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Annotation Processing 101
Hannes Dorfmann
@sockeqwe
+HannesDorfmann
hannesdorfmann.com
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Annotation Processing
● Java 5 (Sep. 2004)
● JSR 269: 6 months after Java 5 released
● Plugin system for Annotation Processors
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Annotation Processing
● Part of javac
● @Annotation based
● Generates java source code files
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Reduces writing
boilerplate code
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public class MyActivity extends Activity {
@InjectView(R.id.title) TextView title;
@InjectView(R.id.text) TextView text;
@InjectView(R.id.submit) Button submit;
@InjectView(R.id.imageView) ImageView image;
}
Butter Knife
http://jakewharton.github.io/butterknife/
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public class MyActivity extends Activity {
@Icicle String username;
@Icicle int counter;
}
Icepick
https://github.com/frankiesardo/icepick
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public class ItemFragment extends Fragment {
@Arg long itemId;
@Arg int categoryId;
}
FragmentArgs
https://github.com/sockeqwe/fragmentargs
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@Parcel
public class Person {
String firstname;
String lastname;
int age;
}
Parceler
http://parceler.org
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public class AnimalsAdapter extends SupportAnnotatedAdapter
implements AnimalsAdapterBinder {
@ViewType(layout = R.layout.list_dog)
public final int dog = 0;
@ViewType(layout = R.layout.list_cat)
public final int cat = 1;
AnnotatedAdapter
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public class AnimalsAdapter extends SupportAnnotatedAdapter
implements AnimalsAdapterBinder {
@Override
public void bindViewHolder(DogViewHolder vh, int position) {
Dog dog = (Dog) animals.get(position);
vh.name.setText(dog.getName());
}
AnnotatedAdapter
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public class AnimalsAdapter extends SupportAnnotatedAdapter
implements AnimalsAdapterBinder {
@Override
public void bindViewHolder(CatViewHolder vh, int position) {
Cat cat = (Cat) animals.get(position);
vh.image.setImageBitmap(cat.getImage());
}
}
AnnotatedAdapter
https://github.com/sockeqwe/AnnotatedAdapter
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Performance
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Performance
● Compile time code generation
● Full JVM
● “Native” java code (as hand-written)
● No reflections!
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LoganSquare
https://github.com/bluelinelabs/LoganSquare
Parsing 60 items
68 ms
Gson
Jackson
LoganSquare
76 ms
Serializing 60 items
74 ms
60 ms
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LoganSquare
https://github.com/bluelinelabs/LoganSquare
Parsing 60 items
68 ms
Gson
Jackson
LoganSquare
76 ms
17
Serializing 60 items
74 ms
60 ms
10
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Dagger 2
● Google Scale
● Replacing Dagger 1 with Dagger 2
● Saving 13 % CPU by just moving DI
https://www.youtube.com/watch?v=oK_XtfXPkqw (36:00)
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Otto 1.3.7
https://github.com/greenrobot/EventBus
EventBus 2.4
2000
4000
18000
16000
8000
12000
EventBus 3.0
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Otto 1.3.7
https://github.com/greenrobot/EventBus
EventBus 2.4 EventBus 3.0
2000
4000
18000
16000
8000
12000
EventBus 3.0
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Limitation
● Can generate only new files
● Can’t manipulate already existing files
○ Bytecode manipulation (ASM, Afterburn)
○ AST manipulation (Project Lombok)
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Not debuggable!
