The document outlines a presentation on creating and debugging annotation processors in Java, with a focus on Android development. It covers the structure of projects using annotation processors, the difference between inheritance and composition, and the creation of boilerplate code. Additionally, it provides insights into code generation techniques and debugging setups for improving annotation processing efficiency.

1. How to code
to code less

2. github.com/anton-novikau
Anton Novikau
Lead Android Developer @ Viber Media

3. Boilerplate Fighters!

4. Agenda
What is Annotation Processor?
How does it work?
Project structure
Create Annotation Processor
How to debug Processor’s code?
Demo time!
How to setup a goal?

5. Java Annotation Processors

6. Processing Rounds
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11. Processing Rounds
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12. Processing Rounds
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15. Processing Rounds
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16. Processing Rounds
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17. public class Person {
private String firstName;
private String lastName;
private Date birthday;
}
@Pojo

18. @Pojo
public class Person {
private String firstName;
private String lastName;
private Date birthday;
}
public String getFirstName() {
return firstName;
}
public String getLastName() {
return lastName;
}
public Date getBirthday() {
return birthday;
}

19. Where to get source data to generate code?
Before we start
Inheritance vs Composition
What should be a start point for our processor?

20. Inheritance
public class Contact implements Parcelable {
}

21. public static final Creator<Contact> CREATOR =
new Creator<Contact>() {
@Override
public Contact createFromParcel(Parcel source) {
return new Contact(source);
}
@Override
public Contact[] newArray(int size) {
return new Contact[size];
}
};
...
Inheritance
public class Contact implements Parcelable {
}

22. public class Contact implements Parcelable {
}
Inheritance
...
public Contact() {
}
Contact(Parcel source) {
...
}
...

23. public class Contact implements Parcelable {
}
Inheritance
...
@Override
public int describeContents() {
return 0;
}
@Override
public void writeToParcel(Parcel parcel, int flags) {
...
}

24. class Smart_Contact extends Contact {
// creator
// constructor
// methods from Parcelable
}
@SmartParcelable
public abstract class Contact implements Parcelable {
}
Inheritance

25. class Smart_Contact extends Contact {
// creator
// constructor
// methods from Parcelable
}
@SmartParcelable
public abstract class Contact implements Parcelable {
public static Contact create() {
return new Smart_Contact();
}
}
Inheritance

26. Composition
@RuntimePermissions
public class MainActivity extends AppCompatActivity {
...
public void onMigrateImageClicked(View v) {
MainActivityPermissionsDispatcher
.migrateImageWithPermissionCheck(this);
}
@NeedsPermission(WRITE_EXTERNAL_STORAGE)
void migrateImage() {
...
}
}

27. Composition
@RuntimePermissions
public class MainActivity extends AppCompatActivity {
...
public void onMigrateImageClicked(View v) {
MainActivityPermissionsDispatcher
.migrateImageWithPermissionCheck(this);
}
@NeedsPermission(WRITE_EXTERNAL_STORAGE)
void migrateImage() {
...
}
}

28. Composition
@RuntimePermissions
public class MainActivity extends AppCompatActivity {
...
public void onMigrateImageClicked(View v) {
MainActivityPermissionsDispatcher
.migrateImageWithPermissionCheck(this);
}
@NeedsPermission(WRITE_EXTERNAL_STORAGE)
void migrateImage() {
...
}
}

29. Where to get source data to generate code?
What should be a start point for our processor?
Before we start
Inheritance vs Composition
Effort of using your generated code vs creating a boilerplate code

30. Cursor boilerplate
public class ContactEntity {
long id;
String name;
Uri photoUri;
}

31. Cursor boilerplate
ContactEntity contact = new ContactEntity();
contact.setId(c.getLong(0));
contact.setName(c.getString(1));
contact.setPhotoUri(Uri.parse(c.getString(2)));
Cursor c = db.query("contacts",
"_ID = ?",
new String[] {"_ID", "NAME", "PHOTO"},
new String[] { String.valueOf(id) },
null, null, null);

32. ContactEntity contact = new ContactEntity();
contact.setId(c.getLong(0));
contact.setName(c.getString(1));
String uri = c.getString(2);
if (uri != null) {
contact.setPhotoUri(Uri.parse(uri));
}
Cursor boilerplate
Cursor c = db.query("contacts",
"_ID = ?",
new String[] {"_ID", "NAME", "PHOTO"},
new String[] { String.valueOf(id) },
null, null, null);

