AOP（Aspect-Oriented Programming），即是面向切面编程，AspectJ是实现AOP的一个重要的框架，它是使用AspectJ编译器（ajc），在编译时期，在关键的的地方插入部分代码，处理相关逻辑，比如可以用于打印方法执行的效率，权限检查等。在Android上的应用主要是做性能监控、基于注解的数据埋点等，Hugo 就是基于AspectJ实现。

教程

修改项目根目录的 build.gradle 文件

buildscript {
    dependencies {
        classpath 'com.hujiang.aspectjx:gradle-android-plugin-aspectjx:2.0.0'
    }
}

在APP和Module的build.gradle增加插件

apply plugin: 'com.android.application'
apply plugin: 'android-aspectjx'

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    // 下面这行不是必须的，但是为了有时候去掉上面插件不报错就需要增加
    implementation 'org.aspectj:aspectjrt:1.9.4'
}

创建注解

用于打印日志

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface AspectDebugLog {
}

用于埋点

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface AspectAnalyze {
    String name();
}

创建配置

@SuppressWarnings("unused")
@Aspect
public class AspectTrace {
    private static AspectTraceListener aspectTraceListener;

    /**
     * 针对所有继承 Activity 类的 onCreate 方法
     */
    @Pointcut("execution(* android.app.Activity+.onCreate(..))")
    public void activityOnCreatePointcut() { 
        
    }
    /**
     * 针对带有AspectAnalyze注解的方法
     */
    @Pointcut("execution(@com.taoweiji.aspect.trace.AspectAnalyze * *(..))")
    public void aspectAnalyzeAnnotation() {
    }
    /**
     * 针对带有AspectDebugLog注解的方法
     */
    @Pointcut("execution(@com.taoweiji.aspect.trace.AspectDebugLog * *(..))")
    public void aspectDebugLogAnnotation() {
    }

    /**
     * 针对前面 aspectAnalyzeAnnotation() 的配置
     */
    @Around("aspectAnalyzeAnnotation()")
    public void aroundJoinAspectAnalyze(final ProceedingJoinPoint joinPoint) throws Throwable {
        Object target = joinPoint.getTarget();
        MethodSignature methodSignature = (MethodSignature) joinPoint.getSignature();
        AspectAnalyze aspectAnalyze = methodSignature.getMethod().getAnnotation(AspectAnalyze.class);
        long startTimeMillis = System.currentTimeMillis();
        joinPoint.proceed();
        if (aspectTraceListener != null) {
            aspectTraceListener.onAspectAnalyze(joinPoint, aspectAnalyze, methodSignature, System.currentTimeMillis() - startTimeMillis);
        }
    }
    /**
     * 针对前面 aspectDebugLogAnnotation() 或 activityOnCreatePointcut() 的配置
     */
    @Around("aspectDebugLogAnnotation() || activityOnCreatePointcut()")
    public void aroundJoinAspectDebugLog(final ProceedingJoinPoint joinPoint) throws Throwable {
        long startTimeMillis = System.currentTimeMillis();
        joinPoint.proceed();
        long duration = System.currentTimeMillis() - startTimeMillis;
        MethodSignature methodSignature = (MethodSignature) joinPoint.getSignature();
        SourceLocation location = joinPoint.getSourceLocation();
        String message = String.format("%s(%s:%s) [%sms]", methodSignature.getMethod().getName(), location.getFileName(), location.getLine(), duration);
        if (aspectTraceListener != null) {
            aspectTraceListener.logger("AspectTrace", message);
        } else {
            Log.e("AspectTrace", message);
        }
    }

    public static void setAspectTraceListener(AspectTraceListener aspectTraceListener) {
        AspectTrace.aspectTraceListener = aspectTraceListener;
    }

    public interface AspectTraceListener {
        void logger(String tag, String message);

        void onAspectAnalyze(ProceedingJoinPoint joinPoint, AspectAnalyze aspectAnalyze, MethodSignature methodSignature, long duration);
    }
}

配置

在 MyApplication 设置监听器

public class MyApplication extends Application {
    @Override
    public void onCreate() {
        super.onCreate();
        AspectTrace.setAspectTraceListener(new AspectTrace.AspectTraceListener() {
            @Override
            public void logger(String tag, String message) {
                Log.e(tag, message);
            }
            @Override
            public void onAspectAnalyze(ProceedingJoinPoint joinPoint, AspectAnalyze aspectAnalyze, MethodSignature methodSignature, long duration) {
                Log.e("onAspectAnalyze", aspectAnalyze.name());
                // TODO 实现统计功能
            }
        });
    }
}

public class MainActivity extends Activity {
    @AspectAnalyze(name = "MainActivity.onCreate")
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        findViewById(R.id.name).setOnClickListener(v -> onNameClick());
    }
    @AspectDebugLog
    @AspectAnalyze(name = "onNameClick")
    public void onNameClick() {
        try {
            Thread.sleep(500);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    @AspectAnalyze(name = "MainActivity.onDestroy")
    @Override
    protected void onDestroy() {
        super.onDestroy();
    }
}

结果

E/onAspectAnalyze: MainActivity.onCreate
E/AspectTrace: onNameClick(MainActivity.java:28) [502ms]
E/onAspectAnalyze: onNameClick
E/onAspectAnalyze: MainActivity.onDestroy

原理分析

app/build/intermediates/ajx/debug/includefiles/com/taoweiji/aspectjexample/MainActivity.class

可以看到通过AspectJ的ajc编译器转换后的class，在生成dex文件之前，在.class文件中插入了一些代码，从而实现AOP技术。

public class MainActivity extends Activity {
    public MainActivity() {
    }

    @AspectAnalyze(
        name = "MainActivity.onCreate"
    )
    protected void onCreate(Bundle savedInstanceState) {
        JoinPoint var3 = Factory.makeJP(ajc$tjp_0, this, this, savedInstanceState);
        AspectTrace var10000 = AspectTrace.aspectOf();
        Object[] var5 = new Object[]{this, savedInstanceState, var3};
        var10000.aroundJoinAspectAnalyze((new MainActivity$AjcClosure3(var5)).linkClosureAndJoinPoint(69648));
    }

    @AspectDebugLog
    @AspectAnalyze(
        name = "onNameClick"
    )
    public void onNameClick() {
        JoinPoint var2 = Factory.makeJP(ajc$tjp_1, this, this);
        AspectTrace var10000 = AspectTrace.aspectOf();
        Object[] var4 = new Object[]{this, var2};
        var10000.aroundJoinAspectAnalyze((new MainActivity$AjcClosure7(var4)).linkClosureAndJoinPoint(69648));
    }

    @AspectAnalyze(
        name = "MainActivity.onDestroy"
    )
    protected void onDestroy() {
        JoinPoint var1 = Factory.makeJP(ajc$tjp_2, this, this);
        AspectTrace var10000 = AspectTrace.aspectOf();
        Object[] var2 = new Object[]{this, var1};
        var10000.aroundJoinAspectAnalyze((new MainActivity$AjcClosure9(var2)).linkClosureAndJoinPoint(69648));
    }

    static {
        ajc$preClinit();
    }
}