datainputstream.java

来自「《移动Agent技术》一书的所有章节源代码。」· Java 代码 · 共 625 行 · 第 1/2 页

     * Reads a Unicode character from this data input stream. This 
     * method reads two bytes from the underlying input stream. If the 
     * bytes read, in order, are <code>b1</code> and <code>b2</code>, 
     * where 0&nbsp;&lt;=&nbsp;<code>b1</code>, 
     * <code>b1</code>&nbsp;&lt;=&nbsp;255, then the result is equal to:
     * <ul><code>
     *     (char)((b1 &lt;&lt; 8) | b2)
     * </code></ul>
     * <p>
     * This method blocks until either the two bytes are read, the end of 
     * the stream is detected, or an exception is thrown. 
     *
     * @return     the next two bytes of this input stream as a Unicode
     *             character.
     * @exception  EOFException  if this input stream reaches the end before
     *               reading two bytes.
     * @exception  IOException   if an I/O error occurs.
     * @see        java.io.FilterInputStream#in
     */
    public final char readChar() throws IOException {
	InputStream in = this.in;
	int ch1 = in.read();
	int ch2 = in.read();
	if ((ch1 | ch2) < 0)
	     throw new EOFException();
	return (char)((ch1 << 8) + (ch2 << 0));
    }

    /**
     * Reads a signed 32-bit integer from this data input stream. This 
     * method reads four bytes from the underlying input stream. If the 
     * bytes read, in order, are <code>b1</code>, <code>b2</code>, 
     * <code>b3</code>, and <code>b4</code>, where 
     * 0&nbsp;&lt;=&nbsp;<code>b1</code>, <code>b2</code>, 
     * <code>b3</code>, <code>b4</code>&nbsp;&lt;=&nbsp;255, then the 
     * result is equal to:
     * <ul><code>
     *     (b1 &lt;&lt; 24) | (b2 &lt;&lt; 16) + (b3 &lt;&lt; 8) +b4
     * </code></ul>
     * <p>
     * This method blocks until the four bytes are read, the end of the 
     * stream is detected, or an exception is thrown. 
     *
     * @return     the next four bytes of this input stream, interpreted as an
     *             <code>int</code>.
     * @exception  EOFException  if this input stream reaches the end before
     *               reading four bytes.
     * @exception  IOException   if an I/O error occurs.
     * @see        java.io.FilterInputStream#in
     */
    public final int readInt() throws IOException {
	InputStream in = this.in;
	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));
    }

    /**
     * Reads a signed 64-bit integer from this data input stream. This 
     * method reads eight bytes from the underlying input stream. If the 
     * bytes read, in order, are <code>b1</code>, <code>b2</code>, 
     * <code>b3</code>, <code>b4</code>, <code>b5</code>, 
     * <code>b6</code>, <code>b7</code>, and <code>b8</code>, where 
     * <ul><code>
     *     0 &lt;= b1, b2, b3, b4, b5, b6, b7, b8 &lt;= 255,
     * </code></ul>
     * <p>
     * then the result is equal to:
     * <p><blockquote><pre>
     *     ((long)b1 &lt;&lt; 56) + ((long)b2 &lt;&lt; 48) +
     *        ((long)b3 &lt;&lt; 40) + ((long)b4 &lt;&lt; 32) +
     *        ((long)b5 &lt;&lt; 24) + (b6 &lt;&lt; 16) +
     *        (b7 &lt;&lt; 8) + b8
     * </pre></blockquote>
     * <p>
     * This method blocks until the eight bytes are read, the end of the 
     * stream is detected, or an exception is thrown. 
     *
     * @return     the next eight bytes of this input stream, interpreted as a
     *             <code>long</code>.
     * @exception  EOFException  if this input stream reaches the end before
     *               reading eight bytes.
     * @exception  IOException   if an I/O error occurs.
     * @see        java.io.FilterInputStream#in
     */
    public final long readLong() throws IOException {
	InputStream in = this.in;
	return ((long)(readInt()) << 32) + (readInt() & 0xFFFFFFFFL);
    }

    /**
     * Reads a <code>float</code> from this data input stream. This 
     * method reads an <code>int</code> value as if by the 
     * <code>readInt</code> method and then converts that 
     * <code>int</code> to a <code>float</code> using the 
     * <code>intBitsToFloat</code> method in class <code>Float</code>. 
     * This method blocks until the four bytes are read, the end of the 
     * stream is detected, or an exception is thrown. 
     *
     * @return     the next four bytes of this input stream, interpreted as a
     *             <code>float</code>.
     * @exception  EOFException  if this input stream reaches the end before
     *               reading four bytes.
     * @exception  IOException   if an I/O error occurs.
     * @see        java.io.DataInputStream#readInt()
     * @see        java.lang.Float#intBitsToFloat(int)
     */
    public final float readFloat() throws IOException {
	return Float.intBitsToFloat(readInt());
    }

    /**
     * Reads a <code>double</code> from this data input stream. This 
     * method reads a <code>long</code> value as if by the 
     * <code>readLong</code> method and then converts that 
     * <code>long</code> to a <code>double</code> using the 
     * <code>longBitsToDouble</code> method in class <code>Double</code>.
     * <p>
     * This method blocks until the eight bytes are read, the end of the 
     * stream is detected, or an exception is thrown. 
     *
     * @return     the next eight bytes of this input stream, interpreted as a
     *             <code>double</code>.
     * @exception  EOFException  if this input stream reaches the end before
     *               reading eight bytes.
     * @exception  IOException   if an I/O error occurs.
     * @see        java.io.DataInputStream#readLong()
     * @see        java.lang.Double#longBitsToDouble(long)
     */
    public final double readDouble() throws IOException {
	return Double.longBitsToDouble(readLong());
    }

    private char lineBuffer[];

