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Java中的InputStreamReader和OutputStreamWriter源碼分析_動力節(jié)點(diǎn)Java學(xué)院整理

更新時(shí)間：2017年05月18日 10:03:16 投稿：mrr

本文通過示例代碼給大家解析了Java中的InputStreamReader和OutputStreamWriter知識，需要的的朋友參考下吧

InputStreamReader和OutputStreamWriter源碼分析

1. InputStreamReader 源碼(基于jdk1.7.40)

package java.io;
 import java.nio.charset.Charset;
 import java.nio.charset.CharsetDecoder;
 import sun.nio.cs.StreamDecoder;
 // 將“字節(jié)輸入流”轉(zhuǎn)換成“字符輸入流”
 public class InputStreamReader extends Reader {
  private final StreamDecoder sd;
  // 根據(jù)in創(chuàng)建InputStreamReader，使用默認(rèn)的編碼
  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);
   }
  }
  // 根據(jù)in創(chuàng)建InputStreamReader，使用編碼charsetName(編碼名)
  public InputStreamReader(InputStream in, String charsetName)
   throws UnsupportedEncodingException
  {
   super(in);
   if (charsetName == null)
    throw new NullPointerException("charsetName");
   sd = StreamDecoder.forInputStreamReader(in, this, charsetName);
  }
  // 根據(jù)in創(chuàng)建InputStreamReader，使用編碼cs
  public InputStreamReader(InputStream in, Charset cs) {
   super(in);
   if (cs == null)
    throw new NullPointerException("charset");
   sd = StreamDecoder.forInputStreamReader(in, this, cs);
  }
  // 根據(jù)in創(chuàng)建InputStreamReader，使用解碼器dec
  public InputStreamReader(InputStream in, CharsetDecoder dec) {
   super(in);
   if (dec == null)
    throw new NullPointerException("charset decoder");
   sd = StreamDecoder.forInputStreamReader(in, this, dec);
  }
  // 獲取解碼器
  public String getEncoding() {
   return sd.getEncoding();
  }
  // 讀取并返回一個(gè)字符
  public int read() throws IOException {
   return sd.read();
  }
  // 將InputStreamReader中的數(shù)據(jù)寫入cbuf中，從cbuf的offset位置開始寫入，寫入長度是length
  public int read(char cbuf[], int offset, int length) throws IOException {
   return sd.read(cbuf, offset, length);
  }
  // 能否從InputStreamReader中讀取數(shù)據(jù)
  public boolean ready() throws IOException {
   return sd.ready();
  }
  // 關(guān)閉InputStreamReader
  public void close() throws IOException {
   sd.close();
  }
 }

2. OutputStreamWriter 源碼(基于jdk1.7.40)

package java.io;
 import java.nio.charset.Charset;
 import java.nio.charset.CharsetEncoder;
 import sun.nio.cs.StreamEncoder;
 // 將“字節(jié)輸出流”轉(zhuǎn)換成“字符輸出流”
 public class OutputStreamWriter extends Writer {
  private final StreamEncoder se;
  // 根據(jù)out創(chuàng)建OutputStreamWriter，使用編碼charsetName(編碼名)
  public OutputStreamWriter(OutputStream out, String charsetName)
   throws UnsupportedEncodingException
  {
   super(out);
   if (charsetName == null)
    throw new NullPointerException("charsetName");
   se = StreamEncoder.forOutputStreamWriter(out, this, charsetName);
  }
  // 根據(jù)out創(chuàng)建OutputStreamWriter，使用默認(rèn)的編碼
  public OutputStreamWriter(OutputStream out) {
   super(out);
   try {
    se = StreamEncoder.forOutputStreamWriter(out, this, (String)null);
   } catch (UnsupportedEncodingException e) {
    throw new Error(e);
   }
  }
  // 根據(jù)out創(chuàng)建OutputStreamWriter，使用編碼cs
  public OutputStreamWriter(OutputStream out, Charset cs) {
   super(out);
   if (cs == null)
    throw new NullPointerException("charset");
   se = StreamEncoder.forOutputStreamWriter(out, this, cs);
  }
  // 根據(jù)out創(chuàng)建OutputStreamWriter，使用編碼器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 "目錄"
  // 獲取編碼器enc
  public String getEncoding() {
   return se.getEncoding();
  }
  // 刷新緩沖區(qū)
  void flushBuffer() throws IOException {
   se.flushBuffer();
  }
  // 將單個(gè)字符寫入到OutputStreamWriter中
  public void write(int c) throws IOException {
   se.write(c);
  }
  // 將字符數(shù)組cbuf從off開始的數(shù)據(jù)寫入到OutputStreamWriter中，寫入長度是len
  public void write(char cbuf[], int off, int len) throws IOException {
   se.write(cbuf, off, len);
  }
  // 將字符串str從off開始的數(shù)據(jù)寫入到OutputStreamWriter中，寫入長度是len
  public void write(String str, int off, int len) throws IOException {
   se.write(str, off, len);
 }java io系列01之 "目錄"
  // 刷新“輸出流”
  // 它與flushBuffer()的區(qū)別是：flushBuffer()只會刷新緩沖，而flush()是刷新流，flush()包括了flushBuffer。
  public void flush() throws IOException {
   se.flush();
  }
  // 關(guān)閉“輸出流”
  public void close() throws IOException {
   se.close();
  }
 }

說明：

OutputStreamWriter 作用和原理都比較簡單。

作用就是將“字節(jié)輸出流”轉(zhuǎn)換成“字符輸出流”。它的原理是，我們創(chuàng)建“字符輸出流”對象時(shí)，會指定“字節(jié)輸出流”以及“字符編碼”。

示例程序

InputStreamReader和OutputStreamWriter的使用示例，參考源碼(StreamConverter.java)：

 import java.io.File;
 import java.io.FileInputStream;
 import java.io.FileOutputStream;
 import java.io.OutputStreamWriter;;
 import java.io.InputStreamReader;
 import java.io.IOException;
 /**
 * InputStreamReader 和 OutputStreamWriter 測試程序
 *
 * 
 */
 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 演示函數(shù)
  *
  */
  private static void testWrite() {
   try {
    // 創(chuàng)建文件“file.txt”對應(yīng)File對象
    File file = new File(FileName);
    // 創(chuàng)建FileOutputStream對應(yīng)OutputStreamWriter：將字節(jié)流轉(zhuǎn)換為字符流，即寫入out的數(shù)據(jù)會自動由字節(jié)轉(zhuǎn)換為字符。
    OutputStreamWriter out1 = new OutputStreamWriter(new FileOutputStream(file), CharsetName);
   // 寫入10個(gè)漢字
   out.write("字節(jié)流轉(zhuǎn)為字符流示例");
   // 向“文件中”寫入"0123456789"+換行符
    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對象
   // 新建文件“file.txt”對應(yīng)File對象
    File file = new File(FileName);
    InputStreamReader in = new InputStreamReader(new FileInputStream(file), CharsetName);
    // 測試read()，從中讀取一個(gè)字符
   char c1 = (char)in1.read();
    System.out.println("c1="+c1);
   // 測試skip(long byteCount)，跳過4個(gè)字符
   in1.skip(6);
    // 測試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)));
    in.close();
   } catch(IOException e) {
    e.printStackTrace();
   }
  }
 }

運(yùn)行結(jié)果：