如何从 jar:file URL 构造路径？

Question

How do I construct a Path to a jar:file URL?

Invoking Paths.get(new URI("jar:file:/C:/foo.jar!/bar.html")) throws FileSystemNotFoundException (notice the file system is missing, not the file itself).

As far as I can tell, both files exist. Any ideas?

Answer 1

Paths tries to resolve a FileSystem which would contain your Path . (Actually this may be an implementation detail. The spec simply states that it will check the default FileSystem .) If you haven't registered/created such a FileSystem , it won't be able to find it.

You would create a new FileSystem from the jar file and access the entry Path through that FileSystem .

Path path = Paths.get("C:/foo.jar");
URI uri = new URI("jar", path.toUri().toString(),  null);

Map<String, String> env = new HashMap<>();
env.put("create", "true");

FileSystem fileSystem = FileSystems.newFileSystem(uri, env);
Path file = fileSystem.getPath("bar.html");
System.out.println(file);

You could then use

Paths.get(new URI("jar:file:/C:/foo.jar!/bar.html"))

Be careful to properly close the FileSystem when finished using it.

For more information about ZipFileSystemProvider, see here .

Answer 2

Starting with version 7, Java allows us to have FileSystems, not only open a file on the local directory, but to also define our own File System. There are many uses for it, such as having a distributed file system, being able to use compression, have an http bridge, so many things...

In your case, what you need is a way to read a jar. Well, since a jar is just a zipped file, you can use the FileSystem with the default. It doesn't get any easier than that:

import java.net.URI;
import java.nio.file.FileSystem;
import java.nio.file.FileSystems;
import java.nio.file.Files;
import java.util.HashMap;
import java.util.Map;


public class Main {
    public static void main(String [] args) throws Throwable {
        String jarName = "/Users/asantos/.m2/repository/ant/ant/1.6/ant-1.6.jar";
        String fileInside = "/META-INF/LICENSE.txt";

        Map<String, String> env = new HashMap<>(); 

        URI uri = URI.create("jar:file:"+jarName);

        try (FileSystem zipfs = FileSystems.newFileSystem(uri, env)) {

            System.out.println(new String(Files.readAllBytes(zipfs.getPath(fileInside))));

        } 
    }
}

I shamelessly copied my code from the documentation, adapting for a jar instead of a zip file: http://docs.oracle.com/javase/8/docs/technotes/guides/io/fsp/zipfilesystemprovider.html

Answer 3

import java.net.URI;
import java.nio.file.FileSystem;
import java.nio.file.*;

public static void method() {
    Map<String, String> env = new HashMap<>();
    // here false is used to indicate the zip file system provider not to create a new zip/jar file if it does not exist.
    env.put("create", Boolean.FALSE.toString());
    Path jarFilePath = Paths.get("C:\\test_jar_parent", "myjarfile.jar");
    String uriPath = "jar:" + jarFilePath.toUri().toString();
    URI uri = URI.create(uriPath);
    try (FileSystem jarFs = FileSystems.newFileSystem(uri, env, null)) {
        ...
    }
}