io-nio-socket步步为营（一）流基础

前沿：半路出家，自学io-nio-socket这块有些时日了，反反复复好多次，收获了很多，也记住了很多，但是好像不成系统，这次想彻底整好，不在简单的记住用法，更要用心理解背后的原理。道可道非常道，实践，写入自己的思考。start...

 

一、流基础____________________________________________________________

 

1、流关闭顺序

结论：只需要关闭外层流即可。

思考：因为外层流使用的是Decorator模式，最终还是底层流underlying stream。

 

public static String testStreamColseSequence( String name )throws Exception {
    FileInputStream fis = new FileInputStream( name );
    // InputStreamReader(fis");默认字符集为UTF-8
    Reader reader = new InputStreamReader( fis );
    BufferedReader br = new BufferedReader( reader );
    String header = br.readLine();
    //设置断点，观察varibales:
    //br.lock.lock.closed-->reader.lock.closed-->fis.closed=false
    br.close();
    // 调用fis.read(), 报java.io.IOException: Stream Closed
    System.out.println( "fis.read()=" + fis.read() );
    return header;
}

   

 

2、io与nio比较

结论：单纯复制byte流方面，io甚至比nio快些，因为从1.4开始io用nio重新实现了，按块读取，但是

nio多个线程复用一个连接的优势，io-socket是无法获得的。

思考：需要操作系统级别的I/O，unix网络编程实践。有待提升

 

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;

/**
 * 测试数据：2个完全一样的的视频,101M的mp4
 * iioCopy=327,nioCopy=422,因为从1.4开始io用nio重写了 ，从FileChannel fc1 = in.getChannel();即可看出端倪
 * 面向流 的 I/O系统一次一个字节地处 理数据。NIO按块处理数据比按(流式的)字节处理数据要快得多，但缺少I/O的简单优雅
 * @author timeriver.wang
 * @date 2012-12-07 9:37:22 AM
 */
public class IOpkNIOCopy {
    private static int LEN_8K = 8192;

    public static void main( String[] args )
        throws Exception {
        ioCopy( "e:/work/1/1.MP4", "e:/work/2/1.MP4" );
        nioCopy( "e:/work/1/2.MP4", "e:/work/2/2.MP4" );
    }

    public static void ioCopy( String name1, String name2 )
        throws Exception {
        long start = System.currentTimeMillis();
        FileInputStream fis = new FileInputStream( name1 );
        FileOutputStream fos = new FileOutputStream( name2 );
        byte[] buf = new byte[LEN_8K];
        while ( true ) {
            int n = fis.read( buf );
            if ( n == -1 ) {
                break;
            }
            fos.write( buf, 0, n );
            // 这行代码会使复制的视频变花屏。
            // fos.write(99);
        }
        fis.close();
        fos.close();
        long end = System.currentTimeMillis();
        long time = end - start;
        System.out.println( "iioCopy=" + time );
    }

    public static void nioCopy( String name1, String name2 )
        throws Exception {
        long start = System.currentTimeMillis();
        FileInputStream in = new FileInputStream( name1 );
        FileOutputStream out = new FileOutputStream( name2 );
        // Since:1.4,java从1.4开始提升性能
        // Returns the unique FileChannel object associated with this file input stream.
        FileChannel fc1 = in.getChannel();
        FileChannel fc2 = out.getChannel();
        ByteBuffer bb = ByteBuffer.allocate( LEN_8K );
        while ( true ) {
            bb.clear();
            int n = fc1.read( bb );
            if ( n == -1 ) {
                break;
            }
            bb.flip();
            fc2.write( bb );
        }
        fc1.close();
        fc2.close();
        long end = System.currentTimeMillis();
        long time = end - start;
        System.out.println( "nioCopy=" + time );
    }
}

 

 

3、最基础的InputStream,OutputStream才是最重要的，源代码显示最终都是调用单字节的read()。而且read是抽象的，让子类去实现，非常犀利

 

RandomAccessFile implements DataOutput, DataInput, Closeable

ByteArrayInputStream extends InputStream

 

