java中的IO的類庫非常的龐大,選擇性非常的多,當面臨一個問題時,往往不知道如何下手!

更具我現在的理解,在效率不是非常重要的情況下,一般情況下可能只需要考慮兩種情況,即想按照位元組去讀取,還是想按照行去讀取,而一般情況無論採取什麼方式去讀取,最佳的方式都莫過於用Buffered...去包裝要是用的類,而如果效率要求比較高則可以考慮是用FileChannel 或者是 file map,其中file Map是讀寫效率最高的一種方式,如果讀取的檔案非常的大這種方式是首選,下面的例子是對常見幾種讀檔案方式的效率比較,通過一個動態代理的模式來統計每個方法的執行時間,測試檔案是100多兆的資料檔案

package com.eric.io;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.ByteArrayInputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStream;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.channels.FileChannel;

import com.eric.reflect.ExecuteTimerHandler;

public class ReadFileTools implements IReadFileTools {
	
	/**
	 * 
	 * execute readByBufferReader spend 444 million sencond!
        execute readByBufferedInputStreamNoArray spend 27903 million sencond!
        execute readByBufferedInputStream spend 192 million sencond!
        execute readByChannel spend 484 million sencond!
        execute readByChannelMap spend 42 million sencond!
        execute readByDataInputStream spend 440 million sencond!
	 * 
	 * @param args
	 * @throws Exception
	 */
	public static final int	    BUFFSIZE	 = 180;
	public static final String	root	     = "E:\\sourcecode\\corejava\\src\\com\\eric\\io\\";
	public static final boolean	printContext	= false;
	
	public static void main(String[] args) throws Exception {
		String file = root + "VISA_INPUT_FULL";
		IReadFileTools bi = (IReadFileTools) ExecuteTimerHandler.newInstance(new ReadFileTools());
		bi.readByBufferReader(file);
		bi.readByBufferedInputStreamNoArray(file);
		bi.readByBufferedInputStream(file);
		bi.readByChannel(file);
		bi.readByChannelMap(file);
		bi.readByDataInputStream(file);
	}
	
	/*
	 * execute readBuffer spend 421 million sencond! execute readByte spend
	 * 36172 million sencond!
	 */
	public String readByBufferReader(String file) {
		StringBuilder sb = new StringBuilder();
		try {
			BufferedReader br = new BufferedReader(new FileReader(new File(file)));
			String line;
			long count = 0;
			while ((line = br.readLine()) != null) {
				if (printContext) {
					System.out.println(line);
				}
				
				sb.append(line);
				count += line.length();
			}
			br.close();
		} catch (Exception ex) {
			ex.printStackTrace();
		}
		return sb.toString();
	}
	
	public void readByDataInputStream(String file) throws Exception {
		
		DataInputStream dis = new DataInputStream(new ByteArrayInputStream(new ReadFileTools().readByBufferReader(file).getBytes()));
		while (dis.available() > 0) {
			char c = (char) dis.read();
			if (printContext) {
				System.out.println(c);
			}
		}
	}
	//this method not use byte array to get byte
	public String readByBufferedInputStreamNoArray(String file) {
		try {
			InputStream is = new BufferedInputStream(new FileInputStream(new File(file)));
			while (is.available() > 0) {
				char c = (char) is.read();
				if (printContext) {
					System.out.println(c);
				}
			}
		} catch (Exception ex) {
			ex.printStackTrace();
		}
		return null;
	}
	//use byte array to get bytes from file
	public void readByBufferedInputStream(String file) throws Exception {
		BufferedInputStream input = new BufferedInputStream(new FileInputStream(file));
		byte[] bytes = new byte [BUFFSIZE];
		while (input.available() > 0) {
			input.read(bytes);
		}
	}
	//use file channel to get byte from file
	public void readByChannel(String file) throws Exception {
		
		FileChannel in = new FileInputStream(file).getChannel();
		ByteBuffer buffer = ByteBuffer.allocate(BUFFSIZE);
		while (in.read(buffer) != -1) {
			buffer.flip(); // Prepare for writing
			if (printContext) {
				System.out.println(buffer.getChar());
			}
			buffer.clear(); // Prepare for reading
		}
		in.close();
	}
	//use MappedByteBuffer to read byte from file
	public void readByChannelMap(String file) throws Exception {
		FileChannel fc = new FileInputStream(new File(file)).getChannel();
		CharBuffer cb = fc.map(FileChannel.MapMode.READ_ONLY, 0, fc.size()).asCharBuffer();
		char c;
		while (cb.hasRemaining())
			c = cb.get();
		if (printContext) {
			System.out.println(c);
		}
		fc.close();
	}
	
	public void copyFileByChannel(String file, String file2) throws Exception {
		
		FileChannel in = new FileInputStream(file).getChannel();
		FileChannel out = new FileOutputStream(file2).getChannel();
		ByteBuffer buffer = ByteBuffer.allocate(BUFFSIZE);
		while (in.read(buffer) != -1) {
			buffer.flip(); // Prepare for writing
			out.write(buffer);
			buffer.clear(); // Prepare for reading
		}
	}
	
	public void test() {
		System.out.println("test");
	}
	
	public void copyFile(String source, String dest) throws Exception {
		BufferedReader br = new BufferedReader(new FileReader(new File(source)));
		BufferedWriter bw = new BufferedWriter(new FileWriter(new File(dest)));
		String temp;
		while ((temp = br.readLine()) != null) {
			bw.write(temp + "\n");
		}
	}
	
	public void storingAndRecoveringData(String file) throws Exception {
		DataInputStream dis = new DataInputStream(new BufferedInputStream(new FileInputStream(file)));
		DataOutputStream dos = new DataOutputStream(new BufferedOutputStream(new FileOutputStream(file)));
		dos.writeBoolean(false);
		dos.writeByte(10);
		dos.writeDouble(1213654);
		dos.writeUTF("aihua");
		dos.close();
		System.out.println(dis.readBoolean());
		System.out.println(dis.readByte());
		System.out.println(dis.readDouble());
		System.out.println(dis.readUTF());
		dis.close();
		
	}
	
	public void doCopyFile(String src, String dest) throws IOException {
		File srcFile = new File(src);
		File destFile = new File(dest);
		if (destFile.exists()) {
			boolean d = destFile.delete();
			
			if (d) {
				System.out.print("刪除成功！");
			} else {
				System.out.print("刪除失敗！");
			}
		}
		BufferedInputStream input = new BufferedInputStream(new FileInputStream(srcFile));
		try {
			BufferedOutputStream output = new BufferedOutputStream(new FileOutputStream(destFile));
			try {
				byte[] buffer = new byte [4096];
				int n = 0;
				while (-1 != (n = input.read(buffer))) {
					output.write(buffer, 0, n);
				}
				System.out.println("Copy Successful::" + dest);
			} finally {
				try {
					if (output != null) {
						output.close();
					}
				} catch (IOException ioe) {
					ioe.printStackTrace();
				}
			}
		} finally {
			try {
				if (input != null) {
					input.close();
				}
			} catch (IOException ioe) {
				System.out.println("failed src file:" + src + " reason:" + ioe.getMessage());
			}
		}
	}
	
}

/*
 * 
 * History:
 * 
 * 
 * 
 * $Log: $
 */
 

希望前輩可以對方法進行補充