@Eliminate("Boilerplate")

Using Java annotations to reduce boilerplate code.

Transcript

1. @Eliminate(“Boilerplate”)
   Ryan Harter
   @rharter
   

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2. JAVA HAS BOILERPLATE
   

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3. JAVA IS BOILERPLATE
   

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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;
   }
   }
   

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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;
   }\
   

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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;
   }\
   }\
   

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7. Annotation Processing
   +
   Code Generation
   

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8. Annotation Processing
   

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9. Annotation Processing
   

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10. Annotation Processing
    • Part of javac
    

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11. Annotation Processing
    • Part of javac
    • Read @Annotated source
    

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12. Annotation Processing
    • Part of javac
    • Read @Annotated source
    • Generate .java source files
    

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13. Benefits
    

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14. Benefits
    • Write your code generator once
    

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15. Benefits
    • Write your code generator once
    • Trust the generated code
    

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16. Components
    

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17. Components
    • Annotations
    

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18. Components
    • Annotations
    • Processor
    

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19. Components
    • Annotations
    • Processor
    • APT (Annotation Processing Tool)
    

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20. Components
    • Annotations
    • Processor
    • APT (Annotation Processing Tool)
    • Annotated Source
    

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21. Annotations
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.SOURCE)
    public @interface Builder {
    }
    

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22. Annotations
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.SOURCE)
    public @interface Builder {
    }
    

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23. Annotations
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.SOURCE)
    public @interface Builder {
    }
    

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24. Annotations
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.SOURCE)
    public @interface Builder {
    }
    

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25. Annotation Processor
    public class FooProcessor extends AbstractProcessor {
    }\\
    

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26. Annotation Processor
    public class FooProcessor extends AbstractProcessor {
    public FooProcessor() {
    super();
    }\
    }\\
    

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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();
    }\
    }\\
    

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28. Annotation Processor
    public class FooProcessor extends AbstractProcessor {
    …
    @Override public SourceVersion getSupportedSourceVersion() {
    return SourceVersion.latestSupported();
    }\
    }\\
    

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29. Annotation Processor
    public class FooProcessor extends AbstractProcessor {
    …
    @Override public Set getSupportedAnnotationTypes() {
    return ImmutableSet.of(Builder.class.getCanonicalName());
    }
    }\\
    

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30. Annotation Processor
    public class FooProcessor extends AbstractProcessor {
    …
    @Override
    public boolean process(Set extends TypeElement> annotations,
    RoundEnvironment roundEnv) {
    ...
    }
    }\\
    

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31. Annotation Processor
    public class FooProcessor extends AbstractProcessor {
    …
    @Override
    public boolean process(Set extends TypeElement> annotations,
    RoundEnvironment roundEnv) {
    ...
    }
    }
    

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32. Processing Rounds
    Java Sources APT Completed
    

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33. Processing Rounds
    Java Sources APT Completed
    Round 1
    

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34. Processing Rounds
    Java Sources APT Completed
    Round 1
    

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35. Processing Rounds
    Java Sources APT Completed
    Round 1
    

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36. Processing Rounds
    Java Sources APT Completed
    Round 1
    

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37. Processing Rounds
    Java Sources APT Completed
    Round 2
    

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38. Processing Rounds
    Java Sources APT Completed
    Round 2
    

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39. Processing Rounds
    Java Sources APT Completed
    Complete
    

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40. Annotation Processor
    • ServiceLoader Discovery File
    com.ryanharter.example.annotations.BuilderProcessor
    META-INF/services/javax.annotation.processing.Processor
    

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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
    

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42. Code Generation
    

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43. Code Generation
    

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44. Code Generation
    • Pair well with Annotation Processors
    

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45. Code Generation
    • Pair well with Annotation Processors
    • Used to generate new Java source files
    

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46. Code Generation
    • Pair well with Annotation Processors
    • Used to generate new Java source files
    • JavaPoet represents Java source as model
    

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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
    

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

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49. JavaPoet
    • Uses Fluent API with builders
    https://github.com/square/javapoet
    

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50. JavaPoet
    • Uses Fluent API with builders
    • Based on Specs
    https://github.com/square/javapoet
    

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51. JavaPoet
    • Uses Fluent API with builders
    • Based on Specs
    • TypeSpec
    https://github.com/square/javapoet
    

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52. JavaPoet
    • Uses Fluent API with builders
    • Based on Specs
    • TypeSpec
    • MethodSpec
    https://github.com/square/javapoet
    

