BufferReader与BufferWriter简介
BufferReader与BufferWriter自JDK1.1就已经存在了.
BufferReader的作用是从字符输入流读取文本字符到字符缓冲区中,以便提供对字符、数组和行的高效读取.
BufferWriter的作用是将文本写入字符输出流到字符缓冲区,以便提供对单个字符、数组和字符串的有效写入.
在操作文件时,为了获得最高效率,一般考虑在BufferReader,BufferedWriter中包装OutputStreamWriter,以避免频繁调用字符编码器StreamEncoder的implWrite方法
BufferWriter类中的方法如下
BufferReader类中的方法如下
查看源码可知,BufferReader与BufferWriter默认的字符缓冲区(defaultCharBufferSize )的大小均为8192个字符,一个字符占用两个字节的空间,所以缓冲区的大小是16kb.
BufferWriter类的基本属性如下所示:
//字符输出流privateWriter out;//字符缓冲区privatechar cb[];//设置的字符缓冲区大小变量privateint nChars;//字符缓冲区中的已存储元素的位置privateint nextChar;//默认字符缓冲区大小privatestaticint defaultCharBufferSize=8192;//行分割字符串privateString lineSeparator;
1.使用BufferWriter写入BufferReader读入的数据示列:
publicstaticvoidmain(String[] args){String inPath="F:\\io_test_file\\test.txt";String outPath="F:\\io_test_file\\mean.txt";try(BufferedReader bufferedReader=newBufferedReader(newInputStreamReader(newFileInputStream(inPath),"UTF-8"));BufferedWriter bufferedWriter=newBufferedWriter(newOutputStreamWriter(newFileOutputStream(outPath),"UTF-8"))){String line=null;LocalDateTime starTime=LocalDateTime.now();while((line= bufferedReader.readLine())!=null){
bufferedWriter.write(line);
bufferedWriter.flush();}System.out.println("耗时:"+Duration.between(starTime,LocalDateTime.now()).toMillis());}catch(Exception e){
e.printStackTrace();}}
读取的文本文件test.txt的大小是1139kb
,但是上面程序执行结果输出的mean.txt的大小是1120kb
,原因是如果没有调用newLine()方法,默认是写满文本一行的空间大小后,再换行追加写入,所以,是少了每一行的\r\n
两个字符,各占两个字节,共四个字节,即一行会少四个字节大小的空间.
2.然后我验证了一下,在write(line)
方法中拼接\r\n
进行写入后,发现mean.txt文本的大小与test.txt的文本大小一致了.
publicstaticvoidmain(String[] args){String inPath="F:\\io_test_file\\test.txt";String outPath="F:\\io_test_file\\mean.txt";try(BufferedReader bufferedReader=newBufferedReader(newInputStreamReader(newFileInputStream(inPath),"UTF-8"));BufferedWriter bufferedWriter=newBufferedWriter(newOutputStreamWriter(newFileOutputStream(outPath),"UTF-8"))){String line=null;LocalDateTime starTime=LocalDateTime.now();while((line= bufferedReader.readLine())!=null){
bufferedWriter.write(line+"\r\n");
bufferedWriter.flush();}System.out.println("耗时:"+Duration.between(starTime,LocalDateTime.now()).toMillis());}catch(Exception e){
e.printStackTrace();}}
3.再去掉2中拼接的\r\n
后,在写入方法write(line)
方法的后面调用BufferWrite()的newLine()
方法,得到的mean.txt文本的大小也与test.txt文本的大小一致.
publicstaticvoidmain(String[] args){String inPath="F:\\io_test_file\\test.txt";String outPath="F:\\io_test_file\\mean.txt";try(BufferedReader bufferedReader=newBufferedReader(newInputStreamReader(newFileInputStream(inPath),"UTF-8"));BufferedWriter bufferedWriter=newBufferedWriter(newOutputStreamWriter(newFileOutputStream(outPath),"UTF-8"))){String line=null;LocalDateTime starTime=LocalDateTime.now();while((line= bufferedReader.readLine())!=null){
bufferedWriter.write(line);
bufferedWriter.newLine();
bufferedWriter.flush();}System.out.println("耗时:"+Duration.between(starTime,LocalDateTime.now()).toMillis());}catch(Exception e){
e.printStackTrace();}}
注:实例采用的是字符流的方式读入写入的方式,对于文本文件是不存在文件读写出错的,一旦采用上面的字符读写方式区操作word就不行了,有两个原因,一个是word的编码是UTF-16,二是处理要求二进制格式,就不可能用字符流而必须是字节流。