Java-IO之ByteArrayInputStream
public ByteArrayInputStream(byte buf[]) public ByteArrayInputStream(byte buf[], int offset, int length) public synchronized int read() public synchronized int read(byte b[], int off, int len) public synchronized long skip(long n) public synchronized int available() public boolean markSupported() public void mark(int readAheadLimit) public synchronized void reset() public void close()
ByteArrayInputStream示例代码:
public class Hello { private static final int LEN = 5; // 对应英文字母“abcddefghijklmnopqrsttuvwxyz” private static final byte[] ArrayLetters = { 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6A, 0x6B, 0x6C, 0x6D, 0x6E, 0x6F, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7A }; public static void main(String[] args) { String tmp = new String(ArrayLetters); System.out.println("ArrayLetters="+tmp); tesByteArrayInputStream() ; } /** * ByteArrayInputStream的API测试函数 */ private static void tesByteArrayInputStream() { // 创建ByteArrayInputStream字节流,内容是ArrayLetters数组 ByteArrayInputStream bais = new ByteArrayInputStream(ArrayLetters); // 从字节流中读取5个字节 for (int i=0; i<LEN; i++) { // 若能继续读取下一个字节,则读取下一个字节 if (bais.available() >= 0) { // 读取“字节流的下一个字节” int tmp = bais.read(); System.out.printf("%d : 0x%s\n", i, Integer.toHexString(tmp)); } } // 若“该字节流”不支持标记功能,则直接退出 if (!bais.markSupported()) { System.out.println("make not supported!"); return ; } // 标记“字节流中下一个被读取的位置”。即--标记“0x66”,因为因为前面已经读取了5个字节,所以下一个被读取的位置是第6个字节” // (01), ByteArrayInputStream类的mark(0)函数中的“参数0”是没有实际意义的。 // (02), mark()与reset()是配套的,reset()会将“字节流中下一个被读取的位置”重置为“mark()中所保存的位置” bais.mark(0); // 跳过5个字节。跳过5个字节后,字节流中下一个被读取的值应该是“0x6B”。 bais.skip(5); // 从字节流中读取5个数据。即读取“0x6B, 0x6C, 0x6D, 0x6E, 0x6F” byte[] buf = new byte[LEN]; bais.read(buf, 0, LEN); // 将buf转换为String字符串。“0x6B, 0x6C, 0x6D, 0x6E, 0x6F”对应字符是“klmno” String str1 = new String(buf); System.out.printf("str1=%s\n", str1); // 重置“字节流”:即,将“字节流中下一个被读取的位置”重置到“mark()所标记的位置”,即0x66。 bais.reset(); // 从“重置后的字节流”中读取5个字节到buf中。即读取“0x66, 0x67, 0x68, 0x69, 0x6A” bais.read(buf, 0, LEN); // 将buf转换为String字符串。“0x66, 0x67, 0x68, 0x69, 0x6A”对应字符是“fghij” String str2 = new String(buf); System.out.printf("str2=%s\n", str2); } }
基于JDK8的ByteArrayInputStream类的源码分析:
public class ByteArrayInputStream extends InputStream { //一个字节数组 protected byte buf[]; /** * The index of the next character to read from the input stream buffer. * This value should always be nonnegative * and not larger than the value of <code>count</code>. * The next byte to be read from the input stream buffer * will be <code>buf[pos]</code>. */ //从输人流缓冲区中读取下一个自负的index protected int pos; /** * The currently 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 the <code>mark()</code> method. * The current buffer position is set to this point by the * <code>reset()</code> method. * <p> * If no mark has been set, then the value of mark is the offset * passed to the constructor (or 0 if the offset was not supplied). * * @since JDK1.1 */ //用来标记在流中的当前位置 protected int mark = 0; /** * The index one greater than the last valid character in the input * stream buffer. * This value should always be nonnegative * and not larger than the length of <code>buf</code>. * It is one greater than the position of * the last byte within <code>buf</code> that * can ever be read from the input stream buffer. */ //下标,比输入流缓冲区中的最后一个有效字符大的 protected int count; //创建一个以buf大小的ByteArrayInputStream public ByteArrayInputStream(byte buf[]) { this.buf = buf; this.pos = 0; this.count = buf.length; } /** * 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. */ //创建一个ByteArrayInputStream,使用buf作为它的缓冲数组,初始位置是offset,初始值的大小为offset+length和length中的最小值 public ByteArrayInputStream(byte buf[], int