@Eliminate("Boilerplate")

Using Java annotations to reduce boilerplate code.

Transcript

1. @Eliminate(“Boilerplate”) Ryan Harter @rharter
2. JAVA HAS BOILERPLATE
3. JAVA IS BOILERPLATE
4. public class User { String username; String firstname; String lastname; int age; public String getUsername() { return username; } public String getFirstname() { return firstname; } public String getLastname() { return lastname; } public int getAge() { return age; } }
5. public final class UserBuilder { private String username; private String firstName; private String lastName; private int age; public UserBuilder() { }\ public UserBuilder username(String username) { this.username = username; return this; }\ public UserBuilder firstName(String firstName) { this.firstName = firstName; return this; }\
6. return this; }\ public UserBuilder lastName(String lastName) { this.lastName = lastName; return this; }\ public UserBuilder age(int age) { this.age = age; return this; }\ public User build() { User user = new User(); user.username = this.username; user.firstName = this.firstName; user.lastName = this.lastName; user.age = this.age; return user; }\ }\
7. Annotation Processing + Code Generation
8. Annotation Processing
9. Annotation Processing
10. Annotation Processing • Part of javac
11. Annotation Processing • Part of javac • Read @Annotated source
12. Annotation Processing • Part of javac • Read @Annotated source • Generate .java source files
13. Benefits
14. Benefits • Write your code generator once
15. Benefits • Write your code generator once • Trust the generated code
16. Components
17. Components • Annotations
18. Components • Annotations • Processor
19. Components • Annotations • Processor • APT (Annotation Processing Tool)
20. Components • Annotations • Processor • APT (Annotation Processing Tool) • Annotated Source
21. Annotations @Target(ElementType.TYPE) @Retention(RetentionPolicy.SOURCE) public @interface Builder { }
22. Annotations @Target(ElementType.TYPE) @Retention(RetentionPolicy.SOURCE) public @interface Builder { }
23. Annotations @Target(ElementType.TYPE) @Retention(RetentionPolicy.SOURCE) public @interface Builder { }
24. Annotations @Target(ElementType.TYPE) @Retention(RetentionPolicy.SOURCE) public @interface Builder { }
25. Annotation Processor public class FooProcessor extends AbstractProcessor { }\\
26. Annotation Processor public class FooProcessor extends AbstractProcessor { public FooProcessor() { super(); }\ }\\
27. Annotation Processor public class FooProcessor extends AbstractProcessor { private Messager messager; private Filer filer; … @Override public synchronized void init( ProcessingEnvironment processingEnv) { super.init(processingEnv); this.messager = processingEnv.getMessager(); this.filer = processingEnv.getFiler(); }\ }\\
28. Annotation Processor public class FooProcessor extends AbstractProcessor { … @Override public SourceVersion getSupportedSourceVersion() { return SourceVersion.latestSupported(); }\ }\\
29. Annotation Processor public class FooProcessor extends AbstractProcessor { … @Override public Set<String> getSupportedAnnotationTypes() { return ImmutableSet.of(Builder.class.getCanonicalName()); } }\\
30. Annotation Processor public class FooProcessor extends AbstractProcessor { … @Override public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) { ... } }\\
31. Annotation Processor public class FooProcessor extends AbstractProcessor { … @Override public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) { ... } }
32. Processing Rounds Java Sources APT Completed
33. Processing Rounds Java Sources APT Completed Round 1
34. Processing Rounds Java Sources APT Completed Round 1
35. Processing Rounds Java Sources APT Completed Round 1
36. Processing Rounds Java Sources APT Completed Round 1
37. Processing Rounds Java Sources APT Completed Round 2
38. Processing Rounds Java Sources APT Completed Round 2
39. Processing Rounds Java Sources APT Completed Complete
40. Annotation Processor • ServiceLoader Discovery File com.ryanharter.example.annotations.BuilderProcessor META-INF/services/javax.annotation.processing.Processor
41. Add to APT Classpath dependencies { compile project(':annotation') apt project(':processor') } app/build.gradle https://github.com/tbroyer/gradle-apt-plugin https://bitbucket.org/hvisser/android-apt
42. Code Generation
43. Code Generation
44. Code Generation • Pair well with Annotation Processors
45. Code Generation • Pair well with Annotation Processors • Used to generate new Java source files
46. Code Generation • Pair well with Annotation Processors • Used to generate new Java source files • JavaPoet represents Java source as model
