How can we write less code by generating code?

Transcript

1. How can we write less code by generating code? (Not skynet) 24/4/2018
2. Gil Goldzweig https://github.com/gilgoldzweig Android developer @ NYX
4. How can we write less code by generating code? 10/01/2019
5. Annotation Processing
6. Annotation Processor tool - APT • A tool for the Javac(Java compiler) • Added JDK 1.5 • Reads & Process @Annotated sources
7. Chain of events Write (.java) Compile (.class) Package (.jar) Dex (.dex) Package (.apk) APT (.java) Project lifecycle - APT
8. Project lifecycle Write (.java) Compile (.class) Package (.jar)
9. Chain of events Write (.java) Compile (.class) Package (.jar) Dex (.dex) Package (.apk) Project lifecycle - android
10. Example
11. Before - Gencycler RecyclerView
12. Before - Gencycler ViewHolder class LectureViewHolder extends RecyclerView.ViewHolder { TextView title; TextView description; TextView date; LectureViewHolder(View itemView) { super(itemView); title = itemView.findViewById(R.id.lecture_title); description = itemView.findViewById(R.id.lecture_desc); date = itemView.findViewById(R.id.lecture_date); } }
13. Before - Gencycler Adapter - OnCreateViewHolder public class LectureAdapter extends RecyclerView.Adapter<LectureViewHolder> { … @Override public LectureViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { return new LectureViewHolder(inflater .inflate(R.layout.item_lecture, parent, false)); } }
14. Before - Gencycler Adapter - GetItemCount public class LectureAdapter extends RecyclerView.Adapter<LectureViewHolder> { … @Override public int getItemCount() { return lectures.size(); } }
15. Before - Gencycler Adapter - GetItemViewType public class LectureAdapter extends RecyclerView.Adapter<LectureViewHolder> { … @Override public int getItemViewType(int position) { return super.getItemViewType(position); } }
16. Before - Gencycler RecyclerView - OnBindViewHolder public class LectureAdapter extends RecyclerView.Adapter<LectureViewHolder> { … @Override public void onBindViewHolder(LectureViewHolder holder, int position) { Lecture lecture = lectures.get(position); } }
17. Fun Fact 81
18. Gencycler
19. RecyclerView + Gencycler public class LectureAdapter { } Recyclerview - Gencycler
20. RecyclerView + Gencycler @RecyclerAdapter(data = Lecture.class, ui = R.layout.item_lecture) public class LectureAdapter { } Recyclerview - Gencycler
21. RecyclerView + Gencycler @RecyclerAdapter public class LectureAdapter { } Recyclerview - Gencycler
22. RecyclerView + Gencycler @RecyclerAdapter(data = Lecture.class) public class LectureAdapter { } Recyclerview - Gencycler
23. RecyclerView + Gencycler @RecyclerAdapter(data = Lecture.class, ui = R.layout.item_lecture) public class LectureAdapter { } Recyclerview - Gencycler
24. RecyclerView + Gencycler @RecyclerAdapter(data = Lecture.class, ui = R.layout.item_lecture) public class LectureAdapter { } Recyclerview - Gencycler
25. RecyclerView + Gencycler @RecyclerAdapter(data = Lecture.class, ui = R.layout.item_lecture) public class LectureAdapter extends GeneratedLectureAdapter { } Recyclerview - Gencycler
26. RecyclerView + Gencycler @RecyclerAdapter(data = Lecture.class, ui = R.layout.item_lecture) public class LectureAdapter extends GeneratedLectureAdapter { @Override public void onBindLectureViewHolder(LectureViewHolder holder, int position, @NotNull Lecture lecture) { //Actual logic (setText etc… ) } } Recyclerview - Gencycler
27. 7 Lines
28. 81 vs 7 Lines
29. Questions?
30. 1. Annotations 2. Processor 2.1 Code Generator Components
31. 1. Annotations 2. Processor 2.1 Code Generator Components
32. Annotation public interface RecyclerAdapter {}
33. Annotation public @interface RecyclerAdapter {}
34. Annotation @Target(ElementType.TYPE) public @interface RecyclerAdapter {}
35. Target - Limit where the annotation can be placed • Type(Class) • Field • Method • Parameter • AnnotationType • Constructor • Package • LocalVariable (Java 1.8) • TypeParameter (Java 1.8)
36. Annotation @Retention(RetentionPolicy.SOURCE) @Target(ElementType.TYPE) public @interface RecyclerAdapter {}
37. Retention - When will the annotation can be used • Source(Annotation processor) • Runtime(Reflection) • Class(Annotation processor + Reflection)
38. Reflection Reflection • Create new instances of objects • Invoke methods • Examine properties of classes (fields, methods, constructors) • Modify field values
39. Reflection Reflection
40. Reflection Reflection - drawbacks • No compile-time verification • Breaks easily • Expensive • Hard to maintain
41. Annotation @Retention(RetentionPolicy.SOURCE) //Compile-time @Target(ElementType.TYPE) //Can be placed on a class public @interface RecyclerAdapter {}
