Java "module X does not read module Y" (JPMS) - Fix in CI

Under the Java Platform Module System, a module can only use types from modules it explicitly reads. Your module-info.java is missing a requires for a module whose types your code uses, so compilation (or launch) fails.

What this error means

javac fails with module com.example.app does not read module com.fasterxml.jackson.databind, or the equivalent at runtime. The type is on the module path but not readable because no requires declares the edge.

src/main/java/module-info.java:1: error: module com.example.app does not
read module com.google.gson
    Gson gson = new Gson();
    ^
1 error

Common causes

Missing requires directive

Your module uses a type from another module but module-info.java does not declare requires that.module.

Wrong module name

The requires uses the jar name rather than the actual module name (automatic module name differs from the artifact id).

Transitive readability not propagated

A dependency exposes a type from a third module in its API but did not declare requires transitive, so you cannot read it implicitly.

How to fix it

Add the requires directive

Declare the module your code reads.

module com.example.app {
  requires com.google.gson;   // now readable
}

Use the correct module name

Find the real module name rather than guessing from the jar.

jar --describe-module --file gson-2.11.0.jar
# prints the module name to put in requires

Request transitive readability where appropriate

If your module re-exposes a type in its own API, use requires transitive.

module com.example.app {
  requires transitive com.google.gson;
}

How to prevent it

• Keep module-info.java in sync with the types each module actually uses.
• Resolve module names with jar --describe-module, not the jar filename.
• Use requires transitive only when re-exposing a type in your API.

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