Java Virtual Machine implementation in Rust

rjvm is a fast JVM that supports a fairly high number of Java features while still remaining portable. It can be compiled on any platform that supports Rust and has alloc support.

rjvm provides a partial set of Java builtin classes, as rjvm_globals. This means that running it does not require users to have an existing Java installation.

rjvm is also very modular. The core JVM, rjvm_core, is no_std and requires only a few standard classes to be provided during its bootstrap process. The base globals implementations, rjvm_globals, is also no_std and remains under 1 MB. Users of the VM, such as rjvm_web and rjvm_desktop, provide their own implementations for platform-dependent behavior, such as loading classes from the filesystem, I/O, and reading date and time.

Both rjvm_core and to a lesser extent rjvm_globals try to have as few direct and indirect dependencies as possible.

Features

• bytecode verifier
• not-painfully-slow interpreter
• All language features before Java 7 except for threads
• I/O operations, including file I/O (only for native platforms)
• support for many classes in the java.io, java.lang, java.lang.reflect, and java.util packages
• some regex support
• implementations for most ClassLoader and reflection methods
• ability to run Java on the browser through WASM
• no_std support
  • alloc is still required

Upcoming features

• Proper encoding/decoding
• Implementations for the remaining stack operations
• Windows support
• Array type verification in verifier
• Object class verification in verifier
• Better performance
  • 8-byte Value
  • other?

Missing features

• Proper charset support
• invokedynamic (Java 8 lambdas) support
• Multithreading (Thread.start) support
• Lots of API
• Better garbage collection
• A JIT compiler