Code generation on the Java VM 2019-12-05

Transcript

1. Code generation on the Java VM Sean Sullivan 2019-12-05

2. Code generation Java Kotlin Scala

3. Why code generation?

4. less boilerplate more consistency Why code generation?

5. class names parameter names method names exception names Consistency error

   handling logging JSON serialization network I/O

6. Code generation is not a new idea

7. 2001: Apache Axis

8. wsdl2java August 2001

9. 2003: Apache XmlBeans

10. September 2003 SchemaCodeGenerator

11. The most common use case for source code generation…

12. generating client libraries for REST API’s

13. bytecode source code Two kinds of code generation

14. Code generation Bytecode generation

15. Bytecode generators produce Java class definitions

16. ByteBuddy ObjectWeb ASM cglib Bytecode libraries Javassist Commons BCEL AspectJ

17. Spring Framework

18. cglib spring-core

19. cglib spring-beans

20. Micronaut framework

21. “Unlike Spring which relies exclusively on runtime reflection and proxies,

    Micronaut uses compile time data to implement dependency injection” micronaut https://docs.micronaut.io/latest/guide/ioc.html

22. “This goal is achieved through the use of Java’s annotation

    processors" micronaut https://docs.micronaut.io/latest/guide/index.html

23. micronaut https://github.com/micronaut-projects/micronaut-core Annotation processors

24. micronaut ObjectWeb ASM https://github.com/micronaut-projects/micronaut-core

25. Mockito

26. mockito 2.x ByteBuddy https://github.com/mockito/mockito

27. “Mockito switched from CGLIB to the great library ByteBuddy to

    make mocks” https://github.com/mockito/mockito/wiki/What%27s-new-in-Mockito-2 mockito 2.x

28. Datadog Java agent

29. Datadog Java agent ByteBuddy https://github.com/DataDog/dd-trace-java

30. How can I implement a custom Java agent?

31. Java agent example https://github.com/sullis/java-lang-instrument-example/

32. Java agent example “premain” method https://github.com/sullis/java-lang-instrument-example/

33. Java agent example https://github.com/sullis/java-lang-instrument-example/ ByteBuddy AgentBuilder

34. Code generation Source code generation

35. java.lang.StringBuilder java.io.StringWriter Source generation

36. javapoet CodeModel jdeparser2 javaparser Source generation

37. kotlinpoet kotlinx-ast kastree Source generation

38. scalameta treehugger.scala Source generation

39. JavaPoet

40. JavaPoet https://github.com/square/javapoet

41. package com.example.helloworld; public final class HelloWorld { public static void

    main(String[] args) { System.out.println("Hello, JavaPoet!"); } } JavaPoet

42. import com.squareup.javapoet.*; MethodSpec main = MethodSpec.methodBuilder("main") .addModifiers(Modifier.PUBLIC, Modifier.STATIC) .returns(void.class) .addParameter(String[].class,

    "args") .addStatement("$T.out.println($S)", System.class, "Hello, JavaPoet!") .build(); TypeSpec helloWorld = TypeSpec.classBuilder("HelloWorld") .addModifiers(Modifier.PUBLIC, Modifier.FINAL) .addMethod(main) .build(); JavaFile javaFile = JavaFile.builder("com.example.helloworld", helloWorld) .build(); javaFile.writeTo(System.out); JavaPoet method builder class builder file builder

43. AWS SDK for Java v2

44. AWS SDK for Java v2 “To provide SDK support for

    the many services that AWS owns, the AWS SDKs make extensive use of code generation” https://aws.amazon.com/blogs/developer/aws-sdk-for-java-2-x-released/

45. AWS SDK for Java v2

46. JavaPoet AWS SDK for Java v2

47. Dagger

48. “Dagger 2 is the first to implement the full stack

    with generated code” Dagger 2.x “Dependency injection frameworks have existed for years with a whole variety of APIs for configuring and injecting” https://dagger.dev/users-guide.html

49. Dagger 2.x https://dagger.dev/users-guide.html

50. JavaPoet Dagger 2.x

51. REST API code generators apibuilder project guardrail project openapi-generator

52. ApiBuilder project

53. https://www.apibuilder.io/ ApiBuilder

54. https://github.com/apicollective/apibuilder-generator/ ApiBuilder

55. ApiBuilder demo

56. Guardrail project

57. https://guardrail.dev/ Guardrail

58. https://github.com/twilio/guardrail Guardrail

59. https://github.com/twilio/guardrail Guardrail: Scala ScalaMeta

60. https://github.com/twilio/guardrail Guardrail: Java JavaParser

61. Guardrail example

62. guardrail-maven-plugin <plugin> <groupId>com.twilio</groupId> <artifactId>guardrail-maven-plugin_2.12</artifactId> <version>0.54.5</version> <executions> … </executions> </plugin>

63. guardrail-maven-plugin <configuration> <language>java</language> <kind>client</kind> <framework>dropwizard</framework> <specPath>${project.basedir}/src/main/openapi/petstore.json</specPath> <packageName>com.example.clients.petstore</packageName> </configuration> Java client

64. guardrail-maven-plugin

65. openapi-generator project

66. openapi-generator

67. openapi-generator

68. openapi-generator

69. Final thoughts code generation is a powerful technique use a

    code generator to generate client libraries contribute to open source projects

70. Code generation Questions?

71. The End