使用構建器模式創建異常？

Question

我有一個例外，在我的java代碼中有幾個屬性將被傳遞給構造函數。因此，我認爲這將是很好的創造與生成器模式異常，所以我創造了這樣的例外：

public class ApplicationException extends Exception { 

    private static final long serialVersionUID = -8999932578270387947L; 

    /** 
    * contains redundantly the HTTP status of the response sent back to the client in case of error, so that 
    * the developer does not have to look into the response headers. If null a default 
    */ 
    Integer status; 

    /** application specific error code */ 
    int code; 

    /** link documenting the exception */ 
    String link; 

    /** detailed error description for developers*/ 
    String developerMessage;  

    /** 
    * 
    * @param status 
    * @param code 
    * @param message 
    * @param developerMessage 
    * @param link 
    */ 
    protected ApplicationException(String message) { 
     super(message); 
    } 

    ... 

    public static Builder getBuilder(String message) { 
     return new Builder(message); 
    } 

    public static class Builder { 
     private Integer status; 
     private int code; 
     private String link; 
     private String message; 
     private String developerMessage;  

     public Builder(String message) { 
      this.message = message; 
     } 

     public Builder status(int status) { 
      this.status = status; 
      return this; 
     } 


     public Builder code(int code) { 
      this.code = code; 
      return this;    
     }   

     public Builder developerMessage(String developerMessage) { 
      this.developerMessage = developerMessage; 
      return this;    
     }  

     public Builder link(String link) { 
      this.link = link; 
      return this;    
     } 

     public ApplicationException build() { 
      if (StringUtils.isBlank(message)) { 
       throw new IllegalStateException("message cannot be null or empty"); 
      } 

      if (StringUtils.isBlank(link)){ 
       link = AppConstants.API_SUPPORT_EMAIL; 
      } 

      ApplicationException created = new ApplicationException(message); 
      created.status = status; 
      created.code = code; 
      created.developerMessage = developerMessage; 
      created.link = link; 

      return created; 
     }   
    } 
} 

現在，我可以創造一個例外是這樣的：

throw ApplicationException.getBuilder("This is the general error message") 
    .status(404) 
    .code(StatusCode.RESOURCE_DOES_NOT_EXIST) 
    .developerMessage("The resource does not exist") 
    .build(); 

的問題，我目前我希望從這個基本例外中創建不同的例外。例如。 ValidationException應該從ApplicationException擴展。

但build（）方法已經返回具體類型ApplicationException。目前我被卡住了，因爲我不熟悉使用泛型，如果它甚至可以在異常類中使用。

Answer 1

您可以通過Class<? extends Exception>您build方法，並使用newInstance()內創建所需類型的Exception對象：

throw ExceptionBuilder.getBuilder("This is the general error message") 
    .status(404) 
    .code(StatusCode.RESOURCE_DOES_NOT_EXIST) 
    .developerMessage("The resource does not exist") 
    .build(ValidationException.class); // <<== Choose type here 

Exception對象不應直到build調用創建的;在build裏面你可以這樣做：

Exception build(Class<? extends Exception> eClass) { 
    Exception res = null; 
    try { 
     res = eClass.newInstance(); 
    } catch (.......) { 
     // Catch the appropriate exceptions here 
    } 
    res.setAbc(); // Set values as needed 
    ... 
    return res; 
} 

Answer 2

你要處理多少個不同的異常子類型？如果它不是太多，你可以只讓一個build()方法在您的建造者爲每種類型的異常：

throw ApplicationException.getBuilder("This is the general error message") 
    .status(404) 
    .code(StatusCode.RESOURCE_DOES_NOT_EXIST) 
    .developerMessage("The resource does not exist") 
    .buildValidation(); // or buildSomeOther() 

這不是普通的，但它是非常簡單，將與IDE自動完成發揮很好