JDK 25 Upgrade Blocker Lint

Reads .java files and reports the calls that JDK 21 and JDK 25 removed, disabled, or refuse to run — with the JEP that removed each one and the call that replaces it.

Hub page: https://getreadystack.com/tools/jdk25-upgrade-blocker-lint

Why a linter and not the compiler

javac treats "deprecated for removal" as a warning. It prints the warning and writes a working class file, so the pipeline stays green and the failure moves to run time on the new JDK:

• System.setSecurityManager() throws UnsupportedOperationException on JDK 24 and later. JEP 486 permanently disabled the Security Manager; a .policy file now grants nothing.
• AccessController.doPrivileged still compiles and still returns — it simply no longer elevates anything.
• An import javax.persistence.Entity; compiles fine against a Jakarta EE 10 runtime. The runtime scans jakarta.*, so the entity is never registered and the table is never mapped.
• The Applet API was removed in JDK 25 (JEP 504). That one does fail the build, in a file nobody has opened in nine years.
• Thread.stop() throws UnsupportedOperationException since JDK 20.

The same gap applies to code written this week. An assistant trained largely on Java 8 and Java 11 will write javax.servlet imports, new Integer(3), and Class.forName(...).newInstance() into the very service you are migrating.

What it checks

18 rules over **/*.java, in two severities:

Errors — the call fails or silently does nothing on the target JDK: security_manager_set, access_controller, security_policy, unsafe_memory (JEP 471/498), javax_to_jakarta, jaxb_removed (JEP 320), applet_api (JEP 504), thread_stop, finalize_override (JEP 421), run_finalization, jdk_internal_import (JEP 403).

Warnings — deprecated with a one-line replacement: subject_do_as, native_access (JEP 472), set_accessible, url_constructor, wrapper_constructor, class_new_instance, locale_constructor.

Comments are stripped before matching, so a JEP number quoted in a javadoc is not a finding.

Measured on the bundled fixtures

_fixtures/dirty.java — a 64-line invoice exporter: 23 findings, 15 errors and 8 warnings, and every one of the 18 rules fires at least once. _fixtures/clean.java — the same class after each fix is applied: 0 findings.

Free and paid

Free, no key: all 18 rules on the file you have open, with no cap. The reading job finishes there.

Paid: the workspace sweep — it reads every .java file in the repository and writes one dated Markdown migration report with each file, blocker, JEP and replacement. The sweep is free for its first seven days; after that a key covers it, with commercial and CI-seat use. https://getreadystack.com/api/buy/cl/polar_cl_YK2CXL7Hd4TEoxQ76oOVQpVAsrLK9zUpcK7oV2MKwJs

Yardstick: a Java migration consultant bills $120–$200 an hour, and a two-day audit of one repository runs past $2,000.

Scope

It reads source text. It does not compile your project, resolve your dependency tree, or rewrite files — the replacement is named, the edit is yours. A finding inside a string literal is possible; the line number tells you in one glance.

Oracle premier support for Java 17 ends in September 2026.