java 字符缓冲流BufferedReader和BufferedWriter

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本节概要:

目录

BufferedReader

BufferedWriter

字符缓冲流复制文本文件:

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BufferedReader

继承自Reader

构造方法:

     private static int defaultCharBufferSize = 8192;
//可以手动设置缓存去char数组的大小public BufferedReader(Reader in, int sz) {super(in);if (sz <= 0)throw new IllegalArgumentException("Buffer size <= 0");this.in = in;cb = new char[sz];nextChar = nChars = 0;}//创建一个char数组,大小为8192,用来缓存public BufferedReader(Reader in) {this(in, defaultCharBufferSize);}

工作过程:使用BufferedReader时,先从Reader对象(FileReader)中读取数据写入到char[],然后从 自身的char数组中访问数据,当char数组的数据被访问完毕,就调用fill()方法重新填充char数组。关闭BufferedReader时,其构造参数的Reader也被关闭

特有方法:

String readLine() 从BufferedReader自身的char数组中读取一行文本,遇到以下字符会认为完成一行的读取,换行('\n'),回车('\r')或者回车后直接换行,返回包含该行内容的字符串,如果达到流末尾,返回null

看下BufferedReader的read方法:read()访问的BufferedReader本身的char数组，当数组的内容被访问完毕时调用调用fill()方法重新填充char数组。

   private Reader in;public int read(char cbuf[], int off, int len) throws IOException {synchronized (lock) {ensureOpen();if ((off < 0) || (off > cbuf.length) || (len < 0) ||((off + len) > cbuf.length) || ((off + len) < 0)) {throw new IndexOutOfBoundsException();} else if (len == 0) {return 0;}int n = read1(cbuf, off, len);if (n <= 0) return n;while ((n < len) && in.ready()) {int n1 = read1(cbuf, off + n, len - n);if (n1 <= 0) break;n += n1;}return n; private int read1(char[] cbuf, int off, int len) throws IOException {if (nextChar >= nChars) {if (len >= cb.length && markedChar <= UNMARKED && !skipLF) {return in.read(cbuf, off, len);}fill();}if (nextChar >= nChars) return -1;if (skipLF) {skipLF = false;if (cb[nextChar] == '\n') {nextChar++;if (nextChar >= nChars)fill();if (nextChar >= nChars)return -1;}}int n = Math.min(len, nChars - nextChar);System.arraycopy(cb, nextChar, cbuf, off, n);nextChar += n;return n;}

BufferedReader示例:

源文件word.txt内容:
好啊
你好
天天
///
import java.io.*;public class BufferedReaderTest01 {public static void main(String[] args){try (BufferedReader br =new BufferedReader(new FileReader("word.txt"));){String s;//每次读取一行,读到末尾处为nullwhile ((s=br.readLine())!=null){System.out.println( s);}} catch (FileNotFoundException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();}}
}
out:
好啊
你好
天天

BufferedWriter

继承自Writer

构造方法:

 private static int defaultCharBufferSize = 8192;
//创建默认8192大小的char数组,用来缓存public BufferedWriter(Writer out) {this(out, defaultCharBufferSize);}
//根据指定大小创建char数组,用来缓存public BufferedWriter(Writer out, int sz) {super(out);if (sz <= 0)throw new IllegalArgumentException("Buffer size <= 0");this.out = out;cb = new char[sz];nChars = sz;nextChar = 0;}

工作工程: BufferedWriter先将数据写入自身的char数组，当调用write方法时,将内容写到自身的char数组,再调用参数Writer对象的write方法从char数组中读取内容写入到文件中

关闭BufferedWriter时,自动关闭作为参数的Writer对象

特有方法:

newLine()换行

write方法,可以写字符串和char数组,可以指定他们的起始位置和长度,看下write的源码:

先将内容保存到自身的char数组中,再访问自身char数组,再将内容写入到文件中

private Writer out;//构造方法中传入的Writer对象
private char cb[];
//调用flushBuffer方法来写
public void write(int c) throws IOException {synchronized (lock) {ensureOpen();if (nextChar >= nChars)flushBuffer();cb[nextChar++] = (char) c;}}
//调用out的write方法,out是创建BufferedWriter对象时,传进来的Writer对象
void flushBuffer() throws IOException {synchronized (lock) {ensureOpen();if (nextChar == 0)return;out.write(cb, 0, nextChar);nextChar = 0;}}

示例:

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;public class BufferedWriterTest01 {public static void main(String[] args){try (BufferedWriter bw=new BufferedWriter(new FileWriter("test\\test6.txt"));){bw.write("我们要加油");bw.newLine();//换行char [] charArr={'我','们','热','爱','祖','国'};bw.write(charArr,0,4);} catch (IOException e) {e.printStackTrace();}}
}
out:
test6.txt的内容为:
我们要加油
我们热爱

字符缓冲流复制文本文件:

import java.io.*;public class FileCopy02 {public static void main(String[] args){try (BufferedReader br=new BufferedReader(new FileReader("word1.txt"));BufferedWriter bw=new BufferedWriter(new FileWriter("test\\test7.txt"));){String s;//通过每次读取一行,提高效率while((s=br.readLine())!=null){bw.write(s);bw.newLine();}} catch (FileNotFoundException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();}}
}
out:
源文件word1.txt内容:
好吗
天天
目标文件test7.txt内容:
好吗
天天

画个示意图:

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