first commit

.gitignore

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+/annotation-processor/target/
+/annotation-user/target/
+/annotation_processing.iml
+/annotation-processor/annotationprocessor.iml
+/.idea/

README.md

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+refer to: https://www.baeldung.com/java-annotation-processing-builder
+
+# 1 主要演示效果
+在编译期，将
+annotation-user/target/classes/com/roadl/annouser/Person.class
+
+setter上的注解生成辅助类：
+annotation-user/target/classes/com/roadl/annouser/PersonBuilder.class
+
+# 2 module化
+annotation_processing 父project 
+annotation_processing/annotation-user 子module A，依赖module B
+annotation_processing/annotation-processor 子module B

annotation-processor/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <parent>
+    <artifactId>annotation_processing</artifactId>
+    <groupId>com.roadl</groupId>
+    <version>1.0-SNAPSHOT</version>
+  </parent>
+  <modelVersion>4.0.0</modelVersion>
+
+  <artifactId>annotation-processor</artifactId>
+
+  <properties>
+    <auto-service.version>1.0-rc2</auto-service.version>
+  </properties>
+
+  <dependencies>
+
+    <dependency>
+      <groupId>com.google.auto.service</groupId>
+      <artifactId>auto-service</artifactId>
+      <version>${auto-service.version}</version>
+      <scope>provided</scope>
+    </dependency>
+
+  </dependencies>
+
+</project>

annotation-processor/src/main/java/com/roadl/annoprocessor/BuilderProcessor.java

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+package com.roadl.annoprocessor;
+
+import com.google.auto.service.AutoService;
+import java.io.IOException;
+import java.io.PrintWriter;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.stream.Collectors;
+import javax.annotation.processing.AbstractProcessor;
+import javax.annotation.processing.Processor;
+import javax.annotation.processing.RoundEnvironment;
+import javax.annotation.processing.SupportedAnnotationTypes;
+import javax.annotation.processing.SupportedSourceVersion;
+import javax.lang.model.SourceVersion;
+import javax.lang.model.element.Element;
+import javax.lang.model.element.TypeElement;
+import javax.lang.model.type.ExecutableType;
+import javax.tools.Diagnostic;
+import javax.tools.JavaFileObject;
+
+@SupportedAnnotationTypes("com.roadl.annoprocessor.BuilderProperty")
+@SupportedSourceVersion(SourceVersion.RELEASE_8)
+@AutoService(Processor.class)
+public class BuilderProcessor extends AbstractProcessor {
+
+  @Override
+  public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
+    for (TypeElement annotation : annotations) {
+      Set<? extends Element> annotatedElements = roundEnv.getElementsAnnotatedWith(annotation);
+
+      Map<Boolean, List<Element>> annotatedMethods = annotatedElements.stream().collect(
+          Collectors.partitioningBy(element ->
+              ((ExecutableType) element.asType()).getParameterTypes().size() == 1
+                  && element.getSimpleName().toString().startsWith("set")));
+
+      List<Element> setters = annotatedMethods.get(true);
+      List<Element> otherMethods = annotatedMethods.get(false);
+
+      otherMethods.forEach(element ->
+          processingEnv.getMessager().printMessage(Diagnostic.Kind.ERROR,
+              "@com.roadl.annoprocessor.BuilderProperty must be applied to a setXxx method "
+                  + "with a single argument", element));
+
+      if (setters.isEmpty()) {
+        continue;
+      }
+      String className = ((TypeElement) setters.get(0)
+          .getEnclosingElement()).getQualifiedName().toString();
+
+      Map<String, String> setterMap = setters.stream().collect(Collectors.toMap(
+          setter -> setter.getSimpleName().toString(),
+          setter -> ((ExecutableType) setter.asType())
+              .getParameterTypes().get(0).toString()
+      ));
+
+      try {
+        writeBuilderFile(className, setterMap);
+      } catch (IOException e) {
+        e.printStackTrace();
+      }
+    }
+    return true;
+  }
+
+  private void writeBuilderFile(
+      String className, Map<String, String> setterMap)
+      throws IOException {
+
+    String packageName = null;
+    int lastDot = className.lastIndexOf('.');
+    if (lastDot > 0) {
+      packageName = className.substring(0, lastDot);
+    }
+
+    String simpleClassName = className.substring(lastDot + 1);
+    String builderClassName = className + "Builder";
+    String builderSimpleClassName = builderClassName
+        .substring(lastDot + 1);
+
+    JavaFileObject builderFile = processingEnv.getFiler()
+        .createSourceFile(builderClassName);
+
+    try (PrintWriter out = new PrintWriter(builderFile.openWriter())) {
+
+      if (packageName != null) {
+        out.print("package ");
+        out.print(packageName);
+        out.println(";");
+        out.println();
+      }
+
+      out.print("public class ");
+      out.print(builderSimpleClassName);
+      out.println(" {");
+      out.println();
+
+      out.print("    private ");
+      out.print(simpleClassName);
+      out.print(" object = new ");
+      out.print(simpleClassName);
+      out.println("();");
+      out.println();
+
+      out.print("    public ");
+      out.print(simpleClassName);
+      out.println(" build() {");
+      out.println("        return object;");
+      out.println("    }");
+      out.println();
+
+      setterMap.entrySet().forEach(setter -> {
+        String methodName = setter.getKey();
+        String argumentType = setter.getValue();
+
+        out.print("    public ");
+        out.print(builderSimpleClassName);
+        out.print(" ");
+        out.print(methodName);
+
+        out.print("(");
+
+        out.print(argumentType);
+        out.println(" value) {");
+        out.print("        object.");
+        out.print(methodName);
+        out.println("(value);");
+        out.println("        return this;");
+        out.println("    }");
+        out.println();
+      });
+
+      out.println("}");
+    }
+  }
+}

