java笔记八：IO流之字符流与字符缓冲流

　　java中字符流主要都是继承于Reader和Writer两个抽象类。用于对字符文本的读写操作。

一、转换类流

package com.iotest;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;

public class ConverseStreamDemo {

    public static void main(String[] args) {
        String s = "F:\\shar\\test\\test3.txt";
        try {
            //将字节流转为字符流
            OutputStreamWriter osw = new OutputStreamWriter(new FileOutputStream(s));
            osw.write("中国北京");
            System.out.println(osw.getEncoding());
            osw.close();
            osw = new OutputStreamWriter(new FileOutputStream(s,true),"GB2312");
            osw.write("中国北京");
            System.out.println(osw.getEncoding());
            osw.close();
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        try {
            //将字节流转为字符流
            InputStreamReader isr = new InputStreamReader(new FileInputStream(s),"GB2312");
            int c;
            while((c=isr.read()) != -1){
                System.out.print((char)c);
            }
            System.out.println();
            isr.close();
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();

        }
    }

}

二、FileReader和FileWriter

package com.iotest;

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
/*
 * 使用flush（）将流数据刷到目标里，这时流还存活着，还可以继续使用该流进行别的操作。
 * close（）虽然也有flush（）的效果但是这时流已经死了，你如果想继续使用流的话就必须在此建立流
 */
public class MutiplicationTable {
    
    public static void main(String[] args) throws IOException {
        String s = "F:\\shar\\test\\test5.txt";
        FileWriter fw = new FileWriter(s);
        FileReader fr = new FileReader(s);
        for (int i = 1; i <= 9; i++) {
            for (int j = 1; j <= i; j++) {
                String str = i + "*" + j + "=" + i*j + " ";
                fw.write(str);
            }
            fw.write("\r\n");
            /*flush是指强行将输出流中的数据写到文件里面去。如果写到这里的话就是一行一行的写入文件
             *最好每写完一部分就刷新一次，如果最后刷新的话可能会造成数据的丢失
             */
            fw.flush(); 
        }
        //如果又不写flush()又不写close()，则不会写入任何内容到文本里。只是写到了缓冲区
        //fw.flush(); 写到这里的话就是所有的内容一起写进文件
        //fw.close(); close之前会调用flush()
        //读字符输入流的数据
        int c;
        while ((c=fr.read())!=-1) {
            System.out.print((char)c);
        }
    }

}

三、BufferedReader和BufferedWriter

package com.iotest;

import java.io.BufferedOutputStream;
import java.io.BufferedWriter;
import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.IOException;

public class PrimeNumber {
    BufferedWriter bw = null;
    String fileName = "F:\\shar\\test\\test7.txt";
    //判断是否是质数
    public boolean isPrime(int n){
        for(int i=2;i<=n/2;i++){
            if(n%i == 0){
                return false;
            }
        }
        return true;
    }
    void printPrime(int m) throws IOException{
        //将字节流转缓冲流
        bw = new BufferedWriter(new FileWriter(fileName));
        int j = 0;
        for (int i = 2; i < m; i++) {
            if(isPrime(i)){
                j++;
                String s = String.valueOf(i);
                String s1 = s + " ";
                bw.write(s1);  //写入文本文件
                if(j==10){
                    j = 0;
                    bw.newLine();  //写入一个行分隔符
                    bw.flush();  //强制刷新
                }
            }
        }
        
        bw.close();
    }
    public static void main(String[] args) throws IOException {
        PrimeNumber pn = new PrimeNumber();
        pn.printPrime(100);
    }

}

四、PrintWriter

package com.iotest;

import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;

public class PrintWriterDemo {

    public static void main(String[] args) throws IOException {
        int A = 0;  //千位
        int B = 0;  //百位
        int C = 0;  //十位
        int num = 0;
        String fileName = "F:\\shar\\test\\test8.txt";
        FileWriter fw = new FileWriter(fileName); //字符输出流
        PrintWriter pw = new PrintWriter(fw);     //将字节输出流转为PrintWriter
        for (int i = 1000; i < 10000; i++) {
            A = i/1000;
            B = i/100 % 10;
            C = i/10 % 10;            
            if(i%11==0 && A == B+C){
                pw.print(i+" ");
                if(++num % 7 == 0){
                    pw.println();  //写入回车换行
                    pw.flush();    //强制刷新流
                }
            }
        }
        fw.close();
        
    }

}

五、标准IO

package com.iotest;

import java.io.BufferedReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.Scanner;

public class PackStardIO {

    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        PrintWriter o = new PrintWriter(System.out);  //包装标准输出
        String s;
        while((s=br.readLine())!=null && s.length()!=0){
            o.println(s.toUpperCase());
            //o.flush();   //一定要强制刷新让其输出来，否则不会输出
        }
    }

}

package com.iotest;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintStream;

public class StandardIORedirect {

    public static void main(String[] args) throws IOException {
        PrintStream console = System.out;
        BufferedInputStream in = new BufferedInputStream(new FileInputStream("C:\\Documents and Settings\\01\\桌面\\Test\\src\\com\\iotest\\StandardIORedirect.java"));
        PrintStream out = new PrintStream(new BufferedOutputStream(new FileOutputStream("F:\\shar\\test\\test9.txt")));
        System.setIn(in);     //对标准输入流重定向
        System.setOut(out);
        System.setErr(out);
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String s;
        while((s=br.readLine())!=null){   //从BufferedReader中读取一行数据
            System.out.println(s);
        }
        out.close();
        System.setOut(console);
    }

}

六、随即访问文件类

package com.iotest;

import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;

public class RandomRW {
    public static void main(String[] args) throws IOException {
        RandomAccessFile raf = new RandomAccessFile("F:\\shar\\test\\test10.dat","rw");
        final int DOUBLE_SIZE = 8;
        for (int i = 0; i < 10; i++) {
            raf.writeDouble(i);
            System.out.print(" " + (double)i);
        }
        System.out.println();
        raf.close();
        RandomAccessFile raf1 = new RandomAccessFile("F:\\shar\\test\\test10.dat","rw");
        raf1.seek(3*DOUBLE_SIZE);  //找到某个位置
        raf1.writeDouble(300);     //往该位置插入数据
        raf1.seek(5*DOUBLE_SIZE);
        raf1.writeDouble(500);
        raf1.close();
        RandomAccessFile raf2 = new RandomAccessFile("F:\\shar\\test\\test10.dat","r");
        for (int i = 0; i < 10; i++) {
            System.out.print(" "+raf2.readDouble());
        }
        raf2.close();
    }

}