Java 7: New Feature – Automatically Close Files and Resources in try-catch-finally

Vineet Manohar

Mar. 24, 11 · Interview

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Try with resources is a new feature in Java 7 which lets us write more elegant code by automatically closing resources like FileInputStream at the end of the try-block.

Old Try Catch Finally

Dealing with resources like InputStreams is painful when it comes to the try-catch-finally blocks. You need to declare the resources outside the try so that they are is accessible from finally, then you must initialize the variable to null and check for non-null when closing the resource in finally.

  File file = new File("input.txt");

   InputStream is = null;

   try {
     is = new FileInputStream(file);

     // do something with this input stream
     // ...

   }
   catch (FileNotFoundException ex) {
     System.err.println("Missing file " + file.getAbsolutePath());
   }
   finally {
     if (is != null) {
       is.close();
     }
   }

Java 7: Try with resources

With Java 7, you can create one or more “resources” in the try statement. A “resources” is something that implements the java.lang.AutoCloseable interface. This resource would be automatically closed and the end of the try block.

  File file = new File("input.txt");  
      
    try (InputStream is = new FileInputStream(file)) {  
      // do something with this input stream  
      // ...  
  }  
   catch (FileNotFoundException ex) {  
     System.err.println("Missing file " + file.getAbsolutePath());  
    }

Exception handling

If both the (explicit) try block and the (implicit) resource handling code throw an exception, then the try block exception is the one which will be thrown. The resource handling exception will be made available via the Throwable.getSupressed() method of the thrown exception. Throwable.getSupressed() is a new method added to the Throwable class since 1.7 specifically for this purpose. If there were no suppressed exceptions then this will return an empty array.

Reference

http://download.java.net/jdk7/docs/technotes/guides/language/try-with-resources.html

From http://www.vineetmanohar.com/2011/03/java-7-try-with-auto-closable-resources/

Java (programming language)

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