47. Code Generation • Pair well with Annotation Processors • Used to generate new Java source files • JavaPoet represents Java source as model https://github.com/square/javapoet
48. JavaPoet https://github.com/square/javapoet
49. JavaPoet • Uses Fluent API with builders https://github.com/square/javapoet
50. JavaPoet • Uses Fluent API with builders • Based on Specs https://github.com/square/javapoet
51. JavaPoet • Uses Fluent API with builders • Based on Specs • TypeSpec https://github.com/square/javapoet
52. JavaPoet • Uses Fluent API with builders • Based on Specs • TypeSpec • MethodSpec https://github.com/square/javapoet
53. JavaPoet • Uses Fluent API with builders • Based on Specs • TypeSpec • MethodSpec • ParameterSpec https://github.com/square/javapoet
54. JavaPoet • Uses Fluent API with builders • Based on Specs • TypeSpec • MethodSpec • ParameterSpec • FieldSpec https://github.com/square/javapoet
55. JavaPoet public final class UserBuilder { // fields private String username; … // methods public UserBuilder username(String username) { this.username = username; return this; } … }\
56. JavaPoet public final class UserBuilder { // fields private String username; … // methods public UserBuilder username(String username) { this.username = username; return this; } … }\
57. JavaPoet public final class UserBuilder String builderName = String.format("%sBuilder", type.getSimpleName()); ClassName builderType = ClassName.get(packageName, builderName);
58. JavaPoet public final class UserBuilder { // fields private String username; … // methods public UserBuilder username(String username) { this.username = username; return this; } … }\
59. private String username; JavaPoet
60. JavaPoet Modifiers private String username;
61. JavaPoet Modifiers Type private String username;
62. JavaPoet Modifiers Type private String username; Name
63. JavaPoet FieldSpec username = FieldSpec .builder(String.class, "username", Modifier.PRIVATE) .build(); private String username; Modifiers Type private String username; Name
64. private String username; JavaPoet Modifiers Type Name FieldSpec username = FieldSpec .builder(String.class, "username", Modifier.PRIVATE) .build(); private String username;
65. JavaPoet FieldSpec username = FieldSpec .builder(String.class, "username", Modifier.PRIVATE) .build(); private String username;
66. JavaPoet public final class UserBuilder {\ // fields private String username; … // methods public UserBuilder username(String username) {\ this.username = username; return this; }\ … }\
67. JavaPoet // methods public UserBuilder username(String username) {\ this.username = username; return this; }\
68. JavaPoet Modifiers // methods public UserBuilder username(String username) {\ this.username = username; return this; }\
69. JavaPoet Modifiers Return Type // methods public UserBuilder username(String username) {\ this.username = username; return this; }\
70. JavaPoet Modifiers Return Type Name // methods public UserBuilder username(String username) {\ this.username = username; return this; }\
71. JavaPoet Modifiers Return Type Name Parameters // methods public UserBuilder username(String username) {\ this.username = username; return this; }\
72. JavaPoet Modifiers Return Type Name Parameters Statements // methods public UserBuilder username(String username) {\ this.username = username; return this; }\
73. JavaPoet MethodSpec usernameSetter = MethodSpec.methodBuilder("username") .addModifiers(PUBLIC) .returns(builderType) .addParameter(String.class, "username") .addStatement("this.$N = username", username) .addStatement("return this") .build(); Modifiers Return Type Name Parameters Statements // methods public UserBuilder username(String username) {\ this.username = username; return this; }\
74. JavaPoet Modifiers Return Type Name Parameters Statements MethodSpec usernameSetter = MethodSpec.methodBuilder("username") .addModifiers(PUBLIC) .returns(builderType) .addParameter(String.class, "username") .addStatement("this.$N = username", username) .addStatement("return this") .build(); // methods public UserBuilder username(String username) {\ this.username = username; return this; }\
75. JavaPoet Modifiers Return Type Name Parameters Statements // methods public UserBuilder username(String username) {\ this.username = username; return this; }\ MethodSpec usernameSetter = MethodSpec.methodBuilder("username") .addModifiers(PUBLIC) .returns(builderType) .addParameter(String.class, "username") .addStatement("this.$N = username", username) .addStatement("return this") .build();
