第一章：navigation注解生成器生成json配置文件

创建注解处理器

创建两个java Library

• 创建注解lib_navanotation

@Target(ElementType.TYPE)
public @interface ActivityDestination {
    String pageUrl();
    boolean needLogin() default false;
    boolean asStarter() default false;
}

@Target(ElementType.TYPE)
public @interface FragmentDestination {
    String pageUrl();
    boolean needLogin() default false;
    boolean asStarter() default false;
}

apply plugin: 'java-library'

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
}
//中文乱码问题（错误：编码GBK不可映射字符）
tasks.withType(JavaCompile) {
    options.encoding = "UTF-8"
}
sourceCompatibility = "8"
targetCompatibility = "8"

• 创建生成器navcompiler

package cn.example.lib_navcompiler;

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONObject;
import com.google.auto.service.AutoService;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.lang.annotation.Annotation;
import java.util.HashMap;
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.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.tools.Diagnostic;
import javax.tools.FileObject;
import javax.tools.StandardLocation;

import cn.example.lib_navannotation.ActivityDestination;
import cn.example.lib_navannotation.FragmentDestination;

@AutoService(Processor.class)
@SupportedSourceVersion(SourceVersion.RELEASE_8)
@SupportedAnnotationTypes({"cn.example.lib_navannotation.FragmentDestination",
        "cn.example.lib_navannotation.ActivityDestination"})
public class NavProcessor extends AbstractProcessor {

    private Messager messager;
    private Filer filer;
    private static final String OUTPUT_FILE_NAME = "destination.json";


    @Override
    public synchronized void init(ProcessingEnvironment processingEnvironment) {
        super.init(processingEnvironment);
        //日志打印,在java环境下不能使用android.util.log.e()
        messager = processingEnv.getMessager();
        //文件处理工具
        filer = processingEnv.getFiler();
    }

    @Override
    public boolean process(Set<? extends TypeElement> set, RoundEnvironment roundEnv) {
        //通过处理器环境上下文roundEnv分别获取 项目中标记的FragmentDestination.class 和ActivityDestination.class注解。
        //此目的就是为了收集项目中哪些类 被注解标记了
        Set<? extends Element> fragmentElements = roundEnv.getElementsAnnotatedWith(FragmentDestination.class);
        Set<? extends Element> activityElements = roundEnv.getElementsAnnotatedWith(ActivityDestination.class);
        if (!fragmentElements.isEmpty() || !activityElements.isEmpty()) {
            HashMap<String, JSONObject> destMap = new HashMap<>();
            //分别 处理FragmentDestination  和 ActivityDestination 注解类型
            //并收集到destMap 这个map中。以此就能记录下所有的页面信息了
            handleDestination(fragmentElements, FragmentDestination.class, destMap);
            handleDestination(activityElements, ActivityDestination.class, destMap);

            //app/src/main/assets
            FileOutputStream fos = null;
            OutputStreamWriter writer = null;
            try {
                //filer.createResource()意思是创建源文件
                //我们可以指定为class文件输出的地方，
                //StandardLocation.CLASS_OUTPUT：java文件生成class文件的位置，/app/build/intermediates/javac/debug/classes/目录下
                //StandardLocation.SOURCE_OUTPUT：java文件的位置，一般在/app/build/generated/source/apt/目录下
                //StandardLocation.CLASS_PATH 和 StandardLocation.SOURCE_PATH用的不多，指的了这个参数，就要指定生成文件的pkg包名了
                FileObject resource = filer.createResource(StandardLocation.CLASS_OUTPUT, "", OUTPUT_FILE_NAME);
                String resourcePath = resource.toUri().getPath();
                messager.printMessage(Diagnostic.Kind.NOTE, "resourcePath:" + resourcePath);

