耦合性 (Coupling)

Posted by Bruce Tsai

狀況：在 service / facade / dao / util 等實作中直接呼叫取值

• 案例
  • 使用 RequestContextHolder 取得 HttpServletRequest / HttpSession
  • 使用 ServletActionContext 取得 HttpServletRequest / HttpSession
• 未考慮流程及生命週期問題，同時對環境或套件的耦合性過高，在多執行緒作業或測試上將發生錯誤

直接透過 spring framework 取得 request 物件

// 在非 http request 生命週期時，將發生錯誤
ServletRequestAttributes sra = 
    (ServletRequestAttributes)RequestContextHolder.
        getRequestAttributes();
HttpServletRequest req = sra.getRequest();

直接透過 struts 取得 request 物件

// 在非 http request 生命週期時，將發生錯誤
HttpServletRequest req = ServletActionContext.getRequest();

正確做法

• 透過替代的界面取得 HttpServletRequest / HttpSession，減少對套件的耦合性
• 由外部傳入 HttpServletRequest / HttpSession 中所需要的值

定義一個替代 HttpServletRequest 的介面：

public interface IHttpServletRequestService
    extends IServletRequestService {

    /**
     * 同{@link HttpServletRequest#getAuthType()}
     *
     * @return
     */
    String authType();

    /**
     * 同{@link HttpServletRequest#getCookies()}
     *
     * @return
     */
    List<Cookie> cookies();

    /**
     * 同{@link HttpServletRequest#getDateHeader(String)}
     *
     * @param name
     * @return
     */
    long dateHeader(String name);

    /**
     * 同{@link HttpServletRequest#getHeader(String)}
     *
     * @param name
     * @return
     */
    String header(String name);

    /**
     * 同{@link HttpServletRequest#getHeaders(String)}
     *
     * @param name
     * @return
     */
    Enumeration headers(String name);

    /**
     * 同{@link HttpServletRequest#getHeaderNames()}
     *
     * @return
     */
    Enumeration headerNames();

    /**
     * 同{@link HttpServletRequest#getIntHeader(String)}
     *
     * @param name
     * @return
     */
    int intHeader(String name);

    /**
     * 同{@link HttpServletRequest#getMethod()}
     *
     * @return
     */
    String method();

    /**
     * 同{@link HttpServletRequest#getPathInfo()}
     *
     * @return
     */
    String pathInfo();

    /**
     * 同{@link HttpServletRequest#getPathTranslated()}
     *
     * @return
     */
    String pathTranslated();

    /**
     * 同{@link HttpServletRequest#getContextPath()}
     *
     * @return
     */
    String contextPath();

    /**
     * 同{@link HttpServletRequest#getQueryString()}
     *
     * @return
     */
    String queryString();

    /**
     * 同{@link HttpServletRequest#getRemoteUser()}
     *
     * @return
     */
    String remoteUser();

    /**
     * 同{@link HttpServletRequest#isUserInRole(String)}
     *
     * @param role
     * @return
     */
    boolean userInRole(String role);

    /**
     * 同{@link HttpServletRequest#getUserPrincipal()}
     *
     * @return
     */
    Principal userPrincipal();

    /**
     * 同{@link HttpServletRequest#getRequestedSessionId()}
     *
     * @return
     */
    String requestedSessionId();

    /**
     * 同{@link HttpServletRequest#getRequestURI()}
     *
     * @return
     */
    String requestURI();

    /**
     * 同{@link HttpServletRequest#getRequestURL()}
     *
     * @return
     */
    StringBuffer requestURL();

    /**
     * 同{@link HttpServletRequest#getServletPath()}
     *
     * @return
     */
    String servletPath();

    /**
     * 同{@link HttpServletRequest#getSession(boolean)}
     *
     * @param create
     * @return
     */
    HttpSession session(boolean create);

    /**
     * 同{@link HttpServletRequest#getSession()}
     *
     * @return
     */
    HttpSession session();

    /**
     * 同{@link HttpServletRequest#isRequestedSessionIdValid()}
     *
     * @return
     */
    boolean requestedSessionIdValid();

    /**
     * 同{@link HttpServletRequest#isRequestedSessionIdFromCookie()}
     *
     * @return
     */
    boolean requestedSessionIdFromCookie();

    /**
     * 同{@link HttpServletRequest#isRequestedSessionIdFromURL()}
     *
     * @return
     */
    boolean requestedSessionIdFromURL();

}

定義一個替代 HttpSession 的介面：

public interface IHttpSessionService {

    /**
     * 同{@link HttpSession#getId()}
     *
     * @return
     */
    String id();

    /**
     * 同{@link HttpSession#getCreationTime()}
     *
     * @return
     */
    long creationTime();

    /**
     * 同{@link HttpSession#getAttributeNames()}
     *
     * @return
     */
    Enumeration attributeNames();

    /**
     * 同{@link HttpSession#getLastAccessedTime()}
     *
     * @return
     */
    long lastAccessedTime();

    /**
     * 同{@link HttpSession#getMaxInactiveInterval()}
     *
     * @return
     */
    int maxInactiveInterval();

    /**
     * 同{@link HttpSession#getAttribute(String)}
     *
     * @param name
     * @param <T>
     * @return
     */
    <T> T attribute(String name);

    /**
     * 同{@link HttpSession#setAttribute(String, Object)}
     *
     * @param name
     * @param value
     */
    void attribute(String name, Object value);

    /**
     * 同{@link HttpSession#getServletContext()}
     *
     * @return
     */
    ServletContext servletContext();

    /**
     * 同{@link HttpSession#setMaxInactiveInterval(int)}
     *
     * @param interval
     */
    void maxInactiveInterval(int interval);

    /**
     * 同{@link HttpSession#removeAttribute(String)}
     *
     * @param name
     */
    void removeAttribute(String name);

    /**
     * 同{@link HttpSession#invalidate()}
     */
    void invalidate();

    /**
     * 同{@link HttpSession#isNew()}
     *
     * @return
     */
    boolean isNew();

}

透過介面存取資料

IHttpServletRequestService request;
IHttpSessionService session;

@Override
public String execute(int time) {
    // 透過介面存取
    String key = request.attribute("key");
    String account = session.attribute("account");

    // more code here
}