2019独角兽企业重金招聘Python工程师标准>>> 
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);
}
}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。