package com.example.annotations;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface DebugLog {
    String value();
}

package com.example.processor;
import javax.annotation.processing.*;
import javax.lang.model.SourceVersion;
import javax.lang.model.element.Element;
import javax.lang.model.element.TypeElement;
import java.util.Set;
@SupportedAnnotationTypes("com.example.annotations.DebugLog")
@SupportedSourceVersion(SourceVersion.RELEASE_8)
public class DebugLogProcessor extends AbstractProcessor {
    @Override
    public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
        for (Element element : roundEnv.getElementsAnnotatedWith(DebugLog.class)) {
            String message = String.format("%s called.", element.getSimpleName().toString());
            System.out.println(message);
        }
        return true;
    }
}

package com.example.processor;
import com.example.annotations.DebugLog;
import javax.annotation.processing.*;
import javax.lang.model.SourceVersion;
import javax.lang.model.element.Element;
import javax.lang.model.element.ExecutableElement;
import javax.lang.model.element.TypeElement;
import javax.tools.Diagnostic;
import javax.tools.JavaFileObject;
import java.io.IOException;
import java.io.PrintWriter;
@SupportedAnnotationTypes("com.example.annotations.DebugLog")
@SupportedSourceVersion(SourceVersion.RELEASE_8)
public class DebugLogProcessor extends AbstractProcessor {
    @Override
    public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
        for (Element element : roundEnv.getElementsAnnotatedWith(DebugLog.class)) {
            if (element.getKind().isMethod()) {
                ExecutableElement method = (ExecutableElement) element;
                // 獲取方法所在類(lèi)的信息
                TypeElement classElement = (TypeElement) method.getEnclosingElement();
                String packageName = processingEnv.getElementUtils().getPackageOf(classElement).toString();
                String className = classElement.getSimpleName().toString();
                // 生成新的方法名
                String newMethodName = method.getSimpleName().toString() + "$debug";
                // 生成新的方法體，將原來(lái)的方法體置于其中
                StringBuilder builder = new StringBuilder();
                builder.append("public void ").append(newMethodName).append("(){\n");
                builder.append("System.out.println(\"" + method.getSimpleName() + " called.\");\n");
                builder.append("try{\n");
                builder.append(method.getSimpleName()).append("();\n");
                builder.append("}catch(Exception e){\n");
                builder.append("e.printStackTrace();\n");
                builder.append("}\n");
                builder.append("}");
                // 在原有類(lèi)中添加新的方法
                try {
                    JavaFileObject sourceFile = processingEnv.getFiler().createSourceFile(packageName + "." + className);
                    PrintWriter writer = new PrintWriter(sourceFile.openWriter());
                    writer.println("package " + packageName + ";\n");
                    writer.println("public class " + className + "{\n");
                    writer.println("private " + className + "(){}\n");
                    writer.println("public static void main(String[] args){new " + className + "()." + newMethodName + "();}");
                    processingEnv.getMessager().printMessage(Diagnostic.Kind.NOTE, "Generated Method: " + className + "." + newMethodName);
                    writer.println(builder.toString());
                    writer.println("}");
                    writer.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        return true;
    }
}