关闭字节缓冲流还需要关闭字节流吗

Question

public void download() throws MyException, IOException {
        ClientGlobal.init("D:\\project_work_changgou\\changgou-service\\changgou-service-file\\src\\main\\resources\\fdfs_client.conf");

        TrackerServer trackerServer = new TrackerClient().getConnection();

        StorageClient storageClient = new StorageClient(trackerServer,null);


        byte[] group1s = storageClient.download_file("group1", "M00/00/00/wKjThGEWlNqAY3G9AASGXSYJjlQ243.jpg");

        FileOutputStream fileOutputStream = new FileOutputStream(new File("D://abcd.jpg"));

        BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(fileOutputStream);

        try {

            bufferedOutputStream.write(group1s);

            bufferedOutputStream.flush();

        } finally {
            bufferedOutputStream.close();
        }

    }

关闭字节缓冲流还需要关闭字节流吗

Answer 1

去看了一下源码，BufferedOutputStream构造方法如下：

public class BufferedOutputStream extends FilterOutputStream {
    /**
     * The internal buffer where data is stored.
     */
    protected byte buf[];

    /**
     * The number of valid bytes in the buffer. This value is always
     * in the range <tt>0</tt> through <tt>buf.length</tt>; elements
     * <tt>buf[0]</tt> through <tt>buf[count-1]</tt> contain valid
     * byte data.
     */
    protected int count;

    /**
     * Creates a new buffered output stream to write data to the
     * specified underlying output stream.
     *
     * @param   out   the underlying output stream.
     */
    public BufferedOutputStream(OutputStream out) {
        this(out, 8192);
    }

    /**
     * Creates a new buffered output stream to write data to the
     * specified underlying output stream with the specified buffer
     * size.
     *
     * @param   out    the underlying output stream.
     * @param   size   the buffer size.
     * @exception IllegalArgumentException if size &lt;= 0.
     */
    public BufferedOutputStream(OutputStream out, int size) {
        super(out);
        if (size <= 0) {
            throw new IllegalArgumentException("Buffer size <= 0");
        }
        buf = new byte[size];
    }

可以看出BufferedOutputStream继承FilterOutputStream，BufferedOutputStream构造方法调用了super(out)，其源码如下：

public class FilterOutputStream extends OutputStream {
    /**
     * The underlying output stream to be filtered.
     */
    protected OutputStream out;

    /**
     * Creates an output stream filter built on top of the specified
     * underlying output stream.
     *
     * @param   out   the underlying output stream to be assigned to
     *                the field <tt>this.out</tt> for later use, or
     *                <code>null</code> if this instance is to be
     *                created without an underlying stream.
     */
    public FilterOutputStream(OutputStream out) {
        this.out = out;
    }

    /**
     * Closes this output stream and releases any system resources
     * associated with the stream.
     * <p>
     * The <code>close</code> method of <code>FilterOutputStream</code>
     * calls its <code>flush</code> method, and then calls the
     * <code>close</code> method of its underlying output stream.
     *
     * @exception  IOException  if an I/O error occurs.
     * @see        java.io.FilterOutputStream#flush()
     * @see        java.io.FilterOutputStream#out
     */
    @SuppressWarnings("try")
    public void close() throws IOException {
        try (OutputStream ostream = out) {
            flush();
        }
    }

因BufferedOutputStream继承FilterOutputStream，且并未重写close方法，所以在BufferedOutputStream调用close方法时，会调用父类FilterOutputStream的close方法。从该方法可以看出，将构造时的OutputStream（也就是上面的FileOutputStream）包裹在了try语句扩括号内，针对jdk1.8的特性，会对实现了Closeable接口的类自动调用close方法。也就是说，不需要再手动关闭字节流，BufferedOutputStream会在close的时候，关闭构造它的FileOutputStream。