File

public class File implements Serializable, Comparable<File>{
    //......
}

Construction method

Use

/**
 * Creating objects from a given Abstract path simply creates file objects rather than creating files
 * Use relative paths as far as possible for file paths
*/
File file = new File("." + File.separator + "1.txt");

common method

IO flow

Byte stream

InputStream

       InputStream Is the parent of all byte input streams, and isAbstract classes (not directly) new). The source code is as follows:

public abstract class InputStream implements Closeable {
    //MAX_SKIP_BUFFER_SIZE is used to determine the maximum buffer size to use when skipping.
    private static final int MAX_SKIP_BUFFER_SIZE = 2048;
    public abstract int read() throws IOException;
    public int read(byte b[]) throws IOException {
        return read(b, 0, b.length);
    }
    public int read(byte b[], int off, int len) throws IOException {
        if (b == null) {
            throw new NullPointerException();
        } else if (off < 0 || len < 0 || len > b.length - off) {
            throw new IndexOutOfBoundsException();
        } else if (len == 0) {
            return 0;
        }

        int c = read();
        if (c == -1) {
            return -1;
        }
        b[off] = (byte)c;

        int i = 1;
        try {
            for (; i < len ; i++) {
                c = read();
                if (c == -1) {
                    break;
                }
                b[off + i] = (byte)c;
            }
        } catch (IOException ee) {
        }
        return i;
    }
    public long skip(long n) throws IOException {
        long remaining = n;
        int nr;

        if (n <= 0) {
            return 0;
        }

        int size = (int)Math.min(MAX_SKIP_BUFFER_SIZE, remaining);
        byte[] skipBuffer = new byte[size];
        while (remaining > 0) {
            nr = read(skipBuffer, 0, (int)Math.min(size, remaining));
            if (nr < 0) {
                break;
            }
            remaining -= nr;
        }

        return n - remaining;
    }
    public int available() throws IOException {
        return 0;
    }
    public void close() throws IOException {}
    public synchronized void mark(int readlimit) {}
    public synchronized void reset() throws IOException {
        throw new IOException("mark/reset not supported");
    }
    public boolean markSupported() {
        return false;
    }

}

• common method

OutputStream

OutputStream is the parent of all byte output streams and is an abstract class (not new directly). The source code is as follows:

public abstract class OutputStream implements Closeable, Flushable {
    public abstract void write(int b) throws IOException;
    public void write(byte b[]) throws IOException {
        write(b, 0, b.length);
    }   
    public void write(byte b[], int off, int len) throws IOException {
        if (b == null) {
            throw new NullPointerException();
        } else if ((off < 0) || (off > b.length) || (len < 0) ||
                   ((off + len) > b.length) || ((off + len) < 0)) {
            throw new IndexOutOfBoundsException();
        } else if (len == 0) {
            return;
        }
        for (int i = 0 ; i < len ; i++) {
            write(b[off + i]);
        }
    }
    public void flush() throws IOException {}
    public void close() throws IOException {}
}

• common method

Closing flow

Close the file input stream and release all system resources associated with the stream, calling its close() method.

Notes

For example, the close() method source code of ObjectOutputStream is as follows, calling the flush() method:

public class ObjectOutputStream extends OutputStream implements ObjectOutput, ObjectStreamConstants{
    //......
    public void close() throws IOException {
        flush();
        clear();
        bout.close();
    }
}

Subclasses of InputStream and OutputStream

public class FileOutputStream extends OutputStream{
    //......
}

• Construction method

FileOutputStream

FileOutputStream is a file output stream that writes a byte to a file at a time in bytes. A stream for writing raw bytes such as image data. To write to the character stream, use FileWriter.

• Source code

public class FileInputStream extends InputStream{
    //......
}

• Construction method

BufferedInputStream

When BufferedInputStream is created, an internal buffer array is created. When reading or skipping the bytes in the stream, the internal buffer can be filled again from the included input stream as needed, filling more than one byte at a time. The mark operation records a point in the input stream, and the reset operation causes all bytes read since the last mark operation to be read again before obtaining new bytes from the included input stream.

Read data into memory, and get data from memory is more efficient than from files.