42. Questions?
43. 1. Annotations 2. Processor 2.1 Code Generator Components
44. AbstractProcessor public class RecyclerProcessor extends AbstractProcessor { } Processor
45. AbstractProcessor public class RecyclerProcessor extends AbstractProcessor { } Processor
46. AbstractProcessor public class RecyclerProcessor extends AbstractProcessor { @Override public synchronized void init(ProcessingEnvironment env) { } } Processor
47. AbstractProcessor public class RecyclerProcessor extends AbstractProcessor { @Override public synchronized void init(ProcessingEnvironment env) { } } Processor
48. AbstractProcessor ProcessingEnvironment • Filer - used to create new source, class, or auxiliary files • Opptions • Messenger - Reports errors, warnings, and other notices • Utility methods for using elements/types
49. AbstractProcessor public class RecyclerProcessor extends AbstractProcessor { … @Override public Set<String> getSupportedAnnotationTypes() { return ImmutableSet.of(RecyclerAdapter.class .getCanonicalName()); } } Processor
50. AbstractProcessor public class RecyclerProcessor extends AbstractProcessor { … @Override public SourceVersion getSupportedSourceVersion() { return SourceVersion.latestSupported(); } } Processor
51. AbstractProcessor public class RecyclerProcessor extends AbstractProcessor { … @Override public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment env) { } } Processor
52. AbstractProcessor public class RecyclerProcessor extends AbstractProcessor { … @Override public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment env) { } } Processor
53. AbstractProcessor public class RecyclerProcessor extends AbstractProcessor { … @Override public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment env) { } } Processor
55. AbstractProcessor Java sources APT Completed Round one - sources LectureAdapter.java OtherAdapter.java Processing rounds
56. AbstractProcessor Java sources APT Completed Round one - sources Processing rounds LectureAdapter.java OtherAdapter.java Processing rounds
57. AbstractProcessor public class RecyclerProcessor extends AbstractProcessor { … @Override public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment env) { //RoundEnvironment will hold information about //the LectureAdapter.java & OtherAdapter.Java } } Processor
58. AbstractProcessor Java sources APT Completed Round one - new source files generated Processing rounds LectureGenrated.java OtherGenrated.java LectureAdapter.java OtherAdapter.java Processing rounds
59. AbstractProcessor Processing rounds Java sources APT Completed Round one - Completed Processing rounds LectureGenrated.java OtherGenrated.java LectureAdapter.java OtherAdapter.java Processing rounds
60. AbstractProcessor Processing rounds Java sources APT Completed Round two - generated sources Processing rounds LectureGenrated.java OtherGenrated.java LectureAdapter.java OtherAdapter.java Processing rounds Processing rounds Processing rounds
61. AbstractProcessor Processing rounds Java sources APT Completed Processing rounds LectureAdapter.java OtherAdapter.java LectureGenrated.java OtherGenrated.java Round two - generated sources Processing rounds
62. AbstractProcessor Processing rounds Java sources APT Completed LectureGenrated.java OtherGenrated.java Round two - Completed Processing rounds LectureAdapter.java OtherAdapter.java Processing rounds