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53. JavaPoet
    • Uses Fluent API with builders
    • Based on Specs
    • TypeSpec
    • MethodSpec
    • ParameterSpec
    https://github.com/square/javapoet
    

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54. JavaPoet
    • Uses Fluent API with builders
    • Based on Specs
    • TypeSpec
    • MethodSpec
    • ParameterSpec
    • FieldSpec
    https://github.com/square/javapoet
    

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55. JavaPoet
    public final class UserBuilder {
    // fields
    private String username;
    …
    // methods
    public UserBuilder username(String username) {
    this.username = username;
    return this;
    }
    …
    }\
    

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56. JavaPoet
    public final class UserBuilder {
    // fields
    private String username;
    …
    // methods
    public UserBuilder username(String username) {
    this.username = username;
    return this;
    }
    …
    }\
    

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57. JavaPoet
    public final class UserBuilder
    String builderName = String.format("%sBuilder", type.getSimpleName());
    ClassName builderType = ClassName.get(packageName, builderName);
    

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58. JavaPoet
    public final class UserBuilder {
    // fields
    private String username;
    …
    // methods
    public UserBuilder username(String username) {
    this.username = username;
    return this;
    }
    …
    }\
    

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59. private String username;
    JavaPoet
    

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60. JavaPoet
    Modifiers
    private String username;
    

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61. JavaPoet
    Modifiers Type
    private String username;
    

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62. JavaPoet
    Modifiers Type
    private String username;
    Name
    

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63. JavaPoet
    FieldSpec username = FieldSpec
    .builder(String.class, "username", Modifier.PRIVATE)
    .build();
    private String username;
    Modifiers Type
    private String username;
    Name
    

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64. private String username;
    JavaPoet
    Modifiers Type Name
    FieldSpec username = FieldSpec
    .builder(String.class, "username", Modifier.PRIVATE)
    .build();
    private String username;
    

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65. JavaPoet
    FieldSpec username = FieldSpec
    .builder(String.class, "username", Modifier.PRIVATE)
    .build();
    private String username;
    

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66. JavaPoet
    public final class UserBuilder {\
    // fields
    private String username;
    …
    // methods
    public UserBuilder username(String username) {\
    this.username = username;
    return this;
    }\
    …
    }\
    

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67. JavaPoet
    // methods
    public UserBuilder username(String username) {\
    this.username = username;
    return this;
    }\
    

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68. JavaPoet
    Modifiers
    // methods
    public UserBuilder username(String username) {\
    this.username = username;
    return this;
    }\
    

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69. JavaPoet
    Modifiers Return Type
    // methods
    public UserBuilder username(String username) {\
    this.username = username;
    return this;
    }\
    

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70. JavaPoet
    Modifiers Return Type Name
    // methods
    public UserBuilder username(String username) {\
    this.username = username;
    return this;
    }\
    

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71. JavaPoet
    Modifiers Return Type Name Parameters
    // methods
    public UserBuilder username(String username) {\
    this.username = username;
    return this;
    }\
    

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72. JavaPoet
    Modifiers Return Type Name Parameters
    Statements
    // methods
    public UserBuilder username(String username) {\
    this.username = username;
    return this;
    }\
    

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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;
    }\
    

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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;
    }\
    

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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();
    

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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();
    

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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();
    

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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();
    

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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();
    

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80. JavaPoet
    public final class UserBuilder {\
    // fields
    private String username;
    …
    // methods
    public UserBuilder username(String username) {\
    this.username = username;
    return this;
    }\
    …
    }\
    

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81. JavaPoet
    public final class UserBuilder {\
    }\
    

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82. JavaPoet
    Modifiers
    public final class UserBuilder {\
    }\
    

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83. JavaPoet
    Modifiers Name
    public final class UserBuilder {\
    }\
    

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84. JavaPoet
    Modifiers Name
    Content
    public final class UserBuilder {\
    }\
    

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85. JavaPoet
    TypeSpec builder = TypeSpec.classBuilder(builderType)
    .addModifiers(PUBLIC, FINAL)
    .addField(username)
    .addMethod(usernameSetter)
    .build();
    Modifiers Name
    Content
    public final class UserBuilder {\
    }\
    

