1. 程式人生 > >Java IO讀寫大檔案的幾種方式及測試

Java IO讀寫大檔案的幾種方式及測試

讀取檔案大小:1.45G
第一種,OldIO:
Java程式碼 複製程式碼收藏程式碼
  1. publicstaticvoid oldIOReadFile() throws IOException{
  2. BufferedReader br = new BufferedReader(new FileReader("G://lily_947.txt"));
  3. PrintWriter pw = new PrintWriter("G://oldIO.tmp");
  4. char[] c = newchar[100*1024*1024];
  5. for(;;){
  6. if(br.read(c)!=-1){
  7. pw.print(c);
  8. }else{
  9. break;
  10. }
  11. }
  12. pw.close();
  13. br.close();
  14. }
	public static void oldIOReadFile() throws IOException{
		BufferedReader br = new BufferedReader(new FileReader("G://lily_947.txt"));
		PrintWriter pw = new PrintWriter("G://oldIO.tmp");
		char[] c = new char[100*1024*1024];
		for(;;){
			if(br.read(c)!=-1){
				pw.print(c);
			}else{
				break;
			}
		}
		pw.close();
		br.close();
	}

耗時70.79s


第二種,newIO:
Java程式碼 複製程式碼收藏程式碼
  1. publicstaticvoid newIOReadFile() throws IOException{
  2. FileChannel read = new RandomAccessFile("G://lily_947.txt","r").getChannel();
  3. FileChannel writer = new RandomAccessFile("G://newIO.tmp","rw").getChannel();
  4. ByteBuffer bb = ByteBuffer.allocate(200*1024*1024);
  5. while(read.read(bb)!=-
    1){
  6. bb.flip();
  7. writer.write(bb);
  8. bb.clear();
  9. }
  10. read.close();
  11. writer.close();
  12. }
public static void newIOReadFile() throws IOException{
		FileChannel read = new RandomAccessFile("G://lily_947.txt","r").getChannel();
		FileChannel writer = new RandomAccessFile("G://newIO.tmp","rw").getChannel();
		ByteBuffer bb = ByteBuffer.allocate(200*1024*1024);
		while(read.read(bb)!=-1){
			bb.flip();
			writer.write(bb);
			bb.clear();
		}
		read.close();
		writer.close();
		
	}

耗時47.24s


第三種,RandomAccessFile:
Java程式碼 複製程式碼收藏程式碼
  1. publicstaticvoid randomReadFile() throws IOException{
  2. RandomAccessFile read = new RandomAccessFile("G://lily_947.txt","r");
  3. RandomAccessFile writer = new RandomAccessFile("G://random.tmp","rw");
  4. byte[] b = newbyte[200*1024*1024];
  5. while(read.read(b)!=-1){
  6. writer.write(b);
  7. }
  8. writer.close();
  9. read.close();
  10. }
public static void randomReadFile() throws IOException{
		RandomAccessFile read = new RandomAccessFile("G://lily_947.txt","r");
		RandomAccessFile writer = new RandomAccessFile("G://random.tmp","rw");
		byte[] b = new byte[200*1024*1024];
		while(read.read(b)!=-1){
			writer.write(b);
		}
		writer.close();
		read.close();
	}

