Android AbstractProcessor和apt环境配置

AbstractProcessor

AbstractProcessor是抽象处理器，开发apt时都必须实现这个类来生成java文件，实现这个类后叫做

注解处理器，他是在编译时搜索注解并给与相应处理并生成相应的代码。对个注解的处理，是重点，重要在它能够获取所注解的元素的信息。不过这次只重点介绍AbstractProcessor，不把重心放在代码生成上。以后做apt时必定需要这个类。
首先说一下我们要实现这个类的函数
@Override
public synchronized void init(ProcessingEnvironment processingEnvironment)
{ super.init(processingEnvironment);
//初始化我们需要的基础工具
mTypeUtils = processingEnv.getTypeUtils();
mElementUtils = processingEnv.getElementUtils();
mFiler = processingEnv.getFiler();
mMessager = processingEnv.getMessager();
}
在这个类获取很多工具类为了方便获取所注解的类的信息，工具类的具体使用后面说明
@Override
public boolean process(Setset, RoundEnvironment roundEnvironment)
{
Setelements = roundEnvironment.getElementsAnnotatedWith(ZyaoAnnotation.class);
// 遍历所有被注解了@Factory的元素
for (Element annotatedElement : elements) {
// 检查被注解为@Factory的元素是否是一个类
if (annotatedElement.getKind() != ElementKind.CLASS) {
error(annotatedElement, "Only classes can be annotated with @%s",
ZyaoAnnotation.class.getSimpleName());
return true; // 退出处理
}
analysisAnnotated(annotatedElement);
}
return true;
}
遍历被注解的元素并给与相应处理
@Override
public Set getSupportedAnnotationTypes()
{
//支持的注解
Set annotations = new LinkedHashSet<>();
annotations.add(ZyaoAnnotation.class.getCanonicalName());
return annotations;
}
指定注解类型
@Override
public SourceVersion getSupportedSourceVersion()
{
//支持的java版本
return SourceVersion.RELEASE_7;
}
指定编译这个类使用的Java版本

apt环境配置

首先新建一个project，然后再新建两个JavaLibrary的 module，名字为annotation、compiler
其中compiler需要添加依赖
compile 'com.google.auto.service:auto-service:1.0-rc2'
compile 'com.squareup:javapoet:1.7.0'
app这个主module引入这个两个module
compile project(':annotation')
annotationProcessor project(':compiler')
annotation负责注解代码，compiler负责将生成代码
注解负责向依附的类添加运行代码，并且还能够将依附的类的信息传给compiler，使compiler能够生成符合依附的类的代码，这个代码给与注解，让注解在依附的类里运行代码。
因为包名不好判断，代码我就连包名也贴出来
这是annotaion的类

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * Created by ZTH on 2018/1/22.
 */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.CLASS)
public @interface ZyaoAnnotation {

    String name() default "undefined";
    String text() default "";

}

这是compiler的类

import com.example.annotation.ZyaoAnnotation;
import com.google.auto.service.AutoService;

import java.io.IOException;
import java.io.Writer;
import java.util.LinkedHashSet;
import java.util.Set;

import javax.annotation.processing.AbstractProcessor;
import javax.annotation.processing.Filer;
import javax.annotation.processing.Messager;
import javax.annotation.processing.ProcessingEnvironment;
import javax.annotation.processing.Processor;
import javax.annotation.processing.RoundEnvironment;
import javax.lang.model.SourceVersion;
import javax.lang.model.element.Element;
import javax.lang.model.element.ElementKind;
import javax.lang.model.element.TypeElement;
import javax.lang.model.util.Elements;
import javax.lang.model.util.Types;
import javax.tools.Diagnostic;
import javax.tools.JavaFileObject;

@AutoService(Processor.class)
public class MyProcessor extends AbstractProcessor
{
    private Types mTypeUtils;
    private Elements mElementUtils;
    private Filer    mFiler;
    private Messager mMessager;

    @Override
    public synchronized void init(ProcessingEnvironment processingEnvironment)
    {
        super.init(processingEnvironment);

        //初始化我们需要的基础工具
        mTypeUtils = processingEnv.getTypeUtils();
        mElementUtils = processingEnv.getElementUtils();
        mFiler = processingEnv.getFiler();
        mMessager = processingEnv.getMessager();
    }

    @Override
    public SourceVersion getSupportedSourceVersion()
    {
        //支持的java版本
        return SourceVersion.RELEASE_7;
    }

    @Override
    public Set getSupportedAnnotationTypes()
    {
        //支持的注解
        Set annotations = new LinkedHashSet<>();
        annotations.add(ZyaoAnnotation.class.getCanonicalName());
        return annotations;
    }

    @Override
    public boolean process(Set set, RoundEnvironment roundEnvironment)
    {
        if (set == null || set.isEmpty())
        {
            return true;
        }



        Set elements = roundEnvironment.getElementsAnnotatedWith(ZyaoAnnotation.class);
        if (elements == null || elements.isEmpty())
        {
            return true;
        }

        // 遍历所有被注解了@Factory的元素
        for (Element annotatedElement : elements) {

            // 检查被注解为@Factory的元素是否是一个类
            if (annotatedElement.getKind() != ElementKind.CLASS) {

                return true; // 退出处理
            }

            analysisAnnotated(annotatedElement);
        }

        return true;
    }

    private static final String SUFFIX = "$$ZYAO";

    private void analysisAnnotated(Element classElement)
    {
        ZyaoAnnotation annotation = classElement.getAnnotation(ZyaoAnnotation.class);
        String name = annotation.name();
        String text = annotation.text();

//        TypeElement superClassName = mElementUtils.getTypeElement(name);
        String newClassName = name + SUFFIX;

        StringBuilder builder = new StringBuilder()
                .append("package com.example.zth.myapplication;\n\n")
                .append("public class ")
                .append(newClassName)
                .append(" {\n\n") // open class
                .append("\tpublic String getMessage() {\n") // open method
                .append("\t\treturn \"");

        // this is appending to the return statement
        builder.append(text).append(name).append(" !\\n");


        builder.append("\";\n") // end return
                .append("\t}\n") // close method
                .append("}\n"); // close class


        try { // write the file
            JavaFileObject source = mFiler.createSourceFile("com.example.zth.myapplication."+newClassName);
            Writer writer = source.openWriter();
            writer.write(builder.toString());
            writer.flush();
            writer.close();
        } catch (IOException e) {
            // Note: calling e.printStackTrace() will print IO errors
            // that occur from the file already existing after its first run, this is normal
        }

    }


}

这是app的类

@ZyaoAnnotation(
        name = "Zyao",
        text = "Hello !!! Welcome "
)
public class MainActivity extends Activity {


    TextView tv1;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        tv1 = (TextView)findViewById(R.id.tv1);

        tv1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Zyao$$ZYAO zyao$$ZYAO = new Zyao$$ZYAO();
                String message = zyao$$ZYAO.getMessage();
                tv1.setText(message);
            }
        });


    }


}

如果MainActivity说没有什么类，那就先make project再试一下导包

下一次就重点将如何从被注解的元素获取信息，并如何给被注解的元素赋值