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>");
}
}
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
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