If you are searching for call Java from C# jni4net, you probably have a very practical problem: a .NET application needs to use Java code. Maybe it is a Java JAR, a Java library, a pricing engine, a rules engine, a reporting component, or an internal Java API that would be expensive to rewrite in C#.

jni4net can look attractive because it was built to bridge JVM and CLR with generated proxies. It is bidirectional, and its original design includes .NET-to-Java calls through generated .NET proxies that ultimately call real Java implementations (.NET to Java design, SourceForge).

But if this Java-from-.NET requirement matters in production, the better question is not simply “can jni4net call Java?” It is “what bridge can support this application as Java, .NET, operating systems, and deployment models keep moving?”

For modern production work, that answer is JNBridgePro.

What jni4net gets right

jni4net’s core idea is useful: generate proxies so .NET code can call Java without hand-writing JNI calls. That is the right developer experience. A C# developer should not have to manually manage every Java call through raw JNI plumbing.

For a small local application, jni4net may still work:

• .NET Framework application;
• Windows-only deployment;
• compatible Java runtime;
• narrow Java API surface;
• stable generated proxies;
• internal low-risk use case;
• team willing to own bridge debugging.

If that is your environment and the app is already stable, leaving jni4net alone may be reasonable.

The danger is treating that old success as proof that jni4net is a good foundation for new Java-from-.NET production development.

Where Java-from-C# integrations get harder

Calling Java from C# sounds like one requirement, but it can mean several different things:

• use a Java library in C#;
• call a Java JAR from .NET;
• invoke a Java class from a .NET Framework app;
• use Java from .NET Core, .NET 8, or .NET 10;
• run Java code from a Windows service;
• connect a .NET application to a Java engine running elsewhere;
• preserve Java code during a .NET modernization project.

The bridge must support the runtime reality behind the requirement.

That is where jni4net becomes risky. Its public materials and release history are anchored in the older .NET Framework/Java era. The latest GitHub release is 0.8.8.0 from September 2014, and the README/build notes include older runtime references such as .NET SDK 3.5/4.0 and JDK 1.5 (GitHub, GitHub releases). The README also states that Linux/Mono was not supported at the time (GitHub).

If your .NET application is moving to .NET 8, .NET 9, or .NET 10, or your Java dependency is moving to Java 17, Java 21, or Java 25, that legacy posture matters.

Why JNBridgePro is stronger for .NET-to-Java calls

JNBridgePro is built to let .NET code access Java classes through generated proxies while Java continues to run on the JVM (How It Works). That is the key difference for production teams: Java remains Java, and .NET remains .NET.

Current JNBridgePro system requirements list .NET Framework 4.8, .NET 8, .NET 9, .NET 10, Windows, 64-bit Linux, and JDK 8 through 25 (System Requirements). That makes it a better match for both legacy .NET Framework applications and modern .NET services that need Java libraries.

JNBridgePro also supports multiple deployment topologies: same process, separate processes, and networked communication (Overview, User Guide). That matters because “call Java from C#” does not always mean “load the JVM inside this one Windows process forever.” Sometimes production teams need isolation, cloud deployment, or separate scaling.

Performance: design for coarse Java work

The May 22, 2026 benchmark gives a useful example of the right call shape. In the production-shaped BatchEngine.portfolioBatch x400 scenario, .NET crossed the bridge once and Java performed substantial computation. JNBridgePro’s median was 425.147 ms, while jni4net’s median was 1,338.893 ms. JNBridgePro was about 3.15x faster for that workload, and the checksums matched exactly.

That does not mean JNBridgePro is faster for every possible Java-from-C# call. In the same benchmark, jni4net won several tiny-call and bulk-transfer local in-process microbenchmarks.

The practical lesson is more important: do not design Java/.NET integration around thousands or millions of tiny boundary crossings. Expose coarse-grained Java methods. Let Java do meaningful Java work. Return a useful result. That is the call pattern that maps better to production and to JNBridgePro’s strengths.

Java-from-C# options compared

Migration path from jni4net to JNBridgePro

A good migration starts with the Java API surface.

1. Identify the Java classes currently exposed to .NET through jni4net.
2. Remove accidental chattiness by grouping small helper calls into coarse Java operations.
3. Choose the target runtime: .NET Framework 4.8, .NET 8/9/10, and the target JDK.
4. Decide whether same-process, separate-process, or network deployment fits production.
5. Generate JNBridgePro proxies for the Java classes .NET needs.
6. Port the C# call sites to the JNBridgePro proxy model.
7. Test exceptions, object lifetime, strings, arrays, callbacks, and deployment startup.
8. Benchmark production-shaped workloads.

The goal is not to rewrite Java in C#. The goal is to preserve Java code while replacing the old bridge with a supported one.

FAQ

Can jni4net call Java from C#?

Yes. jni4net supports .NET-to-Java calls through generated proxies. The concern is not whether the direction exists; it is whether the bridge is a good production foundation today.

How can I use a Java library in C#?

You can use a bridge such as JNBridgePro to generate .NET proxies for Java classes. That lets C# code call Java APIs while Java continues to run on the JVM.

Can I call a Java JAR from .NET 8 or .NET 10?

For modern .NET, JNBridgePro is the safer production path because it lists current .NET support and JDK support. jni4net’s public materials do not show a current supported path for modern .NET.

Is jni4net faster than JNBridgePro?

It depends on workload shape. jni4net won some local in-process microbenchmarks in the May 22 benchmark. JNBridgePro was about 3.15x faster on the production-shaped batch workload where .NET crossed once and Java did substantial work.

Next step

If your .NET app depends on Java, keep the Java code intact and evaluate the bridge layer separately. For a small legacy app, jni4net may still be enough. For production Java-from-C# interoperability, review JNBridgePro, the How It Works page, and the JNBridgePro download.