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Example
Pizza Store
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public interface Meal {
public float getPrice();
}
public class MargheritaPizza implements Meal {
@Override public float getPrice() {
return 6f;
}
}
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public class CalzonePizza implements Meal {
@Override public float getPrice() {
return 8.5f;
}
}
public class Tiramisu implements Meal {
@Override public float getPrice() {
return 4.5f;
}
}
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public class PizzaStore {
private MealFactory factory = new MealFactory();
public static void main(String[] args) throws IOException {
PizzaStore pizzaStore = new PizzaStore();
Meal meal = pizzaStore.order( readConsole() );
System.out.println("Bill: $" + meal.getPrice());
}
public Meal order(String mealName) {
return factory.create(mealName);
}
}
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public class MealFactory {
public Meal create(String id) {
if ("Margherita".equals(id)) return new MargheritaPizza();
if ("Calzone".equals(id)) return new CalzonePizza();
if ("Tiramisu".equals(id)) return new Tiramisu();
throw new IllegalArgumentException("Unknown meal”);
}
}
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@Target(ElementType.TYPE)
public @interface Factory {
String id();
Class type();
}
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@Factory(
id = "Margherita",
type = Meal.class
)
public class MargheritaPizza implements Meal {
@Override
public float getPrice() {
return 6f;
}
}
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@Factory(
id = "Calzone",
type = Meal.class
)
public class CalzonePizza implements Meal {
@Override
public float getPrice() {
return 8.5f;
}
}
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Pizza Store Factory
1. Only classes can be @Factory
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Pizza Store Factory
1. Only classes can be @Factory
2. @Factory classes must have empty constructor
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Pizza Store Factory
1. Only classes can be @Factory
2. @Factory classes must have empty constructor
3. Same types are grouped to one factory
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Pizza Store Factory
1. Only classes can be @Factory
2. @Factory classes must have empty constructor
3. Same types are grouped to one factory
4. id is String and must be unique in factory group
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Pizza Store Factory
1. Only classes can be @Factory
2. @Factory classes must have empty constructor
3. Same types are grouped to one factory
4. id is String and must be unique in factory group
5. @Factory classes must inherit from specified type
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@Factory(
id = "Margherita",
type = Meal.class
)
public class MargheritaPizza implements Meal {
@Override
public float getPrice() {
return 6f;
}
}
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@Factory(
id = "Margherita",
type = Meal.class
)
public class MargheritaPizza implements Meal {
@Override
public float getPrice() {
return 6f;
}
}
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public class FactoryProcessor extends AbstractProcessor {
private Types typeUtils;
private Elements elementUtils;
private Filer filer;
private Messager messager;
private Map factoryClasses;
@Override
public synchronized void init(ProcessingEnvironment processingEnv) {
typeUtils = processingEnv.getTypeUtils();
elementUtils = processingEnv.getElementUtils();
filer = processingEnv.getFiler();
messager = processingEnv.getMessager();
}
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public class FactoryProcessor extends AbstractProcessor {
@Override
public Set getSupportedAnnotationTypes() {
Set annotations = new LinkedHashSet();
annotations.add(Factory.class.getCanonicalName());
return annotations;
}
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public class FactoryProcessor extends AbstractProcessor {
@Override
public boolean process(Set extends TypeElement> annotations,
RoundEnvironment rv) {
for (Element annotatedElement : rv.getElementsAnnotatedWith(Factory.class)) {
}
}
}
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@Example
public class Foo {
private int a;
private Other other;
public Foo () { ... }
public void setA (
int newA
) { ... }
}
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@Example
public class Foo {
private int a;
private Other other;
public Foo () { ... }
public void setA (
int newA
) { ... }
}
TypeElement
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@Example
public class Foo {
private int a;
private Other other;
public Foo () { ... }
public void setA (
int newA
) { ... }
}
TypeElement
VariableElement
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@Example
public class Foo {
