Using eclipse in order to find the opencv native library doesn't work - eclipse

Question

I'm attempting to use opencv on an ubuntu installation and am following this tutorial. Everything seemed fine and it even listed amongst the installed parts so I proceeded into this tutorial. This went well up until the moment where you have to add opencv as a user library as it was not amongst the (completely empty) list of libraries found. I have looked throughout the opencv folder and can't find anything like a library either am I missing something? Any idea on how to fix this?
Note that it did manage to produce .jar file however the library is still missing. If it matters opencv is installed in usr/local/src.
If in order fix this you require any extra information feel free to ask in the comments.
This might have something to do with the problem:
ulap:/usr/local/src/opencv-2.4.8/opencv/build/bin$ ant -DocvJarDir=path/to/dir/containing/opencv-248.jar -DocvLibDir=/usr/local/src/opencv-2.4.8/opencv/build/bin /opencv_java248/native/library
Buildfile: /usr/local/src/opencv-2.4.8/opencv/build/bin/build.xml
BUILD FAILED
Target "/opencv_java248/native/library" does not exist in the project "SimpleSample".
Total time: 0 seconds
thijs#thijs-ulap:/usr/local/src/opencv-2.4.8/opencv/build/bin$ ant -DocvJarDir=path/to/dir/containing/opencv-248.jar -DocvLibDir=/usr/local/src/opencv-2.4.8/opencv/build/bin /opencv_java248/native/library
Buildfile: /usr/local/src/opencv-2.4.8/opencv/build/bin/build.xml
BUILD FAILED
Target "/opencv_java248/native/library" does not exist in the project "SimpleSample".
Total time: 0 seconds
This is my build.xml:
<property name="src.dir" value="src"/>
<property name="lib.dir" value="${ocvJarDir}"/>
<path id="classpath">
<fileset dir="${lib.dir}" includes="**/*.jar"/>
</path>
<property name="build.dir" value="build"/>
<property name="classes.dir" value="${build.dir}/classes"/>
<property name="jar.dir" value="${build.dir}/jar"/>
<property name="main-class" value="${ant.project.name}"/>
<target name="clean">
<delete dir="${build.dir}"/>
</target>
<target name="compile">
<mkdir dir="${classes.dir}"/>
<javac includeantruntime="false" srcdir="${src.dir}" destdir="${classes.dir}" classpathref="classpath"/>
</target>
<target name="jar" depends="compile">
<mkdir dir="${jar.dir}"/>
<jar destfile="${jar.dir}/${ant.project.name}.jar" basedir="${classes.dir}">
<manifest>
<attribute name="Main-Class" value="${main-class}"/>
</manifest>
</jar>
</target>
<target name="run" depends="jar">
<java fork="true" classname="${main-class}">
<sysproperty key="java.library.path" path="${ocvLibDir}"/>
<classpath>
<path refid="classpath"/>
<path location="${jar.dir}/${ant.project.name}.jar"/>
</classpath>
</java>
</target>
<target name="rebuild" depends="clean,jar"/>
<target name="rebuild-run" depends="clean,run"/>
running
ulap:/usr/local/src/opencv-2.4.8/opencv/samples/java/ant$ ant -DocvJarDir=/usr/local/src/opencv-2.4.8/opencv/build/bin rebuild-run
gave me:
clean:
compile:
[mkdir] Created dir: /usr/local/src/opencv-2.4.8/opencv/samples/java/ant/build/classes
[javac] Compiling 1 source file to /usr/local/src/opencv-2.4.8/opencv/samples/java/ant/build/classes
jar:
[mkdir] Created dir: /usr/local/src/opencv-2.4.8/opencv/samples/java/ant/build/jar
[jar] Building jar: /usr/local/src/opencv-2.4.8/opencv/samples/java/ant/build/jar/SimpleSample.jar
run:
[java] Exception in thread "main" java.lang.UnsatisfiedLinkError: no opencv_java248 in java.library.path
[java] at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1709)
[java] at java.lang.Runtime.loadLibrary0(Runtime.java:844)
[java] at java.lang.System.loadLibrary(System.java:1051)
[java] at SimpleSample.<clinit>(Unknown Source)
[java] Could not find the main class: SimpleSample. Program will exit.
[java] Java Result: 1
rebuild-run:
BUILD SUCCESSFUL
Total time: 1 second

Answer 1

According to the first tutorial (how to build OpenCV from source), the result should be a JAR file and a .so native lib in the bin/ directory of your OpenCV directory. In the "SETTING UP ECLIPSE FOR USING OPENCV (JAVA) IN UBUNTU" tutorial, you must create the User Library by following the steps in the tutorial. That process involves browsing your file system to select the OpenCV JAR that was produced by the first tutorial and then selecting the .so file as the native library. Eclipse will not automatically "find" your OpenCV library, you have to configure it to know about it, that's what the second tutorial is doing.

Answer 2

I think you were running the wrong command with ant. You can read the manual here: https://ant.apache.org/manual/running.html
Below is the format to run ant:
ant [options] [target [target2 [target3] ...]]
So maybe your command line should look like:
ant -DocvJarDir=/usr/local/src/opencv-2.4.8/opencv/build/bin rebuild-run
given that /usr/local/src/opencv-2.4.8/opencv/build/bin contains the opencv-248.jar
As shown on your build.xml file that the property ocvJarDir is pointing to the location of the classpath requires to build the project:
<property name="lib.dir" value="${ocvJarDir}"/>
<path id="classpath">
<fileset dir="${lib.dir}" includes="**/*.jar"/>
</path>
And you need to specify the target "rebuild-run" in the command line since your build.xml does not have a default target specified.

Answer 3

Try installing 2.4.6 version. I have similar problems when installing in VS. Older version worked. Maybe it's the same in Eclipse, too.