OutputStreamWriter 的作用是将“字节输出流”转换成“字符输出流”。它继承于Writer。
InputStreamReader和OutputStreamWriter源码分析
1. InputStreamReader 源码(基于jdk1.7.40)
package java.io; import java.nio.charset.Charset; import java.nio.charset.CharsetDecoder; import sun.nio.cs.StreamDecoder; // 将“字节输入流”转换成“字符输入流” public class InputStreamReader extends Reader { private final StreamDecoder sd; // 根据in创建InputStreamReader，使用默认的编码 public InputStreamReader(InputStream in) { super(in); try { sd = StreamDecoder.forInputStreamReader(in, this, (String)null); // ## check lock object } catch (UnsupportedEncodingException e) { // The default encoding should always be available throw new Error(e); } } // 根据in创建InputStreamReader，使用编码charsetName(编码名) public InputStreamReader(InputStream in, String charsetName) throws UnsupportedEncodingException { super(in); if (charsetName == null) throw new NullPointerException("charsetName"); sd = StreamDecoder.forInputStreamReader(in, this, charsetName); } // 根据in创建InputStreamReader，使用编码cs public InputStreamReader(InputStream in, Charset cs) { super(in); if (cs == null) throw new NullPointerException("charset"); sd = StreamDecoder.forInputStreamReader(in, this, cs); } // 根据in创建InputStreamReader，使用解码器dec public InputStreamReader(InputStream in, CharsetDecoder dec) { super(in); if (dec == null) throw new NullPointerException("charset decoder"); sd = StreamDecoder.forInputStreamReader(in, this, dec); } // 获取解码器 public String getEncoding() { return sd.getEncoding(); } // 读取并返回一个字符 public int read() throws IOException { return sd.read(); } // 将InputStreamReader中的数据写入cbuf中，从cbuf的offset位置开始写入，写入长度是length public int read(char cbuf[], int offset, int length) throws IOException { return sd.read(cbuf, offset, length); } // 能否从InputStreamReader中读取数据 public boolean ready() throws IOException { return sd.ready(); } // 关闭InputStreamReader public void close() throws IOException { sd.close(); } } 2. OutputStreamWriter 源码(基于jdk1.7.40)
package java.io; import java.nio.charset.Charset; import java.nio.charset.CharsetEncoder; import sun.nio.cs.StreamEncoder; // 将“字节输出流”转换成“字符输出流” public class OutputStreamWriter extends Writer { private final StreamEncoder se; // 根据out创建OutputStreamWriter，使用编码charsetName(编码名) public OutputStreamWriter(OutputStream out, String charsetName) throws UnsupportedEncodingException { super(out); if (charsetName == null) throw new NullPointerException("charsetName"); se = StreamEncoder.forOutputStreamWriter(out, this, charsetName); } // 根据out创建OutputStreamWriter，使用默认的编码 public OutputStreamWriter(OutputStream out) { super(out); try { se = StreamEncoder.forOutputStreamWriter(out, this, (String)null); } catch (UnsupportedEncodingException e) { throw new Error(e); } } // 根据out创建OutputStreamWriter，使用编码cs public OutputStreamWriter(OutputStream out, Charset cs) { super(out); if (cs == null) throw new NullPointerException("charset"); se = StreamEncoder.forOutputStreamWriter(out, this, cs); } // 根据out创建OutputStreamWriter，使用编码器enc public OutputStreamWriter(OutputStream out, CharsetEncoder enc) { super(out); if (enc == null) throw new NullPointerException("charset encoder"); se = StreamEncoder.forOutputStreamWriter(out, this, enc); }java io系列01之 "目录" // 获取编码器enc public String getEncoding() { return se.getEncoding(); } // 刷新缓冲区 void flushBuffer() throws IOException { se.flushBuffer(); } // 将单个字符写入到OutputStreamWriter中 public void write(int c) throws IOException { se.write(c); } // 将字符数组cbuf从off开始的数据写入到OutputStreamWriter中，写入长度是len public void write(char cbuf[], int off, int len) throws IOException { se.write(cbuf, off, len); } // 将字符串str从off开始的数据写入到OutputStreamWriter中，写入长度是len public void write(String str, int off, int len) throws IOException { se.write(str, off, len); }java io系列01之 "目录" // 刷新“输出流” // 它与flushBuffer()的区别是：flushBuffer()只会刷新缓冲，而flush()是刷新流，flush()包括了flushBuffer。 public void flush() throws IOException { se.flush(); } // 关闭“输出流” public void close() throws IOException { se.close(); } } 说明：
OutputStreamWriter 作用和原理都比较简单。
作用就是将“字节输出流”转换成“字符输出流”。它的原理是，我们创建“字符输出流”对象时，会指定“字节输出流”以及“字符编码”示例程序
package org.credo.jdk.io;import java.io.File;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStreamReader;import java.io.OutputStreamWriter;import java.io.UnsupportedEncodingException;public class StreamConverterTest{ private static final String FileName = "file.txt"; private static final String CharsetName = "utf-8"; public static void main(String[] args) throws IOException { testWrite(); testRead(); } private static void testWrite() throws IOException { File file=new File(FileName); OutputStreamWriter outputStreamWriter=new OutputStreamWriter(new FileOutputStream(file), CharsetName); outputStreamWriter.write("中国人民站起来啦!"); outputStreamWriter.write("gogogo!\n"); outputStreamWriter.close(); } private static void testRead() throws IOException { File file = new File(FileName); InputStreamReader inputStreamReader=new InputStreamReader(new FileInputStream(file), CharsetName); char temp=(char) inputStreamReader.read(); System.out.println(temp+""+inputStreamReader.read()); inputStreamReader.skip(5); if(!inputStreamReader.markSupported()){ System.out.println("不支持mark"); } char[] buf = new char[2]; inputStreamReader.read(buf, 0, buf.length); System.out.println("buf="+(new String(buf))); System.out.println("temp3:"+(char)inputStreamReader.read());// inputStreamReader.reset();// char temp2=(char) inputStreamReader.read();// System.out.println(temp2); }} 中22269 不支持mark buf=啦! temp3:g
结果说明：
(01) testWrite() 的作用是将“内容写入到输出流”。写入的时候，会将写入的内容转换utf-8编码并写入。(02) testRead() 的作用是将“内容读取到输入流”。读取的时候，会将内容转换成utf-8的内容转换成字节并读出来。