Jimfs is an in-memory file system for Java 7 and above, implementing the java.nio.file abstract file system APIs.

Build Status Maven Central

Getting started

The latest release is 1.1.

It is available in Maven Central as com.google.jimfs:jimfs:1.1:


Basic use

The simplest way to use Jimfs is to just get a new FileSystem instance from the Jimfs class and start using it:

import com.google.common.jimfs.Configuration;
import com.google.common.jimfs.Jimfs;

// For a simple file system with Unix-style paths and behavior:
FileSystem fs = Jimfs.newFileSystem(Configuration.unix());
Path foo = fs.getPath("/foo");

Path hello = foo.resolve("hello.txt"); // /foo/hello.txt
Files.write(hello, ImmutableList.of("hello world"), StandardCharsets.UTF_8);

What's supported?

Jimfs supports almost all the APIs under java.nio.file. It supports:

  • Creating, deleting, moving and copying files and directories.
  • Reading and writing files with FileChannel or SeekableByteChannel, InputStream, OutputStream, etc.
  • Symbolic links.
  • Hard links to regular files.
  • SecureDirectoryStream, for operations relative to an open directory.
  • Glob and regex path filtering with PathMatcher.
  • Watching for changes to a directory with a WatchService.
  • File attributes. Built-in attribute views that can be supported include “basic”, “owner”, “posix”, “unix”, “dos”, “acl” and “user”. Do note, however, that not all attribute views provide useful attributes. For example, while setting and reading POSIX file permissions is possible with the “posix” view, those permissions will not actually affect the behavior of the file system.

Jimfs also supports creating file systems that, for example, use Windows-style paths and (to an extent) behavior. In general, however, file system behavior is modeled after UNIX and may not exactly match any particular real file system or platform.


Copyright 2013 Google Inc.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at


Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
See the License for the specific language governing permissions and
limitations under the License.