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Java中的InputStreamReader和OutputStreamWriter源码

Java中的InputStreamReader和OutputStreamWriter源码 1. InputStreamReader 源码(基于jdk1....

Java中的InputStreamReader和OutputStreamWriter源码

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
");
    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:

c1=字
buf=流示例0123456

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。

生成的文件utf-8的file.txt的16进制效果图如下:

Java中的InputStreamReader和OutputStreamWriter源码

将StreamConverter.java中的CharsetName修改为"gb2312"。运行程序,生产的file.txt的16进制效果图如下: