1 使用方法
ByteArrayInputStream 包含一個内部緩沖區，該緩沖區包含從流中讀取的位元組。内部計數器跟蹤 read 方法要提供的下一個位元組。ByteArrayOutputStream實作了一個輸出流，其中的資料被寫入一個 byte 數組。緩沖區會随着資料的不斷寫入而自動增長。可使用 toByteArray()和 toString()擷取資料。
1.1 方法介紹
ByteArrayInputStream提供的API如下：
// 構造函數
ByteArrayInputStream(byte[] buf)
ByteArrayInputStream(byte[] buf, int offset, int length)
synchronized int available() //能否讀取位元組流的下一位元組
void close() //關閉位元組流
synchronized void mark(int readlimit) //儲存目前位置
boolean markSupported() //是否支援mark
synchronized int read() //讀取下一位元組
synchronized int read(byte[] buffer, int offset, int length) //将位元組流寫入buffer數組
synchronized void reset() //重置索引到mark位置
synchronized long skip(long byteCount) //跳過n個位元組
}
1.2 使用示例
public class TestByteArray {
// 對應英文字母“abcddefghijklmnopqrsttuvwxyz”
private final byte[] ArrayLetters = {
, , , , , , , , , , , , , , ,
, , , , , , , , , ,
};
public void testByteArrayInputStream() {
//建立位元組流,以ArrayLetters初始化
ByteArrayInputStream inputStream = new ByteArrayInputStream(ArrayLetters);
//讀取5個位元組
int i = ;
System.out.print("前5個位元組為: ");
while (i++ < ) {
//是否可讀
if (inputStream.available() >= ) {
int buf = inputStream.read();
System.out.printf("0x%s ", Integer.toHexString(buf));
}
}
System.out.println();
//是否支援标記
if (!inputStream.markSupported()) {
System.out.println("該位元組流不支援标記");
} else {
System.out.println("該位元組流支援标記");
}
//标記, 已經讀取5個位元組,标記處為0x66
System.out.println("标記該位元組流為位置為0x66(f)");
inputStream.mark();
//跳過2個位元組
inputStream.skip();
//讀取5個位元組到buffer
byte [] buffer = new byte[];
inputStream.read(buffer, , );
System.out.println("buffer: " + new String(buffer));
//重置
inputStream.reset();
inputStream.read(buffer, , );
System.out.println("重置後讀取5個字元為: " + new String(buffer));
}
}
運作結果如下：
前個位元組為:
該位元組流支援标記
标記該位元組流為位置為(f)
buffer: hijkl
重置後讀取個字元為: fghij
2 源碼分析
2.1構造函數
ByteArrayInputStream有兩個構造函數，差別是初始化内容選擇。
/**
* Creates a <code>ByteArrayInputStream</code>
* so that it uses <code>buf</code> as its
* buffer array.
* The buffer array is not copied.
* The initial value of <code>pos</code>
* is <code>0</code> and the initial value
* of <code>count</code> is the length of
* <code>buf</code>.
*
* @param buf the input buffer.
*/
public ByteArrayInputStream(byte buf[]) {
this.buf = buf; //緩沖數組
this.pos = ; //目前位置
this.count = buf.length; //輸入流位元組數
}
/**
* Creates <code>ByteArrayInputStream</code>
* that uses <code>buf</code> as its
* buffer array. The initial value of <code>pos</code>
* is <code>offset</code> and the initial value
* of <code>count</code> is the minimum of <code>offset+length</code>
* and <code>buf.length</code>.
* The buffer array is not copied. The buffer's mark is
* set to the specified offset.
*
* @param buf the input buffer.
* @param offset the offset in the buffer of the first byte to read.
* @param length the maximum number of bytes to read from the buffer.
*/
public ByteArrayInputStream(byte buf[], int offset, int length) {
this.buf = buf; //緩沖數組
this.pos = offset; //目前位置為傳入buf的offset
this.count = Math.min(offset + length, buf.length); //輸入流位元組數
this.mark = offset; //标記
}
2.2 read方法
read方法有兩個，不帶參數的read()每次讀取位元組流中一個位元組，帶參數的read(byte b[], int off, int len)将位元組流從目前位置開始，寫入len個位元組到b中，寫入開始位置為off。
/**
* 讀取位元組流目前位元組
* @return 一個位元組
*/
public synchronized int read() {
return (pos < count) ? (buf[pos++] & ) : -; //&0xff為限制傳回值為一個位元組,即8位
}
/**
* 将位元組流目前位置開始的len個位元組寫入到 b從off開始的len個位置
* @param b
* @param off
* @param len
* @return
*/
public synchronized int read(byte b[], int off, int len) {
if (b == null) {
throw new NullPointerException();
} else if (off < || len < || len > b.length - off) {
throw new IndexOutOfBoundsException();
}
if (pos >= count) { //超出位元組流範圍
return -;
}
int avail = count - pos; //可讀取的位元組數量
if (len > avail) {
len = avail;
}
if (len <= ) {
return ;
}
System.arraycopy(buf, pos, b, off, len); //将buf從pos位置開始的位元組複制到b從off開始的位置,共複制len長
pos += len;
return len;
}
2.4 skip方法
/**
* Skips <code>n</code> bytes of input from this input stream. Fewer
* bytes might be skipped if the end of the input stream is reached.
* The actual number <code>k</code>
* of bytes to be skipped is equal to the smaller
* of <code>n</code> and <code>count-pos</code>.
* The value <code>k</code> is added into <code>pos</code>
* and <code>k</code> is returned.
*
* @param n the number of bytes to be skipped.
* @return the actual number of bytes skipped.
*/
public synchronized long skip(long n) {
long k = count - pos; //剩餘位元組數
if (n < k) {
k = n < ? : n;
}
pos += k;
return k;
}
2.5 mark和reset方法
/**
* Set the current marked position in the stream.
* ByteArrayInputStream objects are marked at position zero by
* default when constructed. They may be marked at another
* position within the buffer by this method.
* <p>
* If no mark has been set, then the value of the mark is the
* offset passed to the constructor (or if the offset was not
* supplied).
*
* <p> Note: The <code>readAheadLimit</code> for this class
* has no meaning.
*
* @since JDK1
*/
public void mark(int readAheadLimit) {
mark = pos;
}
/**
* Resets the buffer to the marked position. The marked position
* is unless another position was marked or an offset was specified
* in the constructor.
*/
public synchronized void reset() {
pos = mark;
}
參考：
[1] http://www.cnblogs.com/skywang12345/p/io_02.html
[2] http://www.cnblogs.com/skywang12345/p/io_03.html
[3] http://blog.csdn.net/rcoder/article/details/6118313
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