 

public abstract class InputStream implements Closeable {
    private static final int MAX_SKIP_BUFFER_SIZE = 2048;
//    各种read方法，各种上层input流最终都依赖这个read,体味编程之美。
    public abstract int read() throws IOException;
    public int read(byte b[]) throws IOException {
        return read(b, 0, b.length);
    }
    public int read(byte b[], int off, int len) throws IOException {
        int c = read();
    }
    public long skip(long n) throws IOException {
        nr = read(skipBuffer, 0, (int)Math.min(size, remaining));
    }
    public int available() throws IOException {
        return 0;
    }
    public void close() throws IOException {}
//    synchronized.
    public synchronized void mark(int readlimit) {}
    public synchronized void reset() throws IOException {
        throw new IOException("mark/reset not supported");
    }
    public boolean markSupported() {return false;}
}

 

FileInputStream extends InputStream，重写了read(),skip()，应该是1.4按块读取提供效率。

 

public class FileInputStream extends InputStream{
    public native int read() throws IOException;
    //不再调用read()了，按块读，不再按byte读取了？
    private native int readBytes(byte b[], int off, int len) throws IOException;
    public int read(byte b[], int off, int len) throws IOException {
        return readBytes(b, off, len);
    }
    //也重写父类的skip为natvie方法了，不再调用read()了，
    public native long skip(long n) throws IOException;
    //since 1.4
    public FileChannel getChannel() {
        synchronized (this) {FileChannelImpl.open...}
    }
}

 

SocketInputStream extends FileInputStream

 

private native int socketRead0(FileDescriptor fd,byte b[], int off, int len,int timeout)

 

4、read()返回[0-255]的int,把有符号的byte数值，转换成了无符号的int数值。可以用来判断是否EOF流结束了与否

，验证代码如下

 

/**
 * @author timeriver.wang
 * @date 2012-12-10 10:45:17 AM
 */
public class Test {
    public static void main( String[] args ) throws Exception{
        String filePath = "d:/12.txt";
        writeFile(filePath);
        readFile( filePath );
    }
    public static void writeFile(String filePath) throws IOException{
        ByteBuffer bb = ByteBuffer.allocate( 20 );
        bb.putChar( 'a' );
        bb.putInt( -255 );
        bb.putShort((short) -255 );
        bb.putChar( 'b' );
        bb.putChar( 'c' );
        FileOutputStream fos = new FileOutputStream(filePath);
        fos.write( bb.array());
    }
    
    public static void readFile(String filePath) throws IOException{
        FileInputStream fis = new FileInputStream(filePath);
        ByteBuffer readbuff = ByteBuffer.allocate( 20 );
        //写入的byte -1,read读取的是255,即无符号的byte数值。
        int i = fis.read();
        while(i != -1){
            readbuff.put( (byte)i);
            System.out.println(i);
            i = fis.read();
        }
        System.out.println(readbuff);
    }
}

 

5、InputStream小技巧

 

 

/**
 * @author wangnaijiang
 * @version 2012-12-30 1:18:12 PM
 */
public class StreamUtils {
	/** 
     * 考虑到网络分包延迟，一直阻塞到填满缓冲区。
     */  
    public static byte[] read1( InputStream is )throws Exception {  
        int bytesRead = 0;  
        byte[] input = new byte[1024];  
        while ( bytesRead < 1024 ) {  
                 bytesRead += is.read( input, bytesRead, 1024 - bytesRead );  
        }  
        return input;  
    }  
  
    /**
     * 考虑到网络分包延迟，一直阻塞到填满缓冲区或读取到-1流结束。
     */
    public static byte[] read2( InputStream is )throws Exception {  
        int bytesRead = 0;  
        byte[] input = new byte[1024];  
        while ( bytesRead < 1024 ) {  
            int result = is.read( input, bytesRead, 1024 - bytesRead );  
            if ( result == -1 )  
                break;  
            bytesRead += result;  
        }  
        return input;  
    } 
}