如果从 try-with-resource 返回 InputStream 是安全的

Question

它是安全的，从一试，与资源的语句返回一个输入流来处理流的结束，一旦调用者已经消耗了呢？

public static InputStream example() throws IOException {
    ...
    try (InputStream is = ...) {
        return is;
    }
}

Answer 1

它是安全的，但它会被关闭，所以我认为它不是特别有用......（你不能重新打开一个关闭的流。）

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（相同的引用），但它将被关闭。通过将示例修改为：

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)