In the folder Libraries I added the folder that contains the jar file of epubcheck (http://code.google.com/p/epubcheck/). But for some reason it does not work.
I also added this line of code:
import com.adobe.epubcheck.api;
Am I missing something?


UPDATE
Even with all the jars in the Libraries folder… It still does not work.

Here is the instructions for adding lib to the code from epubchecker README:
USING AS A LIBRARY
You can also use EpubCheck as a library in your Java application.
EpubCheck public interfaces can be found in com.adobe.epubcheck.api
package. EpubCheck class can be used to instantiate a validation
engine. Use one of its constructors and then call validate() method.
Report is an interface that you can implement to get a list of the
errors and warnings reported by the validation engine (instead of the
error list being printed out).
OUTPUT
deps-jar:
Created dir: /Users/.../NetBeansProjects/epubValidation/build
Updating property file: /Users/.../NetBeansProjects/epubValidation/build/built-jar.properties
Created dir: /Users/.../NetBeansProjects/epubValidation/build/classes
Created dir: /Users/.../NetBeansProjects/epubValidation/build/empty
Created dir: /Users/.../NetBeansProjects/epubValidation/build/generated-sources/ap-source-output
Compiling 1 source file to /Users/.../NetBeansProjects/epubValidation/build/classes
/Users/.../NetBeansProjects/epubValidation/src/epubvalidation/EpubValidation.java:6: package com.adobe.epubcheck does not exist
import com.adobe.epubcheck.api;
1 error
/Users/.../NetBeansProjects/epubValidation/nbproject/build-impl.xml:915: The following error occurred while executing this line:
/Users/.../NetBeansProjects/epubValidation/nbproject/build-impl.xml:268: Compile failed; see the compiler error output for details.
BUILD FAILED (total time: 9 seconds)
To import the epubcheck you need to do the following:
Create a new Java project… Unchecked Create Main Class, this is the only way to make it work.
Right click on Libraries to select Add JAR/Folder…
Add JAR…
Add the other JARs.
New File… New Class…
Make sure that the package input is empty.
Write the import…
There you go.
I am not really sure why you have to do it this way… But that is the only way I found to solve the problem.