(java) try-with-resources

https://www.baeldung.com/java-try-with-resources



try 구문절에 resources 사용구문을 입력할 수 있다.

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try (PrintWriter writer = new PrintWriter(new File("test.txt"))) {     writer.println("Hello World"); }

구문절에 기존에 try-catch-finally를 사용할때는 보통 아래처럼 한다.

try에서 열어주고, finally에서 닫아주고 

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Scanner scanner = null; try {     scanner = new Scanner(new File("test.txt"));     while (scanner.hasNext()) {         System.out.println(scanner.nextLine());     } } catch (FileNotFoundException e) {     e.printStackTrace(); } finally {     if (scanner != null) {         scanner.close();     } }




이걸 다시 try-with-resources 방식으로 하면

1 2 3 4 5 6 7 try (Scanner scanner = new Scanner(new File("test.txt"))) {     while (scanner.hasNext()) {         System.out.println(scanner.nextLine());     } } catch (FileNotFoundException fnfe) {     fnfe.printStackTrace(); }

여기서 다른점은 scanner.close() 가 없다. 

알아서 자원을 반납을 해준다.

java7 부터 사용가능하다. 

AutoCloseable 이라는 인터페이스를 사용해서 커스마이징 하는는 방법도 있다. 

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public class AutoCloseableResourcesFirst implements AutoCloseable {       public AutoCloseableResourcesFirst() {         System.out.println("Constructor -> AutoCloseableResources_First");     }       public void doSomething() {         System.out.println("Something -> AutoCloseableResources_First");     }       @Override     public void close() throws Exception {         System.out.println("Closed AutoCloseableResources_First");     } }

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public class AutoCloseableResourcesSecond implements AutoCloseable {       public AutoCloseableResourcesSecond() {         System.out.println("Constructor -> AutoCloseableResources_Second");     }       public void doSomething() {         System.out.println("Something -> AutoCloseableResources_Second");     }       @Override     public void close() throws Exception {         System.out.println("Closed AutoCloseableResources_Second");     } }

private void orderOfClosingResources() throws Exception {

    try (AutoCloseableResourcesFirst af = new AutoCloseableResourcesFirst();

        AutoCloseableResourcesSecond as = new AutoCloseableResourcesSecond()) {

 

        af.doSomething();

        as.doSomething();

    }

}







Constructor -> AutoCloseableResources_First
Constructor -> AutoCloseableResources_Second
Something -> AutoCloseableResources_First
Something -> AutoCloseableResources_Second
Closed AutoCloseableResources_Second
Closed AutoCloseableResources_First