Java IO - Data

Java IO - Data

目錄

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DataInputStream 和 DataOutputStream.

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DataInputStream

package java.io;

/**
 * data input stream 允許 應用讀取 Java 基本數據類型。應用程序使用 data output stream 寫入的數據
 * 可以在後面使用 data input stream 來讀取。
 * 線程不安全，需要用戶自己保證多線程的安全使用。
 */
public
class DataInputStream extends FilterInputStream implements DataInput {

    public DataInputStream(InputStream in) {
        super(in);
    }

    /**
     * working arrays initialized on demand by readUTF
     */
    private byte bytearr[] = new byte[80];
    private char chararr[] = new char[80];

    /**
     * 從輸入流中讀取一些字節到字節數組中。返回讀取的字節數。
     * 阻塞方法。
     */
    public final int read(byte b[]) throws IOException {
        return in.read(b, 0, b.length);
    }

    /**
     * 讀取最多 len 長度字節的數據到數組。
     * 阻塞方法。
     */
    public final int read(byte b[], int off, int len) throws IOException {
        return in.read(b, off, len);
    }

    public final void readFully(byte b[]) throws IOException {
        readFully(b, 0, b.length);
    }

    /**
     * 一定要讀到 len 長度的數據，不然會拋異常
     */
    public final void readFully(byte b[], int off, int len) throws IOException {
        if (len < 0)
            throw new IndexOutOfBoundsException();
        int n = 0;
        while (n < len) {
            int count = in.read(b, off + n, len - n);
            if (count < 0)
                throw new EOFException();
            n += count;
        }
    }

    public final int skipBytes(int n) throws IOException {
        int total = 0;
        int cur = 0;

        while ((total<n) && ((cur = (int) in.skip(n-total)) > 0)) {
            total += cur;
        }

        return total;
    }

    // 下面這些方法在 RandomAccessFile中已經介紹過了。

    public final boolean readBoolean() throws IOException {
        int ch = in.read();
        if (ch < 0)
            throw new EOFException();
        return (ch != 0);
    }

    public final byte readByte() throws IOException {
        int ch = in.read();
        if (ch < 0)
            throw new EOFException();
        return (byte)(ch);
    }

    public final int readUnsignedByte() throws IOException {
        int ch = in.read();
        if (ch < 0)
            throw new EOFException();
        return ch;
    }

    public final short readShort() throws IOException {
        int ch1 = in.read();
        int ch2 = in.read();
        if ((ch1 | ch2) < 0)
            throw new EOFException();
        return (short)((ch1 << 8) + (ch2 << 0));
    }

    public final int readUnsignedShort() throws IOException {
        int ch1 = in.read();
        int ch2 = in.read();
        if ((ch1 | ch2) < 0)
            throw new EOFException();
        return (ch1 << 8) + (ch2 << 0);
    }

    public final char readChar() throws IOException {
        int ch1 = in.read();
        int ch2 = in.read();
        if ((ch1 | ch2) < 0)
            throw new EOFException();
        return (char)((ch1 << 8) + (ch2 << 0));
    }

    public final int readInt() throws IOException {
        int ch1 = in.read();
        int ch2 = in.read();
        int ch3 = in.read();
        int ch4 = in.read();
        if ((ch1 | ch2 | ch3 | ch4) < 0)
            throw new EOFException();
        return ((ch1 << 24) + (ch2 << 16) + (ch3 << 8) + (ch4 << 0));
    }

    private byte readBuffer[] = new byte[8];

    public final long readLong() throws IOException {
        readFully(readBuffer, 0, 8);
        return (((long)readBuffer[0] << 56) +
                ((long)(readBuffer[1] & 255) << 48) +
                ((long)(readBuffer[2] & 255) << 40) +
                ((long)(readBuffer[3] & 255) << 32) +
                ((long)(readBuffer[4] & 255) << 24) +
                ((readBuffer[5] & 255) << 16) +
                ((readBuffer[6] & 255) <<  8) +
                ((readBuffer[7] & 255) <<  0));
    }

    public final float readFloat() throws IOException {
        return Float.intBitsToFloat(readInt());
    }

    public final double readDouble() throws IOException {
        return Double.longBitsToDouble(readLong());
    }

    private char lineBuffer[];