private int a;
private Other other;
public Foo () { ... }
public void setA (
int newA
) { ... }
}
TypeElement
VariableElement
VariableElement
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@Example
public class Foo {
private int a;
private Other other;
public Foo () { ... }
public void setA (
int newA
) { ... }
}
TypeElement
VariableElement
VariableElement
ExecuteableElement
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@Example
public class Foo {
private int a;
private Other other;
public Foo () { ... }
public void setA (
int newA
) { ... }
}
TypeElement
VariableElement
VariableElement
ExecuteableElement
ExecuteableElement
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@Example
public class Foo {
private int a;
private Other other;
public Foo () { ... }
public void setA (
int newA
) { ... }
}
TypeElement
VariableElement
VariableElement
ExecuteableElement
ExecuteableElement
TypeElement
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@Example
public class Foo {
private int a;
private Other other;
public Foo () { ... }
public void setA (
int newA
) { ... }
}
TypeElement
VariableElement
VariableElement
ExecuteableElement
ExecuteableElement
TypeElement
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@Example
public class Foo {
private int a;
private Other other;
public Foo () { ... }
public void setA (
int newA
) { ... }
}
TypeElement
VariableElement
VariableElement
ExecuteableElement
ExecuteableElement
TypeElement
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@Example
public class Foo {
private int a;
private Other other;
public Foo () { ... }
public void setA (
int newA
) { ... }
}
TypeMirror
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public class FactoryProcessor extends AbstractProcessor {
@Override
public synchronized void init(ProcessingEnvironment processingEnv);
@Override
public Set getSupportedAnnotationTypes();
@Override
public boolean process(Set extends TypeElement> annotations,
RoundEnvironment rv);
}
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FactoryProcessor.jar
- com
- example
- FactoryProcessor.class
- META-INF
- services
- javax.annotation.processing.Processor
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@AutoService(Processor.class)
public class FactoryProcessor extends AbstractProcessor {
@Override
public synchronized void init(ProcessingEnvironment processingEnv);
@Override
public Set getSupportedAnnotationTypes();
@Override
public boolean process(Set extends TypeElement> annotations,
RoundEnvironment rv);
}
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Pizza Store Factory
1. Only classes can be @Factory
2. @Factory classes must have empty constructor
3. Same types are grouped to one factory
4. id is String and must be unique in factory group
5. @Factory classes must inherit from specified type
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public boolean process(Set<> annotations, RoundEnvironment rv) {
for (Element annotatedElement : rv.getElementsAnnotatedWith(Factory.class)) {
if (! (annotatedElement instanceof TypeElement) ){
...
}
}
}
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public boolean process(Set<> annotations, RoundEnvironment rv) {
for (Element annotatedElement : rv.getElementsAnnotatedWith(Factory.class)) {
if (! (annotatedElement instanceof TypeElement) ){
...
}
}
}
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public boolean process(Set<> annotations, RoundEnvironment rv) {
for (Element annotatedElement : rv.getElementsAnnotatedWith(Factory.class)) {
if (annotatedElement.getKind() != ElementKind.CLASS) {
messager.printMessage(
Diagnostic.Kind.ERROR,
"Only classes can be annotated with @Factory",
annotatedElement );
}
}
}
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public boolean process(Set<> annotations, RoundEnvironment rv) {
for (Element annotatedElement : rv.getElementsAnnotatedWith(Factory.class)) {
if (annotatedElement.getKind() != ElementKind.CLASS) {
error( annotatedElement, "Only classes can be annotated with @Factory");
}
}
}
public void error(Element e, String msg) {
messager.printMessage(Diagnostic.Kind.ERROR, "Error", e);
}
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public boolean process(Set<> annotations, RoundEnvironment rv) {
for (Element annotatedElement : rv.getElementsAnnotatedWith(Factory.class)) {
if (annotatedElement.getKind() != ElementKind.CLASS) {
error( annotatedElement, "Only classes can be annotated with @Factory");
annotatedElement = null;
}
annotatedElement.getSimpleName();
}
}
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Caused by: java.lang.NullPointerException
at com.example.processor.FactoryProcessor.process(FactoryProcessor.java:161)
at com.sun.tools.javac.processing.JavacProcessingEnvironment.callProcessor
(JavacProcessingEnvironment.java:793)
at com.sun.tools.javac.processing.JavacProcessingEnvironment.
