Download Preamble Prerequisites Step 1 create a Java project

Source: https://jena.apache.org/tutorials/using_jena_with_eclipse.html
Preamble
Jena is a programmer's API (application programming interface) for Java semantic web applications. It isn't a program or tool that you run - if that is what you
are looking for, I would suggest perhaps TopBraid Composer as a good option. So the primary use of Jena is to help you write Java code that handles RDF
and OWL documents and descriptions. I use Eclipse as my Java development of choice, other environments are available, but I don't use them and so the
experience I can pass along is based on Eclipse.
Prerequisites
You will need to:
1. Download and install eclipse. This article was written with Eclipse 3.3.1, but the exact version number should not matter as the main Eclipse user
interface has been stable for a while.
2. Download and unzip Jena. At the time of writing, the current version of Jena is 2.5.5, but again it won't matter if you use a different version.
I'm going to use Windows for this tutorial, but the same steps apply to Linux and, I presume, MacOS. In fact, on my Windows machine I use a directory
structure similar to Linux: rather than c:\Documents and Settings\ijd as the base directory, I use c:\home\ijd. This is a personal choice that makes it
easier to write scripts that run on Linux and Cygwin on Windows, but there's no special reason for you to do the same. However, it is often a good idea to
avoid path names with spaces in them if you can. So my Jena installation is in c:\home\ijd\projects\jena2. Wherever you see this path in the notes
below, substitute the location where you have installed your own copy of Jena.
Step-by-step guide
This tutorial really is aimed at Eclipse newcomers, so I'm going to take it a step at a time. Feel free to skip ahead if you have some experience with Eclipse
already.
Step 1 create a Java project
Eclipse organizes files into projects, so we need a project for this tutorial. Depending on the plugins installed, Eclipse may show a large number of different
types of project. A plain Java project is fine for a basic Jena application. If you want to, for example, develop a Java servlet that uses Jena, then choose a
suitable project type.
For clarity, I'm starting with an empty Eclipse workspace:
I need to
o create a new Java project:
Next I ne
eed to set up the
e internal structu
ure of the projecct. There are many schools of thought on this. I usually
u
use a ba
asic structure tha
at is taken from Maven.
Source ccode is in src/m
main, with Java code
c
in src/mai
in/java, ontolog
gies insrc/main
n/owl, etc. Compiled Java class
s files go into target/classes. So when
I create a new project, I edit the defaults
s to reflect these
e preferences. H
However, if the defaults suit you, or you don't kno
ow enough to ca
are about those details
ernatively, if yourr project or educcational institutio
on has suggested guidelines, the
en go with those
e.
yet, just accept the default settings. Alte
Step 2: create the hello world class
c
Java cod
de is stored in filles that correspo
ond to the declaration of a Java class, so I need
d to create a clas
ss for my hello world
w
example. In the project explorer
pane (wh
hich is on the lefft by default, butt you can move it around in Eclipse), I select the
e project's Java source folder an
nd right-click to get the context menu to
show:
Step 3: adding the
e Jena libraries
OK, so n
now let's write so
ome Jena code. The first thing I'll need to work w
with is a Model: a container for RDF statements
s. TheModel clas
ss is in
package
e com.hp.hpl.jena.rdf.model
l, so I'll first impo
ort that class, an
nd then create an instance of it.
OK, so why the red wavy lines? These are Eclipse's way of indicating a problem. If I tried to compile this code using javac on the command line, I'd get an
error saying that the package com.hp.hpl.jena.rdf.model can't be found anywhere, and that the class Model isn't defined. On the command line, I would
fix this by setting the Java classpath. Essentially, that's what I do in Eclipse too, but Eclipse makes it rather easier to do. Notice that I haven't actually said
anywhere yet that this is a Jena project. All I've said is that it's a Java project. What's the difference? Simply this: Eclipse has to know where to find the Jena
classes I would like to refer to from my program. Eclipse calls the locations where it can find the supporting code I want to refer to as the build path.
