InputStreamReader和OutputStreamWriter是字节流通向字符流的桥梁。它使用指定的差染色体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，继承于Reader。OutputStreamWriter是作用是字节输出流转换成字符输出流，继承于Writer。
InputStreamReader和OutputStreamWriter的示例代码
public class StreamConverter {
private static final String FileName = "file.txt";
private static final String CharsetName = "utf-8";
//private static final String CharsetName = "gb2312";
public static void main(String[] args) {
testWrite();
testRead();
}
/**
* OutputStreamWriter 演示函数
*
*/
private static void testWrite() {
try {
// 创建文件“file.txt”对应File对象
File file = new File(FileName);
// 创建FileOutputStream对应OutputStreamWriter：将字节流转换为字符流，即写入out1的数据会自动由字节转换为字符。
OutputStreamWriter out1 = new OutputStreamWriter(new FileOutputStream(file), CharsetName);
// 写入10个汉字
out1.write("字节流转为字符流示例");
// 向“文件中”写入"0123456789"+换行符
out1.write("0123456789\n");
out1.close();
} catch(IOException e) {
e.printStackTrace();
}
}
/**
* InputStreamReader 演示程序
*/
private static void testRead() {
try {
// 方法1：新建FileInputStream对象
// 新建文件“file.txt”对应File对象
File file = new File(FileName);
InputStreamReader in1 = new InputStreamReader(new FileInputStream(file), CharsetName);
// 测试read()，从中读取一个字符
char c1 = (char)in1.read();
System.out.println("c1="+c1);
// 测试skip(long byteCount)，跳过4个字符
in1.skip(6);
// 测试read(char[] cbuf, int off, int len)
char[] buf = new char[10];
in1.read(buf, 0, buf.length);
System.out.println("buf="+(new String(buf)));
in1.close();
} catch(IOException e) {
e.printStackTrace();
}
}
}
运行结果：
c1=字
buf=流示例0123456
基于JDK8的InputStreamReader的源码：
public class InputStreamReader extends Reader {
private final StreamDecoder sd;
//构造函数，使用平台默认的字符类型
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);
}
}
/**
* Creates an InputStreamReader that uses the named charset.
*
* @param in
* An InputStream
*
* @param charsetName
* The name of a supported
* {@link java.nio.charset.Charset charset}
*
* @exception UnsupportedEncodingException
* If the named charset is not supported
*/
//构造函数，使用提供的字符类型
public InputStreamReader(InputStream in, String charsetName)throws UnsupportedEncodingException
{
super(in);
if (charsetName == null)
throw new NullPointerException("charsetName");
sd = StreamDecoder.forInputStreamReader(in, this, charsetName);
}
//构造函数，使用提供的字符类型
public InputStreamReader(InputStream in, Charset cs) {
super(in);
if (cs == null)
throw new NullPointerException("charset");
sd = StreamDecoder.forInputStreamReader(in, this, cs);
}
//使用提供的字符译码器
public InputStreamReader(InputStream in, CharsetDecoder dec) {
super(in);
if (dec == null)
throw new NullPointerException("charset decoder");
sd = StreamDecoder.forInputStreamReader(in, this, dec);
}
//返回字符编码
public String getEncoding() {
return sd.getEncoding();
}
//读单个字符
public int read() throws IOException {
return sd.read();
}
//读字符到cbuf中
public int read(char cbuf[], int offset, int length) throws IOException {
return sd.read(cbuf, offset, length);
}
//是否准备好读
public boolean ready() throws IOException {
return sd.ready();
}
//关闭资源
public void close() throws IOException {
sd.close();
}
}
基于JDK8的OutputStreamWriter的源码：
public class OutputStreamWriter extends Writer {
private final StreamEncoder se;
//构造函数，使用被命名的字符集
public OutputStreamWriter(OutputStream out, String charsetName)throws UnsupportedEncodingException
{
super(out);
if (charsetName == null)
throw new NullPointerException("charsetName");
se = StreamEncoder.forOutputStreamWriter(out, this, charsetName);
}
//构造函数，使用系统默认的字符集
public OutputStreamWriter(OutputStream out) {
super(out);
try {
se = StreamEncoder.forOutputStreamWriter(out, this, (String)null);
} catch (UnsupportedEncodingException e) {
throw new Error(e);
}
}
//构造函数，使用给定的字符集
public OutputStreamWriter(OutputStream out, Charset cs) {
super(out);
if (cs == null)
throw new NullPointerException("charset");
se = StreamEncoder.forOutputStreamWriter(out, this, cs);
}
//构造函数，使用给定的字符编码器
public OutputStreamWriter(OutputStream out, CharsetEncoder enc) {
super(out);
if (enc == null)
throw new NullPointerException("charset encoder");
se = StreamEncoder.forOutputStreamWriter(out, this, enc);
}
//获得编码器
public String getEncoding() {
return se.getEncoding();
}
//刷新缓冲区，
void flushBuffer() throws IOException {
se.flushBuffer();
}
//写单个字符
public void write(int c) throws IOException {
se.write(c);
}
//写字符数组的一部分
public void write(char cbuf[], int off, int len) throws IOException {
se.write(cbuf, off, len);
}
//写字符串的一部分
public void write(String str, int off, int len) throws IOException {
se.write(str, off, len);
}
//刷新流
public void flush() throws IOException {
se.flush();
}
//关闭资源
public void close() throws IOException {
se.close();
}
}