差異處

這裏顯示兩個版本的差異處。

--- java:basic:exception:try-with-resource [2016/05/03 20:16]
tony 建立
+++ java:basic:exception:try-with-resource [2023/06/25 09:48] (目前版本)
@@ 行 1: / 行 1: @@
 {{tag>java}}
-====== Try-With-Resource ======
+====== Try-With-Resources ======
 ===== Introduction =====
+在操作與資源有關的API時，常常有人會忘記做close的動作，而造成memory-leak。而資源相關的API常常會伴隨著check-exception，我的習慣會在finally去做close的動作(可參考[[java:basic:memoryleakwithproperties|此篇]])。今天剛好看到同事用了try-with-resource寫法，才知道這種寫法，可以避免掉忘記關閉資源的問題。
+===== How to? =====
+以我的例子來示範該如何修改:
+<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);
+        }
+    }
+</code>
+使用try-with-resources:
+<code java>
+        try( InputStream is = new FileInputStream(mConfigFilePath) ){
+    		mProp.load(is);
+    	} catch (IOException e) {
+            // need to handle ..
+        }
+</code>
+需要注意的是，使用這種方式try()內被assign的物件必須實做closable，它在發生exception或正常執行完成都會自動呼叫close。可以自行透過以下程式模擬:
+<code java>
+public class TestClosable implements Closeable {
+	@Override
+	public void close() throws IOException {
+		System.out.println("close");
+	}
+}
+public class TryWithResourcePractice {
+	@Test
+	public void testCatch(){
+		try( TestClosable tc = new TestClosable() ){
+			System.out.println("gg");
+			throw new IOException();
+		} catch (IOException e) {
+			System.out.println("tt");
+		}  finally {
+			System.out.println("yy");
+		}
+    }
+}
+</code>
 ===== Resource =====
   * [[http://stackoverflow.com/questions/17739362/java7-try-with-resources-statement-advantages|java7-try-with-resources-statement-advantages]]
   * [[http://stackoverflow.com/questions/17650970/am-i-using-the-java-7-try-with-resources-correctly|am-i-using-the-java-7-try-with-resources-correctly]]
-  * [[http://docs.oracle.com/javase/specs/jls/se7/html/jls-14.html#jls-14.20.3|]]
+  * [[http://docs.oracle.com/javase/specs/jls/se7/html/jls-14.html#jls-14.20.3|Java7 - Try With Resources]]