1. Code Generation with Annotation Processors: State of the Art in Java 9
[CON3282]

2. About the speakers Welcome to our session! Jorge Hidalgo
Coordinator – Málaga JUG
Global Java Lead – Accenture Technology
Java, Architecture & DevOps Lead
Accenture Delivery Center in Spain
Father of two children, husband, whistle player, video gamer, sci-fi ‘junkie’, Star Wars ‘addict’, Lego brick ‘wielder’, Raspberry Pi fan, … LLAP!
@_deors
Julio Palma Vázquez
Member – Málaga JUG
Technology Architect – Accenture Technology
Accenture Global Java Champion
Accenture Delivery Center in Spain
Mountain biker, AD&D player, Sid Meier’s Civilization gamer, LotR fan, …
@restalion
Copyright © 2017 Accenture. All rights reserved.

3. Code Generation in the Java Compiler
Objetives for the session
Overview of Annotations and Annotation Processors in Java
What’s new in Java 9 APT API
Learn how to create Annotation Processors
Learn how to use Annotation Processors to generate source code
Annotation Processors and Modules in Java 9
With lots of examples and source code
Copyright © 2017 Accenture. All rights reserved.

4. Poll #1
Please raise your hands if you are familiar with Annotations, know how to use them or are even capable of writing Annotation Types
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5. Annotations in Java language
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6. Annotations in the java language
History
Annotations were first introduced in Java 5
Add metadata capabilities to the Java language:
Build/deployment information
Configuration properties
Compiler behavior
Quality checks
Dependency injection
Persistence mapping
...
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7. Annotations in the java language
Overview
Annotations always appear before the annotated piece of code
Annotations can ‘decorate’...
Packages
Types (classes, interfaces, enums, annotation types)
Variables (class, instance and local variables)
Constructors, methods and their parameters
Generic type parameter (since Java 8)
Any type use (since Java 8)
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8. Annotations in the java language
Overview
Can be grouped, nested, repeated... very powerful!
Document>> docStore;
Annotations may be used just as a ‘marker’
@NonNull String ;
They may contain name-value pairs, and arrays
@Author(name = "Albert", created = "17/09/2010", revision = 3, reviewers = {"George", "Fred"}) public class SomeClass {...}
Can be defined with default values, and then omitted when used
When it has only one attribute named value, it can be omitted, too
@DatabaseTable(“MY_TABLE”) public class MyTable {...}
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9. how to create Annotations and Annotation Processors
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10. Poll #2
Please raise your hands if you are familiar with Annotation Processors, their capabilities or know how to write new ones
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11. Annotations Create an Annotation Type A special type of interface
Author { String name(); String created(); int revision() default 1; String[] reviewers() default {}; }
Only primitives, enum types, annotation types, String, Class and arrays of them are allowed as elements
May be annotated itself, i.e. to define the retention policy or targets
@Retention(RetentionPolicy.SOURCE) @Target({ElementType.ANNOTATION_TYPE, ElementType.TYPE}) Author {...}
Can trigger custom actions at compile time managed by Annotation Processors!
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12. Annotation Processors
Annotation Processing API
Annotation Processor:
Implements javax.annotation.processing.Processor
Or extends javax.annotation.processing.AbstractProcessor
May use three annotations to configure itself:
jx.a.p.SupportedAnnotationTypes – Used to flag which Annotation Types are managed by the processor
jx.a.p.SupportedSourceVersion – Used to flag the latest Java source level supported by the processor
jx.a.p.SupportedOptions – Used to register custom parameters that may be passed through the command line
TL;DR – Implement the process() method
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13. Annotation Processors
Annotation Processing API
Annotation processing happens in ‘rounds’
In each round, a subset of sources are compiled, and then processors matching the annotations found on those sources are called
Processing ends when no more sources/annotations are pending
Processors may claim all annotation types with a wildcard
process() method has two parameters:
Set<? extends jx.lang.model.element.TypeElement> – subset of annotations being processed
jx.a.p.RoundEnvironment – access to information about the current and previous round
Copyright © 2017 Accenture. All rights reserved.