• Source code

public class BufferedInputStream extends FilterInputStream {
    private static int DEFAULT_BUFFER_SIZE = 8192;
    private static int MAX_BUFFER_SIZE = Integer.MAX_VALUE - 8;
    protected volatile byte buf[];
    private static final
        AtomicReferenceFieldUpdater<BufferedInputStream, byte[]> bufUpdater =
        AtomicReferenceFieldUpdater.newUpdater
        (BufferedInputStream.class,  byte[].class, "buf");
    protected int count;
    protected int pos;
    protected int markpos = -1;
    protected int marklimit;

    private InputStream getInIfOpen() throws IOException {
        InputStream input = in;
        if (input == null)
            throw new IOException("Stream closed");
        return input;
    }

    private byte[] getBufIfOpen() throws IOException {
        byte[] buffer = buf;
        if (buffer == null)
            throw new IOException("Stream closed");
        return buffer;
    }

    public BufferedInputStream(InputStream in) {
        this(in, DEFAULT_BUFFER_SIZE);
    }

    public BufferedInputStream(InputStream in, int size) {
        super(in);
        if (size <= 0) {
            throw new IllegalArgumentException("Buffer size <= 0");
        }
        buf = new byte[size];
    }

    private void fill() throws IOException {
        byte[] buffer = getBufIfOpen();
        if (markpos < 0)
            pos = 0;            /* no mark: throw away the buffer */
        else if (pos >= buffer.length)  /* no room left in buffer */
            if (markpos > 0) {  /* can throw away early part of the buffer */
                int sz = pos - markpos;
                System.arraycopy(buffer, markpos, buffer, 0, sz);
                pos = sz;
                markpos = 0;
            } else if (buffer.length >= marklimit) {
                markpos = -1;   /* buffer got too big, invalidate mark */
                pos = 0;        /* drop buffer contents */
            } else if (buffer.length >= MAX_BUFFER_SIZE) {
                throw new OutOfMemoryError("Required array size too large");
            } else {            /* grow buffer */
                int nsz = (pos <= MAX_BUFFER_SIZE - pos) ?
                        pos * 2 : MAX_BUFFER_SIZE;
                if (nsz > marklimit)
                    nsz = marklimit;
                byte nbuf[] = new byte[nsz];
                System.arraycopy(buffer, 0, nbuf, 0, pos);
                if (!bufUpdater.compareAndSet(this, buffer, nbuf)) {
                    // Can't replace buf if there was an async close.
                    // Note: This would need to be changed if fill()
                    // is ever made accessible to multiple threads.
                    // But for now, the only way CAS can fail is via close.
                    // assert buf == null;
                    throw new IOException("Stream closed");
                }
                buffer = nbuf;
            }
        count = pos;
        int n = getInIfOpen().read(buffer, pos, buffer.length - pos);
        if (n > 0)
            count = n + pos;
    }

    public synchronized int read() throws IOException {
        if (pos >= count) {
            fill();
            if (pos >= count)
                return -1;
        }
        return getBufIfOpen()[pos++] & 0xff;
    }

    private int read1(byte[] b, int off, int len) throws IOException {
        int avail = count - pos;
        if (avail <= 0) {
            /* If the requested length is at least as large as the buffer, and
               if there is no mark/reset activity, do not bother to copy the
               bytes into the local buffer.  In this way buffered streams will
               cascade harmlessly. */
            if (len >= getBufIfOpen().length && markpos < 0) {
                return getInIfOpen().read(b, off, len);
            }
            fill();
            avail = count - pos;
            if (avail <= 0) return -1;
        }
        int cnt = (avail < len) ? avail : len;
        System.arraycopy(getBufIfOpen(), pos, b, off, cnt);
        pos += cnt;
        return cnt;
    }

    public synchronized int read(byte b[], int off, int len)
        throws IOException
    {
        getBufIfOpen(); // Check for closed stream
        if ((off | len | (off + len) | (b.length - (off + len))) < 0) {
            throw new IndexOutOfBoundsException();
        } else if (len == 0) {
            return 0;
        }

        int n = 0;
        for (;;) {
            int nread = read1(b, off + n, len - n);
            if (nread <= 0)
                return (n == 0) ? nread : n;
            n += nread;
            if (n >= len)
                return n;
            // if not closed but no bytes available, return
            InputStream input = in;
            if (input != null && input.available() <= 0)
                return n;
        }
    }

    public synchronized long skip(long n) throws IOException {
        getBufIfOpen(); // Check for closed stream
        if (n <= 0) {
            return 0;
        }
        long avail = count - pos;

        if (avail <= 0) {
            // If no mark position set then don't keep in buffer
            if (markpos <0)
                return getInIfOpen().skip(n);

