Servlet 4.0.1 升级至 Servlet 5.0：Jakarta API相关疑问及升级要点咨询

Hey folks, let's walk through all your questions about upgrading from Servlet 4.0.1 to 5.0 and the whole Jakarta transition—this is a common pain point when moving to newer EE stacks, so let's break it down clearly:

1. What's the origin of the "Jakarta" term? #

This all traces back to a big shift in Java EE's ownership. Back in 2017, Oracle donated Java EE to the Eclipse Foundation. But due to trademark restrictions, the Foundation couldn't keep using the "Java EE" name or the javax.* package namespace.

To solve this, they rebranded the platform as Jakarta EE, and migrated all Java EE APIs to the jakarta.* package prefix. Servlet 5.0 is a core component of the Jakarta EE 9 specification, which is the first full release under this new brand.

2. Do I have to use the Jakarta API when upgrading to Servlet 5.0? Can I stick with the old javax.servlet-api? #

Short answer: Yes, you must switch to the Jakarta API—there's no way around it.

Servlet 5.0 is built exclusively on the jakarta.* namespace, and it's incompatible with the old javax.servlet-api (which maps to Servlet 4.0 and earlier Java EE versions). If you try to keep using the old dependency, your code's import javax.servlet.* statements will fail to find classes, because Servlet 5.0-compatible containers (like Tomcat 10+, Jetty 11+) only provide jakarta.servlet.* implementations. Conversely, older containers (like Tomcat 9) don't support Jakarta API at all, so they can't run Servlet 5.0 apps.

3. I noticed a Jakarta-related dependency for Servlet 4.0—what's that about, and does it relate to Servlet 4.0? #

That Jakarta-flavored Servlet 4.0 dependency is a repackaged version of the original Java EE 8 Servlet 4.0 spec, with the package names changed from javax.servlet to jakarta.servlet—but the functionality is identical to javax.servlet-api:4.0.1.

It was released as a transitional tool to help developers get used to the new Jakarta namespace before the full jump to Jakarta EE 9 (Servlet 5.0). Most projects didn't use it back then, since Java EE 8 containers (like Tomcat 9) still relied on the javax.* packages, so it was optional for pre-upgrade testing.

4. What other steps do I need to take to upgrade from Servlet 4.0 to 5.0? #

Beyond switching the Maven dependency, here are the key tasks:

• Update all import statements: Replace every import javax.servlet.*, import javax.servlet.http.*, and other related EE imports with their jakarta.* equivalents. Most IDEs have a global replace tool for this, or you can use dedicated migration plugins (like Eclipse's Jakarta Migration Tool) to automate it.
• Upgrade your Servlet container: You'll need a container that supports Jakarta EE 9, such as Tomcat 10.x, Jetty 11.x, WildFly 22+, or Payara 6.x. Older containers won't recognize the Jakarta API classes.
• Sync other EE dependencies: If your project uses other Java EE APIs (like JSP, JSTL, JSF, or CDI), you need to upgrade those to their Jakarta EE 9 versions too. For example, replace javax.servlet.jsp.jstl:jstl-api with jakarta.servlet.jsp.jstl:jakarta.servlet.jsp.jstl-api.
• Update configuration files: If you use a web.xml deployment descriptor, update its XML namespace to the Jakarta EE 9 schema:

  <web-app xmlns="https://jakarta.ee/xml/ns/jakartaee"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="https://jakarta.ee/xml/ns/jakartaee https://jakarta.ee/xml/ns/jakartaee/web-app_5_0.xsd"
           version="5.0">
  

  Also, replace any EE-related annotations (like @WebServlet) from javax.servlet.annotation to jakarta.servlet.annotation.
• Test for compatibility: While most core functionality stays the same, some deprecated methods from Servlet 4.0 were removed in 5.0. Run your full suite of unit and integration tests to catch any breakages.

5. Recommended reference docs #

• Jakarta EE 9 Migration Guide: Covers all the ins and outs of moving from Java EE 8 to Jakarta EE 9, including Servlet-specific changes.
• Jakarta Servlet 5.0 Specification: The official document detailing the Servlet 5.0 API, including any new features or removed functionality.
• Container-specific migration guides: Check the docs for your chosen container (e.g., Tomcat 10 Migration Guide) for tailored tips on adapting to Servlet 5.0 and Jakarta EE.

内容的提问来源于stack exchange，提问作者Ashish Goyanka