@Eliminate("Boilerplate")

DroidconNYC talk about using Annotation Processors to eliminate boilerplate in Java.

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 • Part of javac • Read @Annotated source • Generate .java source files
10. APT (.java) Package (.apk) Dex (.dex) Package (.jar) Compile (.class) Write (.java) Annotation Processing
11. APT (.java) Package (.apk) Dex (.dex) Package (.jar) Compile (.class) Write (.java) Annotation Processing
12. APT (.java) Package (.apk) Dex (.dex) Package (.jar) Compile (.class) Write (.java) Annotation Processing
13. APT (.java) Package (.apk) Dex (.dex) Package (.jar) Compile (.class) Write (.java) Annotation Processing
14. APT (.java) Package (.apk) Dex (.dex) Package (.jar) Compile (.class) Write (.java) Annotation Processing
15. APT (.java) Package (.apk) Dex (.dex) Package (.jar) Compile (.class) Write (.java) Annotation Processing
16. Benefits • Write your code generator once • Trust the generated code
17. Components • Annotations • Processor • APT (Annotation Processing Tool) • Annotated Source
18. Annotations @Target(ElementType.TYPE) @Retention(RetentionPolicy.SOURCE) public @interface Builder { }
19. Annotations @Target(ElementType.TYPE) @Retention(RetentionPolicy.SOURCE) public @interface Builder { }
20. Annotations @Target(ElementType.TYPE) @Retention(RetentionPolicy.SOURCE) public @interface Builder { }
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 { } @Builder public class Builder
24. Annotation Processor public class FooProcessor extends AbstractProcessor { }\\
25. Annotation Processor public class FooProcessor extends AbstractProcessor { public FooProcessor() { super(); }\ }\\
26. 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(); }\ }\\
27. Annotation Processor public class FooProcessor extends AbstractProcessor { … @Override public SourceVersion getSupportedSourceVersion() { return SourceVersion.latestSupported(); }\ }\\
28. Annotation Processor public class FooProcessor extends AbstractProcessor { … @Override public SourceVersion getSupportedSourceVersion() { return SourceVersion.latestSupported(); } @Override public Set<String> getSupportedAnnotationTypes() { return ImmutableSet.of(Builder.class.getCanonicalName()); } }\\
29. Annotation Processor public class FooProcessor extends AbstractProcessor { … @Override public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) { ... } }\\
30. Annotation Processor public class FooProcessor extends AbstractProcessor { … @Override public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) { ... } }
31. Processing Rounds Java Sources APT Completed
32. Processing Rounds Java Sources APT Completed Round 1
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 2
36. Processing Rounds Java Sources APT Completed Complete
37. Annotation Processor • ServiceLoader Discovery File com.ryanharter.example.annotations.BuilderProcessor META-INF/services/javax.annotation.processing.Processor
38. 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
39. Code Generation
40. 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
41. JavaPoet • Uses Fluent API with builders • Based on Specs • TypeSpec • MethodSpec • ParameterSpec • FieldSpec https://github.com/square/javapoet
42. JavaPoet public final class UserBuilder { // fields private String username; … // methods public UserBuilder username(String username) { this.username = username; return this; } … }\
43. JavaPoet public final class UserBuilder { // fields private String username; … // methods public UserBuilder username(String username) { this.username = username; return this; } … }\
44. JavaPoet public final class UserBuilder String builderName = String.format("%sBuilder", type.getSimpleName()); ClassName builderType = ClassName.get(packageName, builderName);
45. JavaPoet public final class UserBuilder { // fields private String username; … // methods public UserBuilder username(String username) { this.username = username; return this; } … }\
46. private String username; JavaPoet
47. JavaPoet Modifiers private String username;
48. JavaPoet Modifiers Type private String username;
49. JavaPoet Modifiers Type private String username; Name
50. JavaPoet FieldSpec username = FieldSpec .builder(String.class, "username", Modifier.PRIVATE) .build(); private String username; Modifiers Type private String username; Name
51. private String username; JavaPoet Modifiers Type Name FieldSpec username = FieldSpec .builder(String.class, "username", Modifier.PRIVATE) .build(); private String username;
52. JavaPoet FieldSpec username = FieldSpec .builder(String.class, "username", Modifier.PRIVATE) .build(); private String username;