            // Fill in buffer to save bytes for reset
            fill();
            avail = count - pos;
            if (avail <= 0)
                return 0;
        }

        long skipped = (avail < n) ? avail : n;
        pos += skipped;
        return skipped;
    }

    public synchronized int available() throws IOException {
        int n = count - pos;
        int avail = getInIfOpen().available();
        return n > (Integer.MAX_VALUE - avail)
                    ? Integer.MAX_VALUE
                    : n + avail;
    }

    public synchronized void mark(int readlimit) {
        marklimit = readlimit;
        markpos = pos;
    }

    public synchronized void reset() throws IOException {
        getBufIfOpen(); // Cause exception if closed
        if (markpos < 0)
            throw new IOException("Resetting to invalid mark");
        pos = markpos;
    }

    public boolean markSupported() {
        return true;
    }

    public void close() throws IOException {
        byte[] buffer;
        while ( (buffer = buf) != null) {
            if (bufUpdater.compareAndSet(this, buffer, null)) {
                InputStream input = in;
                in = null;
                if (input != null)
                    input.close();
                return;
            }
            // Else retry in case a new buf was CASed in fill()
        }
    }
}

Where the FilterInputStream class inherits from InputStream

• Construction method

• common method

See InputStream class

BufferedOutputStream

This class implements buffered output streams. By setting this output stream, the application can write each byte to the underlying output stream without calling the underlying system for each byte write.

• Source code

public class BufferedOutputStream extends FilterOutputStream {
    protected byte buf[];
    protected int count;

    public BufferedOutputStream(OutputStream out) {
        this(out, 8192);
    }
    public BufferedOutputStream(OutputStream out, int size) {
        super(out);
        if (size <= 0) {
            throw new IllegalArgumentException("Buffer size <= 0");
        }
        buf = new byte[size];
    }
    /** Flush the internal buffer */
    private void flushBuffer() throws IOException {
        if (count > 0) {
            out.write(buf, 0, count);
            count = 0;
        }
    }

    public synchronized void write(int b) throws IOException {
        if (count >= buf.length) {
            flushBuffer();
        }
        buf[count++] = (byte)b;
    }

    public synchronized void write(byte b[], int off, int len) throws IOException{
        if (len >= buf.length) {
            /* If the request length exceeds the size of the output buffer,
               flush the output buffer and then write the data directly.
               In this way buffered streams will cascade harmlessly. */
            flushBuffer();
            out.write(b, off, len);
            return;
        }
        if (len > buf.length - count) {
            flushBuffer();
        }
        System.arraycopy(b, off, buf, count, len);
        count += len;
    }

    public synchronized void flush() throws IOException {
        flushBuffer();
        out.flush();
    }
}

Where the FilterOutputStream class inherits from OutputStream

• Construction method

• common method

See the OutputStream class

ObjectInputStream

• concept

ObjectInputStream represents the object input stream. Deserialize basic data and objects written using ObjectOutputStream.  

• Source code

public class ObjectInputStreamextends InputStream implements ObjectInput, ObjectStreamConstants{
    //......
}

• Construction method

• common method

ObjectOutputStream

• concept

ObjectOutputStream represents the object output stream, writes the basic data type of Java object into the OutputStream stream, and implements the object persistent storage by using files in the stream.

• Source code

public class ObjectOutputStream extends OutputStream implements ObjectOutput, ObjectStreamConstants{
    //......
}

• Construction method

• common method

Character stream

Reader

       Reader Is the parent of all character input streams.

Writer

       Writer Is the parent of all character output streams.