耗時46.65

第四種,MappedByteBuffer:
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  1. publicstaticvoid mappedBuffer() throws IOException{
  2. FileChannel read = new FileInputStream("G://lily_947.txt").getChannel();
  3. FileChannel writer = new RandomAccessFile("G://buffer.tmp","rw").getChannel();
  4. long i = 0;
  5. long size = read.size()/30;
  6. ByteBuffer bb,cc = null;
  7. while(i<read.size()&&(read.size()-i)>size){
  8. bb = read.map(FileChannel.MapMode.READ_ONLY, i, size);
  9. cc = writer.map(FileChannel.MapMode.READ_WRITE, i, size);
  10. cc.put(bb);
  11. i+=size;
  12. bb.clear();
  13. cc.clear();
  14. }
  15. bb = read.map(FileChannel.MapMode.READ_ONLY, i, read.size()-i);
  16. cc.put(bb);
  17. bb.clear();
  18. cc.clear();
  19. read.close();
  20. writer.close();
  21. }
public static void mappedBuffer() throws IOException{
		FileChannel read = new FileInputStream("G://lily_947.txt").getChannel();
		FileChannel writer = new RandomAccessFile("G://buffer.tmp","rw").getChannel();
		long i = 0;
		long size = read.size()/30;
		ByteBuffer bb,cc = null;
		while(i<read.size()&&(read.size()-i)>size){
			bb = read.map(FileChannel.MapMode.READ_ONLY, i, size);
			cc = writer.map(FileChannel.MapMode.READ_WRITE, i, size);
			cc.put(bb);
			i+=size;
			bb.clear();
			cc.clear();
		}
		bb = read.map(FileChannel.MapMode.READ_ONLY, i, read.size()-i);
		cc.put(bb);
		bb.clear();
		cc.clear();
		read.close();
		writer.close();
		
	}

耗時:36

前三種讀法對應的資源佔用圖如下:
相對於最後一種記憶體直接對映方式前面的測試其實無意義,基本秒殺。。。。。
對於很大的檔案直接分塊對映時記憶體會不夠,這是因為MappedByteBuffer未被釋放造成的,sun未提供直接回收MappedByteBuffer區域的方法,這個時候有兩種方法解決,第一種比較愚笨的:
Java程式碼 複製程式碼收藏程式碼
  1. System.gc();
  2. System.runFinalization();
  3. try {
  4. Thread.sleep(3000);
  5. } catch (InterruptedException e) {
  6. e.printStackTrace();
  7. }
             System.gc(); 
            System.runFinalization(); 
            try {
				Thread.sleep(3000);
			} catch (InterruptedException e) {
				
				e.printStackTrace();
			}

第二種網上找來的,利用反射呼叫clean方法:
Java程式碼 複製程式碼收藏程式碼
  1. publicstaticvoid unmap(final MappedByteBuffer buffer) {
  2. if (buffer == null) {
  3. return;
  4. }
  5. AccessController.doPrivileged(new PrivilegedAction<Object>() {
  6. public Object run() {
  7. try {
  8. Method getCleanerMethod = buffer.getClass().getMethod("cleaner", new Class[0]);
  9. if (getCleanerMethod != null) {
  10. getCleanerMethod.setAccessible(true);
  11. Object cleaner = getCleanerMethod.invoke(buffer, new Object[0]);
  12. Method cleanMethod = cleaner.getClass().getMethod("clean", new Class[0]);
  13. if (cleanMethod != null) {
  14. cleanMethod.invoke(cleaner, new Object[0]);
  15. }
  16. }
  17. } catch (Exception e) {
  18. e.printStackTrace();
  19. }
  20. returnnull;
  21. }
  22. });
  23. }
public static void unmap(final MappedByteBuffer buffer) {
		if (buffer == null) {
			return;
		}
		AccessController.doPrivileged(new PrivilegedAction<Object>() {
			public Object run() {
				try {
					Method getCleanerMethod = buffer.getClass().getMethod("cleaner", new Class[0]);
					if (getCleanerMethod != null) {
						getCleanerMethod.setAccessible(true);
						Object cleaner = getCleanerMethod.invoke(buffer, new Object[0]);
						Method cleanMethod = cleaner.getClass().getMethod("clean", new Class[0]);
						if (cleanMethod != null) {
							cleanMethod.invoke(cleaner, new Object[0]);
						}
					}
				} catch (Exception e) {
					e.printStackTrace();
				}
				return null;
			}
 
		});
	}

以上兩種方法感覺都彆扭,還有就是可以自己分割成物理檔案再迴圈呼叫,這個也不太美觀。
速度也會減慢好多。