Easiest way to unpack a jar in java

Question

Basically, I have a jar file that i want to unzip to a specific folder from a junit test.

What is the easiest way to do this? I am willing to use a free third party

Answer 1

Here's my version in Scala, would be the same in Java, that unpacks into separate files and directories:

import java.io.{BufferedInputStream, BufferedOutputStream, ByteArrayInputStream}
import java.io.{File, FileInputStream, FileOutputStream}
import java.util.jar._

def unpackJar(jar: File, target: File): Seq[File] = {
  val b   = Seq.newBuilder[File]
  val in  = new JarInputStream(new BufferedInputStream(new FileInputStream(jar)))

  try while ({
    val entry: JarEntry = in.getNextJarEntry
    (entry != null) && {
      val f = new File(target, entry.getName)
      if (entry.isDirectory) {
        f.mkdirs()
      } else {
        val bs  = new BufferedOutputStream(new FileOutputStream(f))
        try {
          val arr = new Array[Byte](1024)
          while ({
            val sz = in.read(arr, 0, 1024)
            (sz > 0) && { bs.write(arr, 0, sz); true }
          }) ()
        } finally {
          bs.close()
        }
      }
      b += f
      true
    }
  }) () finally {
    in.close()
  }

  b.result()
}