Annotation Processor在Android下的应用

1. 新建一个Java Library(processor)，注意这一步是必须的，否则无法导入某些java的注解类，估计是Android 的限制。

build.gradle配置如下:

applyplugin:'java'

dependencies {

compile fileTree(dir:'libs',include: ['*.jar'])

}

sourceCompatibility ="1.8"

targetCompatibility ="1.8"

2. 编写Annotation声明类HelloAnnotation.java

packageorg.penguin.study.annotationprocessor.processor;

/**

* Created by terry on 12/07/2017.

*/

public @interface HelloAnnotation {

}

3. 编写对应Annotation的处理类HelloAnnotationProcessor.java

packageorg.penguin.study.annotationprocessor.processor;

importjava.io.IOException;

importjava.io.Writer;

importjava.util.Set;

importjavax.annotation.processing.AbstractProcessor;

importjavax.annotation.processing.RoundEnvironment;

importjavax.annotation.processing.SupportedAnnotationTypes;

importjavax.annotation.processing.SupportedSourceVersion;

importjavax.lang.model.SourceVersion;

importjavax.lang.model.element.Element;

importjavax.lang.model.element.TypeElement;

importjavax.tools.JavaFileObject;

@SupportedAnnotationTypes("org.penguin.study.annotationprocessor.processor.HelloAnnotation")

@SupportedSourceVersion(SourceVersion.RELEASE_8)

public class HelloAnnotationProcessorextendsAbstractProcessor {

@Override

public boolean process(Set annotations,RoundEnvironment roundEnv) {

StringBuilder builder =newStringBuilder()

.append("package org.penguin.study.annotationprocessor.generated;\n\n")

.append("public class GeneratedClass {\n\n").append("\tpublic String getMessage() {\n")

.append("\t\treturn\"");

// for each javax.lang.model.element.Element annotated with the CustomAnnotation

for(Element element : roundEnv.getElementsAnnotatedWith(HelloAnnotation.class)) {

String objectType = element.getSimpleName().toString();

// this is appending to the return statement

builder.append(objectType).append(" Java Annotation Process 入门经典!\\n");

}

builder.append("\";\n")

.append("\t}\n")

.append("}\n");

try{

JavaFileObject source =processingEnv.getFiler().createSourceFile("org.penguin.study.annotationprocessor.generated.GeneratedClass");

Writer writer = source.openWriter();

writer.write(builder.toString());

writer.flush();

writer.close();

}catch(IOException e) {

// 此处的IO异常一般发生在第一次编译的时候，基本不用处理。

}

return true;

}

}

4. 在Java Library(processor)下创建目录resources

5. 在Java Library(processor)下resources目录下创建目录META-INF下创建目录services

6. 在Java Library(processor)下resources/META-INF/services目录下创建文件javax.annotation.processing.Processor

7. 在Java Library(processor)下resources/META-INF/services/javax.annotation.processing.Processor文件中标明Annotation处理类

org.penguin.study.annotationprocessor.processor.HelloAnnotationProcessor

8. 在Android app module或其它module中引入依赖的 processor module：compile project(path:':processor')，然后就可以使用注解He'llAnnotation了

packageorg.penguin.study.android;

importandroid.os.Bundle;

importandroid.support.v7.app.AppCompatActivity;

importandroid.widget.TextView;

importorg.penguin.study.annotationprocessor.generated.GeneratedClass;

importorg.penguin.study.annotationprocessor.processor.HelloAnnotation;

importbutterknife.BindView;

importbutterknife.ButterKnife;

@HelloAnnotation

public classMainActivityextendsAppCompatActivity {

@BindView(R.id.txtMessage)

TextViewtxtMessage;

@Override

protected voidonCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

ButterKnife.bind(this);

GeneratedClass generatedClass =newGeneratedClass();

txtMessage.setText(generatedClass.getMessage());

}

}

9.  app module的build.gradle内容如下:

applyplugin:'com.android.application'

android {

compileSdkVersion26

buildToolsVersion"26.0.0"

defaultConfig {

applicationId"org.penguin.study.android"

minSdkVersion19

targetSdkVersion26

versionCode1

versionName"1.0"

testInstrumentationRunner"android.support.test.runner.AndroidJUnitRunner"

jackOptions {

enabledtrue

}

}

buildTypes {

release {

minifyEnabledfalse

proguardFiles getDefaultProguardFile('proguard-android.txt'),'proguard-rules.pro'

}

}

compileOptions {

sourceCompatibilityJavaVersion.VERSION_1_8

targetCompatibilityJavaVersion.VERSION_1_8

}

packagingOptions {

exclude'META-INF/ASL2.0'

exclude'META-INF/LICENSE'

exclude'META-INF/license.txt'

exclude'META-INF/NOTICE'

exclude'META-INF/notice.txt'

}

}

dependencies {

compile fileTree(dir:'libs',include: ['*.jar'])

compile'com.android.support:appcompat-v7:26.+'

compile'com.android.support.constraint:constraint-layout:1.0.2'

compile'com.jakewharton:butterknife:8.7.0'

annotationProcessor'com.jakewharton:butterknife-compiler:8.7.0'

compile project(path:':processor')

testCompile'junit:junit:4.12'

androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {

excludegroup:'com.android.support',module:'support-annotations'

})

}

经过上面的配置，一个demo就可以跑起来了，生成的java源码app/build/generated/source/apt/debug/org/penguin/study/annotationprocessor/generated/GeneratedClass.java

package org.penguin.study.annotationprocessor.generated;

public class GeneratedClass {

    public String getMessage() {

        return "MainActivity Java Annotation Process 入门经典!\n";

    }

}