Why write Try-With-Resources without Catch or Finally?

Question

Why write Try without a Catch or Finally as in the following example?

protected void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html;charset=UTF-8"); try (PrintWriter out = response.getWriter()) { /* TODO output your page here. You may use following sample code. */ out.println("<!DOCTYPE html>"); out.println("<html>"); out.println("<head>"); out.println("<title>Servlet tryse</title>"); out.println("</head>"); out.println("<body>"); out.println("<h1>Servlet tryse at " + request.getContextPath() + "</h1>"); out.println("</body>"); out.println("</html>"); } }

Duplicate of "Does it make sense to do “try-finally” without “catch”?" — Juru
– Juru, Commented Oct 14, 2014 at 9:12
Having said that, I don't imagine this is the first question on try-with-resources. Nevertheless, +1 simply because I'd never heard of this feature before! — Oliver Charlesworth
– Oliver Charlesworth, Commented Oct 14, 2014 at 9:13

zb226 · Accepted Answer · 2021-03-10 14:10:05Z

As explained above this is a feature in Java 7 and beyond. try with resources allows to skip writing the finally and closes all the resources being used in try-block itself. As stated in Docs

Any object that implements java.lang.AutoCloseable, which includes all objects which implement java.io.Closeable, can be used as a resource.

See this code example

static String readFirstLineFromFile(String path) throws IOException { try (BufferedReader br = new BufferedReader(new FileReader(path))) { return br.readLine(); } }

In this example the resource is BufferReader object as the class implements the interface java.lang.AutoCloseable and it will be closed whether the try block executes successfully or not which means that you won't have to write br.close() explicitly.

Another important thing to notice here is that if you are writing the finally block yourself and both your try and finally block throw exception then the exception from try block is supressed.

While on the other hand if you are using try-with-resources statement and exception is thrown by both try block and try-with-resources statement then in this case the exception from try-with-resources statement is suppressed.

As the @Aaron has answered already above I just tried to explain you. Hope it helps.

Source: http://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html

@roufamatic yes, analogous, though the large difference is that C#'s using does not protect in any way against exceptions, it just guarantees resource closure at the end of the block. In C#, you most often have to combine using blocks with try blocks. Java's try-with-resources does this together.
If an exception is thrown from both the try-with-resources statement and the try-with-resources block, only the try-with-resources statement exception would be encountered (would not be suppressed) because the try-with-resources block wouldn't have an opportunity to execute.

Aaron Digulla · Accepted Answer · 2017-12-30 10:27:15Z

This is a new feature in Java 7 and beyond. Without this, you'd need a finally block which closes the resource PrintWriter out. So the code above is equivalent to:

PrintWriter out = null; try { PrintWriter out = ... } finally { if(null != out) { try { out.close(); } catch(Exception e) {} // silently ignore! } }

See The try-with-resources Statement

They are not equivalent. If the exception throws from both try and finally blocks, the exception from try block will be suppressed with try-and-catch. On the other hand, if you use the try-with-resources statement, the exception from finally block (auto close throws exception) will be suppressed.

Collectives™ on Stack Overflow

Why write Try-With-Resources without Catch or Finally?

2 Answers 2

3 Comments

2 Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

2 Comments

Linked

Related