寫大二進制數據到文件

Question

嗨，我正在編寫我們自己的霍夫曼編碼項目。我目前無法將二進制1和0寫入輸出文件。它適用於較小的輸入文件，但對於非常大的文件，它不會將任何內容寫入輸出文件。負責書寫的方法是compress方法。任何幫助，將不勝感激。謝謝！

package proj3; 

import java.io.File; 
import java.io.FileInputStream; 
import java.io.FileNotFoundException; 
import java.io.FileOutputStream; 
import java.io.IOException; 
import java.util.ArrayList; 
import java.util.Collections; 
import java.util.LinkedHashMap; 
import java.util.Map; 
import java.util.Scanner; 
import java.util.PriorityQueue; 

public class Project3 { 

//variables for PriorityQueue and Huffman Tree 
private static PriorityQueue<BinaryNode<Character>> queue; 
private static BinaryNode<Character> huffTree; 
private static Map<Character, String> table = new LinkedHashMap<Character, String>(); 

/** 
* Method for creating Huffman Tree 
* @param counts Map that contains all characters and their frequencies 
* @return the Huffman Tree 
*/ 
public static BinaryNode<Character> makeTree(Map<Character, Integer> counts) 
{ 
    queue = new PriorityQueue<BinaryNode<Character>>(); 

    for(Character c : counts.keySet()) 
    { 
     BinaryNode<Character> tree = new BinaryNode<Character>(c, counts.get(c), null, null); 
     queue.add(tree); 
    } 

    while(!queue.isEmpty()) 
    { 
     if(queue.size() >= 2) 
     { 
      BinaryNode<Character> n1 = queue.remove(); 
      BinaryNode<Character> n2 = queue.remove(); 
      Integer weight = n1.getFreq() + n2.getFreq(); 
      huffTree = new BinaryNode<Character>(null, weight, n1, n2); 
      queue.add(huffTree); 
     } 
     if(queue.size() == 1) 
     { 
      return queue.remove(); 
     } 
    } 
    return huffTree; 
} 

public static void encode(BinaryNode<Character> node, String s) 
{ 
    if(!node.isLeaf()) 
    { 
     encode(node.getLeft(), s + "0"); 
     encode(node.getRight(), s + "1"); 
    } 
    else 
    { 
     table.put(node.getElement(), s); 
    } 
} 

public static void compress(String in, String out) throws IOException 
{ 
    try 
    { 
     File outFile = new File(out); 
     FileOutputStream compressedFile = new FileOutputStream(outFile); 
     Scanner infile = new Scanner(new FileInputStream(in)); 
     while(infile.hasNext()) 
     { 
      infile.useDelimiter(""); 
      String str = infile.next(); 
      Character character = str.charAt(0); 
      for(Character c : table.keySet()) 
      { 
       if(c == character){ 
        compressedFile.write(table.get(c).getBytes()); 
        compressedFile.flush(); 
       } 
      } 
     } 
     for(Byte b : table.get('^').getBytes()) 
     { 
      compressedFile.write(b); 
     } 
     infile.close(); 
     compressedFile.close(); 
    } 
    catch (FileNotFoundException e) 
    { 
     System.err.println("File not found."); 
     e.printStackTrace(); 
    } 
} 

public static void decompress(String s) 
{ 

} 

public static void printEncodings(Map<Character, String> m) 
{ 
    ArrayList<Character> chars = new ArrayList<Character>(); 

    System.out.println("Character Encodings"); 
    System.out.println("---------------------"); 
    for(Character c : m.keySet()) 
    { 
     chars.add(c); 
     Collections.sort(chars); 
    } 
    for(Character c : chars) 
    { 
     System.out.print(c + "\t" + m.get(c) + "\n"); 
    } 
    System.out.println(); 
    System.out.println("Total Characters: " + chars.size()); 
} 

/** 
* Method for creating map with character and its frequencies 
* @param s the file name to be opened 
* @return the Map containing characters and frequencies 
*/ 
public static Map<Character, Integer> charCount(String s){ 

    Map<Character, Integer> counts = new LinkedHashMap<Character, Integer>(); 
    ArrayList<Character> chars = new ArrayList<Character>(); 

    try { 
     Scanner file = new Scanner(new FileInputStream(s)); 
     while(file.hasNext()){ 
      file.useDelimiter(""); 
      String str = file.next(); 
      Character c = str.charAt(0); 
      if(counts.containsKey(c)){ 
       counts.put(c, counts.get(c) + 1); 
      } 
      else{ 
       counts.put(c, 1); 
      } 
     } 
     counts.put('^', 1); 
     System.out.println("Character Frequencies"); 
     System.out.println("---------------------"); 
     for(Character c : counts.keySet()) 
     { 
      chars.add(c); 
      Collections.sort(chars); 
     } 
     for(Character c : chars){ 
      System.out.println(c + "\t" + counts.get(c)); 
     } 
     System.out.println(); 
     System.out.println("Total characters: " + chars.size() + "\n"); 
     file.close(); 
    } 
    catch (FileNotFoundException e) { 
     System.err.println("File not found."); 
     System.exit(0); 
    } 
    return counts; 
} 

public static void main(String[] args){ 

    if(args.length != 3) 
    { 
     throw new IllegalArgumentException("Invalid number of arguments."); 
    } 
    encode(makeTree(charCount(args[0])), ""); 
    printEncodings(table); 
    try { 
     compress(args[0], args[1]); 
    } catch (IOException e) { 
     e.printStackTrace(); 
    } 
} 

} 

Answer 1

我很確定你正在面對compress（）方法中的性能/內存問題。編碼打印在你的主要方法中，但我相信文件輸出會卡住。我可以看到優化至少三種可能在你的代碼：

1. 您使用的是Scanner讀取由字符輸入文件字符，但您不使用由掃描儀提供的任何解析功能。改爲使用InputStreamReader。

2. 您正在循環查找Huffman表中的一組鍵並檢查相等性。您可以簡單地使用當前字符來獲取它映射到的字符串並省略循環。

3. 您不需要循環字節數組將其寫入輸出文件。 write（）方法FileOutputStream可以將整個字節數組作爲參數。

憑藉我卑微的Java技能，我寧願以下面的方式實現它;請注意，這是未經測試的代碼，因爲我沒有你BinaryNode類：

public static void compress(String in, String out) throws IOException 
{ 
    try 
     { 
      File outFile = new File(out); 
      FileOutputStream compressedFile = new FileOutputStream(outFile); 

      // 1. Use a Reader instead of a Scanner; 
      // make sure to use the correct charset 
      FileInputStream fis= new FileInputStream(in); 
      Reader reader = new InputStreamReader(fis,   
       Charset.forName("US-ASCII")); 

      // use BufferedReader for even better performance 
      Reader bufferedReader = new BufferedReader(reader); 

      int r; 
      while ((r = bufferedReader.read()) != -1) { 
       char ch= (char) r; 

       // 2. Get the string for this character directly instead of 
       // looping the keySet and checking for equivalence 
       String s= table.get(ch); 
       if (s != null) { 
        // 3. Write entire array of bytes instead of 
        // looping and writing bytes one by one 
        compressedFile.write(s.getBytes()); 
       } 
      } 
      fis.close(); 
      compressedFile.close(); 
     } 
    ... 

Answer 2

很可能需要調用compressedFile.flush()

提高它像這樣

  if(c == character){ 
       compressedFile.write(table.get(c).getBytes()); 
       compressedFile.flush(); 
      } 

---

另外考慮使用try/catch。將提高執行的完整性。