There are actually a few different ways of setting the build path in Eclipse. One way I could do it is to create a lib directory in my project top-level folder, then
copy the Jena .jar files there, and then link that directory to my project's build path. That works, but there's a better way: defining a user library. A user library
is a declaration of a library (collection of supporting code) that I can reference from any project. Once I have this set up once, I can use the same library
definition in multiple different projects. Moreover, if I subsequently update Jena to a new release, then once the library is updated every project in my Eclipse
workspace will see the new version. With the copy-files-to-the-lib-folder method, I have to re-copy to every project that uses Jena. Here's how I create the
Jena user library, starting from the Preferences menu:
Click new
w to create a new
w user-library:
Now I cliick on add jars tto add the .jar files from Jena. .jar files conta
ain the compiled Java libraries th
hat Jena uses, to
ogether with the
e Jena code itself
in jena.jar. The JAR sselection dialogu
ue that pops up a
allows me to select which .jar files are in my user-library. I hav
ve selected all of
o the .jar files in
i
the lib/
/ directory of my
y Jena install dire
ectory:
Result:
That's acctually enough to allow me to us
se Jena in Eclipsse, but there's a couple of additiional optional ste
eps that make programming
p
a bit
b easier. I can tell
t
Eclipse w
where to find the
e source code and the javadoc ffor the Jena classses (I'll show ho
ow that's helpfull later on). Next to the jena.jar
r entry in the use
er library,
there's a little + icon. Clicking that expan
nds the details o
of the .jar entryy:
I can telll Eclipse that the
e source code is
s in the src/ fold
der of my Jena in
nstall directory. I click on the So
ource attachmen
nt line, then the Edit...
E
button. In the
source a
attachment configuration dialogu
ue, I click the Exxternal folder buttton and then bro
owse to the right location:
Similarlyy, I can notify Ecclipse of the loca
ation of the Javad
doc by first selecting the Javado
oc location line of
o the library entry, then following a similar proce
ess.
Notice here that the loca
ation path is a URL (it starts fil
le:). This is because the locatio
on can also be a Javadoc web siite, though I'm not using that capability
here.
With the Jena user library configured, I click
c
OK to close
e the library configuration dialog
gue.
Step 4
4: Finishing tthe hello worrld program
Now I ca
an go back to myy project, and co
onfigure the Java
use the library I just created. To start, I right-click
k on the project node in the explorer
a build path to u
window tto bring up the p
project properties menu, navigatte to the build pa
ath menu option and add the library:
Having u
updated the build
d path, Eclipse will
w automaticallyy rebuild the pro
oject (i.e. recomp
pile the Java cod
de). With that, so
ome of the errorrs will go away, since
the impo
ort statement ca
an now find the class to be impo
orted, and so the
e Model class na
ame is meaningfful to the compiler.
However, there is still a remaining error because ModelFactory is not d
defined. What is
s needed is a suitable importsta
atement. This is easily fixed in Eclipse,
E
either byy clicking on the error symbol (th
he red 'x' on the left margin), or b
by positioning th
he cursor just aftter the ModelFac
ctory class nam
me, and pressing
g ctrlspace, w
which triggers Ecclipse to show th
he possible com
mpletions for the name:
When I sselect the first off the presented options
o
(i.e. Mod
delFactory rath
her than ModelFa
actoryBase), Ec
clipse will fill in the
t import statem
ment automatica
ally:
Look, ma
a, no errors!
Eclipse'ss auto-complete feature is also useful when add
ding code. For exxample, if I type Resou followed by ctrl-space I g
get the possible completions tha
at match
that nam
me:
Notice th
he Javadoc com
mment in yellow on
o the candidate
e completion (Re
esource in this case).
c
This extra
a information com
mes from having
g added the source code
and java
adoc locations w
when I specified the
t library in step 2, above. If yo
ou miss out spec
cifying the sourc
ce code and java
adoc, Eclipse can't be so helpful in
describin
ng possible auto
o-completions. Itt also will affect tthe debugging vview, though I'm not discussing that
t
in this article
e.
Here is tthe completed hello world progra
am:
Step 5
5: running the
e hello world
d program
To run th
his program with
hin Eclipse, I use
e the run menu, accessed from the button show
wing a white trian
ngle on a green circle.
c
Since I ha
aven't run any co
ode yet, I
have to ttell Eclipse whatt program to run
n. Click on the drrop-down menu to the right of th
he run button, an
nd tell Eclipse to run HelloRDFWorld as a Java
application:
Which gives the followin
ng output in the Eclipse
E
console::
And thatt's it: from emptyy Eclipse to a wo
orking RDF hello
o-world application. Obviously th
here is lot's more
e to learn (see th
he tutorial links at the top for som
me
jumping--off points), but h
hopefully you ca
an now have fun
n developing new
w semantic web applications!