Java: IO 字节流

　　FileReader是InputStreamReader的子类，InputStreamReader是Reader的子类。Reader系列是输入字符流。

1.一个字符一个字符的读取

import java.io.*;

public class FileReaderDemo {

    public static void main(String[] args) {
        FileReader fr = null;
        try{
            fr = new FileReader("FileWriterDemo.txt");
            int ch =0;
            while((ch = fr.read())!=-1){
                System.out.print((char)ch);
            }
        }
        catch(IOException e){
            System.out.println(e.toString());            
        }
        finally{
            try{
                if(fr!=null)
                    fr.close();
            }
            catch(IOException e){
                System.out.println(e.toString());
            }

        }

    }

}

2.使用字符数组临时存储读取的字符，数组长度可以自定义

import java.io.FileReader;
import java.io.IOException;

public class FileReaderDemo2 {

    public static void main(String[] args) {
        FileReader fr = null;
        try{
            fr = new FileReader("FileWriterDemo.txt");
            //定义字符数组用于存储读到的字符
            char[] buf = new char[1024];
            int aLength = fr.read(buf);
            for(int x = 0;x< aLength;x++)
            {
                System.out.print(buf[x]);
            }
            
        }
        catch(IOException e){
            System.out.println(e.toString());
        }
        finally{
            try{
                if(fr!=null)
                    fr.close();
            }
            catch(IOException e){
                System.out.println(e.getStackTrace());
            }
        }

    }

}

　　为了提高读取效率，加入BufferedReader(Reader in)缓冲技术，该类可以使用readLine方法，一次读取一行。

import java.io.*;

public class BufferedReaderDemo {

    public static void main(String[] args) {
        //创建一个读取流对象
        FileReader fr = null;
        try{
            fr = new FileReader("xinwen.txt");
            //加入缓冲技术，提高读取效率
            BufferedReader bufr = new BufferedReader(fr);
            
            String line = null;
            while((line=bufr.readLine())!=null){
                System.out.println(line);
            }
            bufr.close();
        }
        catch(IOException e){
            e.printStackTrace();
        }
        finally{
            try{
                if(fr!=null)
                    fr.close();
            }
            catch(IOException e){
                e.printStackTrace();
            }            
        }
    }
}

　　FileWriter是OutputStreamWriter的子类，而OutputStreamWriter是Writer的子类。Writer系列是输出字符流。

import java.io.*;

public class FileWriterDemo {

    public static void main(String[] args)throws IOException {
        FileWriter fw = null;
        try {
            fw = new FileWriter("FileWriterDemo.txt",true);
            fw.write("2015");
            fw.write("
");
            fw.write("一起努力！");
            
            fw.flush();            
        }
        catch(IOException e){
            System.out.println(e.toString());
        }
        finally{
            try{
                if(fw!=null)
                    fw.close();
            }
            catch(IOException e){
                System.out.println(e.toString());
            }
        }
    }

}

　　为了提阿写入效率，使用BufferedWriter(Writer wr)缓冲技术，该类中的newLine方法可以输出一个换行符，而且是跨平台的。　　

　　把输入、输出结合起来，模拟复制文件。方法一，不使用缓冲技术

import java.io.*;

public class FileCopyDemo {

    public static void main(String[] args) {
        
        //copy1();
        copy2();
    }
    //读一个字符就存一个
    public static void copy1(){
    //创建目的文件
        FileWriter fw = null;
    //与已有文件关联
        FileReader fr = null;
        
        try{
            fw = new FileWriter("/home/owen/news_copy.txt");
            fr = new FileReader("news.txt");
            int ch = 0;
            while((ch=fr.read())!=-1){
                fw.write(ch);
            }
        }
        catch(IOException e){
            System.out.println(e.getStackTrace());
        }
        finally{
            try{
                if(fw!=null)
                    fw.close();
                if(fr!=null)
                    fr.close();
            }
            catch(IOException e){
                System.out.println(e.getStackTrace());
            }
        }
    }
    public static void copy2(){
        FileWriter fw = null;
        FileReader fr = null;
        try{
            fw = new FileWriter("news_copy2.txt");
            fr = new FileReader("news.txt");
            
            char[] buf = new char[1024];
            int len = 0;
            while((len = fr.read(buf))!=-1){
                fw.write(buf,0,len);
            }
        }
        catch(IOException e){
            throw new RuntimeException("读写失败");
        }
        finally{
            if(fr!=null){
                try{
                    fr.close();
                }
                catch(IOException e){
                    System.out.println(e.getStackTrace());
                }
            }
            if(fw!=null){
                try{
                    fw.close();
                }
                catch(IOException e){
                    System.out.println(e.getStackTrace());
                }
            }
        }
    }

}

　　方法二，使用缓冲技术

import java.io.*;

public class CopyByBuffered {

    public static void main(String[] args) {
        BufferedReader bufr = null;
        BufferedWriter bufw = null;
        try{
            bufr = new BufferedReader(new FileReader("BufferedReaderDemo.java"));
            bufw = new BufferedWriter(new FileWriter("BufferedReaderDemo_copy.txt"));
            
            String line = null;
            while((line = bufr.readLine())!=null){
                bufw.write(line);
                bufw.flush();
                bufw.newLine();
            }
        }
        catch(IOException e){
            throw new RuntimeException("复制失败！");
        }
        finally{
            try{
                if(bufr!=null)
                    bufr.close();
            }
            catch(IOException e){
                throw new RuntimeException("Read file mission failed!");
            }
            try{
                if(bufw!=null)
                    bufw.close();
            }
            catch(IOException e){
                throw new RuntimeException("Write file mission failed!");
            }
        }

    }

}