14. ANNOTATION PROCESSORS
Creating Files
jx.a.p.ProcessingEnvironment also provides access to the Filer utility that allows for easy file creation
Files are placed in the right folder as required by the compiler settings
Folder hierarchy matching the package name
JavaFileObject jfo = processingEnv.getFiler()
.createSourceFile(newClassQualifiedName);
Writer writer = jfo.openWriter();
...or...
.createClassFile(newClassQualifiedName);
OutputStream os = jfo.openOutputStream();
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15. ANNOTATION PROCESSORS
How the compiler knows?
Annotation Processors leverage the standard services mechanism
Package the processors in a Jar file
Include file META-INF/services/javax.annotation.processing.Processor
Contents are the fully qualified names of the bundled processors, one per line
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16. Annotation Processors
Running Annotation Processors
Find more information about APT in JavaOne 2014 session:
annotation-processors-do-the-hard-work
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17. Annotation Processors
Running Annotation Processors
Multiple ways:
javac
Apache Maven builds
Continuous Integration builds
IDE
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18. Adapt legacy APT projects to Java 9
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19. Adapt legacy code Upgrading your code to Java 9
Update <java.version> tag in pom.xml
<java.version>1.9</java.version>
Update version of maven-compiler-plugin
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.6.2</version>
Upgrade the supported source version in Processor class
@SupportedAnnotationTypes(“com.foo.AnnotationSample")
@SupportedSourceVersion(SourceVersion.RELEASE_9)
public class AnnotationSampleProcessor
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20. Annotations api in java 9
Upgrading your code to Java 9
mvn clean install finish without errors:
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21. Annotations api in java 9
Executing upgraded projects
DEMO
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22. Adapt legacy code Upgrading your code to Java 9
Upgraded legacy code sample can be found in github:
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23. What’s new in Java 9 APT API
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24. Annotations api in java 9
Overview
Annotation
To add information about the annotation processor, date, and comments:
@Generated(value = "com.foo.processors.SampleProcessor",
date = " T09:43: ",
comments = "Sample")
Processed as a subsequent step by the annotation processor.
Two new methods in RoundEnvironment interface
Simplify processing of multiple annotations
default Set<? extends Element> getElementsAnnotatedWithAny​(
Set<Class<? extends Annotation>> annotations);
TypeElement... annotations);
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25. Annotations api in java 9
Overview
Changes in all methods of Filer interface.
To manage files in a module, module name is prefixed to the type name and separated using a “/” character, i.e.:
JavaFileObject jfo = processingEnv.getFiler().createSourceFile(
"com.foo/com.foo.Bar");
JavaFileObject jfo = processingEnv.getFiler().getResource(location, "com.foo/com.foo", "Bar");
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26. NEW features in java 9 Generated Annotation
It’s a best practice to include this annotation in the generated code:
= \"" + this.getClass().getName() +
"\" , date = \"" +
LocalDateTime.now() +
"\", comments = \"Test generator\")");
MUST have the name of
the code generator
Date when the source was generated
Comments
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27. New features in java 9 Generated Annotation
During annotation processing,the Generated annotation will be found but nothing is done, it’s just informational.
Generated code:
Name of the code generator
Generation date
Comments
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28. Annotations api in java 9
Module
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29. Annotation Processors and Modules in Java 9
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30. aNNOTATION PROCESSORS and modules
Creating classes in modules
In previous examples we have three different jar files:
Annotation type
Annotation processor
classes that use annotations
Dependencies are managed using the regular classpath
annotation.processor
annotation
client
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31. aNNOTATION PROCESSORS and modules
Grouping classes in modules
One module per jar file.
Put a module-info.java file into each module.
Each module-info file needs to define exported packages and required modules.
annotation.processor
annotation
client
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32. aNNOTATION PROCESSORS and modules
Creating classes in modules
annotation module:
module com.foo.annotation {
exports com.foo.annotation; }
annotation.processor module:
module com.foo.annotation.processors {
requires com.foo.annotation;
requires java.compiler;
client module:
module com.foo.client {
exports com.foo.client;
annotation.processor
annotation
client
Why? Because we annotation
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33. aNNOTATION PROCESSORS and modules
Creating classes in modules
DEMO
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34. SUMMARY APT API is as powerful as in previous versions.
All your legacy code still works as expected.
You can add a couple a of new functionalities:
@Generator annotation
Simplified processing of multiple annotations
You can also manage file generation in other modules
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35. Q & A
Many thanks for
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