Java中的InputStreamReader和OutputStreamWriter源码分析_动力节点Java学院整理

程序员文章站 2024-02-23 09:00:10

inputstreamreader和outputstreamwriter源码分析 1. inputstreamreader 源码(基于jdk1.7.40)...

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

inputstreamreader和outputstreamwriter的使用示例，参考源码(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 测试程序
 *
 * 
 */
 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out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
   out.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 in = 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)));
    in.close();
   } catch(ioexception e) {
    e.printstacktrace();
   }
  }
 }

运行结果：