discoverAndRunProcs(JavacProcessingEnvironment.java:722)
at com.sun.tools.javac.processing.JavacProcessingEnvironment.access$1700
(JavacProcessingEnvironment.java:97)
... 32 more
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public boolean process(Set<> annotations, RoundEnvironment rv) {
for (Element annotatedElement : rv.getElementsAnnotatedWith(Factory.class)) {
if (annotatedElement.getKind() != ElementKind.CLASS) {
error( annotatedElement, "Only classes can be annotated with @Factory");
annotatedElement = null;
}
annotatedElement.getSimpleName();
}
}
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public boolean process(Set<> annotations, RoundEnvironment rv) {
for (Element annotatedElement : rv.getElementsAnnotatedWith(Factory.class)) {
if (annotatedElement.getKind() != ElementKind.CLASS) {
error( annotatedElement, "Only classes can be annotated with @Factory");
}
checkOtherThings( annotatedElement );
}
}
public void checkOtherThings(Element element) { ... }
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public boolean process(Set<> annotations, RoundEnvironment rv) {
try {
for (Element annotatedElement : rv.getElementsAnnotatedWith(Factory.class)) {
if (annotatedElement.getKind() != ElementKind.CLASS) {
error( annotatedElement, "Only classes can be annotated with @Factory");
}
checkOtherThings( annotatedElement );
}
} catch (ProcessingException e) {
error(e.getElement(), e.getMessage());
}
}
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public void checkOtherThings(Element element) throws ProcessingException
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public void checkOtherThings(Element element) throws ProcessingException
public class ProcessingException extends Exception {
Element element;
public ProcessingException(Element element, String msg, Object... args) {
super(String.format(msg, args));
this.element = element;
}
public Element getElement() {
return element;
}
}
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Pizza Store Factory
1. Only classes can be @Factory
2. @Factory classes must have empty constructor
3. Same types are grouped to one factory
4. id is String and must be unique in factory group
5. @Factory classes must inherit from specified type
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public void checkConstructor(TypeElement e) throws ProcessingException {
for (Element enclosed : e.getEnclosedElements()) {
if (enclosed.getKind() == ElementKind.CONSTRUCTOR) {
ExecutableElement constructorElement = (ExecutableElement) enclosed;
if (constructorElement.getParameters().size() == 0 &&
constructorElement.getModifiers().contains(Modifier.PUBLIC)) {
return;
}
}
throw new ProcessingException(e, "No public empty constructor");
}
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Pizza Store Factory
1. Only classes can be @Factory
2. @Factory classes must have empty constructor
3. Same types are grouped to one factory
4. id is String and must be unique in factory group
5. @Factory classes must inherit from specified type
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public class FactoryAnnotatedClass {
TypeElement annotatedClassElement;
String id;
String qualifiedGroupClassName;
public FactoryAnnotatedClass(TypeElement element) throws ProcessingException {
this.annotatedClassElement = classElement;
}
}
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public FactoryAnnotatedClass(TypeElement element) throws ProcessingException {
Factory annotation = classElement.getAnnotation(Factory.class);
this.id = annotation.id();
if (StringUtils.isEmpty(id)) {
throw new ProcessingException(classElement,
"id() is null or empty!);
}
}
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public FactoryAnnotatedClass(TypeElement element) throws ProcessingException {
Factory annotation = classElement.getAnnotation(Factory.class);
try {
Class> clazz = annotation.type();
qualifiedGroupClassName = clazz.getCanonicalName();
} catch (MirroredTypeException mte) {
}
}
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public FactoryAnnotatedClass(TypeElement element) throws ProcessingException {
Factory annotation = classElement.getAnnotation(Factory.class);
try {
Class> clazz = annotation.type();
qualifiedGroupClassName = clazz.getCanonicalName();
} catch (MirroredTypeException mte) {
DeclaredType classTypeMirror = (DeclaredType) mte.getTypeMirror();
TypeElement classTypeElement = (TypeElement) classTypeMirror.asElement();
qualifiedGroupClassName = classTypeElement.getQualifiedName().toString();
}
}
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public class FactoryGroupedClasses {
String qualifiedClassName;
Map itemsMap =
new LinkedHashMap();
public FactoryGroupedClasses(String qualifiedClassName) {
this.qualifiedClassName = qualifiedClassName;
}
}
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public class FactoryGroupedClasses {
public void add(FactoryAnnotatedClass toInsert) throws ProcessingException {
}
}
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public class FactoryGroupedClasses {
public void add(FactoryAnnotatedClass toInsert) throws ProcessingException {
FactoryAnnotatedClass existing = itemsMap.get(toInsert.getId());
}
}
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public class FactoryGroupedClasses {
public void add(FactoryAnnotatedClass toInsert) throws ProcessingException {
FactoryAnnotatedClass existing = itemsMap.get(toInsert.getId());
if (existing != null) {
throw new ProcessingException(toInsert.getTypeElement(),