33. Cursor boilerplate
ContentValues values = new ContentValues();
values.put("_ID", contact.getId());
values.put("NAME", contact.getName());
values.put("PHOTO", contact.getPhotoUri().toString());
db.update("contacts",
values,
"_ID = ?",
new String[] { String.valueOf(contact.getId()) });

34. ContentValues values = new ContentValues();
values.put("_ID", contact.getId());
values.put("NAME", contact.getName());
String photoUri = contact.getPhotoUri() != null
? contact.getPhotoUri().toString()
: null
values.put("PHOTO", photoUri);
Cursor boilerplate
db.update("contacts",
values,
"_ID = ?",
new String[] { String.valueOf(contact.getId()) });

35. Goal
public class ContactEntity {
long id;
String name;
Uri photoUri;
}

36. Goal
@Entity(table = "contacts")
public class ContactEntity {
@Column(name = "_ID")
@PrimaryKey
long id;
@Column(name = "NAME")
String name;
@Column(name = "PHOTO", adapter = UriTypeAdapter.class)
Uri photoUri;
}

37. Project Structure
Project
api
processors
application

38. API Module
apply plugin: 'java-library'
sourceCompatibility = JavaVersion.VERSION_1_8
targetCompatibility = JavaVersion.VERSION_1_8
dependencies {
compileOnly 'com.google.android:android:4.1.1.4'
}

39. API Module
apply plugin: 'java-library'
sourceCompatibility = JavaVersion.VERSION_1_8
targetCompatibility = JavaVersion.VERSION_1_8
dependencies {
compileOnly 'com.google.android:android:4.1.1.4'
}

40. API Module
@Retention(RetentionPolicy.CLASS)
@Target(ElementType.TYPE)
public @interface Entity {
String table();
}
@Retention(RetentionPolicy.CLASS)
@Target(ElementType.FIELD)
public @interface Column {
String name();
Class<? extends TypeAdapter<?>> adapter();
}

41. API Module
@Retention(RetentionPolicy.CLASS)
@Target(ElementType.TYPE)
public @interface Entity {
String table();
}
@Retention(RetentionPolicy.CLASS)
@Target(ElementType.FIELD)
public @interface Column {
String name();
Class<? extends TypeAdapter<?>> adapter();
}

42. Processors Module
apply plugin: 'java-library'
sourceCompatibility = JavaVersion.VERSION_1_8
targetCompatibility = JavaVersion.VERSION_1_8
dependencies {
implementation project(':api')
}

43. Processors Module
apply plugin: 'java-library'
sourceCompatibility = JavaVersion.VERSION_1_8
targetCompatibility = JavaVersion.VERSION_1_8
dependencies {
implementation project(':api')
}

44. Create Annotation Processor
@SupportedAnnotationTypes("roomie.api.Entity")
@SupportedSourceVersion(SourceVersion.RELEASE_8)
public class EntityHelperProcessor extends AbstractProcessor {
@Override
public void init(ProcessingEnvironment processingEnv) {
super.init(processingEnv);
...
}
@Override
public boolean process(
Set<? extends TypeElement> annotations,
RoundEnvironment roundEnv) {
...
}
}

45. Create Annotation Processor
@SupportedAnnotationTypes("roomie.api.Entity")
@SupportedSourceVersion(SourceVersion.RELEASE_8)
public class EntityHelperProcessor extends AbstractProcessor {
@Override
public void init(ProcessingEnvironment processingEnv) {
super.init(processingEnv);
...
}
@Override
public boolean process(
Set<? extends TypeElement> annotations,
RoundEnvironment roundEnv) {
...
}
}

46. Create Annotation Processor
@SupportedAnnotationTypes("roomie.api.Entity")
@SupportedSourceVersion(SourceVersion.RELEASE_8)
public class EntityHelperProcessor extends AbstractProcessor {
@Override
public void init(ProcessingEnvironment processingEnv) {
super.init(processingEnv);
...
}
@Override
public boolean process(
Set<? extends TypeElement> annotations,
RoundEnvironment roundEnv) {
...
}
}

47. Create Annotation Processor
@SupportedAnnotationTypes("roomie.api.Entity")
@SupportedSourceVersion(SourceVersion.RELEASE_8)
public class EntityHelperProcessor extends AbstractProcessor {
@Override
public void init(ProcessingEnvironment processingEnv) {
super.init(processingEnv);
...
}
@Override
public boolean process(
Set<? extends TypeElement> annotations,
RoundEnvironment roundEnv) {
...
}
}

48. Register Processor
Project
processors
src
main
resources
META-INF
services
Old Fashioned way
javax.annotation.processing.Processor
roomie.codegen.EntityHelperProcessor
...

