Downgrade Java target from 21 to 17 and remove Records for Android compatibility

[aslan564]

Problem

OpenPDF 3.0.x targets Java 21 and uses several Java 21+ features that cause
compatibility issues for downstream consumers:

1. Java Records (28 usages across 15 files) — Android's D8/R8 desugaring
   cannot handle java.lang.Record without explicit global-synthetics
   consumer configuration (AGP 8.3+). This causes build failures for Android
   SDK developers who depend on OpenPDF:

2. Virtual Threads (Executors.newVirtualThreadPerTaskExecutor()) —
   Java 21 only, excludes Java 17 LTS users.

3. SequencedCollection methods (getFirst(), getLast() on List) —
   Java 21 only.

Many enterprise environments and Android projects still target Java 17 LTS.
Supporting Java 17 as the minimum version would significantly expand
OpenPDF's compatibility.

Changes

Java version: 21 → 17

• pom.xml: Changed <java.version> from 21 to 17

Virtual Threads → CachedThreadPool (1 file)

• PdfBatch.java: Replaced newVirtualThreadPerTaskExecutor() with
  newCachedThreadPool() + proper shutdown() in finally block

SequencedCollection methods (2 files)

• PdfContentStreamHandler.java: getLast() → get(size()-1),
  getFirst() → get(0)
• PdfTextLocator.java: getLast() → get(size()-1)

Java Records → Regular classes (15 files, 28 records)

openpdf-core:

• PdfBatchUtils.java: MergeJob, WatermarkJob, EncryptJob, SplitJob

openpdf-html:

• HtmlToPdfBatchUtils.java: HtmlStringJob, HtmlFileJob, UrlJob
• JustificationInfo.java, FontDescription.java (Decorations),
  HSBColor.java, CSSName.java (CSSSideProperties)
• BorderPropertySet.java: Styles, Colors, Corners
• BorderRadiusCorner.java: Length
• FloatManager.java: BoxOffset, BoxDistance
• PageBox.java: PageDimensions, MarginAreaContainer
• InlineBoxing.java: StaticFloatDistances, DynamicFloatDistances
• DefaultLineBreakingStrategy.java: DefaultBreakPointsProvider
• DocumentSplitter.java: ProcessingInstruction
• SelectField.java: NameValuePair
• SwingReplacedElementFactory.java: CacheKey
• ImageResourceLoader.java: CacheKey

All replacement classes provide:

• public final fields (for direct access compatibility)
• Accessor methods matching record naming convention (e.g., input() not getInput())
• equals()/hashCode()/toString() where needed (HashMap keys, test assertions)

Test fixes

• Removed Thread.isVirtual() assertions (Java 21 API)
• Added platform-safe font handling in FontTest for macOS Courier.ttc

Verification

• BUILD SUCCESS — all 2264 tests pass (0 failures, 0 errors)
• Zero java.lang.Record references in compiled bytecode
  (verified via grep -l "java/lang/Record" on all .class files)
• Full backward API compatibility maintained

Impact

This change allows OpenPDF to be used by:

• Java 17 LTS environments
• Android projects without desugaring configuration
• SDK developers who bundle OpenPDF as a transitive dependency

Your real name
Aslan Aslanov

[andreasrosdal]

If you need to use OpenPDF on Java 17, you can use the OpenPDF 2.0.5 release. The 2.0 branch supports Java 17.

Java on Android is it's very unique special creation. Maybe a fork of OpenPDF which is specific for Android would be a good idea. Yes, I suggest someone creates a fork of OpenPDF for Android. So I suggest OpenPDF will focus on the main modern Java version, for which Java 21 is a good choice in 2026.

There has been a significant effort to modernize OpenPDF 3.x for Java 21, so this PR you propose will halt the modernization.

https://github.com/LibrePDF/OpenPDF/releases/tag/2.0.5

<dependency>
  <groupId>com.github.librepdf</groupId>
  <artifactId>openpdf</artifactId>
  <version>2.0.5</version>
</dependency>