差異處
這裏顯示兩個版本的差異處。
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java:basic:close_systemin_of_scanner [2016/11/30 11:44] tony [Solutions] |
java:basic:close_systemin_of_scanner [2017/08/19 23:33] |
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| - | {{tag>java}} | ||
| - | ====== Close the System.in of the Scanner ====== | ||
| - | ===== Problem ===== | ||
| - | 如果有寫到CLI的tool，使用Scanner物件是很平常的事情，因此應會遇到是否該close Scanner物件的問題。假如有兩個類別都會使用到使用System.in的Scanner，先close的就會讓後面的發生問題。 | ||
| - | ===== Solutions ===== | ||
| - | 閱讀幾篇文章後，有以下做法: | ||
| - | - 不理它，反正不會造成memory leak。 | ||
| - | - 使用Decorator樣式，將System.in包裝在不會真的close的InputStream中。 | ||
| - | - 使用Singleton樣式，大家都用同一個Global Scanner。 | ||
| - | 第一個做法對於寫code有潔癖的人來說，不會去使用的。而第二和第三個做法，以單元測試方便性來說與，我比較偏愛Decorator方式；使用Singleton的作法，還要考慮到底是誰負責close。如果大家都說好，你可以透過shutdown hook去close。 | ||
| - | \\ | ||
| - | \\ | ||
| - | 分享decorator作法，參考apache common io程式碼: | ||
| - | <code java> | ||
| - | public class CloseShieldInputStream extends ProxyInputStream { | ||
| - | |||
| - | /** | ||
| - | * Creates a proxy that shields the given input stream from being | ||
| - | * closed. | ||
| - | * | ||
| - | * @param in underlying input stream | ||
| - | */ | ||
| - | public CloseShieldInputStream(InputStream in) { | ||
| - | super(in); | ||
| - | } | ||
| - | |||
| - | /** | ||
| - | * Replaces the underlying input stream with a {@link ClosedInputStream} | ||
| - | * sentinel. The original input stream will remain open, but this proxy | ||
| - | * will appear closed. | ||
| - | */ | ||
| - | public void close() { | ||
| - | in = new ClosedInputStream(); | ||
| - | } | ||
| - | |||
| - | } | ||
| - | </code> | ||
| - | Client可以這樣使用: | ||
| - | <code java> | ||
| - | try( Scanner scanner = new Scanner(new CloseShieldInputStream(System.in))){ | ||
| - | // some operations | ||
| - | } | ||
| - | </code> | ||
| - | |||
| - | ===== Reference ===== | ||
| - | * [[http://stackoverflow.com/questions/14142853/close-a-scanner-linked-to-system-in|close-a-scanner-linked-to-system-in]] | ||
| - | * [[http://stackoverflow.com/questions/14962082/close-scanner-without-closing-system-in|close-scanner-without-closing-system-in]] | ||
| - | * [[http://stackoverflow.com/questions/23621668/java-closing-scanner-and-resource-leak|java-closing-scanner-and-resource-leak]] | ||
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