76. JavaPoet Modifiers Return Type Name Parameters Statements // methods public UserBuilder username(String username) {\ this.username = username; return this; }\ MethodSpec usernameSetter = MethodSpec.methodBuilder("username") .addModifiers(PUBLIC) .returns(builderType) .addParameter(String.class, "username") .addStatement("this.$N = username", username) .addStatement("return this") .build();
77. JavaPoet Modifiers Return Type Name Parameters Statements // methods public UserBuilder username(String username) {\ this.username = username; return this; }\ MethodSpec usernameSetter = MethodSpec.methodBuilder("username") .addModifiers(PUBLIC) .returns(builderType) .addParameter(String.class, "username") .addStatement("this.$N = username", username) .addStatement("return this") .build();
78. JavaPoet Modifiers Return Type Name Parameters Statements // methods public UserBuilder username(String username) {\ this.username = username; return this; }\ MethodSpec usernameSetter = MethodSpec.methodBuilder("username") .addModifiers(PUBLIC) .returns(builderType) .addParameter(String.class, "username") .addStatement("this.$N = username", username) .addStatement("return this") .build();
79. // methods public UserBuilder username(String username) {\ this.username = username; return this; }\ JavaPoet MethodSpec usernameSetter = MethodSpec.methodBuilder("username") .addModifiers(PUBLIC) .returns(builderType) .addParameter(String.class, "username") .addStatement("this.$N = username", username) .addStatement("return this") .build();
80. JavaPoet public final class UserBuilder {\ // fields private String username; … // methods public UserBuilder username(String username) {\ this.username = username; return this; }\ … }\
81. JavaPoet public final class UserBuilder {\ }\
82. JavaPoet Modifiers public final class UserBuilder {\ }\
83. JavaPoet Modifiers Name public final class UserBuilder {\ }\
84. JavaPoet Modifiers Name Content public final class UserBuilder {\ }\
85. JavaPoet TypeSpec builder = TypeSpec.classBuilder(builderType) .addModifiers(PUBLIC, FINAL) .addField(username) .addMethod(usernameSetter) .build(); Modifiers Name Content public final class UserBuilder {\ }\
86. JavaPoet Modifiers Name Content TypeSpec builder = TypeSpec.classBuilder(builderType) .addModifiers(PUBLIC, FINAL) .addField(username) .addMethod(usernameSetter) .build(); public final class UserBuilder {\ }\
87. JavaPoet Modifiers Name Content TypeSpec builder = TypeSpec.classBuilder(builderType) .addModifiers(PUBLIC, FINAL) .addField(username) .addMethod(usernameSetter) .build(); public final class UserBuilder {\ }\
88. JavaPoet Modifiers Name Content TypeSpec builder = TypeSpec.classBuilder(builderType) .addModifiers(PUBLIC, FINAL) .addField(username) .addMethod(usernameSetter) .build(); public final class UserBuilder {\ }\
89. JavaPoet TypeSpec builder = TypeSpec.classBuilder(builderType) .addModifiers(PUBLIC, FINAL) .addField(username) .addMethod(usernameSetter) .build(); public final class UserBuilder {\ }\
90. Annotation Processor @Override public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) { }
91. @Override public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) { for (Element el : roundEnv.getElementsAnnotatedWith(Builder.class)) { } } @Override public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) { for (Element el : roundEnv.getElementsAnnotatedWith(Builder.class)) { } } Annotation Processor
92. @Override public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) { for (Element el : roundEnv.getElementsAnnotatedWith(Builder.class)) { } } @Override public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) { for (Element el : roundEnv.getElementsAnnotatedWith(Builder.class)) { } } Annotation Processor
93. @Override public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) { for (Element el : roundEnv.getElementsAnnotatedWith(Builder.class)) { // get element metadata // create private fields and public setters // create the build method // create the builder type // write the java source file } } Annotation Processor
94. // get element metadata String packageName = getPackageName(type); String targetName = lowerCamelCase(type.getSimpleName().toString()); Set<VariableElement> vars = getNonPrivateVariables(type); String builderName = String.format("%sBuilder", type.getSimpleName()); ClassName builderType = ClassName.get(packageName, builderName); Annotation Processor
95. // get element metadata String packageName = getPackageName(type); String targetName = lowerCamelCase(type.getSimpleName().toString()); Set<VariableElement> vars = getNonPrivateVariables(type); String builderName = String.format("%sBuilder", type.getSimpleName()); ClassName builderType = ClassName.get(packageName, builderName); Annotation Processor
