sudo chmod a+x /usr/bin/java
sudo chmod a+x /usr/bin/javac
sudo chmod a+x /usr/bin/javaws
sudo chown -R root:root /usr/lib/jvm/jdk1.8.0

So basically 777 just to be sure that the permissions are correct.

There is so much wrong with that phrase... 777 are -almost always- the wrong permissions. 777 would let anyone execute the program, but 755 would have worked perfectly as well.

Is the provider able to disallow the user to run any executables in his home directory?

Yes. If they mount the home directories with noexec flag they can produce the behavior you are seeing (mount command may show you the mount flags, if you're not too constrained).

You may be able to work around it with a command such /lib64/ld-linux-x86-64.so.2 bin/java

It's also possible that the permission denied is for one of the libraries your java binary depends on.

To create a File into the same folder in your project, your path has to be relative.

The path that you are giving is absolute, because it is starting from /. For your path to be relative, remove / from the path and try this :

File file = new File("textfile.txt");

Like the message says, you probably don't have permissions to read that file. To troubleshoot, you can add:

System.out.println(sourceFile.getAbsolutePath());

to find the exact location of the file that you're trying to read and then checking the file system permissions for it:

ls -la <path to your file>

Verify that you have the r permission, otherwise this is the error that you get.

Try sudo chmod a+x /usr/bin/java

for it to work you need to be able to use the command "java"
could you try adding the binary directly to settings.conf?
you can find the binary on any linux distro by using the command

sudo find / -name "libjli.so" | sed "s/\/lib\/\(i386\|amd64\)\/jli\/libjli.so/\/bin\/java/g"

example for the settings in settings.conf can be found inside settings.conf.example

I had a similar problem and the solution was to chmod +x lib/jspawnhelper in the JRE folder.