问题描述
从 try-with-resource 语句返回输入流以在调用者使用后处理流的关闭是否安全?
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; } }
推荐答案
是安全的,但是会被关闭,所以我觉得不是特别有用...(不能重新打开关闭的流.)
It's safe, but it will be closed, so I don't think it is particularly useful... (You can't reopen a closed stream.)
看这个例子:
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; } }
输出:
sun.nio.ch.ChannelInputStream@1db9742 sun.nio.ch.ChannelInputStream@1db9742
返回(相同的)输入流(通过引用相同),但它将被关闭.通过将示例修改为:
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; } }
输出:
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)