Cytodynamics is a library that makes dynamic JAR loading and classloader isolation on the JVM easy and painless.
Simplicity. Cytodynamics is a zero-dependency library that allows one to dynamically load classes in a few lines of code.
ClassLoader loader = LoaderBuilder
.anIsolatingLoader()
.withClasspath(new File("myjar.jar").getUri())
.withParentRelationship(DelegateRelationshipBuilder.builder()
.withIsolationLevel(IsolationLevel.FULL)
.build())
.build();
MyApi myApiImpl = (MyApi) loader.loadClass("com.myapi.MyApiImpl").newInstance();
myApiImpl.doIt();In contrast with other dynamic classloading systems, Cytodynamics also allows for isolating the child classloader from parent dependencies. This avoids issues where loaded code depends on classes that are present in the parent classloader, which can break whenever these classes are updated.
For example, if the parent application uses Guava version x and the loaded code depends on those classes being present, when the parent application updates to a later version, this can break if the new version is not binary compatible. In Cytodynamics, if the classloaders are isolated, this forces the loaded code to ship with its appropriate version of Guava, leading to more stable code in the long term.
As Cytodynamics focuses on simplicity, there is no versioning system, dependency system, or other complexity; more complex systems can be built on top of Cytodynamics. Since Cytodynamics does not have a versioning system, multiple versions of the same code can be loaded concurrently, allowing for runtime swap of code implementations.
As mentioned earlier, Cytodynamics supports classloader isolation. The parent classloader is always isolated from the classes contained in the child classloader (other than classes explicitly loaded through the Cytodynamics loader), but the child classloader can also be isolated from the classes in the parent classloader.
Classes can be annotated so that they are visible in the child classloader, as follows:
@Api(name = "my-interface")
public interface MyInterface {
void doSomething();
}When loading classes, classes annotated with the @Api annotation are always visible to the child classloader.
Cytodynamics supports three isolation modes: NONE, TRANSITIONAL, and FULL.
In FULL isolation mode, no classes from the parent classloader are visible, except for classes annotated with @Api
and classes that have been whitelisted. In the NONE isolation mode, all classes from the parent classloader are
visible to the child classloader (this is the default behavior when creating a classloader in Java). TRANSITIONAL mode
behaves like the NONE mode, but logs accesses to classes that would not be visible in the FULL mode, as to make
transitions between classloader isolation levels smoother.
Classes can also be whitelisted or blacklisted using glob-style patterns, making it easy to allow access to libraries in the loaded code:
ClassLoader loader = LoaderBuilder
.anIsolatingLoader()
.withClasspath(new File("myjar.jar").getUri())
.withParentRelationship(DelegateRelationshipBuilder.builder()
.withIsolationLevel(IsolationLevel.FULL)
.addWhitelistedClassPredicate(new GlobMatcher("com.example.*"))
.build())
.build();This project uses Maven, so a simple mvn install will do.
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