Java 如果从try with resource返回InputStream是安全的

从try with resource语句返回输入流以在调用方使用该流后处理该流的关闭是否安全

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

---

它是安全的，但它将被关闭，所以我认为它不是特别有用。。。无法重新打开已关闭的流

请参见此示例：

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

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)

通过引用返回相同的输入流，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
sun.nio.ch.ChannelInputStream@1db9742

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)

---

它是安全的，但它将被关闭，所以我认为它不是特别有用。。。无法重新打开已关闭的流

请参见此示例：

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

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)

通过引用返回相同的输入流，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
sun.nio.ch.ChannelInputStream@1db9742

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)

---

一旦退出函数执行，资源就会超出范围，因此会被垃圾收集。。。总而言之安全但无用….@CoderNeji除了通常无法判断何时将垃圾收集未引用对象的部分之外，InputStream是关闭的，而不是垃圾收集的，因为仍然存在从方法返回的“活动”引用。超出范围的是is变量，但这是另一个在编译时解决的问题。感谢您的解释一旦退出函数执行，资源就超出范围，因此垃圾被收集。。。总而言之安全但无用….@CoderNeji除了通常无法判断何时将垃圾收集未引用对象的部分之外，InputStream是关闭的，而不是垃圾收集的，因为仍然存在从方法返回的“活动”引用。超出范围的是is变量，但这是另一个在编译时解决的问题。感谢您的解释