當對象狀態發生變化時調用方法

Question

我正在提供任何人都可以在其代碼中包含的註釋@validateName。假設一些一個編碼

class Person { 
    @validateName 
    private String name; 
    .... 
} 

然後，他們可以調用NameValidator.validate(personObject)或驗證該領域的一些類似的方法。

我想確保名稱字段始終處於有效狀態，即每當註釋變量發生更改時（無論其在類內部還是外部發生更改），我都會自動調用validate()方法。
我願意編寫一個掛鉤到Eclipse的插件，並在編譯階段被調用。請提供一些可以開始尋找解決方案的指南。
（我想我必須實現某種AOP的或使用中輕或東西應該修改字節碼的我不知道，因爲我還沒有用盡全力。）

Answer 1

使用AspectJ，你可以這樣做：

註釋

package de.scrum_master.aop.app; 

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

@Retention(RetentionPolicy.RUNTIME) 
public @interface ValidateName {} 

Driver類

package de.scrum_master.aop.app; 

public class Application { 
    private int id; 
    @ValidateName 
    private String firstName; 
    @ValidateName 
    private String lastName; 
    private String placeOfBirth; 

    public Application(int id, String firstName, String lastName, String placeOfBirth) { 
     this.id = id; 
     this.firstName = firstName; 
     this.lastName = lastName; 
     this.placeOfBirth = placeOfBirth; 
    } 

    @Override 
    public String toString() { 
     return "Application [id=" + id + ", firstName=" + firstName 
       + ", lastName=" + lastName + ", placeOfBirth=" + placeOfBirth 
       + "]"; 
    } 

    public static void main(String[] args) { 
     System.out.println(new Application(1, "Galileo", "Galilei", "Pisa, Italy")); 
     System.out.println(new Application(2, "Isaac", "Newton", "Woolsthorpe-by-Colsterworth, United Kingdom")); 
     System.out.println(new Application(3, "Albert", "Einstein", "Ulm, Germany")); 
     System.out.println(new Application(4, "Werner", "Heisenberg", "Würzburg, Germany")); 
    } 
} 

驗證方面

package de.scrum_master.aop.aspect; 

import java.util.Random; 
import de.scrum_master.aop.app.ValidateName; 

public aspect NameValidator { 
    void validate(String name) { 
     if (new Random().nextBoolean()) 
      throw new RuntimeException("Invalid name " + name); 
    } 

    void around(String name) : set(@ValidateName * *.*) && args(name) { 
     //System.out.println(thisJoinPointStaticPart); 
     System.out.print("Validating name " + name); 
     try { 
      validate(name); 
      System.out.println(" -> OK"); 
      proceed(name); 
     } 
     catch (Exception e) { 
      name = name.toUpperCase(); 
      System.out.println(" -> " + e.getMessage() + " -> replaced by " + name); 
      proceed(name); 
     } 
    } 
} 

正如你所看到的，我驗證只是隨機失敗的約所有病例的50％基於僞隨機值。當它發生時，它只是用大寫的版本替換「無效的」名稱。輸出看起來像這樣的變化：

Validating name Galileo -> OK 
Validating name Galilei -> Invalid name Galilei -> replaced by GALILEI 
Application [id=1, firstName=Galileo, lastName=GALILEI, placeOfBirth=Pisa, Italy] 
Validating name Isaac -> Invalid name Isaac -> replaced by ISAAC 
Validating name Newton -> Invalid name Newton -> replaced by NEWTON 
Application [id=2, firstName=ISAAC, lastName=NEWTON, placeOfBirth=Woolsthorpe-by-Colsterworth, United Kingdom] 
Validating name Albert -> OK 
Validating name Einstein -> Invalid name Einstein -> replaced by EINSTEIN 
Application [id=3, firstName=Albert, lastName=EINSTEIN, placeOfBirth=Ulm, Germany] 
Validating name Werner -> OK 
Validating name Heisenberg -> Invalid name Heisenberg -> replaced by HEISENBERG 
Application [id=4, firstName=Werner, lastName=HEISENBERG, placeOfBirth=Würzburg, Germany]