问题
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 this example:
public static void main(String[] argv) throws Exception {
System.out.println(example());
}
public static InputStream example() throws IOException {
try (InputStream is = Files.newInputStream(Paths.get("test.txt"))) {
System.out.println(is);
return is;
}
}
Output:
sun.nio.ch.ChannelInputStream@1db9742
sun.nio.ch.ChannelInputStream@1db9742
The (same) input stream is returned (same by reference), but it will be closed. By modifying the example to this:
public static void main(String[] argv) throws Exception {
InputStream is = example();
System.out.println(is + " " + is.available());
}
public static InputStream example() throws IOException {
try (InputStream is = Files.newInputStream(Paths.get("test.txt"))) {
System.out.println(is + " " + is.available());
return is;
}
}
Output:
sun.nio.ch.ChannelInputStream@1db9742 1000000
Exception in thread "main" java.nio.channels.ClosedChannelException
at sun.nio.ch.FileChannelImpl.ensureOpen(FileChannelImpl.java:109)
at sun.nio.ch.FileChannelImpl.size(FileChannelImpl.java:299)
at sun.nio.ch.ChannelInputStream.available(ChannelInputStream.java:116)
at sandbox.app.Main.main(Main.java:13)
来源:https://stackoverflow.com/questions/30643556/if-it-safe-to-return-an-inputstream-from-try-with-resource