offset, int length) { this.buf = buf; this.pos = offset; this.count = Math.min(offset + length, buf.length); this.mark = offset; } /** * 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. * <p> * This <code>read</code> method * cannot block. * * @return the next byte of data, or <code>-1</code> if the end of the * stream has been reached. */ //从输人流中读取下一个字节数据,返回值为0到255,没有值返回-1 public synchronized int read() { return (pos < count) ? (buf[pos++] & 0xff) : -1; } /** * Reads up to <code>len</code> bytes of data into an array of bytes * from this input stream. * If <code>pos</code> equals <code>count</code>, * then <code>-1</code> is returned to indicate * end of file. Otherwise, the number <code>k</code> * of bytes read is equal to the smaller of * <code>len</code> and <code>count-pos</code>. * If <code>k</code> is positive, then bytes * <code>buf[pos]</code> through <code>buf[pos+k-1]</code> * are copied into <code>b[off]</code> through * <code>b[off+k-1]</code> in the manner performed * by <code>System.arraycopy</code>. The * value <code>k</code> is added into <code>pos</code> * and <code>k</code> is returned. * <p> * This <code>read</code> method cannot block. * * @param b the buffer into which the data is read. * @param off the start offset in the destination array <code>b</code> * @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 NullPointerException If <code>b</code> is <code>null</code>. * @exception IndexOutOfBoundsException If <code>off</code> is negative, * <code>len</code> is negative, or <code>len</code> is greater than * <code>b.length - off</code> */ //从输入流b读取len大小,初始位置为off public synchronized int read(byte b[], int off, int len) { if (b == null) { throw new NullPointerException(); } else if (off < 0 || len < 0 || len > b.length - off) { throw new IndexOutOfBoundsException(); } if (pos >= count) { return -1; } int avail = count - pos; if (len > avail) { len = avail; } if (len <= 0) { return 0; } System.arraycopy(buf, pos, b, off, len); pos += len; return len; } /** * 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. */ //从输入流中跳过n字节 public synchronized long skip(long n) { long k = count - pos; if (n < k) { k = n < 0 ? 0 : n; } pos += k; return k; } /** * Returns the number of remaining bytes that can be read (or skipped over) * from this input stream. * <p> * The value returned is <code>count - pos</code>, * which is the number of bytes remaining to be read from the input buffer. * * @return the number of remaining bytes that can be read (or skipped * over) from this input stream without blocking. */ //返回从输入流中可以读取到的数据 public synchronized int available() { return count - pos; } /** * Tests if this <code>InputStream</code> supports mark/reset. The * <code>markSupported</code> method of <code>ByteArrayInputStream</code> * always returns <code>true</code>. * * @since JDK1.1 */ //是否支持标记 public boolean markSupported() { return true; } /** * 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 0 if the offset was not * supplied). * * <p> Note: The <code>readAheadLimit</code> for this class * has no meaning. * * @since JDK1.1 */ //设置当前的mark标记 public void mark(int readAheadLimit) { mark = pos; } /** * Resets the buffer to the marked position. The marked position * is 0 unless another position was marked or an offset was specified * in the constructor. */ //重置buffer到mark位置 public synchronized void reset() { pos = mark; } /** * Closing a <tt>ByteArrayInputStream</tt> has no effect. The methods in * this class can be called after the stream has been closed without * generating an <tt>IOException</tt>. */ //关闭 public void close() throws IOException { } }
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