    @Deprecated
    public final String readLine() throws IOException {
        char buf[] = lineBuffer;

        if (buf == null) {
            buf = lineBuffer = new char[128];
        }

        int room = buf.length;
        int offset = 0;
        int c;

loop:   while (true) {
            switch (c = in.read()) {
              case -1:
              case '\n':
                break loop;

              case '\r':
                int c2 = in.read();
                if ((c2 != '\n') && (c2 != -1)) {
                    if (!(in instanceof PushbackInputStream)) {
                        this.in = new PushbackInputStream(in);
                    }
                    ((PushbackInputStream)in).unread(c2);
                }
                break loop;

              default:
                if (--room < 0) {
                    buf = new char[offset + 128];
                    room = buf.length - offset - 1;
                    System.arraycopy(lineBuffer, 0, buf, 0, offset);
                    lineBuffer = buf;
                }
                buf[offset++] = (char) c;
                break;
            }
        }
        if ((c == -1) && (offset == 0)) {
            return null;
        }
        return String.copyValueOf(buf, 0, offset);
    }

    public final String readUTF() throws IOException {
        return readUTF(this);
    }

    public final static String readUTF(DataInput in) throws IOException {
        int utflen = in.readUnsignedShort();
        byte[] bytearr = null;
        char[] chararr = null;
        if (in instanceof DataInputStream) {
            DataInputStream dis = (DataInputStream)in;
            if (dis.bytearr.length < utflen){
                dis.bytearr = new byte[utflen*2];
                dis.chararr = new char[utflen*2];
            }
            chararr = dis.chararr;
            bytearr = dis.bytearr;
        } else {
            bytearr = new byte[utflen];
            chararr = new char[utflen];
        }

        int c, char2, char3;
        int count = 0;
        int chararr_count=0;

        in.readFully(bytearr, 0, utflen);

        while (count < utflen) {
            c = (int) bytearr[count] & 0xff;
            if (c > 127) break;
            count++;
            chararr[chararr_count++]=(char)c;
        }

        while (count < utflen) {
            c = (int) bytearr[count] & 0xff;
            switch (c >> 4) {
                case 0: case 1: case 2: case 3: case 4: case 5: case 6: case 7:
                    /* 0xxxxxxx*/
                    count++;
                    chararr[chararr_count++]=(char)c;
                    break;
                case 12: case 13:
                    /* 110x xxxx   10xx xxxx*/
                    count += 2;
                    if (count > utflen)
                        throw new UTFDataFormatException(
                            "malformed input: partial character at end");
                    char2 = (int) bytearr[count-1];
                    if ((char2 & 0xC0) != 0x80)
                        throw new UTFDataFormatException(
                            "malformed input around byte " + count);
                    chararr[chararr_count++]=(char)(((c & 0x1F) << 6) |
                                                    (char2 & 0x3F));
                    break;
                case 14:
                    /* 1110 xxxx  10xx xxxx  10xx xxxx */
                    count += 3;
                    if (count > utflen)
                        throw new UTFDataFormatException(
                            "malformed input: partial character at end");
                    char2 = (int) bytearr[count-2];
                    char3 = (int) bytearr[count-1];
                    if (((char2 & 0xC0) != 0x80) || ((char3 & 0xC0) != 0x80))
                        throw new UTFDataFormatException(
                            "malformed input around byte " + (count-1));
                    chararr[chararr_count++]=(char)(((c     & 0x0F) << 12) |
                                                    ((char2 & 0x3F) << 6)  |
                                                    ((char3 & 0x3F) << 0));
                    break;
                default:
                    /* 10xx xxxx,  1111 xxxx */
                    throw new UTFDataFormatException(
                        "malformed input around byte " + count);
            }
        }
        // The number of chars produced may be less than utflen
        return new String(chararr, 0, chararr_count);
    }
}

---

DataOutputStream

package java.io;

/**
 * data output stream 允許應用往 output stream 中寫入原始類型的數據。
 * 應用程序使用 data output stream 寫入的數據可以被 data input stream 讀取。 
 */
public
class DataOutputStream extends FilterOutputStream implements DataOutput {
    /**
     * 已經寫入到 data output stream 的字節數。
     */
    protected int written;

    private byte[] bytearr = null;

    public DataOutputStream(OutputStream out) {
        super(out);
    }

    private void incCount(int value) {
        int temp = written + value;
        if (temp < 0) {
            temp = Integer.MAX_VALUE;
        }
        written = temp;
    }

    /**
     * 寫入一個字節(只寫 低 8 位，高 24 位忽略)
     */
    public synchronized void write(int b) throws IOException {
        out.write(b);
        incCount(1);
    }

    public synchronized void write(byte b[], int off, int len)
        throws IOException
    {
        out.write(b, off, len);
        incCount(len);
    }

