Java的I/O 笔记（2）

 

FileInputStream的练习：

import java.io.*;
public class TestFileInputStream {
  public static void main(String[] args) {
    int b = 0;
    FileInputStream in = null;
    try {
      in = new FileInputStream("d:\\share\\java\\io\\TestFileInputStream.java");
    } catch (FileNotFoundException e) {           //如果没有throws语句，则使用try…catch
      System.out.println("找不到指定文件");
      System.exit(-1);
    }

    try {
      long num = 0;     //num记录读取的字节数
      while((b=in.read())!=-1){
        System.out.print((char)b);
        num++;
      }
      in.close();
      System.out.println();
      System.out.println("共读取了 "+num+" 个字节");
    } catch (IOException e1) {
      System.out.println("文件读取错误"); System.exit(-1);
    }
  }
}

 

  这段代码是用FileInputStream读取d:\share\java\io\TestFileInputStream.java位置的文件，读取的内容就是以上代码。

由于是字节流，只能一个字节一个字节的读取，所以文件中的汉字都无法读取。

 

FileOutPutStream的练习：

import java.io.*;
public class TestFileOutputStream {
  public static void main(String[] args) {
      int b = 0;
      FileInputStream in = null;   //定义流实例in和out，指向null
      FileOutputStream out = null;
      try {
        in = new FileInputStream("d:/share/java/HelloWorld.java");   //将in和out指向具体的文件
        out = new FileOutputStream("d:/share/java/io/HW.java");  如没有此文件，则自动新建
        while((b=in.read())!=-1){
          out.write(b);
        }
        in.close();
        out.close();
      } catch (FileNotFoundException e2) {
        System.out.println("找不到指定文件"); System.exit(-1);
      } catch (IOException e1) {
        System.out.println("文件复制错误"); System.exit(-1);
      }
      System.out.println("文件已复制");
  }
}

 

 

注意：文件地址的写法问题，如果用/的话，要在前面加一个/用来和转义符区别。也可以用\，就不用那么麻烦。转移符里用的是\n,\t之类。

             d:/share/java/HelloWorld.java   

等同于：  d:\\share\\java\\HelloWorld.java

FileReader 练习：

import java.io.*;
public class TestFileReader {
  public static void main(String[] args) {
    FileReader fr = null;
    int c = 0;
    try {
      fr = new FileReader("d:\\share\\java\\io\\TestFileReader.java");
      int ln = 0;
      while ((c = fr.read()) != -1) {
        //char ch = (char) fr.read();
        System.out.print((char)c);
        //if (++ln >= 100) { System.out.println(); ln = 0;}
      }
      fr.close();
    } catch (FileNotFoundException e) {
      System.out.println("找不到指定文件");
    } catch (IOException e) {
      System.out.println("文件读取错误");
    }

  }
}

 

FileWriter 练习：

import java.io.*;
public class TestFileWriter {
  public static void main(String[] args) {
    FileWriter fw = null;
    try {
      fw = new FileWriter("d:\\bak\\unicode.dat");
      for(int c=0;c<=50000;c++){
        fw.write(c);
      }
      fw.close();
    } catch (IOException e1) {
        e1.printStackTrace();
      System.out.println("文件写入错误");
      System.exit(-1);
    }
  }
}

 

 

import java.io.*;

public class TestFileWriter2 {
    public static void main(String[] args) throws Exception {
        FileReader fr = new FileReader("d:/java/io/TestFileWriter2.java");
        FileWriter fw = new FileWriter("d:/java/io/TestFileWriter2.bak");
        int b;
        while((b = fr.read()) != -1) {
            fw.write(b);
        }
        fr.close();
        fw.close();
    }
}

 

---

 

 

缓冲流  要“套接”在相应的节点流之上，对读写的数据提供了缓冲的功能，提高了读写的效率。

J2SDK提供了四种缓冲流&构造方法：

BufferedReader ------(Reader in) , (Reader in , int size)       size为自定义缓冲区的大小

BufferedWriter--------(Writer out) , (Writer out , int size)  

BufferedInputStream----(InputStream in ) , (InputStream in , int size)

BufferedOutputStream---(OutputStream out ) , (OutputStream out , int size)

 

观察构造方法的参数，可看成是Buffer套接在Reader,Writer,InputStream,OutputStream外面。

 

   1:  import java.io.*;

   2:  public class TestBufferStream1 {

   3:    public static void main(String[] args) {

   4:      try {

   5:        FileInputStream fis = 

   6:                new FileInputStream("d:\\share\\java\\HelloWorld.java");

   7:        BufferedInputStream bis = 

   8:                new BufferedInputStream(fis);

   9:        int c = 0;

  10:        System.out.println(bis.read());

  11:        System.out.println(bis.read());

  12:        bis.mark(100);

  13:        for(int i=0;i<=10 && (c=bis.read())!=-1;i++){

  14:          System.out.print((char)c+" ");

  15:        }

  16:        System.out.println(); 

  17:        bis.reset();

  18:        for(int i=0;i<=10 && (c=bis.read())!=-1;i++){

  19:          System.out.print((char)c+" ");

  20:        }

  21:        bis.close();

  22:      } catch (IOException e) {e.printStackTrace();}

  23:    }

  24:  }

import java.io.*;
public class TestBufferStream2 {
  public static void main(String[] args) {
    try {
      BufferedWriter bw = new BufferedWriter(new FileWriter("d:\\share\\java\\dat2.txt"));
      BufferedReader br = new BufferedReader(
             new FileReader("d:\\share\\java\\dat2.txt"));
      String s = null;
      for(int i=1;i<=100;i++){
        s = String.valueOf(Math.random());
        bw.write(s);    //将s输出到文件
        bw.newLine();   //写出一个空行
      }
      bw.flush();   // Writer的flush()方法
      while((s=br.readLine())!=null){    //BufferedReader 的readline方法可以一次读取一行text
        System.out.println(s);
      }
      bw.close();
      br.close();
    } catch (IOException e) { e.printStackTrace();}
  }
}