package java.io;

interface有Closeable、Flushable

abstract class 有InputStream、OutputStream、Reader、Writer

class有InputStreamReader、OutputStreamWriter，FileReader、FileWriter

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InputStream是所有字節輸入流的父類

package java.io;/*** This abstract class is the superclass of all classes representing* an input stream of bytes.** <p> Applications that need to define a subclass of <code>InputStream</code>* must always provide a method that returns the next byte of input.** @author Arthur van Hoff* @see java.io.BufferedInputStream* @see java.io.ByteArrayInputStream* @see java.io.DataInputStream* @see java.io.FilterInputStream* @see java.io.InputStream#read()* @see java.io.OutputStream* @see java.io.PushbackInputStream* @since JDK1.0*/ public abstract class InputStream implements Closeable {

內部有一個抽象函數。read方法會阻塞，除非：1輸入數據可獲得，2流讀完了，3發生io異常。read的返回值是一個0-255的int，表示一個byte

/*** Reads the next byte of data from the input stream. The value byte is* returned as an <code>int</code> in the range <code>0</code> to* <code>255</code>. If no byte is available because the end of the stream* has been reached, the value <code>-1</code> is returned. This method* blocks until input data is available, the end of the stream is detected,* or an exception is thrown.** <p> A subclass must provide an implementation of this method.** @return the next byte of data, or <code>-1</code> if the end of the* stream is reached.* @exception IOException if an I/O error occurs.*/public abstract int read() throws IOException;

對應的，OutputStream是字節輸出流的父類，有一個write抽象函數。參數int中的低8位會被寫入輸出流，高24位會被忽略。

/*** Writes the specified byte to this output stream. The general* contract for <code>write</code> is that one byte is written* to the output stream. The byte to be written is the eight* low-order bits of the argument <code>b</code>. The 24* high-order bits of <code>b</code> are ignored.* <p>* Subclasses of <code>OutputStream</code> must provide an* implementation for this method.** @param b the <code>byte</code>.* @exception IOException if an I/O error occurs. In particular,* an <code>IOException</code> may be thrown if the* output stream has been closed.*/public abstract void write(int b) throws IOException;

FileInputStream直接繼承了InputStream，被設計用來讀取二進制字節流文件，例如圖片。其中read間接調用了本地函數

/*** A <code>FileInputStream</code> obtains input bytes* from a file in a file system. What files* are available depends on the host environment.** <p><code>FileInputStream</code> is meant for reading streams of raw bytes* such as image data. For reading streams of characters, consider using* <code>FileReader</code>.** @author Arthur van Hoff* @see java.io.File* @see java.io.FileDescriptor* @see java.io.FileOutputStream* @see java.nio.file.Files#newInputStream* @since JDK1.0*/ public class FileInputStream extends InputStream -------------------------------------- /*** Reads a byte of data from this input stream. This method blocks* if no input is yet available.** @return the next byte of data, or <code>-1</code> if the end of the* file is reached.* @exception IOException if an I/O error occurs.*/public int read() throws IOException {return read0();}private native int read0() throws IOException;

它有三個構造函數public FileInputStream（String）間接調用了public FileInputStream（File）。

public FileInputStream(String name) throws FileNotFoundException {this(name != null ? new File(name) : null);}public FileInputStream(File file) throws FileNotFoundException {String name = (file != null ? file.getPath() : null);SecurityManager security = System.getSecurityManager();if (security != null) {security.checkRead(name);}if (name == null) {throw new NullPointerException();}if (file.isInvalid()) {throw new FileNotFoundException("Invalid file path");}fd = new FileDescriptor();fd.attach(this);path = name;open(name);}public FileInputStream(FileDescriptor fdObj) {SecurityManager security = System.getSecurityManager();if (fdObj == null) {throw new NullPointerException();}if (security != null) {security.checkRead(fdObj);}fd = fdObj;path = null;/** FileDescriptor is being shared by streams.* Register this stream with FileDescriptor tracker.*/fd.attach(this);}

看一下java.io.File；

首先，類注釋明確指出了java.io.File是文件和文件夾的抽象表示，不單單是文件哦！

/*** An abstract representation of file and directory pathnames.* public class Fileimplements Serializable, Comparable<File> {

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看字符流吧

BufferedReader是直接繼承自Reader的字符流，并且自帶緩沖。緩沖區大小可以指定，不指定采用默認值8192

/*** Reads text from a character-input stream, buffering characters so as to* provide for the efficient reading of characters, arrays, and lines.** <p> The buffer size may be specified, or the default size may be used. The* default is large enough for most purposes.**/public class BufferedReader extends Reader {

構造函數有兩個，BufferedReader（Reader）調用BufferedReader（Reader，int），其中defaultCharBufferSize=8192；