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86. JavaPoet
    Modifiers Name
    Content
    TypeSpec builder = TypeSpec.classBuilder(builderType)
    .addModifiers(PUBLIC, FINAL)
    .addField(username)
    .addMethod(usernameSetter)
    .build();
    public final class UserBuilder {\
    }\
    

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87. JavaPoet
    Modifiers Name
    Content
    TypeSpec builder = TypeSpec.classBuilder(builderType)
    .addModifiers(PUBLIC, FINAL)
    .addField(username)
    .addMethod(usernameSetter)
    .build();
    public final class UserBuilder {\
    }\
    

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88. JavaPoet
    Modifiers Name
    Content
    TypeSpec builder = TypeSpec.classBuilder(builderType)
    .addModifiers(PUBLIC, FINAL)
    .addField(username)
    .addMethod(usernameSetter)
    .build();
    public final class UserBuilder {\
    }\
    

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89. JavaPoet
    TypeSpec builder = TypeSpec.classBuilder(builderType)
    .addModifiers(PUBLIC, FINAL)
    .addField(username)
    .addMethod(usernameSetter)
    .build();
    public final class UserBuilder {\
    }\
    

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90. Annotation Processor
    @Override
    public boolean process(Set extends TypeElement> annotations,
    RoundEnvironment roundEnv) {
    }
    

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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
    

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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
    

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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
    

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94. // get element metadata
    String packageName = getPackageName(type);
    String targetName = lowerCamelCase(type.getSimpleName().toString());
    Set vars = getNonPrivateVariables(type);
    String builderName = String.format("%sBuilder", type.getSimpleName());
    ClassName builderType = ClassName.get(packageName, builderName);
    Annotation Processor
    

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95. // get element metadata
    String packageName = getPackageName(type);
    String targetName = lowerCamelCase(type.getSimpleName().toString());
    Set vars = getNonPrivateVariables(type);
    String builderName = String.format("%sBuilder", type.getSimpleName());
    ClassName builderType = ClassName.get(packageName, builderName);
    Annotation Processor
    

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96. // get element metadata
    String packageName = getPackageName(type);
    String targetName = lowerCamelCase(type.getSimpleName().toString());
    Set vars = getNonPrivateVariables(type);
    String builderName = String.format("%sBuilder", type.getSimpleName());
    ClassName builderType = ClassName.get(packageName, builderName);
    Annotation Processor
    

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97. // get element metadata
    String packageName = getPackageName(type);
    String targetName = lowerCamelCase(type.getSimpleName().toString());
    Set vars = getNonPrivateVariables(type);
    String builderName = String.format("%sBuilder", type.getSimpleName());
    ClassName builderType = ClassName.get(packageName, builderName);
    Annotation Processor
    

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98. // get element metadata
    String packageName = getPackageName(type);
    String targetName = lowerCamelCase(type.getSimpleName().toString());
    Set vars = getNonPrivateVariables(type);
    String builderName = String.format("%sBuilder", type.getSimpleName());
    ClassName builderType = ClassName.get(packageName, builderName);
    Annotation Processor
    

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99. // create private fields and public setters
    List fields = new ArrayList(vars.size());
    List setters = new ArrayList(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
    

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100. // create private fields and public setters
     List fields = new ArrayList(vars.size());
     List setters = new ArrayList(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
     

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101. // create private fields and public setters
     List fields = new ArrayList(vars.size());
     List setters = new ArrayList(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
     

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102. // create private fields and public setters
     List fields = new ArrayList(vars.size());
     List setters = new ArrayList(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
     

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103. // create private fields and public setters
     List fields = new ArrayList(vars.size());
     List setters = new ArrayList(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
     

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104. // create private fields and public setters
     List fields = new ArrayList(vars.size());
     List setters = new ArrayList(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
     

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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
     

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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
     

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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
     

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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
     

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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
     

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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
     

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111. Annotation Processor
     // create the builder
     TypeSpec builder = TypeSpec.classBuilder(builderType)
     .addModifiers(PUBLIC, FINAL)
     .addFields(fields)
     .addMethods(setters)
     .addMethod(buildMethod)
     .build();
     

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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
     

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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
     

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114. Using our Annotation
     public class User {/
     String username;/
     String firstName;/
     String lastName;/
     int age;/
     }/
     

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115. Using our Annotation
     @Builder public class User {/
     String username;/
     String firstName;/
     String lastName;/
     int age;/
     }/
     

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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();
     

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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
     

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118. Find Me
     • @rharter
     • http://ryanharter.com
     

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