96. // get element metadata String packageName = getPackageName(type); String targetName = lowerCamelCase(type.getSimpleName().toString()); Set<VariableElement> vars = getNonPrivateVariables(type); String builderName = String.format("%sBuilder", type.getSimpleName()); ClassName builderType = ClassName.get(packageName, builderName); Annotation Processor
97. // get element metadata String packageName = getPackageName(type); String targetName = lowerCamelCase(type.getSimpleName().toString()); Set<VariableElement> vars = getNonPrivateVariables(type); String builderName = String.format("%sBuilder", type.getSimpleName()); ClassName builderType = ClassName.get(packageName, builderName); Annotation Processor
98. // get element metadata String packageName = getPackageName(type); String targetName = lowerCamelCase(type.getSimpleName().toString()); Set<VariableElement> vars = getNonPrivateVariables(type); String builderName = String.format("%sBuilder", type.getSimpleName()); ClassName builderType = ClassName.get(packageName, builderName); Annotation Processor
99. // create private fields and public setters List<FieldSpec> fields = new ArrayList<FieldSpec>(vars.size()); List<MethodSpec> setters = new ArrayList<MethodSpec>(vars.size()); for (VariableElement var : vars) { TypeName typeName = TypeName.get(var.asType()); String name = var.getSimpleName().toString(); // create the field fields.add(FieldSpec.builder(typeName, name, PRIVATE).build()); // create the setter setters.add(MethodSpec.methodBuilder(name) .addModifiers(PUBLIC) .returns(builderType) .addParameter(typeName, name) .addStatement("this.$N = $N", name, name) .addStatement("return this") .build()); } Annotation Processor
100. // create private fields and public setters List<FieldSpec> fields = new ArrayList<FieldSpec>(vars.size()); List<MethodSpec> setters = new ArrayList<MethodSpec>(vars.size()); for (VariableElement var : vars) { TypeName typeName = TypeName.get(var.asType()); String name = var.getSimpleName().toString(); // create the field fields.add(FieldSpec.builder(typeName, name, PRIVATE).build()); // create the setter setters.add(MethodSpec.methodBuilder(name) .addModifiers(PUBLIC) .returns(builderType) .addParameter(typeName, name) .addStatement("this.$N = $N", name, name) .addStatement("return this") .build()); } Annotation Processor
101. // create private fields and public setters List<FieldSpec> fields = new ArrayList<FieldSpec>(vars.size()); List<MethodSpec> setters = new ArrayList<MethodSpec>(vars.size()); for (VariableElement var : vars) { TypeName typeName = TypeName.get(var.asType()); String name = var.getSimpleName().toString(); // create the field fields.add(FieldSpec.builder(typeName, name, PRIVATE).build()); // create the setter setters.add(MethodSpec.methodBuilder(name) .addModifiers(PUBLIC) .returns(builderType) .addParameter(typeName, name) .addStatement("this.$N = $N", name, name) .addStatement("return this") .build()); } Annotation Processor
102. // create private fields and public setters List<FieldSpec> fields = new ArrayList<FieldSpec>(vars.size()); List<MethodSpec> setters = new ArrayList<MethodSpec>(vars.size()); for (VariableElement var : vars) { TypeName typeName = TypeName.get(var.asType()); String name = var.getSimpleName().toString(); // create the field fields.add(FieldSpec.builder(typeName, name, PRIVATE).build()); // create the setter setters.add(MethodSpec.methodBuilder(name) .addModifiers(PUBLIC) .returns(builderType) .addParameter(typeName, name) .addStatement("this.$N = $N", name, name) .addStatement("return this") .build()); } Annotation Processor
103. // create private fields and public setters List<FieldSpec> fields = new ArrayList<FieldSpec>(vars.size()); List<MethodSpec> setters = new ArrayList<MethodSpec>(vars.size()); for (VariableElement var : vars) { TypeName typeName = TypeName.get(var.asType()); String name = var.getSimpleName().toString(); // create the field fields.add(FieldSpec.builder(typeName, name, PRIVATE).build()); // create the setter setters.add(MethodSpec.methodBuilder(name) .addModifiers(PUBLIC) .returns(builderType) .addParameter(typeName, name) .addStatement("this.$N = $N", name, name) .addStatement("return this") .build()); } Annotation Processor
104. // create private fields and public setters List<FieldSpec> fields = new ArrayList<FieldSpec>(vars.size()); List<MethodSpec> setters = new ArrayList<MethodSpec>(vars.size()); for (VariableElement var : vars) { TypeName typeName = TypeName.get(var.asType()); String name = var.getSimpleName().toString(); // create the field fields.add(FieldSpec.builder(typeName, name, PRIVATE).build()); // create the setter setters.add(MethodSpec.methodBuilder(name) .addModifiers(PUBLIC) .returns(builderType) .addParameter(typeName, name) .addStatement("this.$N = $N", name, name) .addStatement("return this") .build()); } Annotation Processor
