java io系列13之 BufferedOutputStream(緩衝輸出流)的認知、原始碼和示例

BufferedOutputStream(OutputStream out)

BufferedOutputStream(OutputStream out, int size)

synchronized void     close()

synchronized void     flush()

synchronized void     write(byte[] buffer, int offset, int length)

synchronized void     write(int oneByte)

 package java.io;

 public class BufferedOutputStream extends FilterOutputStream {

     // 儲存“緩衝輸出流”資料的位元組陣列

     protected byte buf[];

     // 緩衝中資料的大小

     protected int count;

     // 建構函式：新建位元組陣列大小為8192的“緩衝輸出流”

     public BufferedOutputStream(OutputStream out) {

         this(out, 8192);

     }

     // 建構函式：新建位元組陣列大小為size的“緩衝輸出流”

     public BufferedOutputStream(OutputStream out, int size) {

         super(out);

         if (size <= 0) {

             throw new IllegalArgumentException("Buffer size <= 0");

         }

         buf = new byte[size];

     }

     // 將緩衝資料都寫入到輸出流中

     private void flushBuffer() throws IOException {

         if (count > 0) {

             out.write(buf, 0, count);

             count = 0;

         }

     }

     // 將“資料b(轉換成位元組型別)”寫入到輸出流中

     public synchronized void write(int b) throws IOException {

         // 若緩衝已滿，則先將緩衝資料寫入到輸出流中。

         if (count >= buf.length) {

             flushBuffer();

         }

         // 將“資料b”寫入到緩衝中

         buf[count++] = (byte)b;

     }

     public synchronized void write(byte b[], int off, int len) throws IOException {

         // 若“寫入長度”大於“緩衝區大小”，則先將緩衝中的資料寫入到輸出流，然後直接將陣列b寫入到輸出流中

         if (len >= buf.length) {

             flushBuffer();

             out.write(b, off, len);

             return;

         }

         // 若“剩餘的緩衝空間 不足以 儲存即將寫入的資料”，則先將緩衝中的資料寫入到輸出流中

         if (len > buf.length - count) {

             flushBuffer();

         }

         System.arraycopy(b, off, buf, count, len);

         count += len;

     }

     // 將“緩衝資料”寫入到輸出流中

     public synchronized void flush() throws IOException {

         flushBuffer();

         out.flush();

     }

 }

 import java.io.BufferedOutputStream;

 import java.io.File;

 import java.io.OutputStream;

 import java.io.FileOutputStream;

 import java.io.IOException;

 import java.io.FileNotFoundException;

 import java.lang.SecurityException;

 import java.util.Scanner;

 /**

  * BufferedOutputStream 測試程式

  *

  * @author skywang

  */

 public class BufferedOutputStreamTest {

     private static final int LEN = 5;

     // 對應英文字母“abcddefghijklmnopqrsttuvwxyz”

     private static final byte[] ArrayLetters = {

         0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6A, 0x6B, 0x6C, 0x6D, 0x6E, 0x6F,

         0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7A

     };

     public static void main(String[] args) {

         testBufferedOutputStream() ;

     }

     /**

      * BufferedOutputStream的API測試函式

      */

     private static void testBufferedOutputStream() {

         // 建立“檔案輸出流”對應的BufferedOutputStream

         // 它對應緩衝區的大小是16，即緩衝區的資料>=16時，會自動將緩衝區的內容寫入到輸出流。

         try {

             File file = new File("out.txt");

             OutputStream out =

                   new BufferedOutputStream(

                       new FileOutputStream(file), 16);

             // 將ArrayLetters陣列的前10個位元組寫入到輸出流中

             out.write(ArrayLetters, 0, 10);

             // 將“換行符\n”寫入到輸出流中

             out.write('\n');

             // TODO!

             //out.flush();

             readUserInput() ;

             out.close();

        } catch (FileNotFoundException e) {

            e.printStackTrace();

        } catch (SecurityException e) {

            e.printStackTrace();

        } catch (IOException e) {

            e.printStackTrace();

        }

     }

     /**

      * 讀取使用者輸入

      */

     private static void readUserInput() {

         System.out.println("please input a text:");

         Scanner reader=new Scanner(System.in);

         // 等待一個輸入

         String str = reader.next();

         System.out.printf("the input is : %s\n", str);

     }

 }

out.flush();

out.write(ArrayLetters, 0, 10);

out.write(ArrayLetters, 0, 20);