file - Convert URL to normal windows filename Java

Question

Is there a way to convert this:

/C:/Users/David/Dropbox/My%20Programs/Java/Test/bin/myJar.jar

into this?:

C:UsersDavidDropboxMy ProgramsJavaTestinmyJar.jar

I am using the following code, which will return the full path of the .JAR archive, or the /bin directory.

fullPath = new String(MainInterface.class.getProtectionDomain()
            .getCodeSource().getLocation().getPath());

The problem is, getLocation() returns a URL and I need a normal windows filename. I have tried adding the following after getLocation():

toString() and toExternalForm() both return:

file:/C:/Users/David/Dropbox/My%20Programs/Java/Test/bin/

getPath() returns:

/C:/Users/David/Dropbox/My%20Programs/Java/Test/bin/

Note the %20 which should be converted to space.

Is there a quick and easy way of doing this?

Answer 1

The current recommendation (with JDK 1.7+) is to convert URL → URI → Path. So to convert a URL to File, you would say Paths.get(url.toURI()).toFile(). If you can’t use JDK 1.7 yet, I would recommend new File(URI.getSchemeSpecificPart()).

Converting file → URI: First I’ll show you some examples of what URIs you are likely to get in Java.

                          -classpath URLClassLoader File.toURI()                Path.toUri()
C:Program Files          file:/C:/Program%20Files/ file:/C:/Program%20Files/   file:///C:/Program%20Files/
C:main.c++               file:/C:/main.c++         file:/C:/main.c++           file:///C:/main.c++
\VBOXSVRDownloads       file://VBOXSVR/Downloads/ file:////VBOXSVR/Downloads/ file://VBOXSVR/Downloads/
C:Résume.txt             file:/C:/R%c3%a9sume.txt  file:/C:/Résume.txt         file:///C:/Résume.txt
\?C:Windows (non-path) file://%3f/C:/Windows/    file:////%3F/C:/Windows/    InvalidPathException

Some observations about these URIs:

• The URI specifications are RFC 1738: URL, superseded by RFC 2396: URI, superseded by RFC 3986: URI. (The WHATWG also has a URI spec, but it does not specify how file URIs should be interpreted.) Any reserved characters within the path are percent-quoted, and non-ascii characters in a URI are percent-quoted when you call URI.toASCIIString().
• File.toURI() is worse than Path.toUri() because File.toURI() returns an unusual non-RFC 1738 URI (gives file:/ instead of file:///) and does not format URIs for UNC paths according to Microsoft’s preferred format. None of these UNC URIs work in Firefox though (Firefox requires file://///).
• Path is more strict than File; you cannot construct an invalid Path from “.” prefix. “These prefixes are not used as part of the path itself,” but they can be passed to Win32 APIs.

Converting URI → file: Let’s try converting the preceding examples to files:

                            new File(URI)            Paths.get(URI)           new File(URI.getSchemeSpecificPart())
file:///C:/Program%20Files  C:Program Files         C:Program Files         C:Program Files
file:/C:/Program%20Files    C:Program Files         C:Program Files         C:Program Files
file:///C:/main.c++         C:main.c++              C:main.c++              C:main.c++
file://VBOXSVR/Downloads/   IllegalArgumentException \VBOXSVRDownloads     \VBOXSVRDownloads
file:////VBOXSVR/Downloads/ \VBOXSVRDownloads      \VBOXSVRDownloads     \VBOXSVRDownloads
file://///VBOXSVR/Downloads \VBOXSVRDownloads      \VBOXSVRDownloads     \VBOXSVRDownloads
file://%3f/C:/Windows/      IllegalArgumentException IllegalArgumentException \?C:Windows
file:////%3F/C:/Windows/    \?C:Windows           InvalidPathException     \?C:Windows

Again, using Paths.get(URI) is preferred over new File(URI), because Path is able to handle the UNC URI and reject invalid paths with the ? prefix. But if you can’t use Java 1.7, say new File(URI.getSchemeSpecificPart()) instead.

By the way, do not use URLDecoder to decode a file URL. For files containing “+” such as “file:///C:/main.c++”, URLDecoder will turn it into “C:main.c??”! URLDecoder is only for parsing application/x-www-form-urlencoded HTML form submissions within a URI’s query (param=value&param=value), not for unquoting a URI’s path.

2014-09: edited to add examples.