105. // create the build method TypeName targetType = TypeName.get(type.asType()); MethodSpec.Builder buildMethodBuilder = MethodSpec.methodBuilder("build") .addModifiers(PUBLIC) .returns(targetType) .addStatement("$1T $2N = new $1T()", targetType, targetName); for (FieldSpec field : fields) { buildMethodBuilder .addStatement("$1N.$2N = this.$2N", targetName, field); } buildMethodBuilder.addStatement("return $N", targetName); MethodSpec buildMethod = buildMethodBuilder.build(); Annotation Processor
106. // create the build method TypeName targetType = TypeName.get(type.asType()); MethodSpec.Builder buildMethodBuilder = MethodSpec.methodBuilder("build") .addModifiers(PUBLIC) .returns(targetType) .addStatement("$1T $2N = new $1T()", targetType, targetName); for (FieldSpec field : fields) { buildMethodBuilder .addStatement("$1N.$2N = this.$2N", targetName, field); } buildMethodBuilder.addStatement("return $N", targetName); MethodSpec buildMethod = buildMethodBuilder.build(); Annotation Processor
107. // create the build method TypeName targetType = TypeName.get(type.asType()); MethodSpec.Builder buildMethodBuilder = MethodSpec.methodBuilder("build") .addModifiers(PUBLIC) .returns(targetType) .addStatement("$1T $2N = new $1T()", targetType, targetName); for (FieldSpec field : fields) { buildMethodBuilder .addStatement("$1N.$2N = this.$2N", targetName, field); } buildMethodBuilder.addStatement("return $N", targetName); MethodSpec buildMethod = buildMethodBuilder.build(); Annotation Processor
108. // create the build method TypeName targetType = TypeName.get(type.asType()); MethodSpec.Builder buildMethodBuilder = MethodSpec.methodBuilder("build") .addModifiers(PUBLIC) .returns(targetType) .addStatement("$1T $2N = new $1T()", targetType, targetName); for (FieldSpec field : fields) { buildMethodBuilder .addStatement("$1N.$2N = this.$2N", targetName, field); } buildMethodBuilder.addStatement("return $N", targetName); MethodSpec buildMethod = buildMethodBuilder.build(); Annotation Processor
109. // create the build method TypeName targetType = TypeName.get(type.asType()); MethodSpec.Builder buildMethodBuilder = MethodSpec.methodBuilder("build") .addModifiers(PUBLIC) .returns(targetType) .addStatement("$1T $2N = new $1T()", targetType, targetName); for (FieldSpec field : fields) { buildMethodBuilder .addStatement("$1N.$2N = this.$2N", targetName, field); } buildMethodBuilder.addStatement("return $N", targetName); MethodSpec buildMethod = buildMethodBuilder.build(); Annotation Processor
110. // create the build method TypeName targetType = TypeName.get(type.asType()); MethodSpec.Builder buildMethodBuilder = MethodSpec.methodBuilder("build") .addModifiers(PUBLIC) .returns(targetType) .addStatement("$1T $2N = new $1T()", targetType, targetName); for (FieldSpec field : fields) { buildMethodBuilder .addStatement("$1N.$2N = this.$2N", targetName, field); } buildMethodBuilder.addStatement("return $N", targetName); MethodSpec buildMethod = buildMethodBuilder.build(); Annotation Processor
111. Annotation Processor // create the builder TypeSpec builder = TypeSpec.classBuilder(builderType) .addModifiers(PUBLIC, FINAL) .addFields(fields) .addMethods(setters) .addMethod(buildMethod) .build();
112. // write java source file JavaFile file = JavaFile .builder(builderType.packageName(), builder.build()) .build(); try { file.writeTo(filer); } catch (IOException e) { messager.printMessage(Diagnostic.Kind.ERROR, "Failed to write file for element", el); } Annotation Processor
113. @Override public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) { for (Element el : roundEnv.getElementsAnnotatedWith(Builder.class)) { // get element metadata // create private fields and public setters // create the build method // create the builder type // write the java source file } } Annotation Processor
114. Using our Annotation public class User {/ String username;/ String firstName;/ String lastName;/ int age;/ }/
115. Using our Annotation @Builder public class User {/ String username;/ String firstName;/ String lastName;/ int age;/ }/
116. Using our Annotation @Builder public class User { String username; String firstName; String lastName; int age; } User user = new UserBuilder() .username("rharter") .firstName("Ryan") .lastName("Harter") .age(30) .build();
117. References • Android APT Plugin - https://bitbucket.org/hvisser/android-apt • Gradle APT Plugin - https://github.com/tbroyer/gradle-apt-plugin • JavaPoet - https://github.com/square/javapoet
118. Find Me • @rharter • http://ryanharter.com