J2ME in the browser

English · Русский

A Java ME (MIDP 2.0 / CLDC) emulator written in JavaScript. A fork of pluotsorbet, extended to run ordinary feature-phone games and apps right in the browser, including on a smartphone.

Features

• High-level LCDUI (Form, List, TextBox, Alert, etc.)
• Sockets and HTTP through a WebSocket proxy on the server
• Audio: MIDI, WAV, MP3, AMR
• 3D: M3G (JSR-184, the J2ME-Loader engine compiled to WebAssembly) and Mascot Capsule (micro3d)
• Bluetooth (JSR-82): L2CAP and SPP between tabs and devices via rooms, directly over WebRTC or through TURN
• Screen resolution auto-detection from the manifest, jar name and graphics
• On-screen keypad, rotation, scaling, per-game settings
• Platform selectable per game (default Sony Ericsson): changes microedition.platform and key codes (soft keys, joystick, C/Back) to match Nokia/SE/Samsung, Siemens, Motorola, LG; C (−8) and Back (−11) keys are supported; PC keyboard: arrows, Enter, Q/E as soft keys, Backspace is C, Esc is Back
• System properties (microedition.locale and others) editable per game: Settings → "System properties", with reset to defaults
• Load your own .jar files straight from the page (stored in the browser)
• File manager for the phone's virtual storage (memory card, saves): upload, download, folders

Quick start

Requires Python 3.8+, no dependencies.

python3 server.py 8080

Open http://localhost:8080. Put games into the jar/ folder (they appear in the list for everyone) or add them with the button on the page.

On Windows use startserver.bat (allows the proxy to reach the local network).

Deployment

VPS (systemd)

./deploy.sh            # port 8080
PORT=80 ./deploy.sh    # another port

The script installs coturn, creates a TURN secret in /etc/j2me.env, opens ports in ufw (if enabled) and starts the j2me service. At the end it prints the address and the TURN_URL / TURN_SECRET lines for use in other installations.

Ports: site (TCP), 3478 (TCP/UDP), 49160–49200 (UDP).

systemctl status j2me
journalctl -u j2me -f

Docker / Render

The Dockerfile runs start.sh: if UDP is available, coturn is started next to the server. Render has no UDP, so TURN is not started there. To let players on Render connect through TURN, set TURN_URL and TURN_SECRET from your own VPS in Environment. A render.yaml is included.

Environment variables

Variable	Purpose
PORT	HTTP port (default 8080)
TURN_URL	external TURN, comma-separated: turn:host:3478,turn:host:3478?transport=tcp
TURN_SECRET	shared TURN secret (use-auth-secret in coturn)
TURN_IP	external IP for the built-in coturn if auto-detection is wrong
TURN=0	do not start the built-in coturn
ALLOW_PRIVATE=1	allow the proxy to connect to the local network
PYTHON	interpreter used by start.sh

Bluetooth multiplayer

The first time a game turns Bluetooth on, a window appears:

• Create — a new room with a name and password, which you pass to the other player. A room whose name is already taken cannot be created. Connection mode for the whole room: Auto (both channels, direct and TURN, are brought up on joining, 20 pings each, and the one with the lower 90th-percentile latency is chosen; if neither comes up, the server is used), P2P (direct, falls back to TURN, the server is not used), TURN (always TURN, the server is not used, TURN_URL required);
• Join — enter the room name and password;
• Nearby — no password, for players behind the same public IP.

After that the game behaves as with real Bluetooth: device discovery, service discovery, btl2cap:// and btspp://. The server only introduces players to each other. Once connected, data goes directly (WebRTC) when possible, otherwise through TURN or the server's WebSocket. Connection state is shown by the dot on the gear icon (green — direct or TURN, yellow — via server, red — no connection); details are in Settings, "Network game": room, player count, connection mode, switching rooms.

URL parameters to skip the window: ?room=name&pass=password&btname=Nick joins a room; add &mode=create to create one, and &net=auto|p2p|turn for the connection mode. An empty ?room= means "Nearby".

Page parameters

main.html?jar=jar/game.jar and also:

Parameter	Value
screen	240x320, auto, fit
scale, rotate, keypad, fps, jit	same as in Settings (fps limits the frame rate, 0 means unlimited)
platform	se, nokia, samsung, siemens, motorola, lg or a custom string
debug=1	enable debug output in the console

Building the Java part

java/classes.jar is prebuilt. After changing anything in src/:

src/bt/build.sh     # JSR-82
src/m3g/build.sh    # M3G (needs clang with the wasm32 target)

Layout

bld/        JS runtime: VM (j2me.js), MIDP (main-all.js), LCDUI, network, audio, 3D, Bluetooth
java/       classes.jar — MIDP/CLDC class library
src/bt/     JSR-82 sources
src/m3g/    M3G sources
config/     settings, local jars, URL parameters
server.py   HTTP server, socket proxy, Bluetooth room server

License and credits

• Licensed under the Apache License 2.0 (see LICENSE)
• pluotsorbet — Mozilla, Apache License 2.0; the class library is based on phoneME
• M3G — J2ME-Loader, see src/m3g/NOTICE for details
• webaudio-tinysynth, BenzAMRRecorder, text-encoding