java 文件读写实例

1.dump

将一个文件（图片lion.jpg）复制一份（bbb.bmp）。

主要的部分：使用java.io的InputStream和OutputStream来进行文件输入、输出（write）。

public static void dump(InputStream src, OutputStream dest)
    throws IOException
    {
        InputStream input = new BufferedInputStream(src);
        OutputStream output = new BufferedOutputStream(dest);
        byte[] data = new byte[1024];
        int length = -1;
        while ((length = input.read(data)) != -1) {
            output.write(data, 0, length);
        }
        input.close();
        output.close();
    }

 完整代码：

package ch9;
import java.io.*;

public class dump {
  public static void main(String[] args) {
    try
    {
      dump(new FileInputStream("D:\\lion.jpg"),
         new FileOutputStream("D:\\bbb.bmp"));  
    }
    catch(FileNotFoundException fex)
    {
      fex.printStackTrace();
    }
    catch(IOException ioe)
    {
      ioe.printStackTrace();
    }
  }
  
  public static void dump(InputStream src, OutputStream dest) throws IOException
  {
    InputStream input = new BufferedInputStream(src);
    OutputStream output = new BufferedOutputStream(dest);
    byte[] data = new byte[1024];
    int length = -1;
    while((length = input.read(data))!= -1) {
      output.write(data, 0, length);
    }
    input.close();
    output.close();
  }
  
  
}

2.ReadLineAndAddNum

读入一个java文件，然后去掉注释，加上行号。

主要部分：

try {
      File fin = new File(infname);
      File fout = new File(outfname);
      
      BufferedReader in = new BufferedReader(new FileReader(fin));
      PrintWriter out = new PrintWriter(new FileWriter(fout));
      
      int cnt =0;
      String s = in.readLine();
      while(s!=null) {
        cnt++;
        s = deleteComments(s);
        out.println(cnt+":\t"+s);
        s = in.readLine();
    }
      in.close();
      out.close();
    }catch(FileNotFoundException e1) {
      System.err.println("File not found");
    }catch(IOException e2) {
      e2.printStackTrace();  
    }
  }

package ch9;
import java.io.*;
public class ReadLineAndAddNum {
  public static void main(String[] args) {
    String infname = "C:\\Users\\刘飞\\eclipse-workspace\\ch9\\src\\ch9\\CopyFileAddLineNumber.java";
    String outfname = "C:\\Users\\刘飞\\eclipse-workspace\\ch9\\src\\ch9\\CopyFileAddLineNumber.txt";
    if(args.length >=1) infname = args[0];
    if(args.length>=2) outfname = args[1];
    
    try {
      File fin = new File(infname);
      File fout = new File(outfname);
      
      BufferedReader in = new BufferedReader(new FileReader(fin));
      PrintWriter out = new PrintWriter(new FileWriter(fout));
      
      int cnt =0;
      String s = in.readLine();
      while(s!=null) {
        cnt++;
        s = deleteComments(s);
        out.println(cnt+":\t"+s);
        s = in.readLine();
    }
      in.close();
      out.close();
    }catch(FileNotFoundException e1) {
      System.err.println("File not found");
    }catch(IOException e2) {
      e2.printStackTrace();  
    }
  }
  
  static String deleteComments(String s)
  {
    if(s==null) return s;
    int pos = s.indexOf("//");
    if(pos<0) return s;
    return s.substring(0, pos);
  }
  
}