Copying a folder from a .jar file

Question

I created a class called FileCopyFromJAR that has a static method called copy. This allows me to copy files to outside of the JAR by using getResourceAsStream:

 public static void copy(String source,String dest) throws IOException{
    try{
        File sourceFile = new File(source);
        File destFile = new File(dest);
        InputStream in = FileCopyFromJAR.class.getResourceAsStream(source);
        OutputStream out = new FileOutputStream(destFile);
        int bufferSize = 1024;
        byte[] buf = new byte[bufferSize];
        int len;
        while ((len = in.read(buf)) > 0){
            out.write(buf,0,len);
        }
        in.close();
        out.close();
    }
    catch(IOException e){
        throw e;
    }
}

Inside my code, I will call this by doing something like (this assumes test.txt is in the root of my .jar file):

FileCopyFromJAR.copy("/test.txt","c:\\test.txt");

However, I get a FileNotFoundException if I specify a folder or a file inside a folder. Both of these return an error:

FileCopyFromJAR.copy("folder\test.txt","c:\\test.txt");
FileCopyFromJAR.copy("folder", "c:\\folder");

I've also tried using various combinations like /folder\test.txt, etc. but nothing seems to work. Is there a way to make this work or do I have to use a different method?

This is a duplicate of a question I just had put a bounty on, let me try to find it. — djechlin, Jun 26 '14 at 22:08
possible duplicate of [Copy directory from a jar file](http://stackoverflow.com/questions/1386809/copy-directory-from-a-jar-file) — djechlin, Jun 26 '14 at 22:18
@MadProgrammer yes, I just made sure. I tried FileCopyFromJAR.copy("folder\\test.txt", "c:\\test.txt"); I get a NullPointerException. — Trinculo, Jun 26 '14 at 22:26
@boolean - it says line 25, which is " while ((len = in.read(buf)) > 0){". I tried using the File.pathSeparator with the same results. — Trinculo, Jun 26 '14 at 22:45
Maybe this approach is just wrong. Any other ideas to extract a folder that is inside a JAR file to outside the JAR? — Trinculo, Jun 26 '14 at 22:47
Can you post the implementation of FileCopyFromJAR.class.getResourceAsStream(source);? — Typo, Jun 26 '14 at 22:48
@boolean Not sure that I understand. The entire class FileCopyFromJAR contains only this static method along with a main class I am using to test it. — Trinculo, Jun 26 '14 at 22:52
To read a JAR as a pseudo-directory, use the methods of java.util.zip. — Hot Licks, Jun 26 '14 at 23:53

Trinculo · Accepted Answer · 2014-06-27T04:32:40.030

2

I figured it out! I broke out my "Core Java Volume 1" 9th edition book and it says "Note that you must always use / separator, regardless of the directory separator on the system that actually stores the resource files." (Horstmann, page 571, chapter 10.1 JAR Files).

So this works:

FileCopyFromJAR.copy("/folder/test.txt", "c:\\test12.txt");

Hope this helps anyone out there! It was driving me crazy!

edited Jun 27 '14 at 04:32

answered Jun 26 '14 at 23:54

Trinculo

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Typo · Answer 2 · 2014-06-26T23:46:57.117

According to the class.getResourceAsStream documentation : "The rules for searching resources associated with a given class are implemented by the defining class loader of the class. "

And then for loader class we have:

Any class name provided as a String parameter to methods in ClassLoader must be a binary name as defined by the Java Language Specification.

Examples of valid class names include:

"java.lang.String"
"javax.swing.JSpinner$DefaultEditor"
"java.security.KeyStore$Builder$FileBuilder$1"
"java.net.URLClassLoader$3$1"

Before delegation, an absolute resource name is constructed from the given resource name using this algorithm:

If the name begins with a '/' ('\u002f'), then the absolute name of the resource is the portion of the name following the '/'.
Otherwise, the absolute name is of the following form:
modified_package_name/name

Where the modified_package_name is the package name of this object with '/' substituted for '.' ('\u002e').

So you should use :

source = "Package_name" + ".folder.test" //remove the ".txt" from the file
FileCopyFromJAR.class.getResourceAsStream(source);

If I use "test.txt" and it is in the root of the .jar file, it works? In any case, when I called the static method using FileCopyFromJAR.copy("folder.test","c:\\test12.txt"); I still get a NullPointerException. This passes in folder.test to "source" in the static copy method. — Trinculo, Jun 26 '14 at 23:27

Copying a folder from a .jar file

2 Answers2