JAVA之旅（二十五）——文件复制,字符流的缓冲区，BufferedWriter，BufferedReader，通过缓冲区复制文件，readLine工作原理，自定义readLine

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一.文本复制

• 复制原理：其实就是将C盘下的文件数据存储到D盘的一个文件中

package com.lgl.hellojava;

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

public class HelloJJAVA {
    public static void main(String[] args) {

        copy_1();
        copy_2();
    }

    // 从c盘读一个字符，就往D盘写一个字符
    public static void copy_1() {
        try {
            // 创建目的地
            FileWriter fw = new FileWriter("copy_1.txt");
            // 与已有文件关联
            FileReader fr = new FileReader("copy_1.txt");
            int ch = 0;
            while ((ch = fr.read()) != -1) {
                // 读一个 写一个
                fw.write(ch);
            }
            fw.close();
            fr.close();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    public static void copy_2() {
        FileWriter fw = null;
        FileReader fr = null;

        try {
            fw = new FileWriter("copy_2.txt");
            fr = new FileReader("copy_2.txt");

            char[] buf = new char[1024];

            int len = 0;
            while ((len = fr.read(buf)) != -1) {
                fw.write(buf, 0, len);
            }
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            if (fr != null) {
                try {
                    fr.close();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }

            if (fw != null) {
                try {
                    fw.close();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }
    }
}

二.字符流的缓冲区

• BufferedWriter
• BufferedReader

1.BufferedWriter

package com.lgl.hellojava;

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

public class HelloJJAVA {
    public static void main(String[] args) {

        try {
            // 创建一个字符写入流对象
            FileWriter fw = new FileWriter("buffer.txt");
            // 为了提高写入流的效率加入了缓冲技术
            BufferedWriter bufw = new BufferedWriter(fw);
            //写入数据
            bufw.write("hello");
            //换行
            bufw.newLine();

            //只要用到了缓冲区，就需要刷新
            bufw.flush();

            //缓冲区关闭的就是关联的流
            bufw.close();

        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }
}

2.BufferedReader

package com.lgl.hellojava;

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;

public class HelloJJAVA {
    public static void main(String[] args) {

        try {
            // 创建一个读取流对象和文件相关联
            FileReader fr = new FileReader("buffer.txt");
            // 为了提高效率，加入缓冲技术
            BufferedReader bfr = new BufferedReader(fr);

            String line = null;
            while((line = bfr.readLine()) != null){
                System.out.println(line);
            }
            bfr.close();
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }
}

三.通过缓冲区复制文件

package com.lgl.hellojava;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class HelloJJAVA {
    public static void main(String[] args) {
        /**
         * 缓冲区文件复制
         */
        BufferedReader bufr = null;
        BufferedWriter bufw = null;

        try {
            bufr = new BufferedReader(new FileReader("buffer.txt"));
            bufw = new BufferedWriter(new FileWriter("buffercopy.txt"));

            String line = null;

            while((line = bufr.readLine()) != null){
                bufw.write(line);
            }

            //关闭流
            bufr.close();
            bufw.close();
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

四.readLine工作原理

• 其实他内存中有一个数组，你读完之后并没有立马读，而是临时存储起来，这就是缓冲区，

五.自定义readLine

package com.lgl.hellojava;

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

public class HelloJJAVA {
    public static void main(String[] args) {
        /**
         * 自定义readLine
         */
        FileReader fr;
        try {
            fr = new FileReader("buffer.txt");
            MyBufferReader my = new MyBufferReader(fr);
            String line = null;

            while ((line = my.myReadLine()) != null) {
                System.out.println(line);
            }
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }
}

class MyBufferReader {

    private FileReader fr;

    public MyBufferReader(FileReader fr) {
        this.fr = fr;
    }

    // 一次读取一行的方法
    public String myReadLine() throws IOException {

        // 定义临时容器
        StringBuilder sb = new StringBuilder();
        int ch = 0;
        while ((ch = fr.read()) != -1) {

            if (ch == '\r') {
                continue;
            } else if (ch == '\n') {
                return sb.toString();
            } else {
                sb.append((char) ch);
            }
        }
        if(sb.length() != 0){
            return sb.toString();
        }
        return null;
    }

    public void close() throws IOException {
        fr.close();
    }
}

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