java - How to copy files out of the currently running jar

Question

I have a .jar that has two .dll files that it is dependent on. I would like to know if there is any way for me to copy these files from within the .jar to a users temp folder at runtime. here is the current code that I have (edited to just one .dll load to reduce question size):

public String tempDir = System.getProperty("java.io.tmpdir");
public String workingDir = dllInstall.class.getProtectionDomain().getCodeSource().getLocation().getPath();

public boolean installDLL() throws UnsupportedEncodingException {

try {
             String decodedPath = URLDecoder.decode(workingDir, "UTF-8");
             InputStream fileInStream = null;
             OutputStream fileOutStream = null;

             File fileIn = new File(decodedPath + "\loadAtRuntime.dll");
             File fileOut = new File(tempDir + "loadAtRuntime.dll");

             fileInStream = new FileInputStream(fileIn);
             fileOutStream = new FileOutputStream(fileOut);

             byte[] bufferJNI = new byte[8192000013370000];
             int lengthFileIn;

             while ((lengthFileIn = fileInStream.read(bufferJNI)) > 0) {
                fileOutStream.write(bufferJNI, 0, lengthFileIn);
             }

            //close all steams
        } catch (IOException e) {
      e.printStackTrace();
             return false;
        } catch (UnsupportedEncodingException e) {
             System.out.println(e);
              return false;
        }

My main problem is getting the .dll files out of the jar at runtime. Any way to retrieve the path from within the .jar would be helpful.

Thanks in advance.

Answer 1

Since your dlls are bundeled inside your jar file you could just try to acasses them as resources using ClassLoader#getResourceAsStream and write them as binary files any where you want on the hard drive.

Here is some sample code:

InputStream ddlStream = <SomeClassInsideTheSameJar>.class
    .getClassLoader().getResourceAsStream("some/pack/age/somelib.dll");

try (FileOutputStream fos = new FileOutputStream("somelib.dll");){
    byte[] buf = new byte[2048];
    int r;
    while(-1 != (r = ddlStream.read(buf))) {
        fos.write(buf, 0, r);
    }
}

The code above will extract the dll located in the package some.pack.age to the current working directory.