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

    public final void writeBoolean(boolean v) throws IOException {
        out.write(v ? 1 : 0); // 把 boolean 換成了 1 和 0
        incCount(1);
    }

    public final void writeByte(int v) throws IOException {
        out.write(v);
        incCount(1);
    }

    // 大端？
    public final void writeShort(int v) throws IOException {
        out.write((v >>> 8) & 0xFF);
        out.write((v >>> 0) & 0xFF);
        incCount(2);
    }

    // Java 中的 char 是 16 bit 的
    public final void writeChar(int v) throws IOException {
        out.write((v >>> 8) & 0xFF);
        out.write((v >>> 0) & 0xFF);
        incCount(2);
    }

    public final void writeInt(int v) throws IOException {
        out.write((v >>> 24) & 0xFF);
        out.write((v >>> 16) & 0xFF);
        out.write((v >>>  8) & 0xFF);
        out.write((v >>>  0) & 0xFF);
        incCount(4);
    }

    private byte writeBuffer[] = new byte[8];

    public final void writeLong(long v) throws IOException {
        writeBuffer[0] = (byte)(v >>> 56);
        writeBuffer[1] = (byte)(v >>> 48);
        writeBuffer[2] = (byte)(v >>> 40);
        writeBuffer[3] = (byte)(v >>> 32);
        writeBuffer[4] = (byte)(v >>> 24);
        writeBuffer[5] = (byte)(v >>> 16);
        writeBuffer[6] = (byte)(v >>>  8);
        writeBuffer[7] = (byte)(v >>>  0);
        out.write(writeBuffer, 0, 8);
        incCount(8);
    }

    public final void writeFloat(float v) throws IOException {
        writeInt(Float.floatToIntBits(v));
    }

    public final void writeDouble(double v) throws IOException {
        writeLong(Double.doubleToLongBits(v));
    }

    public final void writeBytes(String s) throws IOException {
        int len = s.length();
        for (int i = 0 ; i < len ; i++) {
            out.write((byte)s.charAt(i));
        }
        incCount(len);
    }

    public final void writeChars(String s) throws IOException {
        int len = s.length();
        for (int i = 0 ; i < len ; i++) {
            int v = s.charAt(i);
            out.write((v >>> 8) & 0xFF);
            out.write((v >>> 0) & 0xFF);
        }
        incCount(len * 2);
    }

    public final void writeUTF(String str) throws IOException {
        writeUTF(str, this);
    }

    static int writeUTF(String str, DataOutput out) throws IOException {
        int strlen = str.length();
        int utflen = 0;
        int c, count = 0;

        /* use charAt instead of copying String to char array */
        for (int i = 0; i < strlen; i++) {
            c = str.charAt(i);
            if ((c >= 0x0001) && (c <= 0x007F)) {
                utflen++;
            } else if (c > 0x07FF) {
                utflen += 3;
            } else {
                utflen += 2;
            }
        }

        if (utflen > 65535)
            throw new UTFDataFormatException(
                "encoded string too long: " + utflen + " bytes");

        byte[] bytearr = null;
        if (out instanceof DataOutputStream) {
            DataOutputStream dos = (DataOutputStream)out;
            if(dos.bytearr == null || (dos.bytearr.length < (utflen+2)))
                dos.bytearr = new byte[(utflen*2) + 2];
            bytearr = dos.bytearr;
        } else {
            bytearr = new byte[utflen+2];
        }

        bytearr[count++] = (byte) ((utflen >>> 8) & 0xFF);
        bytearr[count++] = (byte) ((utflen >>> 0) & 0xFF);

        int i=0;
        for (i=0; i<strlen; i++) {
           c = str.charAt(i);
           if (!((c >= 0x0001) && (c <= 0x007F))) break;
           bytearr[count++] = (byte) c;
        }

        for (;i < strlen; i++){
            c = str.charAt(i);
            if ((c >= 0x0001) && (c <= 0x007F)) {
                bytearr[count++] = (byte) c;

            } else if (c > 0x07FF) {
                bytearr[count++] = (byte) (0xE0 | ((c >> 12) & 0x0F));
                bytearr[count++] = (byte) (0x80 | ((c >>  6) & 0x3F));
                bytearr[count++] = (byte) (0x80 | ((c >>  0) & 0x3F));
            } else {
                bytearr[count++] = (byte) (0xC0 | ((c >>  6) & 0x1F));
                bytearr[count++] = (byte) (0x80 | ((c >>  0) & 0x3F));
            }
        }
        out.write(bytearr, 0, utflen+2);
        return utflen + 2;
    }

    public final int size() {
        return written;
    }
}