53. JavaPoet public final class UserBuilder {\ // fields private String username; … // methods public UserBuilder username(String username) {\ this.username = username; return this; }\ … }\
54. JavaPoet // methods public UserBuilder username(String username) {\ this.username = username; return this; }\
55. JavaPoet Modifiers // methods public UserBuilder username(String username) {\ this.username = username; return this; }\
56. JavaPoet Modifiers Return Type // methods public UserBuilder username(String username) {\ this.username = username; return this; }\
57. JavaPoet Modifiers Return Type Name // methods public UserBuilder username(String username) {\ this.username = username; return this; }\
58. JavaPoet Modifiers Return Type Name Parameters // methods public UserBuilder username(String username) {\ this.username = username; return this; }\
59. JavaPoet Modifiers Return Type Name Parameters Statements // methods public UserBuilder username(String username) {\ this.username = username; return this; }\
60. JavaPoet MethodSpec usernameSetter = MethodSpec.methodBuilder("username") .addModifiers(PUBLIC) .returns(builderType) .addParameter(String.class, "username") .addStatement("this.$N = username", username) .addStatement("return this") .build(); Modifiers Return Type Name Parameters Statements // methods public UserBuilder username(String username) {\ this.username = username; return this; }\
61. JavaPoet Modifiers Return Type Name Parameters Statements MethodSpec usernameSetter = MethodSpec.methodBuilder("username") .addModifiers(PUBLIC) .returns(builderType) .addParameter(String.class, "username") .addStatement("this.$N = username", username) .addStatement("return this") .build(); // methods public UserBuilder username(String username) {\ this.username = username; return this; }\
62. 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.$N = username", username) .addStatement("return this") .build();
63. JavaPoet Modifiers Return Type Name Parameters Statements // methods public UserBuilder username(String username) {\ this.username = username; return this; }\ MethodSpec usernameSetter = MethodSpec.methodBuilder("username") .addModifiers(PUBLIC) .returns(builderType) .addParameter(String.class, "username") .addStatement("this.$N = username", username) .addStatement("return this") .build();
64. 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.$N = username", username) .addStatement("return this") .build();
65. JavaPoet Modifiers Return Type Name Parameters Statements // methods public UserBuilder username(String username) {\ this.username = username; return this; }\ MethodSpec usernameSetter = MethodSpec.methodBuilder("username") .addModifiers(PUBLIC) .returns(builderType) .addParameter(String.class, "username") .addStatement("this.$N = username", username) .addStatement("return this") .build();
66. // 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();
67. JavaPoet public final class UserBuilder {\ // fields private String username; … // methods public UserBuilder username(String username) {\ this.username = username; return this; }\ … }\
68. JavaPoet public final class UserBuilder {\ }\
69. JavaPoet Modifiers public final class UserBuilder {\ }\
70. JavaPoet Modifiers Name public final class UserBuilder {\ }\
71. JavaPoet Modifiers Name Content public final class UserBuilder {\ }\
72. JavaPoet TypeSpec builder = TypeSpec.classBuilder(builderType) .addModifiers(PUBLIC, FINAL) .addField(username) .addMethod(usernameSetter) .build(); Modifiers Name Content public final class UserBuilder {\ }\
73. JavaPoet Modifiers Name Content TypeSpec builder = TypeSpec.classBuilder(builderType) .addModifiers(PUBLIC, FINAL) .addField(username) .addMethod(usernameSetter) .build(); public final class UserBuilder {\ }\
74. JavaPoet Modifiers Name Content TypeSpec builder = TypeSpec.classBuilder(builderType) .addModifiers(PUBLIC, FINAL) .addField(username) .addMethod(usernameSetter) .build(); public final class UserBuilder {\ }\
75. JavaPoet Modifiers Name Content TypeSpec builder = TypeSpec.classBuilder(builderType) .addModifiers(PUBLIC, FINAL) .addField(username) .addMethod(usernameSetter) .build(); public final class UserBuilder {\ }\
76. JavaPoet TypeSpec builder = TypeSpec.classBuilder(builderType) .addModifiers(PUBLIC, FINAL) .addField(username) .addMethod(usernameSetter) .build(); public final class UserBuilder {\ }\
77. Annotation Processor @Override public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) { }
78. @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
79. @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
80. // 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
