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AOP (Aspect-Oriented Programming)

Posted on In Disqus:

常用於 authentication(使用服務前驗證身分)、record log(紀錄行為日誌)
=> 屬橫切面，與系統主要服務功能較無直接關係

基本介紹

  • 基於OOP：把橫切面邏輯封裝

  • 類似 Proxy Pattern

  • 集中處理非核心邏輯之需求

  • 一段話了解AOP

    抽離非核心之共用邏輯，於特定時機點(程式前/後)，執行其他次要業務邏輯的程式，使核心邏輯不受切面邏輯影響

  • 為什麼使用AOP

    OOP是以侵入性方式對原程式碼加入額外程式 => 重複、關注點混淆且難以維護
    AOP可降低系統的耦合，增加程式的可擴充性

  • 專注職責，降低依賴

術語

  • Aspect

    A modularization of a concern that cuts across multiple classes. (打包好的模組)

  • Point Cut

    A predicate that matches join points. (切入點的定義
    )

  • Join Point

    A point during the execution of a program. (aspect 呼叫的時機點)

  • Advice

    Action taken by an aspect at a particular join point. (aspect 的實作)

  • Weaving

    Linking aspects with other application types or objects to create an advised object. (advice被應用至物件上之過程)

Diagram

aop-gif

Code Snippet

Ex1. OOP Method

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public class SettingService {
    public Object saveSetting(String name) { 
        try {
            saveNameToDb(name); // 主功能
            recordLog(Level.INFO, "hello success.");
            return ResponseEntity.ok();
        } catch(Exception e) {
            recordLog(Level.INFO, "hello fail.");
            return ResponseEntity.badRequest(); 
        }
    }
}

Ex2. AOP

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public class SettingService {
    
    @LogRecord(logInfo = "'Save' + #name ", level = "INFO")
    public Object saveSetting(String name) { 
        try {
            saveNameToDb(name); // 主功能
            return ResponseEntity.ok();
        } catch(Exception e) {
            return ResponseEntity.badRequest(); 
        }
    }
}


  • AOP Implementation
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@Aspect 
@Component 
public class LogAOP { 

    @Pointcut(value=“@annotation(logRecord)") 
    public void pointcut() {}; 

    // 執行前
    @Before(value = "pointcut()") 
    public void getLogInfoBefore(JoinPoint joinPoint) { // ... } 

    // 執行後正常回傳
    @AfterReturning(value = "pointcut()", returning = "returnValue") 
    public void getLogInfoAfterReturning(JoinPoint joinPoint, Object returnValue) { // ... } 

    // 執行後
    @After(value = "pointcut()") 
    public void getLogInfoAfter(JoinPoint joinPoint) { // ... } 

    // 包括執行前/後、回傳值
    @Around(value = "pointcut()") 
    public Object getLogInfoAround(ProceedingJoinPoint pjp) { // ... } 

    // 執行出現異常
    @AfterThrowing(value = "pointcut()“,  throwing= “e" ) 
    public void getLogInfoAfterThrowing(Exception e) { // ... } 
   

}
  • Custom Annotation
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@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE, ElementType.METHOD})
public @interface LogRecord{
    
    String title();
    String logInfo();

}