InputStreamReader 源码分析

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InputStreamReader在字节流和字符流之间架起了桥梁。能够读取字节数组并使用指定的字符集解码成字符流。

每次调用InputStreamReader的read方法会从底层字节流读取一个或多个字节。为了确保有效的转换，可能会从底层流中读取更多的字节。

为了提高性能，可以考虑结合BufferedReader使用：
BufferedReader in = new BufferedReader(new InputStreamReader(System.in));

public class InputStreamReader extends Reader {    // 流解码类，所有的调用都是交给它完成。  private final StreamDecoder sd;  // 使用默认的字符集名来创建实例  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);  }  }    // 根据指定的字符集名来创建实例  public InputStreamReader(InputStream in, String charsetName)  throws UnsupportedEncodingException  {  super(in);  if (charsetName == null)  throw new NullPointerException("charsetName");  sd = StreamDecoder.forInputStreamReader(in, this, charsetName);  }  // 根据指定的字符集来创建实例  public InputStreamReader(InputStream in, Charset cs) {  super(in);  if (cs == null)  throw new NullPointerException("charset");  sd = StreamDecoder.forInputStreamReader(in, this, cs);  }  // 根据指定的字符集解码器来创建实例  public InputStreamReader(InputStream in, CharsetDecoder dec) {  super(in);  if (dec == null)  throw new NullPointerException("charset decoder");  sd = StreamDecoder.forInputStreamReader(in, this, dec);  }  // 获取该流使用的字符编码名  public String getEncoding() {  return sd.getEncoding();  }  // 读取一个字符  public int read() throws IOException {  return sd.read();  }  // 读取一串字符到字符数组中  public int read(char cbuf[], int offset, int length) throws IOException {  return sd.read(cbuf, offset, length);  }  // 查看流是否准备好用于读取。  public boolean ready() throws IOException {  return sd.ready();  }  // 关闭Reader  public void close() throws IOException {  sd.close();  }}