Initially I thinked "oh it will very easy" but how wrong I was. The first problem is this:
How I can reference to file inside a jar?We must think that we cannot reference with an absolute or machine path: the project can be runned in hundreds of machines with hundreds of difference paths. So we must use a internal project path. Good. As first thing, read from this file. Java provides a fantastic method that which allows us to get an input stream from file with ponly passing as a parameter the name of file without the absolute path. For example: if my file inside jar has this name "pippo.txt" i can get an InputStream with this method:
getClass().getClassLoader().getResourceAsStream("pippo.txt")To read the file,do this:
InputStream stream = getClass().getClassLoader().getResourceAsStream("pippo.txt");
String sCurrentLine;
BufferedReader br = new BufferedReader(new InputStreamReader(stream ));StringBuilder string = new StringBuilder();
while ((sCurrentLine = br.readLine()) != null) {
string .append(sCurrentLine);
}
string.toString();Easy right? :)
But if I want to write inside a jar? This is a almost "impossible" task. You must think that a file inside a jar is as a file inside a .zip or .rar. Can you write a file inside a compress file? Yeah! But you must unzip the file, write the file and compressagain the entire package. In the same way works a file inside a jar. First you must extract all content of jar file, second you must write into file and third you must re-create the jar file and all of this operation you must do into your java code. It is an hell!
Usually the files inside a jar are a properties files: file that can be read and writed from other classes. But these files are special files: their are not a common files. If you think that for your application there is a file that can be write as text file, you should think a way to create this file outside of jar. For example you can say to a class inside a jar to produce a file at runtime execution to store in file system , save the path of file (you cannot save it on jar for the same problem described above: you cannot write inside a zip file.)and then the project that used this jar can ask to class to retrieve the path of this file and finally he can modify it.