                //由于我们想要把json文件生成在app/src/main/assets/目录下,所以这里可以对字符串做一个截取，
                //以此便能准确获取项目在每个电脑上的 /app/src/main/assets/的路径
                String appPath = resourcePath.substring(0, resourcePath.indexOf("app") + 4);
                String assetsPath = appPath + "src/main/assets/";
                File file = new File(assetsPath);
                if (!file.exists()) {
                    file.mkdir();
                }
                //此处就是稳健的写入了
                File outPutFile = new File(file, OUTPUT_FILE_NAME);
                if (outPutFile.exists()) {
                    outPutFile.delete();
                }
                outPutFile.createNewFile();

                //利用fastjson把收集到的所有的页面信息 转换成JSON格式的。并输出到文件中
                String content = JSON.toJSONString(destMap);
                messager.printMessage(Diagnostic.Kind.NOTE, "content:" + content);
                fos = new FileOutputStream(outPutFile);
                writer = new OutputStreamWriter(fos, "UTF-8");
                writer.write(content);
                writer.flush();
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                if (writer != null) {
                    try {
                        writer.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
                if (fos != null) {
                    try {
                        fos.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }
        }
        return true;
    }

    private void handleDestination(Set<? extends Element> elements,
                                   Class<? extends Annotation> annotationClazz,
                                   HashMap<String, JSONObject> destMap) {
        for (Element element : elements) {
            //TypeElement是Element的一种。
            //如果我们的注解标记在了类名上。所以可以直接强转一下。使用它得到全类名
            TypeElement typeElement = (TypeElement) element;

            //全类名cn.example.jetpackdemo.ui.home.HomeFragment
            String clazName = typeElement.getQualifiedName().toString();
            messager.printMessage(Diagnostic.Kind.NOTE, "clazName:" + clazName);
            //页面的id.此处不能重复,使用页面的类名做hascode即可
            int id = Math.abs(clazName.hashCode());
            //页面的pageUrl相当于隐士跳转意图中的host://schem/path格式
            String pageUrl = null;
            //是否需要登录
            boolean needLogin = false;
            //是否作为首页的第一个展示的页面
            boolean asStarter = false;
            //标记该页面是fragment 还是activity类型的
            boolean isFragment = false;
            Annotation annotation = typeElement.getAnnotation(annotationClazz);
            if (annotation instanceof FragmentDestination) {
                FragmentDestination dest = (FragmentDestination) annotation;
                pageUrl = dest.pageUrl();
                asStarter = dest.asStarter();
                needLogin = dest.needLogin();
                isFragment = true;
            } else if (annotation instanceof ActivityDestination) {
                ActivityDestination dest = (ActivityDestination) annotation;
                pageUrl = dest.pageUrl();
                asStarter = dest.asStarter();
                needLogin = dest.needLogin();
                isFragment = false;
            }
            if (destMap.containsKey(pageUrl)) {
                messager.printMessage(Diagnostic.Kind.ERROR, "不同的页面不允许使用相同的pageUrl：" + clazName);
            } else {
                JSONObject object = new JSONObject();
                object.put("id", id);
                object.put("needLogin", needLogin);
                object.put("asStarter", asStarter);
                object.put("pageUrl", pageUrl);
                object.put("clazName", clazName);
                object.put("isFragment", isFragment);
                destMap.put(pageUrl, object);
            }
        }
    }
}

apply plugin: 'java-library'

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    // AS-3.4.1 + geadles5.1.1-all+ auto-service:1.0-rc6
    annotationProcessor 'com.google.auto.service:auto-service:1.0-rc7'
    compileOnly 'com.google.auto.service:auto-service:1.0-rc7'
    //3.4及其以下
//    api 'com.google.auto.service:auto-service:1.0-rc6'
    implementation 'com.alibaba:fastjson:1.2.68'
    implementation project(path: ':lib_navannotation')
}
//中文乱码问题（错误：编码GBK不可映射字符）
tasks.withType(JavaCompile) {
    options.encoding = "UTF-8"
}
sourceCompatibility = "8"
targetCompatibility = "8"

• 在Fragment上注册注解

• app gradle下

compileOptions {
        sourceCompatibility "1.8"
        targetCompatibility "1.8"
    }