dynapath provides a protocol and util functions for class loaders that make their effective classpaths readable and/or modifiable.
Clojure uses a
clojure.lang.DynamicClassLoader by default (an
java.net.URLClassLoader), which provides
reading the effective classpath and
.addURL for modifying it. It's
common for projects that need to read or modify the effective
classpath to assume that a
URLClassLoader is always available. But
in some environments, the available class loader may not be a
URLClassLoader, and may not be readable or modifiable.
Some projects (notably
pomegranate) handle this by providing a
protocol that can be implemented for other class loaders that may
provide similar functionality.
dynapath provides a protocol that is based on an extraction of pomegranate's protocol, and is intended to be a standard way for accessing or modifying the effective classpath. Using dynapath in your library instead of assuming a class loader or implementing your own protocol provides the following benefits:
- Your library can work with any modifiable/readable class loader without any changes
- Any project that has already implemented
DynamicClasspathfor whatever esoteric class loader they are using will not need any other changes to use your library as well
Add it as a dependency:
For a Leiningen/Boot project:
For a maven project:
<dependency> <groupId>org.tcrawley</groupId> <artifactId>dynapath</artifactId> <version>1.1.0</version> </dependency>
If you need to access or modify the effective classpath:
(require '[dynapath.util :as dp]) ;; returns a seq of the urls for the classloader. Takes any classloader ;; (whether it implements DynamicClasspath or not) and does the right thing (dp/classpath-urls a-classloader) ;; returns a seq of all the urls available from the classloader and its ;; parentage chain (dp/all-classpath-urls a-classloader) ;; adds a url to the given classloader if it is addable (dp/add-classpath-url a-classloader a-url)
dynapath.defaults namespace will automatically implement
If you need to implement
(require '[dynapath.dynamic-classpath :as dc]) (extend-type AReadableButNotModifiableClassLoader dc/DynamicClasspath (can-read? [_] true) (can-add? [_] false) (classpath-urls [cl] (seq ...))) (extend AReadableAndModifiableClassLoader dc/DynamicClasspath (assoc dc/base-readable-addable-classpath ;; implements can-read? and can-add? :classpath-urls (fn [cl] ...) :add-classpath-url (fn [cl url] ...)))
Note on URLClassLoader
Prior versions of dynapath implemented
java.net.URLClassLoader. Doing so required reflective access to its
addURL method, which would result in a warning printed to
stdout under Java 9. To prevent that, that implementation has been
removed, and libraries that were relying on that behavior should
instead ensure they have a modifiable classloader as high in the
classloader tree as they can control. For example,
boot implements its own classloader
to do this.
Who's using it?
Are you using it? If so, add yourself to this list and send me a PR.
Copyright © 2012-2017 Tobias Crawley
Distributed under the Eclipse Public License.