ByteBuffer按行處理資料(readline)

壹頁書發表於2014-05-07
NIO沒有BufferedReader這樣讀取行的方法。
可以查詢ByteBuffer最後一個換行符,在換行符之後的資料，重新放回ByteBuffer


  1. import java.io.FileInputStream;
  2. import java.io.IOException;
  3. import java.io.UnsupportedEncodingException;
  4. import java.nio.ByteBuffer;
  5. import java.nio.channels.FileChannel;
  6. import java.nio.charset.Charset;

  8. interface Callback {
  9.     void action(String line);
  10. }

  12. public class NIOReadline {
  13.     private int buffersize;
  14.     private Charset charset ;
  15.     private Callback callback;
  16.     private FileChannel channel;
  17.     ByteBuffer buffer ;

  19.     public NIOReadline(String file, Callback callback) throws UnsupportedEncodingException, IOException {
  20.         this(file,callback,200,Charset.defaultCharset().displayName());
  21.     }
  22.     
  23.     public NIOReadline(String file, Callback callback,int bufferSize,String charsetName) throws UnsupportedEncodingException, IOException {
  24.         charset=Charset.forName(charsetName);
  25.         buffersize=bufferSize;
  26.         channel = new FileInputStream(file).getChannel();
  27.         buffer=ByteBuffer.allocate(bufferSize);
  28.         this.callback=callback;
  29.         action();
  30.     }

  32.     private void action() throws UnsupportedEncodingException, IOException {
  33.         while (channel.read(buffer) > 0) {
  34.             buffer.flip();
  35.             byte[] data = new byte[buffersize];
  36.             // 陣列最後一個可用資料
  37.             int last = buffer.limit() - 1;
  38.             buffer.get(data, 0, buffer.limit());
  39.             buffer.compact();
  40.             // 找最後一個換行符
  41.             int i = last;
  42.             while (data[i] != (byte) '\n') {
  43.                 i = i - 1;
  44.                 // 如果沒有換行符,直接退出,可能是最後一行
  45.                 if (i < 0) {
  46.                     break;
  47.                 }
  48.             }

  50.             if (i > 0) {
  51.                 // 如果有換行符
  52.                 action(new String(data, 0, i + 1, charset));

  54.                 while (i < last) {
  55.                     buffer.put(data[i + 1]);
  56.                     i++;
  57.                 }
  58.             } else {
  59.                 action(new String(data, 0, buffer.limit(), charset));
  60.             }
  61.         }
  62.         channel.close();
  63.     }

  65.     private void action(String str) {
  66.         String[] data = str.split("\n");
  67.         for (String line : data) {
  68.             callback.action(line);
  69.         }
  70.     }

  72.     public static void main(String[] args) throws UnsupportedEncodingException, IOException {
  73.         NIOReadline r=new NIOReadline("C:\\Users\\new\\Desktop\\test.sql", new Callback() {
  74.             
  75.             @Override
  76.             public void action(String line) {
  77.                 System.out.print(line);
  78.             }
  79.         });
  80.     }
  81. }
這個方法可以解決使用ByteBuffer造成的文字截斷問題。

來自 “ ITPUB部落格 ” ，連結：http://blog.itpub.net/29254281/viewspace-1155749/，如需轉載，請註明出處，否則將追究法律責任。

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