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最初java是不支持对文本文件的处理的,为了弥补这个缺憾而引入了Reader和Writer两个类,这两个类都是抽象类,Writer中write(char[] ch,int off,int length),flush()和close()方法为抽象方法,Reader中read(char[] ch,int off,int length)和close()方法是抽象方法。子类应该分别实现他们。

  当我们读写文本文件的时候,采用Reader是非常方便的,比如FileReader,InputStreamReader和BufferedReader。其中最重要的类是InputStreamReader,它是字节转换为字符的桥梁。你可以在构造器重指定编码的方式,如果不指定的话将采用底层操作系统的默认编码方式,例如GBK等。当使用FileReader读取文件的时候。

  FileReader fr = new FileReader("ming.txt");
  int ch = 0;
  while((ch = fr.read())!=-1 )
  {
  System.out.print((char)ch);
  }

  其中read()方法返回的是读取得下个字符。当然你也可以使用read(char[] ch,int off,int length)这和处理二进制文件的时候类似,不多说了。如果使用InputStreamReader来读取文件的时候

  while((ch = isr.read())!=-1)
  {
  System.out.print((char)ch);
  }

  这和FileReader并没有什么区别,事实上在FileReader中的方法都是从InputStreamReader中继承过来的。read()方法是比较好费时间的,如果为了提高效率我们可以使用BufferedReader对Reader进行包装,这样可以提高读取得速度,我们可以一行一行的读取文本,使用readLine()方法。

  BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream("ming.txt")));
  String data = null;
  while((data = br.readLine())!=null)
  {
  System.out.println(data);
  }

  当你明白了如何用Reader来读取文本文件的时候那么用Writer写文件同样非常简单。有一点需要注意,当你写文件的时候,为了提高效率,写入的数据会先放入缓冲区,然后写入文件。因此有时候你需要主动调用flush()方法。与上面对应的写文件的方法为:

  FileWriter fw = new FileWriter("hello.txt");
  String s = "hello world";
  fw.write(s,0,s.length());
  fw.flush();

  OutputStreamWriter osw = new OutputStreamWriter(new FileOutputStream("hello2.txt"));
  osw.write(s,0,s.length());
  osw.flush();

  PrintWriter pw = new PrintWriter(new OutputStreamWriter(new FileOutputStream("hello3.txt")),true);
  pw.println(s);

  不要忘记用完后关闭流!下面是个小例子,帮助新手理解。其实有的时候java的IO系统是需要我们多记记的,不然哪天就生疏了。

  hello world i like java language

  import java.io.*;

  public class TestFile2
  {
  public static void main(String[] args) throws IOException
  {
  FileReader fr = new FileReader("ming.txt");
  char[] buffer = new char[1024];
  int ch = 0;
  while((ch = fr.read())!=-1 )
  {
   System.out.print((char)ch);
  }

  InputStreamReader isr = new InputStreamReader(new FileInputStream("ming.txt"));
  while((ch = isr.read())!=-1)
  {
   System.out.print((char)ch);
  }

  BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream("ming.txt")));
  String data = null;
  while((data = br.readLine())!=null)
  {
   System.out.println(data);
  }

  FileWriter fw = new FileWriter("hello.txt");
  String s = "hello world";
  fw.write(s,0,s.length());
  fw.flush();

  OutputStreamWriter osw = new OutputStreamWriter(new FileOutputStream("hello2.txt"));
  osw.write(s,0,s.length());
  osw.flush();

  PrintWriter pw = new PrintWriter(new OutputStreamWriter(new FileOutputStream("hello3.txt")),true);
  pw.println(s);

  fr.close();
  isr.close();
  br.close();
  fw.close();
  osw.close();
  pw.close();
  }
  }




import java.io.*;
import java.util.*;
public class test{
 
public static void main(String[] args) {
  String ss="1$2$3$";
  StringTokenizer token = new StringTokenizer(ss, "$", false);
 
  while(token.hasMoreElements()){
   String sToken = (token.nextElement()).toString();
     System.err.println(sToken);
  }
}
}









import java.io.*;

import java.util.*;

import javax.swing.*;


public class ExchangeFile {

    //private String fileName;
    public void transferToTxtFile(String fileName, ArrayList applyBean) throws
            IOException {
        char token = '$';
        StringBuffer sb = new StringBuffer();
        UserInfo[] userInfoArray = new UserInfo[applyBean.size()];
        String saveFileName = "d:\\" + fileName;

        BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(new
                FileOutputStream(saveFileName)));

        for (int i = 0; i < applyBean.size(); i++) {
            userInfoArray[i] = (UserInfo) applyBean.get(i);
            sb.append(userInfoArray[i].getUserName());
            sb.append(token);
            sb.append(userInfoArray[i].getUserAge());
            sb.append(token);
            writer.write(sb.toString());
            writer.newLine(); //line separator as defined by the system property line.separator.
            writer.flush();
            sb.delete(0, sb.length());
        }

        writer.close();
    }

    public ArrayList getFromTxtFile(String fileName) throws IOException {
        String readFileName = "d:\\" + fileName;

        BufferedReader reader = new BufferedReader(new InputStreamReader(new
                FileInputStream(readFileName)));
        String str = null;
        StringTokenizer token;
        ArrayList sToken = new ArrayList();
        ArrayList aL = new ArrayList();
        int i = 0;
        while ((str = reader.readLine()) != null) {
            token = new StringTokenizer(str, "$", false);
            while (token.hasMoreTokens()) {
                String tempToken = (token.nextToken()).toString();
                sToken.add(tempToken);
            }
            UserInfo user = new UserInfo();
            user.setUserName((String) sToken.get(0));
            user.setUserAge((String) sToken.get(1));
            sToken.clear();
            aL.add(user);
            i++;
        }
        reader.close();
        return aL;
    }

    public static void main(String[] args) throws IOException {
        // JOptionPane.showInputDialog("test 'transferToTxtFile' input 1 please;test getFromTxtFile input 2 please" );
        UserInfo user1 = new UserInfo();
        user1.setUserName("ytfei");
        user1.setUserAge("21");
        UserInfo user2 = new UserInfo();
        user2.setUserName("feixiang");
        user2.setUserAge("22");
        ArrayList aL = new ArrayList();
        aL.add(user1);
        aL.add(user2);
        ExchangeFile efile = new ExchangeFile();
        efile.transferToTxtFile("1.txt", aL);
        aL.clear();
        /*
                 ExchangeFile efile = new ExchangeFile();
                 ArrayList aL = efile.getFromTxtFile("1.txt");
                 System.out.println(((UserInfo)aL.get(0)).getUserName());
                 System.out.println(((UserInfo)aL.get(0)).getUserAge());
                 System.out.println(((UserInfo)aL.get(1)).getUserName());
                 System.out.println(((UserInfo)aL.get(1)).getUserAge());
         */

    }
}


class UserInfo {
    private String userName;
    private String userAge;

    public void setUserName(String username) {
        this.userName = username;
    }

    public String getUserName() {
        return this.userName;
    }

    public void setUserAge(String age) {
        this.userAge = age;
    }

    public String getUserAge() {
        return this.userAge;
    }
}









posted on 2005-04-12 17:43  飞翔  阅读(626)  评论(0编辑  收藏  举报