FileOutputStream如果不理解可以查看API描述
这里不再介绍

package cn.bean.demo.inoutstream;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;

public class FileOutPutStreamTest {

	public static void main(String[] args) {
		testReadWrite();
	}

	static void testReadWrite() {

		// 获从输入流，读取目标资源信息
		try (InputStream in = new FileInputStream("String1.txt");
			 OutputStream out = new FileOutputStream("String2.txt")) 
		{
             //每次读取的内容放入到一个缓冲区
			 byte[] b=new byte[20];
			 //每次放入到缓冲区的字节个数
			 int len=0;
			 while((len=in.read(b))!=-1){
				 out.write(b, 0, len);
			 }
           			 
			
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}

	}

}

package cn.bean.demo.readwrite;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.Reader;
import java.io.Writer;

public class WreteTest {

	public static void main(String[] args) {
		//testReadWrite();
		testOutputStreamWriter();
	}

	static void testReadWrite() {
		try (Reader reader = new FileReader("String1.txt"); Writer writer = new FileWriter("String2.txt");) {
			// 创建每次读取数据的缓冲区，可以想象成水桶
			char[] c = new char[19];
			// 每次装入缓冲区的字节个数
			int len = 0;
			while ((len = reader.read(c)) != -1) {
				// 把每次装入桶中的内容写入到文件中，每次写入0到len，因为len是每次读取到的实际内容个数
				writer.write(c, 0, len);
			}

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

	static void testOutputStreamWriter() {

		try (InputStream in = new FileInputStream("hello.txt");
				Reader read = new InputStreamReader(in, "utf-8");
				OutputStream out = new FileOutputStream("hell22.txt");
				Writer writer = new OutputStreamWriter(out, "utf-8");)

		{
			 
			//创建缓冲区用来存放每次读取的数据
			char[] ch=new char[50];
			//每次放入到缓冲区的数据的实际个数
			int len=0;
			String content="";
			while((len=read.read(ch))!=-1){
                                // 这样也可以 writer.write(ch, 0, len);
				content+=new String(ch,0,len);
			}
			writer.write(content);
			System.out.println(content);

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

	}

}