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<title>AspectJ 1.9.8 Readme</title>
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<div align="right"><small>&copy; Copyright 2021 Contributors. All rights reserved.</small></div>

<h1>AspectJ 1.9.8</h1>

<p>
  Please note that Bugzilla for issue management is deprecated and new issues should be filed as
  <a href="https://github.com/eclipse/org.aspectj/issues/new">GitHub issues</a>.
  The list of issues addressed for 1.9.8 can be found
  <a href="https://bugs.eclipse.org/bugs/buglist.cgi?bug_status=RESOLVED&bug_status=VERIFIED&bug_status=CLOSED&f0=OP&f1=OP&f3=CP&f4=CP&j1=OR&list_id=16866879&product=AspectJ&query_format=advanced&target_milestone=1.9.8">here for Bugzilla</a>
  and <a href="https://github.com/eclipse/org.aspectj/issues?q=is%3Aissue+is%3Aclosed++milestone%3A1.9.8">here for GitHub issues</a>.
</p>

<h2>New features</h2>

<p>
  AspectJ 1.9.8 supports <a href="https://openjdk.java.net/projects/jdk/17/">Java 17</a> and its final and preview
  features, such as:
</p>
<ul>
  <li>Sealed classes (final in Java 17, previews in Java 15, 16 and AspectJ 1.9.7)</li>
  <li>Pattern matching for <tt>switch</tt></li>
</ul>

<h2>Improvements</h2>

<p>
  The <tt>--release N</tt> compiler option for correct cross-compilation to previous JDK bytecode + API versions is now
  supported by AJC. Previously, the option existed (inherited by ECJ) but did not work correctly.
</p>

<p>
  The following new properties can improve performance, e.g. Spring start-up time:
</p>
<ul>
  <li><tt>org.aspectj.apache.bcel.useSingleRepositoryInstance</tt></li>
  <li><tt>org.aspectj.apache.bcel.useUnavailableClassesCache</tt></li>
  <li><tt>org.aspectj.apache.bcel.ignoreCacheClearRequests</tt></li>
</ul>
<p>
  For now, they all default to <tt>false</tt> for backward compatibility. This might change in a future Aspect release,
  if user feedback is positive and no negative side effects are found. Please try using them as much as you can and
  report back questions (to the AspectJ users mailing list) or problems (as a GitHub issue), if any. Thanks to Stefan
  Starke for his contribution. See also <a href="https://github.com/eclipse/org.aspectj/pull/37">PR #37</a>.
</p>


<h2>Code examples</h2>

<p>
  You can find some sample code in the AspectJ test suite under the respective AspectJ version in which the features
  were first supported (possibly as JVM preview features):
</p>
<ul>
  <li>
    <a href="https://github.com/eclipse/org.aspectj/tree/master/tests/features198/compiler_release">
      Cross-compilation to legacy JDK
    </a>:
    An example class which only works correctly on JDK 8 when compiled with <tt>--release 8</tt> due to API changes in
    the JDK. Simply <tt>-source 8 -target 8</tt> would not be enough in this case.
  </li>
  <li>
    <a href="https://github.com/eclipse/org.aspectj/tree/master/tests/features198/java17">
      Pattern matching for switch
    </a>
  </li>
</ul>

<h2>Other changes and bug fixes</h2>

<ul>
  <li>
    The AspectJ compiler <tt>ajc</tt> (contained in the <tt>aspectjtools</tt> library) no longer works on JDKs 8 to 10.
    The minimum compile-time requirement is now JDK 11 due to upstream changes in the Eclipse Java Compiler (subset of
    JDT Core), which AspectJ is a fork of. You can still compile to legacy target versions as low as Java 1.3 when
    compiling plain Java code or using plain Java ITD constructs which do not require the AspectJ runtime
    <tt>aspectjrt</tt>, but the compiler itself needs JDK 11+. Just like in previous AspectJ versions, both the runtime
    <tt>aspectjrt</tt> and the load-time weaver <tt>aspectjweaver</tt> still only require JRE 8+.
  </li>
  <li>Document build profiles and properties in <i>docs/developer/BUILD.md</i></li>
  <li>Add a guide for setting up an AspectJ development environment in <i>docs/developer/IDE.md</i></li>
  <li>
    Fix <a href="https://github.com/eclipse/org.aspectj/issues/105">issue #105</a>: Compilation fails when using an
    aspect library via <tt>-aspectpath</tt> in combination with introducing an annotation via ITD. This was broken since
    version 1.9.5 and fixed in 1.9.8.RC3.
  </li>
  <li>
    Fix <a href="https://github.com/eclipse/org.aspectj/issues/68">issue #68</a>: Correctly process class files
    containing <a href="https://openjdk.java.net/jeps/309">dynamic class-file constants (JEP 309)</a>, which were
    introduced in Java 11 and broken in AspectJ ever since their introduction in 1.9.2. Java itself currently does not
    use "condy" and neither do other widespread JVM languages. Byte code engineering libraries like ASM or Byte Buddy
    and some instrumentation tools like JaCoCo can however produce condy code. Therefore, in order to create a
    regression test, we actually had to
    <a href="https://github.com/eclipse/org.aspectj/blob/de63b63d/tests/bugs198/github_68/Generator.java#L50-L61">
      craft a condy class with ASM</a>.
  </li>
  <li>
    Thanks to Andrey Turbanov for several clean code contributions and to Dmitry Mikhaylov for fixing a potential
    concurrency problem.
  </li>
</ul>

<h2>AspectJ usage hints</h2>

<h3>Use LTW on Java 16+</h3>

<p>
  Please note that if you want to use load-time weaving on Java 16+, the weaving agent collides with
  <a href="https://openjdk.java.net/jeps/396">JEP 396 (Strongly Encapsulate JDK Internals by Default)</a>. Therefore,
  you need to set the JVM parameter <tt>--add-opens java.base/java.lang=ALL-UNNAMED</tt> in order to enable aspect
  weaving. This is due to the fact that the weaver uses internal APIs for which we have not found an adequate
  replacement yet when defining classes in different classloaders.
</p>

<h3>Compile with Java preview features</h3>

<p>
  For features marked as preview on a given JDK, you need to compile with <tt>ajc --enable-preview</tt> and run with
  <tt>java --enable-preview</tt> on that JDK.
</p>
<p>
  Please note that you cannot run code compiled with preview features on any other JDK than the one used for
  compilation. For example, records compiled with preview on JDK 15 cannot be used on JDK 16 without recompilation. This
  is a JVM limitation unrelated to AspectJ. Also, e.g. sealed classes are preview-1 on JDK 15 and preview-2 on JDK 16.
  You still need to recompile, no matter what.
</p>

<hr>

<p>
  <b>Available:</b> 1.9.8 available 11-Feb-2022
</p>

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