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Here's what actively uses Java servlets (directly or via Spring MVC/JAX-RS on top of a servlet container), based on current sources plus well-known industry patterns:

Banks / financial services
The Spring Framework powers the core banking systems of HDFC, ICICI, Axis, and SBI. Financial services and insurance remain Java's deepest enterprise verticals, with core systems for trading, banking, claims processing, and policy administration overwhelmingly running on the JVM, mainly through Spring MVC/Spring Boot (servlet-based) for core banking, trading systems, fraud detection, and regulatory reporting.
IT services / consultancies that build these systems
TCS, Infosys, Capgemini, LTIMindtree, Persistent Systems, and other IT majors post large numbers of Java/Spring roles specifically to build and maintain banking and enterprise systems for their clients.

Broader adoption numbers
As of 2026, 3,013 verified companies use Java Servlet Technology, with the top industries being Manufacturing, Finance, Retail, and Insurance, and the majority of these companies are based in the United States.

Why they still use it (in short):

1. Legacy + stability — one financial institution partnered with a Java consultancy across multiple phases from 2011 to 2025, modernizing COBOL-based batch processing with Spring Batch — banks don't rip out decade-old, working systems.
2. Deep enterprise reliance — Azul's 2025 State of Java Survey found 99% of surveyed organizations actively use Java, and nearly 70% reported that more than half of their applications are built with Java or run on the JVM. 
3. Regulatory/compliance fit — Spring Security + servlet-based session/transaction handling aligns well with audit and compliance needs (as covered earlier).
4. Talent pool — huge existing base of Java/Spring engineers, especially in banking tech hubs.

One honest caveat: most of these companies use servlets indirectly, through Spring MVC/Spring Boot (which runs on a servlet container like Tomcat by default), rather than writing raw HttpServlet code — but structurally, it's still the same underlying request-handling model.

How they actually fit together in a real app:

Client Request
↓
Servlet (or Spring's DispatcherServlet) — receives HTTP request
↓
Spring MVC Controller — routes request, business logic
↓
Hibernate — talks to the database (via JPA), maps rows ↔ Java objects
↓
JSP (or JSON response in REST APIs) — renders the view / returns data
↓
Response back to Client
In one line each:

• Servlet = handles the HTTP request/response mechanics
• JSP = generates the HTML view (older tech, mostly replaced by REST + frontend frameworks now)
• Spring = the framework that wires everything together (DI, routing, security, transactions)
• Hibernate = talks to the database so you write Java objects, not raw SQL

Reality check for 2026: JSP is largely legacy now — most modern apps use Spring Boot REST APIs + a separate frontend (React/Angular/Vue) instead of server-rendered JSP pages. Servlets are still foundational (Spring runs on top of them via DispatcherServlet), and Hibernate/JPA remains the standard ORM choice.

Alternatives to JSP (view/templating layer):

• Thymeleaf — most common modern replacement, natural HTML templating, integrates cleanly with Spring Boot
• FreeMarker — template engine, still used in some legacy/enterprise apps
• Mustache — logic-less templates, lightweight
• React / Angular / Vue — the real modern default; backend just returns JSON (REST API), frontend handles all rendering client-side. Most new apps go this route now instead of server-side templating.

Servlet = low-level Java mechanism that handles raw HTTP requests/responses (doGet, doPost, etc.) — general purpose, can output anything (HTML, JSON, etc.), can maintain session state.

RESTful web service = an architectural style for designing resource-based APIs — uses HTTP verbs (GET/POST/PUT/DELETE) mapped to CRUD, typically returns JSON, and should be stateless.

Nutshell :
Servlet = how requests are received;
REST = how your API should be designed/structured.

Why banks use Java + servlets for netbanking:

1. Mature & stable — 25+ years battle-tested, low-risk for financial systems
2. Strong transactions — JTA/JDBC handle ACID transactions well (critical for fund transfers)
3. Security ecosystem — Spring Security, JAAS, long track record trusted by regulators
4. Compliance-friendly — built-in audit logging, session/access control aligns with PCI-DSS/RBI norms
5. Legacy integration — core banking systems (COBOL/Java/mainframes) integrate easily via Java
6. Fits the use case — netbanking is mostly request-response, not high-concurrency streaming, so blocking servlet model works fine
7. Talent pool — huge, stable Java/Spring developer base
8. Enterprise vendor support — WebLogic/WebSphere/JBoss are built around servlets

Caveat: newer fintechs/neobanks use reactive stacks (WebFlux, Node.js, Go) for high-scale real-time needs — but traditional banks stick with servlets for stability + compliance, not raw performance.