java中inputstream的有關類的設計模式-the decorator pattern
inputstream中比較重要的decorator----BufferedInputStream
它的構造函數為BufferedInputStream(InputStream in)
或BufferedInputStream(InputStream in, int size)
可以裝飾繼承了inputsream類的類
自己完成的新的inputstream
public class LowerCaseInputStream extends FilterInputStream {
public LowerCaseInputStream(InputStream in) {
super(in);
}
public int read() throws IOException {
int c = super.read();
return (c == -1 ? c : Character.toLowerCase((char)c));
}
public int read(byte[] b, int offset, int len) throws IOException {
int result = super.read(b, offset, len);
for (int i = offset; i < offset+result; i++) {
b[i] = (byte)Character.toLowerCase((char)b[i]);
}
return result;
}
}
FiterInputStream 便是一種特殊的類，他滿足裝飾器（decorator）的條件，
1。必須繼承需要decorator的類：InputStream
2。在此類中必須包含需要decorator的類的實例，這樣的話此類就擁有decorator的類的功能還能擴展其他功能。
FiterInputStream 的原代碼
/*
* @(#)FilterInputStream.java 1.28 03/12/19
*
* Copyright 2004 Sun Microsystems, Inc. All rights reserved.
* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package java.io;
/**
* A <code>FilterInputStream</code> contains
* some other input stream, which it uses as
* its basic source of data, possibly transforming
* the data along the way or providing additional
* functionality. The class <code>FilterInputStream</code>
* itself simply overrides all methods of
* <code>InputStream</code> with versions that
* pass all requests to the contained input
* stream. Subclasses of <code>FilterInputStream</code>
* may further override some of these methods
* and may also provide additional methods
* and fields.
*
* @author Jonathan Payne
* @version 1.28, 12/19/03
* @since JDK1.0
*/
public
class FilterInputStream extends InputStream {
/**
* The input stream to be filtered.
*/
protected volatile InputStream in;
/**
* Creates a <code>FilterInputStream</code>
* by assigning the argument <code>in</code>
* to the field <code>this.in</code> so as
* to remember it for later use.
*
* @param in the underlying input stream, or <code>null</code> if
* this instance is to be created without an underlying stream.
*/
protected FilterInputStream(InputStream in) {
this.in = in;
}
/**
* Reads the next byte of data from this input stream. The value
* byte is returned as an <code>int</code> in the range
* <code>0</code> to <code>255</code>. If no byte is available
* because the end of the stream has been reached, the value
* <code>-1</code> is returned. This method blocks until input data
* is available, the end of the stream is detected, or an exception
* is thrown.
* <p>
* This method
* simply performs <code>in.read()</code> and returns the result.
*
* @return the next byte of data, or <code>-1</code> if the end of the
* stream is reached.
* @exception IOException if an I/O error occurs.
* @see java.io.FilterInputStream#in
*/
public int read() throws IOException {
return in.read();
}
/**
* Reads up to <code>byte.length</code> bytes of data from this
* input stream into an array of bytes. This method blocks until some
* input is available.
* <p>
* This method simply performs the call
* <code>read(b, 0, b.length)</code> and returns
* the result. It is important that it does
* <i>not</i> do <code>in.read(b)</code> instead;
* certain subclasses of <code>FilterInputStream</code>
* depend on the implementation strategy actually
* used.
*
* @param b the buffer into which the data is read.
* @return the total number of bytes read into the buffer, or
* <code>-1</code> if there is no more data because the end of
* the stream has been reached.
* @exception IOException if an I/O error occurs.
* @see java.io.FilterInputStream#read(byte[], int, int)
*/
public int read(byte b[]) throws IOException {
return read(b, 0, b.length);
}
/**
* Reads up to <code>len</code> bytes of data from this input stream
* into an array of bytes. This method blocks until some input is
* available.
* <p>
* This method simply performs <code>in.read(b, off, len)</code>
* and returns the result.
*
* @param b the buffer into which the data is read.
* @param off the start offset of the data.
* @param len the maximum number of bytes read.
* @return the total number of bytes read into the buffer, or
* <code>-1</code> if there is no more data because the end of
* the stream has been reached.
* @exception IOException if an I/O error occurs.
* @see java.io.FilterInputStream#in
*/
public int read(byte b[], int off, int len) throws IOException {
return in.read(b, off, len);
}
/**
* Skips over and discards <code>n</code> bytes of data from the
* input stream. The <code>skip</code> method may, for a variety of
* reasons, end up skipping over some smaller number of bytes,
* possibly <code>0</code>. The actual number of bytes skipped is
* returned.
* <p>
* This method
* simply performs <code>in.skip(n)</code>.
*
* @param n the number of bytes to be skipped.
* @return the actual number of bytes skipped.
* @exception IOException if an I/O error occurs.
*/
public long skip(long n) throws IOException {
return in.skip(n);
}
/**
* Returns the number of bytes that can be read from this input
* stream without blocking.
* <p>
* This method
* simply performs <code>in.available()</code> and
* returns the result.
*
* @return the number of bytes that can be read from the input stream
* without blocking.
* @exception IOException if an I/O error occurs.
* @see java.io.FilterInputStream#in
*/
public int available() throws IOException {
return in.available();
}
/**
* Closes this input stream and releases any system resources
* associated with the stream.
* This
* method simply performs <code>in.close()</code>.
*
* @exception IOException if an I/O error occurs.
* @see java.io.FilterInputStream#in
*/
public void close() throws IOException {
in.close();
}
/**
* Marks the current position in this input stream. A subsequent
* call to the <code>reset</code> method repositions this stream at
* the last marked position so that subsequent reads re-read the same bytes.
* <p>
* The <code>readlimit</code> argument tells this input stream to
* allow that many bytes to be read before the mark position gets
* invalidated.
* <p>
* This method simply performs <code>in.mark(readlimit)</code>.
*
* @param readlimit the maximum limit of bytes that can be read before
* the mark position becomes invalid.
* @see java.io.FilterInputStream#in
* @see java.io.FilterInputStream#reset()
*/
public synchronized void mark(int readlimit) {
in.mark(readlimit);
}
/**
* Repositions this stream to the position at the time the
* <code>mark</code> method was last called on this input stream.
* <p>
* This method
* simply performs <code>in.reset()</code>.
* <p>
* Stream marks are intended to be used in
* situations where you need to read ahead a little to see what's in
* the stream. Often this is most easily done by invoking some
* general parser. If the stream is of the type handled by the
* parse, it just chugs along happily. If the stream is not of
* that type, the parser should toss an exception when it fails.
* If this happens within readlimit bytes, it allows the outer
* code to reset the stream and try another parser.
*
* @exception IOException if the stream has not been marked or if the
* mark has been invalidated.
* @see java.io.FilterInputStream#in
* @see java.io.FilterInputStream#mark(int)
*/
public synchronized void reset() throws IOException {
in.reset();
}
/**
* Tests if this input stream supports the <code>mark</code>
* and <code>reset</code> methods.
* This method
* simply performs <code>in.markSupported()</code>.
*
* @return <code>true</code> if this stream type supports the
* <code>mark</code> and <code>reset</code> method;
* <code>false</code> otherwise.
* @see java.io.FilterInputStream#in
* @see java.io.InputStream#mark(int)
* @see java.io.InputStream#reset()
*/
public boolean markSupported() {
return in.markSupported();
}
}