NIO的JVM內存和機器內存的選擇

NIO究竟是使用JVM的內存仍是使用機器內存呢？其實，在ByteBuffer中提供了兩個申請內存的方法供咱們選擇。

申請JVM堆內存：

/**
 * Allocates a new byte buffer.
 *
 * <p> The new buffer's position will be zero, its limit will be its * capacity, its mark will be undefined, and each of its elements will be * initialized to zero. It will have a {@link #array backing array}, * and its {@link #arrayOffset array offset} will be zero. * * @param capacity * The new buffer's capacity, in bytes
 *
 * @return  The new byte buffer
 *
 * @throws  IllegalArgumentException
 *          If the <tt>capacity</tt> is a negative integer
 */
public static ByteBuffer allocate(int capacity) {
    if (capacity < 0)
        throw new IllegalArgumentException();
    return new HeapByteBuffer(capacity, capacity);
}
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申請機器內存：

/**
 * Allocates a new direct byte buffer.
 *
 * <p> The new buffer's position will be zero, its limit will be its * capacity, its mark will be undefined, and each of its elements will be * initialized to zero. Whether or not it has a * {@link #hasArray backing array} is unspecified. * * @param capacity * The new buffer's capacity, in bytes
 *
 * @return  The new byte buffer
 *
 * @throws  IllegalArgumentException
 *          If the <tt>capacity</tt> is a negative integer
 */
public static ByteBuffer allocateDirect(int capacity) {
    return new DirectByteBuffer(capacity);
}
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