java基础之java I/O框架(二)

上一篇，主要介绍的是InputStream和OutputStream的功能及其一些具体的实现类。

但是InputStream和OuputStream是都是基于byte来操作的。如果我们需要将Byte转换成Character，这个时候就会面临字符编码的问题。在java 1.0的时候，java只是将 8 bytes转换为 1 character，显然这种做法很不严谨。

因此在java 1.1，引入了Writer和Reader类，这两个类操作的基础是character。每次读取或者写入都是基于character为单元来实现的。并且StringBufferInputStream被弃用。

Reader类及其实现

Reader类实现了Readable的接口。

Readable

int read(CharBuffer cb)
//Attempts to read characters into the specified character buffer.

Reader类的方法与InputStream很相似，所不同的是，Reader读取的单元是char.

abstract void   close()
//Closes the stream and releases any system resources associated with it.
void    mark(int readAheadLimit)
//Marks the present position in the stream.
boolean markSupported()
//Tells whether this stream supports the mark() operation.
int read()
//Reads a single character.
int read(char[] cbuf)
//Reads characters into an array.
abstract int    read(char[] cbuf, int off, int len)
//Reads characters into a portion of an array.
boolean ready()
//Tells whether this stream is ready to be read.
void    reset()
//Resets the stream.
long    skip(long n)
//Skips characters.

Reader类没有了InputStream的available()方法，但是多了一个ready()方法，ready()方法可以判断当前的Reader类是否可读。

InputStreamReader

java 1.0 InputStream与 java 1.1 Reader将如何兼容呢？

InputStreamReader很好的解决了这个问题。InputStreamReader可以将InputStream很好的转换成Reader。

InputStreamReader具有4个构造函数。

InputStreamReader(InputStream in)
//Creates an InputStreamReader that uses the default charset.
InputStreamReader(InputStream in, Charset cs)
//Creates an InputStreamReader that uses the given charset.
InputStreamReader(InputStream in, CharsetDecoder dec)
//Creates an InputStreamReader that uses the given charset decoder.
InputStreamReader(InputStream in, String charsetName)
//Creates an InputStreamReader that uses the named charset.

InputStreamReader还实现了方法获取当前的Encoding：

String  getEncoding()
//Returns the name of the character encoding being used by this stream.

FileReader

FileReader是InputStreamReader的子类，从文件中按字符读取数据。它使用了系统默认的编码。

StringReader

StringReader取代了StringBufferInputStream的功能。它从String中读取字符。

CharArrayReader

CharArrayReader可以从Char数组中读取字符。

BufferedReader

与BufferedInputStream一致，所不同的是BufferedReader内部通过Char数组来实现缓存的。

LineNumberReader

LineNumberReader继承了BufferedReader类，它可以记录当前读取数据所在的行，并且还支持按行读取数据。

int getLineNumber()
//Get the current line number.

String  readLine()
//Read a line of text.

void    setLineNumber(int lineNumber)
//Set the current line number.

FilterReader

FilterReader与FilterInputStream提供了相应的功能。

PushbackReader

与PushbackStream提供了相同的功能。

Writer

Writer实现了Appendable接口，即Writer可以用Formatter交互。关于Formatter类的用法请看我的另一篇博客。

Writer提供了很多方法，向目的地写入数据。

abstract void   close()
//Closes the stream, flushing it first.
abstract void   flush()
//Flushes the stream.
void    write(char[] cbuf)
//Writes an array of characters.
abstract void   write(char[] cbuf, int off, int len)
//Writes a portion of an array of characters.
void    write(int c)
//Writes a single character.
void    write(String str)
//Writes a string.
void    write(String str, int off, int len)
//Writes a portion of a string.

OutputStreamWriter

与Reader很类似，OutputStreamWriter在OutputStream和Writer之间架了一座桥梁。

OutputStreamWriter提供了4个构造函数。

OutputStreamWriter(OutputStream out)
//Creates an OutputStreamWriter that uses the default character encoding.
OutputStreamWriter(OutputStream out, Charset cs)
//Creates an OutputStreamWriter that uses the given charset.
OutputStreamWriter(OutputStream out, CharsetEncoder enc)
//Creates an OutputStreamWriter that uses the given charset encoder.
OutputStreamWriter(OutputStream out, String charsetName)
//Creates an OutputStreamWriter that uses the named charset.

另外它也提供了getEncoding()方法。

String  getEncoding()
//Returns the name of the character encoding being used by this stream.

FileWriter

FileWriter继承了OutputStreamWriter。它可以向文件写入数据，并且它使用的编码是系统默认的编码。

StringWriter

它是提供了将数据写入到String中的功能。它的内部是基于StringBuffer实现的。

另外它还提供了方法getBuffer()将数据转换为StringBuffer。

StringBuffer    getBuffer()
//Return the string buffer itself.

CharArrayWriter

CharArrayWriter可以向Char数组中写入数据。

FilterWriter

FilterWriter与FilterOutputStream相似。

PrintWriter

PrintWriter和PrintStream提供了相同的功能。并且它支持OutputStream作为参数，来构造PrintWriter。PrintWriter是直接继承Writer类的。

PrintWriter(File file)
//Creates a new PrintWriter, without automatic line flushing, with the specified file.
PrintWriter(File file, String csn)
//Creates a new PrintWriter, without automatic line flushing, with the specified file and charset.
PrintWriter(OutputStream out)
//Creates a new PrintWriter, without automatic line flushing, from an existing OutputStream.
PrintWriter(OutputStream out, boolean autoFlush)
//Creates a new PrintWriter from an existing OutputStream.
PrintWriter(String fileName)
//Creates a new PrintWriter, without automatic line flushing, with the specified file name.
PrintWriter(String fileName, String csn)
//Creates a new PrintWriter, without automatic line flushing, with the specified file name and charset.
PrintWriter(Writer out)
//Creates a new PrintWriter, without automatic line flushing.
PrintWriter(Writer out, boolean autoFlush)
//Creates a new PrintWriter.

PrintWriter的其他方法与PrintStream很相似。

PipedReader 和 PipedWriter

这两个类的使用方法同PipedInputStream和PipedOutputStream相同。