JAVA IO 之BufferedInputStream BufferedOutputStream
有时间整理一下fill方法，并且把BufferedOutputStream源码解释翻译一下
1 BufferedInputStream
BufferedInputStream为另一个输入流添加一些功能，即缓冲输入以及支持mark和reset方法，在创建BufferedInputStream时会创建一个内部缓冲区数组。在读取或跳过流中的字节时，可根据需要从包含的输入流再次填充该内部缓冲区。一次填充多个字节。mark操作记录输入流中的某个节点，reset操作使得从包含的输入流中获取新字节之前，再次读取自最后一次mark操作后读取的所有字节。
主要字段：
protected byte[] buf;//存储数据的内部缓冲区数组
protected int count;//缓冲区中有效字节的个数
protected int marklimit;//调用mark方法后,在后续调用reset方法失败之前允许的最大提前读取量
protected int markpos;//最后一次调用mark方法时pos字段的值
protected int pos;//缓冲区中的当前位置
构造方法：
BufferedInputStream(InputStream in)
创建一个BufferedInputStream并保存其参数,即输入流in,以便将来使用。
BufferedInputStream(InputStream in,int size)
创建具有指定缓冲区大小的BufferedInputStream并保存其参数,即输入流in,以便将来使用。
主要方法：
int available(): 返回缓存字节输入流中可读取的字节数
void close(): 关闭此缓存字节输入流并释放与该流有关的系统资源.
void mark(int readlimit): 在流中标记位置
boolean markSupported(): 测试该输入流是否支持mark和reset方法
int read(): 从缓冲输入流中读取一个字节数据
int read(byte[] b,int off,int len): 从缓冲输入流中将最多len个字节的数据读入到字节数组b中
long skip(long n): 从缓冲输入流中跳过并丢弃n个字节的数据
BufferedInputStream的作用就是为其他输入流提供缓冲服务功能。创建BufferedInputSteam时我们会通过它的构造函数指定某个输入流作为参数，BufferedInputStream缓冲字节输入流。它作为FilterInputStream的一个子类，为传入的底层字节输入流提供缓冲功能，通过底层字节输入流读取字节 到自己的buffer中（内置的缓存字节数组），然后程序调用BufferedInputStream的read方法将buffer中的字节读取到程序中，当buffer中的字节被读取完之后，BufferedInputStream会从in中读取下一批数据块到buffer中，直到in中的数据被读取完毕，这样做的好处是提高读取的效率和减少打开存储介质的链接次数。
2 BufferedOutputStream
在BufferedOutputStream内部也提供了一个缓冲区，当缓冲区中的数据满了以后或者直接调用flush()方法就会把缓冲区中的数据写入到输出流。BufferedOutputStream比较简单直接看源码如下：
package java.io;
/**
* The class implements a buffered output stream. By setting up such
* an output stream, an application can write bytes to the underlying
* output stream without necessarily causing a call to the underlying
* system for each byte written.
*
* @author Arthur van Hoff
* @since JDK1.0
*/
public
class BufferedOutputStream extends FilterOutputStream {
/**
* The internal buffer where data is stored.
*/
protected byte buf[];
/**
* The number of valid bytes in the buffer. This value is always
* in the range <tt>0</tt> through <tt>buf.length</tt>; elements
* <tt>buf[0]</tt> through <tt>buf[count-1]</tt> contain valid
* byte data.
*/
protected int count;
/**
* Creates a new buffered output stream to write data to the
* specified underlying output stream.
*
* @param out the underlying output stream.
*/
public BufferedOutputStream(OutputStream out) {
this(out, 8192);
}
/**
* Creates a new buffered output stream to write data to the
* specified underlying output stream with the specified buffer
* size.
*
* @param out the underlying output stream.
* @param size the buffer size.
* @exception IllegalArgumentException if size <= 0.
*/
public BufferedOutputStream(OutputStream out, int size) {
super(out);
if (size <= 0) {
throw new IllegalArgumentException("Buffer size <= 0");
}
buf = new byte[size];
}
/** Flush the internal buffer */
private void flushBuffer() throws IOException {
if (count > 0) {
out.write(buf, 0, count);
count = 0;
}
}
/**
* Writes the specified byte to this buffered output stream.
*
* @param b the byte to be written.
* @exception IOException if an I/O error occurs.
*/
public synchronized void write(int b) throws IOException {
if (count >= buf.length) {
flushBuffer();
}
buf[count++] = (byte)b;
}
/**
* Writes <code>len</code> bytes from the specified byte array
* starting at offset <code>off</code> to this buffered output stream.
*
* <p> Ordinarily this method stores bytes from the given array into this
* stream's buffer, flushing the buffer to the underlying output stream as
* needed. If the requested length is at least as large as this stream's
* buffer, however, then this method will flush the buffer and write the
* bytes directly to the underlying output stream. Thus redundant
* <code>BufferedOutputStream</code>s will not copy data unnecessarily.
*
* @param b the data.
* @param off the start offset in the data.
* @param len the number of bytes to write.
* @exception IOException if an I/O error occurs.
*/
public synchronized void write(byte b[], int off, int len) throws IOException {
if (len >= buf.length) {
/* If the request length exceeds the size of the output buffer,
flush the output buffer and then write the data directly.
In this way buffered streams will cascade harmlessly. */
flushBuffer();
out.write(b, off, len);
return;
}
if (len > buf.length - count) {
flushBuffer();
}
System.arraycopy(b, off, buf, count, len);
count += len;
}
/**
* Flushes this buffered output stream. This forces any buffered
* output bytes to be written out to the underlying output stream.
*
* @exception IOException if an I/O error occurs.
* @see java.io.FilterOutputStream#out
*/
public synchronized void flush() throws IOException {
flushBuffer();
out.flush();
}
}
