try-with-resources

问题 This new Java 7 try-with-resources construct is quite nice. Or at least, it was nice until an exception came along and ruined my day. I've finally managed to boil it down to a reproducible test which uses nothing but JUnit+jMock. @Test public void testAddSuppressedIssue() throws Exception { Mockery mockery = new Mockery(); final Dependency dependency = mockery.mock(Dependency.class); mockery.checking(new Expectations() {{ allowing(dependency).expectedCall(); allowing(dependency).close(); }});

问题 When implementing try with resources I am creating a Scanner object via Scanner sc = new Scanner(System.in) within () of the try statement. In the try block, I am prompting the user to enter a numeric value, reading it via sc.nextLine() and utilizing parseDouble to convert it to a method. I utilize a do-while loop to re-prompt the user to enter a value if an invalid value was entered initially. However, if the user enters an invalid value, the input stream closes, NumberFormatException is

问题 This question already has answers here : Try-with-resources and return statements in java (4 answers) Closed 5 years ago . Is it safe to return an input stream from a try-with-resource statement to handle the closing of the stream once the caller has consumed it? public static InputStream example() throws IOException { ... try (InputStream is = ...) { return is; } } 回答1: It's safe, but it will be closed, so I don't think it is particularly useful... (You can't reopen a closed stream.) See

问题 This question already has answers here : Try-with-resources and return statements in java (4 answers) Closed 5 years ago . Is it safe to return an input stream from a try-with-resource statement to handle the closing of the stream once the caller has consumed it? public static InputStream example() throws IOException { ... try (InputStream is = ...) { return is; } } 回答1: It's safe, but it will be closed, so I don't think it is particularly useful... (You can't reopen a closed stream.) See

问题 I'm using SocketChannel to send message between a server and a client. Once a client connects with a server, the server opens the InputStreams and OutputStream in a try-with-resources try, to receive messages from the client and send messages to the client, like so: try (ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream()); ObjectInputStream in = new ObjectInputStream(socket.getInputStream())) {} I want to access out outside of the try. The try contains a while loop that

问题 I'm using SocketChannel to send message between a server and a client. Once a client connects with a server, the server opens the InputStreams and OutputStream in a try-with-resources try, to receive messages from the client and send messages to the client, like so: try (ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream()); ObjectInputStream in = new ObjectInputStream(socket.getInputStream())) {} I want to access out outside of the try. The try contains a while loop that

问题 I am trying to create a centralized class that connects and returns the ResultSet of a SQL query so that I don't always have to create a new connection every time I am trying to get a query. I am using the try-with-resources , however, I am getting a compile-time error whenever I use the try-with-resources and I don't know why? public class JDBC { // logger declaration is omitted private static final String dbURL = "jdbc:oracle:"; private static final String userName = "blah"; private static

问题 I have a base class Base and a child class Child which extends it. Base implements java.lang.AutoCloseable . Let's suppose that the constructor for Child throws a Foo . Now consider try (Base c = new Child()){ /*Some code*/ } catch (final Foo e){ /*Some more code*/ } Is the Base#close method called if the exception is thrown? It is not on my machine, but is this something that the JLS has standardised? 回答1: Yes, close won't be called. This is specified in the JLS section 14.20.3: Resources

问题 With reference to my question Any risk in a AutoCloseable wrapper for java.util.concurrent.locks.Lock?, I am wondering why trh try-with-resource require a named local variable at all. My current usage is as follows: try (AutoCloseableReentrantReadWiteLock.Lock l = _lock.writeLock()) { // do something } The variable l is unused inside the try block and only pollutes the namespace. From what I can remember the analogous C# using statement does not require a local named variable. Is there any

问题 With reference to my question Any risk in a AutoCloseable wrapper for java.util.concurrent.locks.Lock?, I am wondering why trh try-with-resource require a named local variable at all. My current usage is as follows: try (AutoCloseableReentrantReadWiteLock.Lock l = _lock.writeLock()) { // do something } The variable l is unused inside the try block and only pollutes the namespace. From what I can remember the analogous C# using statement does not require a local named variable. Is there any