java - java或其他gc-lang中的gc会自动关闭未关闭的资源吗？以及为什么

Question

诸如 fileInputStream 之类的资源未关闭。 gc clean后会关闭吗？为什么或为什么不？

Answer 1

引用:When is the finalize() method called in Java?

FileInputStream 覆盖 Object#finalize，如下所示:

/**
 * Ensures that the <code>close</code> method of this file input stream is
 * called when there are no more references to it.
 *
 * @deprecated The {@code finalize} method has been deprecated.
 *     Subclasses that override {@code finalize} in order to perform cleanup
 *     should be modified to use alternative cleanup mechanisms and
 *     to remove the overriding {@code finalize} method.
 *     When overriding the {@code finalize} method, its implementation must explicitly
 *     ensure that {@code super.finalize()} is invoked as described in {@link Object#finalize}.
 *     See the specification for {@link Object#finalize()} for further
 *     information about migration options.
 *
 * @exception  IOException  if an I/O error occurs.
 * @see        java.io.FileInputStream#close()
 */
@Deprecated(since="9")
protected void finalize() throws IOException {
    if ((fd != null) &&  (fd != FileDescriptor.in)) {
        /* if fd is shared, the references in FileDescriptor
         * will ensure that finalizer is only called when
         * safe to do so. All references using the fd have
         * become unreachable. We can call close()
         */
        close();
    }
}

当调用FileInputStream#finalize时，FileInputStream#close将随之调用(在某些条件下)。但是，Object#finalize 在 Java 9 中已被弃用，因此不应依赖它。您应该始终关闭流以防止内存泄漏，即使底层垃圾收集可以为您处理它。