從每個固定字節長度的InputStream中繪製數據？

Question

給定一個InputStream，我想要一個工具，我呼叫next()，當前執行塊直到流中累積了50個字節，此時next()返回一個長度爲50的byte[]，包含相關數據。

在Google上找到正確的短語令人驚訝地很難，這就是我來到這裏的原因。

謝謝。

Answer 1

您一定應該參考標準的JDK庫來獲得優秀的類來讀取和寫入IO。但是你的要求很有趣。您需要輸入流的「迭代器」類接口。所以，這是我的嘗試。當然，一些優化是可能的，但希望它能很好地提出這個想法。讓我知道這是你在找什麼。我承認存在要對潛在輸入流，該方法hasNext()塊合同微妙的變化。我希望這是正確的。

import java.io.BufferedInputStream; 
import java.io.IOException; 
import java.io.InputStream; 
import java.util.Arrays; 
import java.util.Iterator; 
import java.util.function.Consumer; 

/** An attempt for: 
* http://stackoverflow.com/questions/35817251/draw-data-from-inputstream-every-fixed-byte-length 
* <b>This class is NOT thread safe.</b> 
* Created by kmhaswade on 3/5/16. 
*/ 
public class InputStreamIterator extends BufferedInputStream implements Iterator<byte[]> { 

    private final InputStream in; 
    private final byte[] bytes; 
    private int bytesRead; 
    /** 
    * Returns a buffered input stream that "iterates" over a given stream. Follows the decorator pattern. 
    * @param in the input stream that should be buffered 
    * @param n 
    */ 
    public InputStreamIterator(InputStream in, int n) { 
     super(in); 
     this.in = in; 
     if (n <=0 || n > Integer.MAX_VALUE) 
      throw new IllegalArgumentException("illegal value: " + n); 
     bytes = new byte[n]; 
    } 

    @Override 
    public boolean hasNext() { 
     try { 
      bytesRead = super.read(this.bytes); 
      if (bytesRead == -1) { 
       this.close(); 
       return false; 
      } 
      return true; 
     } catch (IOException e) { 
      throw new RuntimeException(e); // could be handled better ... 
     } 
    } 

    @Override 
    public byte[] next() { 
     if (bytes.length == bytesRead) 
      return bytes; 
     else 
      return Arrays.copyOf(bytes, bytesRead); 
    } 

    @Override 
    public void remove() { 
     throw new RuntimeException("no way to push back yet"); 
    } 

    @Override 
    public void forEachRemaining(Consumer<? super byte[]> action) { 
     throw new RuntimeException("not yet implemented"); 
    } 

    public static void main(String[] args) { 
     InputStreamIterator itIn = new InputStreamIterator(System.in, 50); 
     while (itIn.hasNext()) { 
      byte[] bs = itIn.next(); 
      for (byte b : bs) { 
       System.out.println("byte read: " + b); 
      } 
     } 
    } 
} 

Answer 2

有JDK中沒有這樣的工具，但你完全可以包裝你InputStream爲DataInputStream並在其上調用readFully(byte[])：

InputStream is = // ... 
DataInputStream dis = new DataInputStream(is); 
byte[] bytes = new byte[50]; 
dis.readFully(bytes); 
// "bytes" now contains exactly 50 bytes from the stream 

要與一個next()方法的類中，實現Iterator界面並在內部完成上述操作。