JavaIO<14>InputStreamReader和OutputStreamWriter源码分析

InputStreamReader和OutputStreamWriter 是字节流通向字符流的桥梁：它使用指定的 charset 读写字节并将其解码为字符。
InputStreamReader 的作用是将“字节输入流”转换成“字符输入流”。它继承于Reader。

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。