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Add migration-17-25 module: Java 17 class files run on 17 and 25, flags, removed APIs, jdeps and jdeprscan

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Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Gth99spB1CzQmBFofXmU4Z
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Claude
2026-09-28 08:42:19 +00:00
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migration-17-25/README.md
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# migration-17-25
Companion module for the ankurm.com post *Java 17 to Java 25 Migration Guide: The Direct Jump*.
The probes in `src/probes/` are compiled **once** with JDK 17 (`--release 17`) and run unchanged on JDK 17.0.20.1 and JDK 25.0.4.1, which is what a team skipping 21 actually does. `src/removed/` holds four tiny sources that use APIs removed or newly deprecated between 17 and 25; they are compiled with both JDKs.
```bash
export JDK17=/path/to/jdk-17 JDK25=/path/to/jdk-25
./scripts/run-all.sh # regenerates output/
```
| Output | Shows |
|---|---|
| `01-runtime-behaviour.txt` | Security Manager, `Thread.stop`, default charset, `finalize`, `Unsafe` on both runtimes |
| `02-startup-flags.txt` | Which 17-era JVM options still start on 25 |
| `03-compile-removed-apis.txt` | What `javac` says about four APIs on each JDK |
| `04-jdeps-jdeprscan.txt` | The scanners run with JDK 25 tools against the JDK 17-built jar |
| `05-gc-defaults.txt` | Default collector and heap ergonomics with no flags |
| `06-legacy-stack-on-25.txt` | `mvn test` on JDK 25 for four generations of one Spring app (from `spring-boot-demo/openrewrite`) |
| `07-framework-minimums.txt` | Vendor documentation quotes (not produced by running code) |