"Conflict: Class with same id found“ );
}
}
}
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public class FactoryGroupedClasses {
public void add(FactoryAnnotatedClass toInsert) throws ProcessingException {
FactoryAnnotatedClass existing = itemsMap.get(toInsert.getId());
if (existing != null) {
throw new ProcessingException(toInsert.getTypeElement(),
"Conflict: Class with same id found“ );
}
itemsMap.put(toInsert.getId(), toInsert);
}
}
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FactoryProcessor
Map
FactoryGroupedClasses
Map
FactoryAnnotatedClass
String id
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public boolean process(Set<> annotations, RoundEnvironment rv) {
try {
for (Element annotatedElement : rv.getElementsAnnotatedWith(Factory.class)) {
}
} catch (ProcessingException e) { ... }
}
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public boolean process(Set<> annotations, RoundEnvironment rv) {
try {
for (Element annotatedElement : rv.getElementsAnnotatedWith(Factory.class)) {
FactoryAnnotatedClass annotatedClass =
new FactoryAnnotatedClass( annotatedElement );
}
} catch (ProcessingException e) { ... }
}
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public boolean process(Set<> annotations, RoundEnvironment rv) {
try {
for (Element annotatedElement : rv.getElementsAnnotatedWith(Factory.class)) {
FactoryAnnotatedClass annotatedClass =
new FactoryAnnotatedClass( annotatedElement );
FactoryGroupedClasses factoryClass =
getOrCreateFactoryClass( annotatedClass.getQualifiedGroupName() );
}
} catch (ProcessingException e) { ... }
}
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public boolean process(Set<> annotations, RoundEnvironment rv) {
try {
for (Element annotatedElement : rv.getElementsAnnotatedWith(Factory.class)) {
FactoryAnnotatedClass annotatedClass =
new FactoryAnnotatedClass( annotatedElement );
FactoryGroupedClasses factoryClass =
getOrCreateFactoryClass( annotatedClass.getQualifiedGroupName());
factoryClass.add(annotatedClass);
}
} catch (ProcessingException e) { ... }
}
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Pizza Store Factory
1. Only classes can be @Factory
2. @Factory classes must have empty constructor
3. Same types are grouped to one factory
4. id is String and must be unique in factory group
5. @Factory classes must inherit from specified type
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public void checkInheritance(FactoryAnnotatedClass ac) throws ProcessingException {
TypeElement currentClass = ac.getTypeElement();
}
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public void checkInheritance(FactoryAnnotatedClass ac) throws ProcessingException {
TypeElement currentClass = ac.getTypeElement();
while (true) {
TypeMirror superClassType = currentClass.getSuperclass();
currentClass = (TypeElement) typeUtils.asElement(superClassType);
}
}
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public void checkInheritance(FactoryAnnotatedClass ac) throws ProcessingException {
TypeElement currentClass = ac.getTypeElement();
while (true) {
TypeMirror superClassType = currentClass.getSuperclass();
if (superClassType.getKind() == TypeKind.NONE)
throw new ProcessingException( classElement, "Class doesn’t inherit Meal” );
currentClass = (TypeElement) typeUtils.asElement(superClassType);
}
}
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public void checkInheritance(FactoryAnnotatedClass ac) throws ProcessingException {
TypeElement currentClass = ac.getTypeElement();
while (true) {
TypeMirror superClassType = currentClass.getSuperclass();
if (superClassType.getKind() == TypeKind.NONE)
throw new ProcessingException( classElement, "Class doesn’t inherit Meal” );
if (superClassType.toString().equals( ac.getQualifiedFactoryGroupName() ) )
return;
currentClass = (TypeElement) typeUtils.asElement(superClassType);
}
}
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Code generation
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private Map factoryClasses;
public boolean process(Set<> annotations, RoundEnvironment rv) {
try {
...
} catch (ProcessingException e) { ... }
for (FactoryGroupedClasses factoryClass : factoryClasses.values()) {
factoryClass.generateCode(elementUtils, filer);
}
}
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public void generateCode(Elements elementUtils, Filer filer) throws IOException {
MethodSpec.Builder method = MethodSpec.methodBuilder("create")
.addModifiers(Modifier.PUBLIC)
.addParameter(String.class, "id")
.returns(TypeName.get(superClassName.asType()));
}
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public Meal create(String id) {
}
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public void generateCode(Elements elementUtils, Filer filer) throws IOException {
MethodSpec.Builder method = MethodSpec.methodBuilder("create")
...
for (FactoryAnnotatedClass item : itemsMap.values()) {
method
.beginControlFlow("if ($S.equals(id))", item.getId())
.addStatement("return new $L()",
item.getTypeElement().getQualifiedName().toString())
.endControlFlow();
}
}
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public Meal create(String id) {
if ("Margherita".equals(id))
return new MargheritaPizza();
if ("Calzone".equals(id))
return new CalzonePizza();
if ("Tiramisu".equals(id))
return new Tiramisu();
}
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public void generateCode(Elements elementUtils, Filer filer) throws IOException {
MethodSpec.Builder method = MethodSpec.methodBuilder("create")
...