63. Questions?
64. 1. Annotations 2. Processor 2.1 Code Generator Components
65. • Automatic ◦ Java/KotlinPoet (open source library created by square) • Manual ◦ Writer Code generation Code generation
66. Pros & Cons
67. + Easy usage + Very good documentation + Language objects oriented Automatic - Java/kotlinPoet - Very verbose code
68. + Easy usage Manual - StringBuilder - Not language objects oriented - Hard to maintain properly Manual - Writer
69. Example
70. package com.example.helloworld; public final class HelloWorld { public static void main(String[] args) { System.out.println("Hello, JavaPoet!"); } } What we want to generate
71. JavaPoet - method MethodSpec main = MethodSpec.methodBuilder("main") .addModifiers(Modifier.PUBLIC, Modifier.STATIC) .returns(void.class) .addParameter(String[].class, "args") .addStatement("System.out.println(\"Hello, JavaPoet!\")") .build();
72. JavaPoet - method MethodSpec main = MethodSpec.methodBuilder("main") .addModifiers(Modifier.PUBLIC, Modifier.STATIC) .returns(void.class) .addParameter(String[].class, "args") .addStatement("System.out.println(\"Hello, JavaPoet!\")") .build();
73. JavaPoet - method MethodSpec main = MethodSpec.methodBuilder("main") .addModifiers(Modifier.PUBLIC, Modifier.STATIC) .returns(void.class) .addParameter(String[].class, "args") .addStatement("System.out.println(\"Hello, JavaPoet!\")") .build();
74. JavaPoet - method MethodSpec main = MethodSpec.methodBuilder("main") .addModifiers(Modifier.PUBLIC, Modifier.STATIC) .returns(void.class) .addParameter(String[].class, "args") .addStatement("System.out.println(\"Hello, JavaPoet!\")") .build();
75. JavaPoet - method MethodSpec main = MethodSpec.methodBuilder("main") .addModifiers(Modifier.PUBLIC, Modifier.STATIC) .returns(void.class) .addParameter(String[].class, "args") .addStatement("System.out.println(\"Hello, JavaPoet!\")") .build();
76. JavaPoet - method MethodSpec main = MethodSpec.methodBuilder("main") .addModifiers(Modifier.PUBLIC, Modifier.STATIC) .returns(void.class) .addParameter(String[].class, "args") .addStatement("System.out.println(\"Hello, JavaPoet!\")") .build();
77. MethodSpec public static void main(String[] args) { System.out.println("Hello, JavaPoet!"); } JavaPoet - method / generated
78. JavaPoet - class TypeSpec helloWorld = TypeSpec.classBuilder("HelloWorld") .addModifiers(Modifier.PUBLIC, Modifier.FINAL) .addMethod(main) .build(); JavaPoet - class
79. JavaPoet - class TypeSpec helloWorld = TypeSpec.classBuilder("HelloWorld") .addModifiers(Modifier.PUBLIC, Modifier.FINAL) .addMethod(main) .build(); JavaPoet - method JavaPoet - class
80. JavaPoet - class TypeSpec helloWorld = TypeSpec.classBuilder("HelloWorld") .addModifiers(Modifier.PUBLIC, Modifier.FINAL) .addMethod(main) .build(); JavaPoet - method JavaPoet - class
81. JavaPoet - class TypeSpec helloWorld = TypeSpec.classBuilder("HelloWorld") .addModifiers(Modifier.PUBLIC, Modifier.FINAL) .addMethod(main) .build(); JavaPoet - class
82. MethodSpec public final class HelloWorld { public static void main(String[] args) { System.out.println("Hello, JavaPoet!"); } } JavaPoet - class JavaPoet - class JavaPoet - class / generated
83. JavaPoet - file JavaFile javaFile = JavaFile.builder("com.example.helloworld", helloWorld) .build(); JavaPoet - file
84. package com.example.helloworld; public final class HelloWorld { public static void main(String[] args) { System.out.println("Hello, JavaPoet!"); } } JavaPoet - file / generated
85. package com.example.helloworld; public final class HelloWorld { public static void main(String[] args) { System.out.println("Hello, JavaPoet!"); } } JavaPoet - file / generated
86. JavaPoet - file JavaFile javaFile = JavaFile.builder("com.example.helloworld", helloWorld) .build(); javaFile.writeTo(processingEnv.getFiler()); JavaPoet - file
87. JavaPoet MethodSpec main = MethodSpec.methodBuilder("main") .addModifiers(Modifier.PUBLIC, Modifier.STATIC) .returns(void.class) .addParameter(String[].class, "args") .addStatement("System.out.println(\"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(processingEnv.getFiler()); JavaPoet JavaPoet - code needed
88. JavaPoet - file Manual Writer codeWriter = procesingEnc.filer .createSource(StandardLocation.SOURCE_OUTPUT) .openWriter(); codeWriter .append("package com.example.helloworld;") .append("\n\n") .append("public final class HelloWorld {\n") .append(" ") .append("public static void main(String[] args) {\n") .append(" ") .append("System.out.println(\"Hello, JavaPoet!\");\n") .append(" }\n") .append("}");
89. AbstractProcessor • Resources ◦ META_INF ▪ services • javax.annotations.processing.Processor package.name.compiler.RecyclerProcessor Another processor if exist And another ... Declaring our processor
90. Benefits • No Runtime performance impact • Write your code generator once • Trust the generated code Benefits
91. Thank you
92. Here are some helpful links to help you build your own processor :) Annotation Processing : Don’t Repeat Yourself, Generate Your Code. Annotation processing 101 @Eliminate(Boilerplate) JavaPoet KotlinPoet Gencycler