jni4net.com

What It Is

jni4net is an in-process bridge between Java and .NET, designed to let the JVM and CLR call each other within the same process, the same thread, and the same call stack. Instead of communicating through service-style interfaces such as HTTP/RPC, it uses JNI, reflection, and proxy classes to provide object-level interoperability. It is suitable for scenarios where you need to directly reuse Java or .NET class libraries.

Core Capabilities

Based on the main documentation, jni4net supports both Java calling .NET and .NET/C# calling Java. Its mechanism is to use reflection to read public method signatures from Java and .NET, then generate proxy classes for the other side; at runtime, calls are forwarded by the proxy to the real object. It provides a .NET version of the JNI API and uses JNI to forward calls between the two runtimes. Apart from primitive types and arrays, objects are mainly marshaled by reference. As long as circular references are not created between the two VM heaps, proxies and instances can be garbage-collected normally. The proxygen tool can wrap your own libraries based on .jar or .dll files and configuration files, while proxies for core JDK and .NET Framework classes are already included.

Platform, Licensing, and Pricing

Platform support is fairly clear but somewhat dated: the documentation only mentions Windows 32/64-bit, CLR 2.0/4.0, and JRE 1.5 or above. In terms of licensing, the project is open source: the tools are GPL, and the runtime is MIT. The page does not provide any commercial pricing information, so it can be understood as a free and open-source tool. However, enterprise users should pay attention to the licensing boundary between the GPL toolchain and the runtime.

Pros and Cons

The main advantages are that calls happen in-process, so the performance overhead is generally lower than service-based bridging; the bidirectional call model is clear; and it provides binary packages, examples, a Hello World guide, a Wiki, Stackoverflow links, and a mailing list. The drawbacks are also obvious: support is only stated for Windows; the author describes proxygen as “ugly”; maintenance appears focused on keeping the runtime stable and applying occasional bug fixes; and there is little information about modern .NET, cross-platform support, or enterprise-grade support.

Who It’s For and Access from China

jni4net is suitable for development teams maintaining legacy Java/.NET systems on Windows that need to quickly reuse existing jar or dll libraries. It is not a good fit for projects that require cross-platform support, cloud-native architecture, or long-term commercial backing. The source text does not provide information about access from China. Access to the official website and GitHub may be affected by local network conditions. If stable access is not possible, alternatives such as JNI/JNA, IKVM, JEP, or a language-decoupled approach using gRPC/REST may be worth considering.