontology-test/> .
And then writing my data as:
<sensor/AD590/1> a sosa:Sensor ;
rdfs:label "AD590 #1 temperatue sensor"#en ;
sosa:observes <room/1#Temperature> ;
ssn:implements <MeasureRoomTempProcedure> .
Apache Jena is able to read that #base directive and expands the relative URI to its full version, but when I write it out Jena doesn't write the #base directive and the relative URI's. The output is shown as:
<https://valbuena.com/ontology-test/sensor/AD590/1> a sosa:Sensor ;
rdfs:label "AD590 #1 temperatue sensor"#en ;
sosa:observes <https://valbuena.com/ontology-test/room/1#Temperature> ;
ssn:implements <https://valbuena.com/ontology-test/MeasureRoomTempProcedure> .
My code is the following:
Model m = ModelFactory.createOntologyModel();
String base = "https://valbuena.com/ontology-test/";
InputStream in = FileManager.get().open("src/main/files/example.ttl");
if (in == null) {
System.out.println("file error");
return;
} else {
m.read(in, null, "TURTLE");
}
m.write(System.out, "TURTLE");
There are multiple read and write commands that take as parameter the base:
On the read() I've found that if on the data file the #base isn't declared it must be done on the read command, othwerwise it can be set to null.
On the write() the base parameter is optional, it doesn't matter if I specify the base (even like null or an URI) or not, the output is always the same, the #base doesn't appear and all realtive URI's are full URI's.
I'm not sure if this is a bug or it's just not possible.

Answer 1

First - consider using a prefix like ":" -- this is not the same as base but makes the output nice as well.
You can configure the base with (current version of Jena):
RDFWriter.create()
.source(model)
.lang(Lang.TTL)
.base("http://base/")
.output(System.out);

Answer 2

It seems that the command used on the introduction tutorial of Jena RDF API is not updated and they show the reading method I showed before (FileManager) which now is replaced by RDFDataMgr. The FileManager way doesn't work with "base" directive well.
After experimenting I've found that the base directive works well with:
Model model = ModelFactory.createDefaultModel();
RDFDataMgr.read(model,"src/main/files/example.ttl");
model.write(System.out, "TURTLE", base);
or
Model model = ModelFactory.createDefaultModel();
model.read("src/main/files/example.ttl");
model.write(System.out, "TURTLE", base);
Although the model.write() command is said to be legacy on RDF output documentation (whereas model.read() is considered common on RDF input documentation, don't understand why), it is the only one I have found that allows the "base" parameter (required to put the #base directive on the output again), RDFDataMgr write methods don't include it.
Thanks to #AndyS for providing a simpler way to read the data, which led to fix the problem.

Answer 3

#AndyS's answer allowed me to write relative URIs to the file, but did not include the base in use for RDFXML variations. To get the xml base directive added correctly, I had to use the following
RDFDataMgr.read(graph, is, Lang.RDFXML);
Map<String, Object> properties = new HashMap<>();
properties.put("xmlbase", "http://example#");
Context cxt = new Context();
cxt.set(SysRIOT.sysRdfWriterProperties, properties);
RDFWriter.create().source(graph).format(RDFFormat.RDFXML_PLAIN).base("http://example#").context(cxt).output(os);