差異處
這裏顯示兩個版本的差異處。
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java:basic:memoryleakwithproperties [2017/08/19 23:33] |
java:basic:memoryleakwithproperties [2023/06/25 09:48] (目前版本) |
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| + | {{tag>java}} | ||
| + | ====== 使用Properties類別的Memory Leak ====== | ||
| + | ===== Problem ===== | ||
| + | 使用Properties類別來儲存組態設定是非常方便的事情。在某個知名java教學網站中，在使用Properties建立串流物件上，也有因忘記關閉它而造成Leak。舉例來說: | ||
| + | <code java> | ||
| + | private void load(){ | ||
| + | mProp = new Properties(); | ||
| + | try { | ||
| + | mProp.load(new FileInputStream(mConfigFilePath)); | ||
| + | } catch (IOException e) { | ||
| + | // need to handle .. | ||
| + | } | ||
| + | } | ||
| + | |||
| + | public void save(){ | ||
| + | try { | ||
| + | mProp.store(new FileOutputStream(mConfigFilePath), ""); | ||
| + | } catch (IOException e) { | ||
| + | // need to handle .. | ||
| + | } | ||
| + | } | ||
| + | </code> | ||
| + | 上面程式碼問題就在於**FileInputStream**與**FileOutputStream**建構後，沒做close stream的動作。在執行多次後，應會開始出現效能下降或根本無法存取的問題。(可以透過findbug去檢查出來) | ||
| + | ===== How to? ===== | ||
| + | 修改方法也相當簡單： | ||
| + | <code java> | ||
| + | private void close(Closeable closable){ | ||
| + | try { | ||
| + | if( closable != null ) | ||
| + | closable.close(); | ||
| + | } catch (IOException e) { | ||
| + | // log | ||
| + | } | ||
| + | } | ||
| + | |||
| + | private void load(){ | ||
| + | mProp = new Properties(); | ||
| + | InputStream is = null; | ||
| + | try { | ||
| + | is = new FileInputStream(mConfigFilePath); | ||
| + | mProp.load(is ); | ||
| + | } catch (IOException e) { | ||
| + | // need to handle .. | ||
| + | } finally { | ||
| + | close(is); | ||
| + | } | ||
| + | } | ||
| + | |||
| + | public void save(){ | ||
| + | OutputStream os = null; | ||
| + | try { | ||
| + | os = new FileOutputStream(mConfigFilePath); | ||
| + | mProp.store(os, ""); | ||
| + | } catch (IOException e) { | ||
| + | // need to handle .. | ||
| + | } finally { | ||
| + | close(os); | ||
| + | } | ||
| + | } | ||
| + | </code> | ||
| + | 在使用之前先把它assign到local variable上，在finally的地方在執行close的動作即可，這種錯誤其實蠻多人會犯的。另外對於finally處理關閉串流的方式，許多人會把它寫成nested的try block，多層的try block不只不好閱讀，還可能變無窮的block地獄。對於這部分的處理，大家可以參考搞笑談軟工的幾篇文章： [[http://teddy-chen-tw.blogspot.com/2011/06/checked-or-unchecked-exceptions-2.html|Checked or unchecked exceptions (2)]]、[[http://teddy-chen-tw.blogspot.com/2010/03/4-nested-try-block.html|敏捷式例外處理設計 (4)：我到底哪裡做錯之 nested try block]]、[[http://teddy-chen-tw.blogspot.com/2010/03/5-unprotected-main-program.html|敏捷式例外處理設計 (6)：我到底哪裡做錯之 unprotected main program]]，我相信可以增進不少功力。\\ | ||
| + | 友藏內心的獨白: 我的桌機還沒修好，但還是要有產出! | ||
| + | |||
| + | ===== ===== | ||
| + | ---- | ||
| + | \\ | ||
| + | ~~DISQUS~~ | ||
