java - 使用构建器模式创建异常？

Question

我的 java 代码中有一个异常，它有几个属性将被传递到构造函数中。因此，我认为使用构建器模式创建异常会很好，所以我创建了这样的异常:

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;
        }        
    }
}

现在我可以像这样创建一个异常:

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

我目前遇到的问题是我想从这个基本异常中创建不同的异常。例如。应从 ApplicationException 扩展的 ValidationException。

但是 build() 方法已经返回具体类型 ApplicationException。目前我被困住了，因为我不太熟悉使用泛型，甚至不知道它是否可以在异常类中使用。

Answer 1

你可以通过Class<? extends Exception>给你的build方法，并使用 newInstance()在里面创建 Exception所需类型的对象:

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在 build 之前不应创建对象称呼;在build里面你可以这样做:

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;
}