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("\r\n");
             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!");
             }
         }

     }

 }