49. Register Processor
Modern way
apply plugin: 'java-library'
sourceCompatibility = JavaVersion.VERSION_1_8
targetCompatibility = JavaVersion.VERSION_1_8
dependencies {
implementation project(':api')
implementation 'com.google.auto:auto-common:0.8'
compileOnly 'com.google.auto.service:auto-service:1.0-rc4'
}

50. Register Processor
Modern way
@AutoService(Processor.class)
@SupportedAnnotationTypes("roomie.api.Entity")
@SupportedSourceVersion(SourceVersion.RELEASE_8)
public class EntityHelperProcessor extends AbstractProcessor {
...
}

51. Write a simple Class
package roomie.example;
public class DemoImpl extends Demo {
int counter;
public void print(String msg) {
System.out.println(msg);
}
}

52. Write a simple Class: raw text
JavaFileObject sourceFile =
filer.createSourceFile(qualifiedName, annotatedClass);
try (Writer writer = sourceFile.openWriter()) {
writer.append("package ");
writer.append(packageName).append(";nn");
writer.append("public class ").append(className);
writer.append(" extends ");
writer.append(annotatedClass.simpleName()).append(" {n");
writer.append(" int counter;nn");
writer.append(" public void print(String msg) {n");
writer.append(" System.out.println(msg);n");
writer.append(" }n");
writer.append("}n");
writer.flush();
}

53. Processors Module
apply plugin: 'java-library'
sourceCompatibility = JavaVersion.VERSION_1_8
targetCompatibility = JavaVersion.VERSION_1_8
dependencies {
implementation project(':api')
implementation 'com.squareup:javapoet:1.9.0'
implementation 'com.google.auto:auto-common:0.8'
compileOnly 'com.google.auto.service:auto-service:1.0-rc4'
}

54. JavaFile DemoImpl.java
TypeSpec class DemoImpl
MethodSpec void print()
FieldSpec int counter
ParameterSpec String msg
JavaPoet Java
=

55. Write a simple Class: JavaPoet
Define Class
TypeSpec.Builder classContent =
TypeSpec.classBuilder(className)
.addModifiers(Modifier.PUBLIC)
.superclass(annotatedClass);

56. Write a simple Class: JavaPoet
Define Method and Field
MethodSpec print =
MethodSpec.methodBuilder("print")
.addModifiers(Modifier.PUBLIC)
.addParameter(String.class, "msg")
.addStatement(“$L.out.println(msg)",
System.class)
.build();
FieldSpec counter =
FieldSpec.builder(int.class, "counter").build();
classContent.addMethod(print);
classContent.addField(counter);

57. Write a simple Class: JavaPoet
Write our Class to a File
JavaFile javaFile = JavaFile.builder(packageName,
classContent.build())
.indent(" ")
.build();
JavaFileObject sourceFile = filer.createSourceFile(
qualifiedName,
annotatedClass);
try (Writer writer = sourceFile.openWriter()) {
writer.write(javaFile.toString());
}

58. Don’t worry.
We’ve almost finished

59. Application Module
apply plugin: 'com.android.application'
android {
...
compileOptions {
targetCompatibility 1.8
sourceCompatibility 1.8
}
}
dependencies {
implementation project(':api')
annotationProcessor project(':codegen')
...
}

60. Application Module
apply plugin: 'com.android.application'
android {
...
compileOptions {
targetCompatibility 1.8
sourceCompatibility 1.8
}
}
dependencies {
implementation project(':api')
annotationProcessor project(':codegen')
...
}

61. Application Module
apply plugin: 'com.android.application'
android {
...
compileOptions {
targetCompatibility 1.8
sourceCompatibility 1.8
}
}
dependencies {
implementation project(':api')
annotationProcessor project(':codegen')
...
}

62. How to Debug?

63. How to Debug?

64. Setup Gradle Daemon
vim ~/.gradle/gradle.properties
org.gradle.daemon=true
org.gradle.jvmargs=-agentlib:jdwp=transport=dt_socket,
server=y,suspend=n,address=5005

65. Start Daemon and Connect
./gradlew --stop
./gradlew --daemon
./gradlew clean :sample:compileDebugJavaWithJavac

66. Demo Time

67. Conclusion

68. Thank you!

69. Questions?

70. Useful Links
Hannes Dorfmann - Annotation Processing 101
Eugenio Marletti - Pushing the limits of Kotlin annotation processing
Demo App (aka Roomie) Source Code