On February 28, 2017, WhatsApp officially ended support for J2ME (alongside BlackBerry OS and Nokia S40). Reasons:
There is a theoretical method using a server bridge. You run a proxy on a Raspberry Pi or an old Android phone that translates modern WhatsApp traffic into something a Java client can understand. Whatsapp java j2me
Here is the high-level concept:
Feasibility: In theory, yes. In practice, no stable, maintained solution exists for the public. A few GitHub projects attempted this, but they are abandoned due to WhatsApp’s frequent protocol changes. On February 28, 2017, WhatsApp officially ended support
Abstract: Before the era of smartphones, Java Platform, Micro Edition (J2ME) was the dominant runtime environment for feature phones. WhatsApp Messenger, launched in 2009, famously supported J2ME devices long after competitors abandoned them. This paper examines the technical architecture required to port a modern instant messaging protocol to devices with limited RAM (512KB-2MB), slow ARM processors, and unreliable GPRS/EDGE connectivity. It analyzes the memory management strategies, network optimization techniques, and UI constraints of the J2ME version, concluding with the reasons for its eventual deprecation in 2017. Feasibility: In theory, yes