Java invoice example

A multi-package Java app. It has an invoice CLI, a billing library that reads JSON through gson and groups sums through guava, a generated BuildInfo class and a packaged invoices.json resource.

bazel build //examples/java-app/...
bazel test //examples/java-app/...
bazel run //:dx -- generate --check //examples/java-app/...
bazel run //examples/java-app/cli:invoice -- total
bazel run //examples/java-app/cli:invoice -- show INV-1001
bazel run //examples/java-app/cli:invoice -- --file path/to/invoices.json list

Without --file or INVOICE_FILE, invoice reads the invoices.json packaged in the billing jar, so the binary runs from any directory. Relative --file paths resolve against the directory you ran bazel run from. Quantities and prices must be whole numbers from 0 to 1000000.

dx generate owns the billing and cli libraries. Main.java, tests and diagnostics stay handwritten.

Exit codes: 0 ok, 2 usage, 3 unreadable or malformed invoice file, 4 unknown invoice. exit_codes_test runs the binary through each code.

gson and guava come from the locked @maven hub. classpath_test checks that the app classes load from the billing jar and the library classes from their own jars. Tests use JUnit 4. Sources build at the repository Java language level with -Xlint:all -Werror.

format_test checks the sources against the pinned google-java-format. diagnostics_test compiles, lints and formats files with a syntax error, a type error, a compiler warning, an unused import and bad formatting, and expects each to fail. It also compiles the billing sources: they fail without gson or guava on the classpath and pass with both.