需要注意的是，BufferedReader作為一個Reader，本身需要外部的Reader作為參數，我想到了裝飾模式。

BufferedReader是一個Reader但是本身不完整，它本質是對Reader做了裝飾。

/*** Creates a buffering character-input stream that uses an input buffer of* the specified size.** @param in A Reader* @param sz Input-buffer size** @exception IllegalArgumentException If {@code sz <= 0}*/public BufferedReader(Reader in, int sz) {super(in);if (sz <= 0)throw new IllegalArgumentException("Buffer size <= 0");this.in = in;cb = new char[sz];nextChar = nChars = 0;}/*** Creates a buffering character-input stream that uses a default-sized* input buffer.** @param in A Reader*/public BufferedReader(Reader in) {this(in, defaultCharBufferSize);}

BufferedInputStream也是一樣，不同的是BufferedInputStream繼承InputStream，是對字節流的裝飾。并且BufferedInputStream提供了對mark和reset的支持。

/*** A <code>BufferedInputStream</code> adds* functionality to another input stream-namely,* the ability to buffer the input and to* support the <code>mark</code> and <code>reset</code>* methods. When the <code>BufferedInputStream</code>* is created, an internal buffer array is* created. As bytes from the stream are read* or skipped, the internal buffer is refilled* as necessary from the contained input stream,* many bytes at a time. The <code>mark</code>* operation remembers a point in the input* stream and the <code>reset</code> operation* causes all the bytes read since the most* recent <code>mark</code> operation to be* reread before new bytes are taken from* the contained input stream.** @author Arthur van Hoff* @since JDK1.0*/ public class BufferedInputStream extends FilterInputStream {

構造函數如下

/*** Creates a <code>BufferedInputStream</code>* and saves its argument, the input stream* <code>in</code>, for later use. An internal* buffer array is created and stored in <code>buf</code>.** @param in the underlying input stream.*/public BufferedInputStream(InputStream in) {this(in, DEFAULT_BUFFER_SIZE);}/*** Creates a <code>BufferedInputStream</code>* with the specified buffer size,* and saves its argument, the input stream* <code>in</code>, for later use. An internal* buffer array of length <code>size</code>* is created and stored in <code>buf</code>.** @param in the underlying input stream.* @param size the buffer size.* @exception IllegalArgumentException if {@code size <= 0}.*/public BufferedInputStream(InputStream in, int size) {super(in);if (size <= 0) {throw new IllegalArgumentException("Buffer size <= 0");}buf = new byte[size];}

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從字節流到字符流的橋梁

InputStreamReader繼承自Reader，它的主要工作是將字節流解碼成字符流。

InputStreamReader里面有一個變量StreamDecoder sd，實際工作其實都是有這個sd來做的。說不出來這是什么模式，但不是代理模式。sun.nio.cs.StreamDecoder的源碼沒有找到。

/*** An InputStreamReader is a bridge from byte streams to character streams: It* reads bytes and decodes them into characters using a specified {@link* java.nio.charset.Charset charset}. The charset that it uses* may be specified by name or may be given explicitly, or the platform's* default charset may be accepted.** <p> Each invocation of one of an InputStreamReader's read() methods may* cause one or more bytes to be read from the underlying byte-input stream.* To enable the efficient conversion of bytes to characters, more bytes may* be read ahead from the underlying stream than are necessary to satisfy the* current read operation.** <p> For top efficiency, consider wrapping an InputStreamReader within a* BufferedReader. For example:** <pre>* BufferedReader in* = new BufferedReader(new InputStreamReader(System.in));* </pre>** @see BufferedReader* @see InputStream* @see java.nio.charset.Charset** @author Mark Reinhold* @since JDK1.1*/public class InputStreamReader extends Reader {
private final StreamDecoder sd;

其構造函數如下

/*** 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 availablethrow new Error(e);}}/*** Creates an InputStreamReader that uses the named charset.** @param in* An InputStream** @param charsetName* The name of a supported* {@link java.nio.charset.Charset charset}** @exception UnsupportedEncodingException* If the named charset is not supported*/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.** @param in An InputStream* @param cs A charset** @since 1.4* @spec JSR-51*/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.** @param in An InputStream* @param dec A charset decoder** @since 1.4* @spec JSR-51*/public InputStreamReader(InputStream in, CharsetDecoder dec) {super(in);if (dec == null)throw new NullPointerException("charset decoder");sd = StreamDecoder.forInputStreamReader(in, this, dec);}

這四個構造函數都是調用了StreamDecoder.forInputStreamReader函數

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總結一下，在這幾個常用的io流中，本質上說程序員只能從文件構造流，或者使用外部提供的流，例如System.in，socket.getInputStream；

其他的類都是對流的裝飾。

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轉載于:https://www.cnblogs.com/afraidToForget/p/6623503.html

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