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)