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package com.runuts.android.annotation;
import java.lang.annotation.ElementType;import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;import java.lang.annotation.Target;
@Target({ElementType.TYPE})@Retention(RetentionPolicy.CLASS)public @interface ExtractInterface { String interfaceName() default "-!!-";}

package com.runuts.android.annotationprocessor;
import com.google.auto.service.AutoService;import com.runuts.android.annotation.ExtractInterface;
import javax.annotation.processing.*;import javax.lang.model.SourceVersion;import javax.lang.model.element.*;import javax.lang.model.util.*;import java.util.*;import java.util.stream.*;import java.io.*;
@SupportedAnnotationTypes("com.runuts.android.annotation.ExtractInterface")@SupportedSourceVersion(SourceVersion.RELEASE_8)@AutoService(Processor.class)public class IfaceExtractorProcessor extends AbstractProcessor {
 private ArrayList<Element> interfaceMethods = new ArrayList<>(); Elements elementUtils; private ProcessingEnvironment processingEnv;
 @Override public void init(ProcessingEnvironment processingEnv) { this.processingEnv = processingEnv; elementUtils = processingEnv.getElementUtils(); }
 @Override public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment env) { for(Element elem:env.getElementsAnnotatedWith(ExtractInterface.class)) { String interfaceName = elem.getAnnotation( ExtractInterface.class).interfaceName(); for(Element enclosed : elem.getEnclosedElements()) { if(enclosed.getKind() .equals(ElementKind.METHOD) && enclosed.getModifiers() .contains(Modifier.PUBLIC) && !enclosed.getModifiers() .contains(Modifier.STATIC)) { interfaceMethods.add(enclosed); } }
 if(interfaceMethods.size() > 0) writeInterfaceFile(interfaceName); } return false; }
 private void writeInterfaceFile(String interfaceName) { try( Writer writer = processingEnv.getFiler() .createSourceFile(interfaceName) .openWriter() ){ String packageName = elementUtils .getPackageOf(interfaceMethods .get(0)).toString(); writer.write( "package " + packageName + ";\n"); writer.write("public interface " + interfaceName + " {\n"); for(Element elem : interfaceMethods) { ExecutableElement method = (ExecutableElement)elem; String signature = " public "; signature += method.getReturnType() + " "; signature += method.getSimpleName(); signature += createArgList(method.getParameters()); System.out.println(signature); writer.write(signature + ";\n"); } writer.write("}"); } catch(Exception e) { throw new RuntimeException(e); } }
 private String createArgList( List<? extends VariableElement> parameters) { String args = parameters.stream() .map(p -> p.asType() + " " + p.getSimpleName()) .collect(Collectors.joining(", ")); return "(" + args + ")"; }}

package com.runuts.android.aptdemo;
import com.runuts.android.annotation.ExtractInterface;
@ExtractInterface(interfaceName="IMultiplier")public class Multiplier {public boolean flag = false;private int n = 0;
public int multiply(int x, int y) {int total = 0;for(int i = 0; i < x; i++) total = add(total, y);return total; }
public int fortySeven() { return 47; }
private int add(int x, int y) {return x + y; }
public double timesTen(double arg) { return arg * 10; }
public static void main(String[] args) { Multiplier m = new Multiplier(); System.out.println( "11 * 16 = " + m.multiply(11,16)); }}

// annotationprocessor - build.gradleplugins { id 'java-library'}
java { sourceCompatibility = JavaVersion.VERSION_1_8 targetCompatibility = JavaVersion.VERSION_1_8}
dependencies {   implementation project(path: ':annotation') // 谷歌的 AutoService 可以让我们的注解处理器自动注册上 implementation 'com.google.auto.service:auto-service:1.0-rc7' // 这个一定要添加，否则是无法在app/build/generated/ap_generated_sources/debug/out生成文件的 annotationProcessor 'com.google.auto.service:auto-service:1.0-rc7'}

// app - build.gradledependecies { annotationProcessor project(':annotationprocessor') implementation project(path: ':annotation')}

package com.runuts.android.aptdemo;public interface IMultiplier {public int multiply(int x, int y);public int fortySeven();public double timesTen(double arg);}