An x3270-aligned IBM 3270 mainframe terminal emulator written in pure Java. Designed for high compatibility with IBM z/OS, z/VM, CMS, and TSO systems over TN3270 and TN3270E.

🚀 Quick Download & Run

Latest Standalone JAR

You can download the ready-to-run executable JAR directly from the releases or CI builds:

Download Latest Tagged Release (j3270.jar)
Latest Nightly CI Artifacts (Download under the latest successful workflow run)

Running `j3270`

Requires Java 11 or higher (Java 11, 17, 21+):

# Launch interactive GUI
java -jar j3270.jar

# Connect to TLS/SSL mainframe with custom port
java -jar j3270.jar -s mainframe.example.com 992
# Or using standard x3270 L: prefix
java -jar j3270.jar L:mainframe.example.com:992

# Connect via Plain TN3270 (Non-E)
java -jar j3270.jar -P mainframe.example.com 23
# Or using standard x3270 P: prefix
java -jar j3270.jar P:mainframe.example.com:23

# Connect with unverified/self-signed certificate verification bypass
java -jar j3270.jar --tls --insecure mainframe.example.com 992

# Launch with custom configuration file
java -jar j3270.jar -c config.ini

# Launch directly from source runner
./run.sh

✨ Features

TN3270 & TN3270E Protocol Support: RFC 2355 compliant state machine, negotiation, Device-Type query, plain TN3270 fallback, and SSL/TLS encryption.
SSL/TLS Security:
- Encrypted TN3270 over TLS connections on standard port 992 or custom ports.
- Interactive certificate verification prompt for self-signed or untrusted certificates with fingerprint, subject, issuer, and validity inspection.
- Optional unverified/insecure mode for testing and headless scripting.
IND$FILE File Transfer: Full support for both CUT and DFT (DDM) high-speed structured field transfers with ASCII/binary translation, CRLF handling, and recfm/lrecl formatting for TSO, VM/CMS, and CICS.
z/VM & Line-Mode Support: Proper SSCP-LU and unformatted line handling (CP TERM CONMODE 3270 supported).
APL & Graphic Escape: Comprehensive box-drawing and math symbol character rendering.
Terminal Models:
- Model 2 (24x80)
- Model 3 (32x80)
- Model 4 (43x80)
- Model 5 (27x132)
Zero-Dependency Core: Modular architecture separated into:
- lib3270j: Reusable Java 3270 protocol, data stream parser, charset translation, and telnet state machine.
- j3270: Desktop Swing user interface and session management.

🛠️ Building from Source

Standalone Build (No Gradle Required)

The project includes self-contained, portable build scripts:

# Build executable JAR in 2 seconds:
sh ./build_all.sh

# Run all 57 automated unit tests in ~500ms:
sh ./test_all.sh

The resulting standalone JAR is created at build/j3270.jar.

Gradle Build (Optional)

./gradlew build
./gradlew test

📜 Acknowledgements

x3270 — Reference C implementation and protocol specifications
Antigravity
Claude Opus 4.6
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GPT-OSS 120B
Qwen3 4B and 32B

README.md

j3270