method.addStatement(
"throw new IllegalArgumentException($S + id)",
"Unknown id = "
);
}
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public Meal create(String id) {
if ("Margherita".equals(id))
return new MargheritaPizza();
if ("Calzone".equals(id))
return new CalzonePizza();
if ("Tiramisu".equals(id))
return new Tiramisu();
throw new IllegalArgumentException( "Unknown id = ” +id );
}
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public void generateCode(Elements elementUtils, Filer filer) throws IOException {
MethodSpec.Builder method = MethodSpec.methodBuilder("create")
...
TypeSpec typeSpec =
TypeSpec.classBuilder( factoryClassName )
.addMethod( method.build() ).build();
// Write MealFactory.java
JavaFile.builder(packageName, typeSpec).build().writeTo(filer);
}
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public class MealFactory {
public Meal create(String id) {
if ("Margherita".equals(id))
return new MargheritaPizza();
if ("Calzone".equals(id))
return new CalzonePizza();
if ("Tiramisu".equals(id))
return new Tiramisu();
throw new IllegalArgumentException( "Unknown id = ” +id );
}
}
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Attempt to recreate a file for type
com.example.MealFactory
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Processing Rounds
Round Input Output
1. PizzaStore.java
Meal.java
CalzonePizza.java
Tiramisu.java
Magerita.java
MealFactory.java
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Processing Rounds
Round Input Output
1. PizzaStore.java
Meal.java
CalzonePizza.java
Tiramisu.java
Magerita.java
MealFactory.java
2. MealFactory.java -- none --
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Processing Rounds
Round Input Output
1. PizzaStore.java
Meal.java
CalzonePizza.java
Tiramisu.java
Magerita.java
MealFactory.java
2. MealFactory.java -- none --
3. -- none -- -- none --
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public class FactoryProcessor extends AbstractProcessor {
private Map factoryClasses;
public boolean process(Set<> annotations, RoundEnvironment rv) {
try {
// scan annotations
} catch (ProcessingException e) { ... }
for (FactoryGroupedClasses factoryClass : factoryClasses.values()) {
factoryClass.generateCode(elementUtils, filer);
}
}
}
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public class FactoryProcessor extends AbstractProcessor {
private Map factoryClasses;
public boolean process(Set<> annotations, RoundEnvironment rv) {
try {
// scan annotations
} catch (ProcessingException e) { ... }
for (FactoryGroupedClasses factoryClass : factoryClasses.values()) {
factoryClass.generateCode(elementUtils, filer);
}
}
}
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public class FactoryProcessor extends AbstractProcessor {
private Map factoryClasses;
public boolean process(Set<> annotations, RoundEnvironment rv) {
try {
// scan annotations
} catch (ProcessingException e) { ... }
for (FactoryGroupedClasses factoryClass : factoryClasses.values()) {
factoryClass.generateCode(elementUtils, filer);
}
}
}
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public class FactoryProcessor extends AbstractProcessor {
private Map factoryClasses;
public boolean process(Set<> annotations, RoundEnvironment rv) {
try {
// scan annotations
} catch (ProcessingException e) { ... }
for (FactoryGroupedClasses factoryClass : factoryClasses.values()) {
factoryClass.generateCode(elementUtils, filer);
}
factoryClasses.clear();
}
}
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Instantiation
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public class PizzaStore {
private MealFactory factory = new MealFactory();
public static void main(String[] args) throws IOException {
PizzaStore pizzaStore = new PizzaStore();
Meal meal = pizzaStore.order( readConsole() );
System.out.println("Bill: $" + meal.getPrice());
}
public Meal order(String mealName) {
return factory.create(mealName);
}
}
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Instantiation using Reflections
ButterKnife.inject(Activity);
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Instantiation using Reflections
ButterKnife.inject(Activity);
try {
Class> injector = Class.forName(activityClassName + "$$ViewInjector");
} catch (ClassNotFoundException e) { ... }
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https://github.com/sockeqwe/annotationprocessing101