Java IO体系之InputStreamReader

叁歲伎倆 2022-03-06 01:12 233阅读 0赞

## 介绍 ##

>  *  字符输入流Reader的实现类
>  *  [Java IO体系之Reader][Java IO_Reader]

## 继承关系图 ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3RoZWJpZ2RpcHBlcmJkeA_size_16_color_FFFFFF_t_70]

## 源码 ##

package java.io;
    
    import java.nio.charset.Charset;
    import java.nio.charset.CharsetDecoder;
    import sun.nio.cs.StreamDecoder;
    
    
    public class InputStreamReader extends Reader { 
    
        private final StreamDecoder sd;
    
        /** * Creates an InputStreamReader that uses the default charset. * @param in An InputStream */
        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. */
        public InputStreamReader(InputStream in, String charsetName)
            throws UnsupportedEncodingException
        { 
            super(in);
            if (charsetName == null)
                throw new NullPointerException("charsetName");
            sd = StreamDecoder.forInputStreamReader(in, this, charsetName);
        }
    
        /** * Creates an InputStreamReader that uses the given charset. */
        public InputStreamReader(InputStream in, Charset cs) { 
            super(in);
            if (cs == null)
                throw new NullPointerException("charset");
            sd = StreamDecoder.forInputStreamReader(in, this, cs);
        }
    
        /** * Creates an InputStreamReader that uses the given charset decoder. */
        public InputStreamReader(InputStream in, CharsetDecoder dec) { 
            super(in);
            if (dec == null)
                throw new NullPointerException("charset decoder");
            sd = StreamDecoder.forInputStreamReader(in, this, dec);
        }
    
        /** * Returns the name of the character encoding being used by this stream. * * <p> If the encoding has an historical name then that name is returned; * otherwise the encoding's canonical name is returned. * * <p> If this instance was created with the {@link * #InputStreamReader(InputStream, String)} constructor then the returned * name, being unique for the encoding, may differ from the name passed to * the constructor. This method will return <code>null</code> if the * stream has been closed. * </p> * @return The historical name of this encoding, or * <code>null</code> if the stream has been closed * * @see java.nio.charset.Charset * * @revised 1.4 * @spec JSR-51 */
        public String getEncoding() { 
            return sd.getEncoding();
        }
    
        /** * Reads a single character. * * @return The character read, or -1 if the end of the stream has been * reached * * @exception IOException If an I/O error occurs */
        public int read() throws IOException { 
            return sd.read();
        }
    
        /** * Reads characters into a portion of an array. * * @param cbuf Destination buffer * @param offset Offset at which to start storing characters * @param length Maximum number of characters to read * * @return The number of characters read, or -1 if the end of the * stream has been reached * * @exception IOException If an I/O error occurs */
        public int read(char cbuf[], int offset, int length) throws IOException { 
            return sd.read(cbuf, offset, length);
        }
    
        /** * Tells whether this stream is ready to be read. An InputStreamReader is * ready if its input buffer is not empty, or if bytes are available to be * read from the underlying byte stream. * * @exception IOException If an I/O error occurs */
        public boolean ready() throws IOException { 
            return sd.ready();
        }
    
        public void close() throws IOException { 
            sd.close();
        }
    }

## FileReader源码 ##

package java.io;
    
    /** * Convenience class for reading character files. The constructors of this * class assume that the default character encoding and the default byte-buffer * size are appropriate. To specify these values yourself, construct an * InputStreamReader on a FileInputStream. * * <p><code>FileReader</code> is meant for reading streams of characters. * For reading streams of raw bytes, consider using a * <code>FileInputStream</code>. * * @see InputStreamReader * @see FileInputStream * * @author Mark Reinhold * @since JDK1.1 */
    public class FileReader extends InputStreamReader { 
    
       /** * Creates a new <tt>FileReader</tt>, given the name of the * file to read from. * * @param fileName the name of the file to read from * @exception FileNotFoundException if the named file does not exist, * is a directory rather than a regular file, * or for some other reason cannot be opened for * reading. */
        public FileReader(String fileName) throws FileNotFoundException { 
            super(new FileInputStream(fileName));
        }
    
       /** * Creates a new <tt>FileReader</tt>, given the <tt>File</tt> * to read from. * * @param file the <tt>File</tt> to read from * @exception FileNotFoundException if the file does not exist, * is a directory rather than a regular file, * or for some other reason cannot be opened for * reading. */
        public FileReader(File file) throws FileNotFoundException { 
            super(new FileInputStream(file));
        }
    
       /** * Creates a new <tt>FileReader</tt>, given the * <tt>FileDescriptor</tt> to read from. * * @param fd the FileDescriptor to read from */
        public FileReader(FileDescriptor fd) { 
            super(new FileInputStream(fd));
        }
    
    }

[Java IO_Reader]: https://blog.csdn.net/thebigdipperbdx/article/details/80954751
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