annotation-processor/src/main/java/com/roadl/annoprocessor/BuilderProperty.java

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+package com.roadl.annoprocessor;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+@Target(ElementType.METHOD)
+@Retention(RetentionPolicy.SOURCE)
+public @interface BuilderProperty {
+
+}

annotation-user/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <parent>
+    <artifactId>annotation_processing</artifactId>
+    <groupId>com.roadl</groupId>
+    <version>1.0-SNAPSHOT</version>
+  </parent>
+  <modelVersion>4.0.0</modelVersion>
+
+  <artifactId>annotation-user</artifactId>
+
+  <dependencies>
+    <dependency>
+      <groupId>com.roadl</groupId>
+      <artifactId>annotation-processor</artifactId>
+      <version>1.0-SNAPSHOT</version>
+    </dependency>
+  </dependencies>
+</project>

annotation-user/src/main/java/com/roadl/annouser/Person.java

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+package com.roadl.annouser;
+
+import com.roadl.annoprocessor.BuilderProperty;
+
+public class Person {
+  private int age;
+  private String name;
+
+
+  public int getAge() {
+    return age;
+  }
+
+  @BuilderProperty
+  public void setAge(int age) {
+    this.age = age;
+  }
+
+  public String getName() {
+    return name;
+  }
+  @BuilderProperty
+  public void setName(String name) {
+    this.name = name;
+  }
+}

annotation-user/src/test/java/com/roadl/annouser/PersonBuilderUnitTest.java

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+package com.roadl.annouser;
+
+import org.junit.Test;
+import static org.junit.Assert.assertEquals;
+
+public class PersonBuilderUnitTest {
+  @Test
+  public void whenBuildPersonWithBuilder_thenObjectHasPropertyValues() {
+
+    Person person = new PersonBuilder().setAge(25).setName("John").build();
+
+    assertEquals(25, person.getAge());
+    assertEquals("John", person.getName());
+  }
+}

pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <groupId>com.roadl</groupId>
+  <artifactId>annotation_processing</artifactId>
+  <packaging>pom</packaging>
+  <version>1.0-SNAPSHOT</version>
+
+  <modules>
+    <module>annotation-processor</module>
+    <module>annotation-user</module>
+  </modules>
+
+  <dependencies>
+    <!-- https://mvnrepository.com/artifact/junit/junit -->
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <version>4.12</version>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+
+
+  <!--
+  [ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.1:compile (default-compile) on project annotation-processor: Compilation failure: Compilation failure:
+  [ERROR] Source option 5 is no longer supported. Use 6 or later.
+  -->
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-compiler-plugin</artifactId>
+        <configuration>
+          <source>1.8</source>
+          <target>1.8</target>
+        </configuration>
+      </plugin>
+    </plugins>
+  </build>
+
+</project>