（一）FileReader

（1）第一种读取方式

package com.songyan.fileReader;

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

/**
 * FileReader第一种读取方式
 * @author Administrator
 *
 */
public class Demo1 {
    public static void main(String[] args) throws IOException {
        FileReader fileReader=new FileReader("demo.txt");
        int ch=0;
        while((ch=fileReader.read())!=-1)
        {
            System.out.print((char)ch);
        }
        fileReader.close();
    }

}

（2）第二种读取方式

package com.songyan.fileReader;

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

public class Demo2 {
public static void main(String[] args) throws IOException {
    FileReader reader=new FileReader("demo.txt");
    char[] arr=new char[8192];
    int len=0;
    while((len=reader.read(arr))!=-1)
    {
        System.out.print(new String(arr));
    }
    reader.close();
}
}

（二）FileWriter

package com.songyan.filewriter;

import java.io.FileWriter;
import java.io.IOException;
/**
 * 第一个demo
 * @author Administrator
 *
 */
public class Demo1 {
    public static void main(String[] args) {
        try {
            FileWriter fileWriter=new FileWriter("/src/com/songyan/fileReader/Demo2.java");
            fileWriter.write("hahha");
            fileWriter.flush();
            fileWriter.close();
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

}

异常处理

package com.songyan.filewriter;

import java.io.FileWriter;
import java.io.IOException;
/**
 * 标准IO处理异常的方式
 * @author Administrator
 *
 */
public class Demo2 {
public static void main(String[] args) {
    FileWriter fileWriter=null;
    try {
        fileWriter = new FileWriter("demo1.txt");
        fileWriter.write("hahahh");
        fileWriter.flush();
    } catch (IOException e) {
        e.printStackTrace();
    }finally{
        try {
            if(fileWriter!=null)
                fileWriter.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

}
}

换行符&&续写

package com.songyan.filewriter;

import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.IOException;
/**
 *
 * @author Administrator
 * 回车符：\r\n
 * 续写：
 */
public class Demo3 {
public static void main(String[] args) {
    FileWriter writer=null;
    try {
        writer = new FileWriter("demo1.txt");
        writer.write("dddd\r\n");
        writer.write("dddd\r\n");
        writer.write("dddd\r\n");
        writer.flush();
    } catch (IOException e) {
        e.printStackTrace();
    }finally{
        try {
            if(writer!=null)
                writer.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

}
}

（三）代码练习

打印一个java文件控制台

package com.songyan.test;

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

/**
 * 打印一个java文件到控制台
 * @author Administrator
 *
 */
public class Test1 {
public static void main(String[] args) throws IOException {
    FileReader reader=new FileReader("src/com/songyan/fileReader/Demo2.java");
    char[] arr=new char[8192];
    int len=0;
    while((len=reader.read(arr))!=-1)
    {
        System.out.print(new String(arr));
    }
    reader.close();

}
}

将c盘一个文件拷贝到D盘

package com.songyan.test;

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

/**
 * 将c盘一个文件拷贝到D盘
 * @author Administrator
 *
 */
public class Test2 {
    /**
     * 读一个写一个
     * @throws IOException
     */
    public static void copy1() throws IOException
    {
        FileReader reader=new FileReader("C:\\Users\\langchao1\\AppData\\Local\\IconCache.db");
        FileWriter writer=new FileWriter("D:\\IconCache1.db");
        int sig=0;
        while((sig=reader.read())!=-1)
        {
            writer.write((char)sig);
        }
        reader.close();
        writer.close();
    }

    /**
     * 先读后写
     * @throws IOException
     */
    public static void copy_my() throws IOException
    {
        //读取C盘文件
        FileReader reader=new FileReader("C:\\Users\\langchao1\\AppData\\Local\\IconCache.db");
        char[] arr=new char[8192];
        int len=0;
        String str="";
        while((len=reader.read(arr))!=-1)
        {
            str=str+new String(arr);
        }
        //写入D盘
        FileWriter writer=new FileWriter("D:\\IconCache.db");
        writer.write(str);
        writer.flush();
        writer.close();
    }

    /**
     * 一次读取arr【】
     */
    public static void copy2()
    {
        FileReader reader=null;
        FileWriter writer=null;

        try{
             reader=new FileReader("C:\\Users\\langchao1\\AppData\\Local\\IconCache.db");
             writer=new FileWriter("D:\\I.db");
             char[] arr=new char[8192];
             int len=0;
             while((len=reader.read(arr))!=-1)
             {
                 writer.write(arr);
             }

        }catch(IOException e)
        {
            e.printStackTrace();
        }finally{
            try {
                if(reader!=null)
                    reader.close();
                if(writer!=null)
                    writer.close();
            } catch (Exception e2) {
            }
        }
    }

    /**
     * 最优形式：只读取有效部分
     */
    public static void copy_final()
    {
        FileReader reader=null;
        FileWriter writer=null;

        try{
             reader=new FileReader("C:\\Users\\langchao1\\AppData\\Local\\IconCache.db");
             writer=new FileWriter("D:\\I.db");
             char[] arr=new char[8192];
             int len=0;
             while((len=reader.read(arr))!=-1)
             {
                 writer.write(arr,0,len);
             }

        }catch(IOException e)
        {
            e.printStackTrace();
        }finally{
            try {
                if(reader!=null)
                    reader.close();
                if(writer!=null)
                    writer.close();
            } catch (Exception e2) {
            }
        }
    }
public static void main(String[] args) throws Exception {

    copy2();

}
}

原文地址：https://www.cnblogs.com/excellencesy/p/9188944.html