Annotations 2

simple example， IDE为IntelliJ

• 创建项目
  创建一个标准的带maven的Java项目
  项目的结构如下:

SimpleAnnotationProcessor
--.idea
--src
----main
------java
------resources
----test
--pom.xml
--SimpleAnnotationProcessor.imi

更改Source Folders

java0.png

• 创建package和class

package:com.wsl.annotation
class:SimpleAnnotation、SimpleProcessor

目录结构如下

java1.png

• SimpleAnnotation
  自定义Annotation, 保留规则为SOURCE, 编译期被丢弃

package com.wsl.annotation;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
@Retention(RetentionPolicy.SOURCE)
public @interface SimpleAnnotation {
}

• SimpleProcessor
  这里process的逻辑比较简单，仅仅是打印一下目标Element的name

public class SimpleProcessor extends AbstractProcessor {

    public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment env) {
        Messager messager = processingEnv.getMessager();

        for (TypeElement te : annotations) {
            for (Element e : env.getElementsAnnotatedWith(te)) {
                messager.printMessage(Diagnostic.Kind.NOTE, "Printing: " + e.toString());
            }
        }
        return true;
    }

    @Override
    public Set<String> getSupportedAnnotationTypes() {
        Set<String> annotations = new LinkedHashSet<String>();
        annotations.add(SimpleAnnotation.class.getCanonicalName());
        return annotations;
    }

    @Override
    public SourceVersion getSupportedSourceVersion() {
        return SourceVersion.latestSupported();
    }
}

• javax.annotation.processing.Processor
  resources目录下新建META-INF/services,services目录下新建javax.annotation.processing.Processor,Processor指定自定义的processor

com.wsl.annotation.SimpleProcessor

• package JAR
  这里用maven打包，修改pom.xml

<?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>groupId</groupId>
    <artifactId>SimpleAnnotationProcessor</artifactId>
    <version>1.0-SNAPSHOT</version>

    <!--增加如下代码-->
    <packaging>jar</packaging>
    <build>
        <plugins>
            <plugin>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>2.3.2</version>
                <configuration>
                    <source>1.6</source>
                    <target>1.6</target>
                    <!-- Disable annotation processing for ourselves. -->
                    <compilerArgument>-proc:none</compilerArgument>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

执行mvn clean package, 在target目录生成JAR

• 验证
  编写验证类Test.java，如下

import com.wsl.annotation.SimpleAnnotation;
@SimpleAnnotation
public class Test {
  @SimpleAnnotation
  public static void a1(int x) {
  }

  public static void a2(String[] arr) {
  }
}

wushuanglongdeMac-mini:SimpleAnnotationProcessor wushuanglong$ javac -cp ~/tmp/Simple0.jar Test.java
注: Printing: Test
注: Printing: a1(int)

NOTE:Artifact方式打出来的包没有MATA-INF,具体原因需要进一步研究