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Java学习-IO流-字节缓冲流

						 IO流体系↙                  ↘字节流 						   字符流↙         ↘                   ↙      ↘InputStream      OutputStream 	 Reader 	 Writer↓                ↓             ↓           ↓
FileInputStream  FileOutputStream  FileReader  FileWriter

FileInputStream、FileOutputStream、FileReader、FileWriter 称之为基本流
高级流：缓冲流、转换流、序列化流、打印流、压缩流、Commons-io
缓冲流：BufferedInputStream、BufferedOutputStream、BufferedReader、BufferedWriter

缓冲流

                       缓冲流↙                  ↘字节缓冲流                 字符缓冲流↙        ↘                ↙        ↘Buffered        Buffered       Buffered      Buffered
InputStream    OutputStream      Reader        Writer
字节缓冲输入流  字节缓冲输出流  字符缓冲输入流  字符缓冲输出流

字节缓冲流

底层自带长度为8192的缓冲区提高性能

public BufferedInputStream(InputStream is)：把基本流包装成高级流，提高读取数据性能
public BufferedOutputStream(OutputStream os)：把基本流包装成高级流，提高写出数据性能

练习：利用字节缓冲流拷贝文件

BufferedInputStream bis = new BufferedInputStream(new FileInputStream("..\\xx.txt"));
BufferedOutputStream bis = new BufferedOutputStream(new FileOutputStream("..\\copy.txt"));
int b;
while((b=bis.read())!=-1){bos.write(b);}
bos.close();
bis.close();

BufferedInputStream 的缓冲区

public BufferedInputStream(InputStream in){this(in,DEFAULT_BUFFER_SIZE);//DEFAULT_BUFFER_SIZE=8192
}

public BufferedInputStream(InputStream in,int size){super(in);if(size<=0){throw new IllegalArgumentException("BUffer size <= 0");}buf = new byte[size];//缓冲区
}

为什么只需关闭高级流，不需要关闭基本流
高级流底层关闭了基本流

public void close() throws IOException{...finally{if(flushException == null){out.close();}//关闭基本流else{try{out.close();}//关闭基本流...}}
}

字节缓冲流拷贝文件（一次读写多个字节）

BufferedInputStream bis = new BufferedInputStream(new FileInputStream("..\\xx.txt"));
BufferedOutputStream bis = new BufferedOutputStream(new FileOutputStream("..\\copy.txt"));
byte[] bytes = new byte[1024];
int len;
while((len=bis.read(bytes))!=-1){bos.write(bytes,0,len);}
bos.close();
bis.close();

字节缓冲流的读写原理

数据源→基本流→缓冲输入流→内存→缓冲输出流→基本流→文件