81. // 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
82. // 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
83. // 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
84. // 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
85. // 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 = $N", name, name) .addStatement("return this") .build()); } Annotation Processor
86. // create private fields and public setters List<FieldSpec> fields = new ArrayList<FieldSpec>(vars.size()); List<MethodSpec> setters = new ArrayList<MethodSpec>(vars.size()); for (VariableElement var : vars) { TypeName typeName = TypeName.get(var.asType()); String name = var.getSimpleName().toString(); // create the field fields.add(FieldSpec.builder(typeName, name, PRIVATE).build()); // create the setter setters.add(MethodSpec.methodBuilder(name) .addModifiers(PUBLIC) .returns(builderType) .addParameter(typeName, name) .addStatement("this.$N = $N", name, name) .addStatement("return this") .build()); } Annotation Processor
87. // create private fields and public setters List<FieldSpec> fields = new ArrayList<FieldSpec>(vars.size()); List<MethodSpec> setters = new ArrayList<MethodSpec>(vars.size()); for (VariableElement var : vars) { TypeName typeName = TypeName.get(var.asType()); String name = var.getSimpleName().toString(); // create the field fields.add(FieldSpec.builder(typeName, name, PRIVATE).build()); // create the setter setters.add(MethodSpec.methodBuilder(name) .addModifiers(PUBLIC) .returns(builderType) .addParameter(typeName, name) .addStatement("this.$N = $N", name, name) .addStatement("return this") .build()); } Annotation Processor
88. // create private fields and public setters List<FieldSpec> fields = new ArrayList<FieldSpec>(vars.size()); List<MethodSpec> setters = new ArrayList<MethodSpec>(vars.size()); for (VariableElement var : vars) { TypeName typeName = TypeName.get(var.asType()); String name = var.getSimpleName().toString(); // create the field fields.add(FieldSpec.builder(typeName, name, PRIVATE).build()); // create the setter setters.add(MethodSpec.methodBuilder(name) .addModifiers(PUBLIC) .returns(builderType) .addParameter(typeName, name) .addStatement("this.$N = $N", name, name) .addStatement("return this") .build()); } Annotation Processor
89. // create private fields and public setters List<FieldSpec> fields = new ArrayList<FieldSpec>(vars.size()); List<MethodSpec> setters = new ArrayList<MethodSpec>(vars.size()); for (VariableElement var : vars) { TypeName typeName = TypeName.get(var.asType()); String name = var.getSimpleName().toString(); // create the field fields.add(FieldSpec.builder(typeName, name, PRIVATE).build()); // create the setter setters.add(MethodSpec.methodBuilder(name) .addModifiers(PUBLIC) .returns(builderType) .addParameter(typeName, name) .addStatement("this.$N = $N", name, name) .addStatement("return this") .build()); } Annotation Processor
90. // create private fields and public setters List<FieldSpec> fields = new ArrayList<FieldSpec>(vars.size()); List<MethodSpec> setters = new ArrayList<MethodSpec>(vars.size()); for (VariableElement var : vars) { TypeName typeName = TypeName.get(var.asType()); String name = var.getSimpleName().toString(); // create the field fields.add(FieldSpec.builder(typeName, name, PRIVATE).build()); // create the setter setters.add(MethodSpec.methodBuilder(name) .addModifiers(PUBLIC) .returns(builderType) .addParameter(typeName, name) .addStatement("this.$N = $N", name, name) .addStatement("return this") .build()); } Annotation Processor
91. // 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
92. // 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
93. // 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
94. // 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
95. // 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
96. // 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
97. Annotation Processor // create the builder TypeSpec builder = TypeSpec.classBuilder(builderType) .addModifiers(PUBLIC, FINAL) .addFields(fields) .addMethods(setters) .addMethod(buildMethod) .build();
98. // 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
99. @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
100. Using our Annotation public class User {/ String username;/ String firstName;/ String lastName;/ int age;/ }/
101. Using our Annotation @Builder public class User {/ String username;/ String firstName;/ String lastName;/ int age;/ }/
102. 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();
103. 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
104. Find Me • @rharter • http://ryanharter.com