    /**
     * Reads the next line of text from this data input stream. This 
     * method successively reads bytes from the underlying input stream 
     * until it reaches the end of a line of text. 
     * <p>
     * A line of text is terminated by a carriage return character 
     * (<code>'&#92;r'</code>), a newline character (<code>'&#92;n'</code>), a 
     * carriage return character immediately followed by a newline 
     * character, or the end of the input stream. The line-terminating 
     * character(s), if any, are not returned as part of the string that 
     * is returned. 
     * <p>
     * This method blocks until a newline character is read, a carriage 
     * return and the byte following it are read (to see if it is a 
     * newline), the end of the stream is detected, or an exception is 
     * thrown.
     *
     * @deprecated This method does not properly convert bytes to characters.
     * As of JDK&nbsp;1.1, the preferred way to read lines of text is via the
     * <code>BufferedReader.readLine()</code> method.  Programs that use the
     * <code>DataInputStream</code> class to read lines can be converted to use
     * the <code>BufferedReader</code> class by replacing code of the form
     * <ul>
     *     <code>DataInputStream d =&nbsp;new&nbsp;DataInputStream(in);</code>
     * </ul>
     * with
     * <ul>
     *     <code>BufferedReader d
     *          =&nbsp;new&nbsp;BufferedReader(new&nbsp;InputStreamReader(in));
     *      </code>
     * </ul>
     *
     * @return     the next line of text from this input stream, or 
     *             <tt>null</tt> if no bytes are read before end-of-file 
     *             is reached.
     * @exception  IOException  if an I/O error occurs.
     * @see        java.io.BufferedReader#readLine()
     * @see        java.io.FilterInputStream#in
     */
    public final String readLine() throws IOException {
	InputStream in = this.in;
	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') {
		    if (!(in instanceof PushbackInputStream)) {
			in = 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);
    }

    /**
     * Reads in a string that has been encoded using a modified UTF-8 
     * format from this data input stream. This method calls 
     * <code>readUTF(this)</code>.
     * See <code>readUTF(java.io.DataInput)</code> for a more 
     * complete description of the format. 
     * <p>
     * This method blocks until all the bytes are read, the end of the 
     * stream is detected, or an exception is thrown. 
     *
     * @return     a Unicode string.
     * @exception  EOFException  if this input stream reaches the end before
     *               reading all the bytes.
     * @exception  IOException   if an I/O error occurs.
     * @see        java.io.DataInputStream#readUTF(java.io.DataInput)
     */
    public final String readUTF() throws IOException {
        return readUTF(this);
    }

    /**
     * Reads in a string from the specified data input stream. The 
     * string has been encoded using a modified UTF-8 format. 
     * <p>
     * The first two bytes are read as if by 
     * <code>readUnsignedShort</code>. This value gives the number of 
     * following bytes that are in the encoded string, not
     * the length of the resulting string. The following bytes are then 
     * interpreted as bytes encoding characters in the UTF-8 format 
     * and are converted into characters. 
     * <p>
     * This method blocks until all the bytes are read, the end of the 
     * stream is detected, or an exception is thrown. 
     *
     * @param      in   a data input stream.
     * @return     a Unicode string.
     * @exception  EOFException            if the input stream reaches the end
     *               before all the bytes.
     * @exception  IOException             if an I/O error occurs.
     * @exception  UTFDataFormatException  if the bytes do not represent a
     *               valid UTF-8 encoding of a Unicode string.
     * @see        java.io.DataInputStream#readUnsignedShort()
     */
    public final static String readUTF(DataInput in) throws IOException {
        int utflen = in.readUnsignedShort();
        char str[] = new char[utflen];
	int count = 0;
	int strlen = 0;
	while (count < utflen) {
	    int c = in.readUnsignedByte();
	    int char2, char3;
	    switch (c >> 4) { 
	        case 0: case 1: case 2: case 3: case 4: case 5: case 6: case 7:
		    // 0xxxxxxx
		    count++;
		    str[strlen++] = (char)c;
		    break;
	        case 12: case 13:
		    // 110x xxxx   10xx xxxx
		    count += 2;
		    if (count > utflen) 
			throw new UTFDataFormatException();		  
		    char2 = in.readUnsignedByte();
		    if ((char2 & 0xC0) != 0x80)
			throw new UTFDataFormatException();		  
		    str[strlen++] = (char)(((c & 0x1F) << 6) | (char2 & 0x3F));
		    break;
	        case 14:
		    // 1110 xxxx  10xx xxxx  10xx xxxx
		    count += 3;
		    if (count > utflen) 
			throw new UTFDataFormatException();		  
		    char2 = in.readUnsignedByte();
		    char3 = in.readUnsignedByte();
		    if (((char2 & 0xC0) != 0x80) || ((char3 & 0xC0) != 0x80))
			throw new UTFDataFormatException();		  
		    str[strlen++] = (char)(((c & 0x0F) << 12) |
					   ((char2 & 0x3F) << 6) |
					   ((char3 & 0x3F) << 0));
		    break;
	        default:
		    // 10xx xxxx,  1111 xxxx
		    throw new UTFDataFormatException();		  
		}
	}
        return new String(str, 0, strlen);
    }
}