JAVA IO

一、关于Java IO的概述

• IO流用来处理设备之间的数据传输
• Java对数据的操作是通过流的方式
• Java用于操作流的对象都在IO包中
• IO流按照流向划分为输入流、输出流
• IO流按照操作数据划分为字符流（专门处理文字）、字节流

我理解的程序处理数据过程大致如下：

二、File相关操作

一个File类的实例代表一个文件或文件夹，File.pathSeparator指的是分隔连续多个路径字符串的分隔符，File.separator才是用来分隔同一个路径字符串中的目录的。由于java可跨平台，所以当new一个File时，路径中的“;"和"/"要用File.pathSeparator和File.separator代替。

File常用的构造方法

import java.io.File;

public class IOTest {
	public static void main(String[] args) {
		File file1=new File("D:"+File.separator+"IOTest.Java");//文件绝对路径
		File file2=new File("D:"+File.separator+"IO");//目录的绝对路径
		File file3=new File(file2, "IOTest.java");//第一个参数File实例代表一个目录file2，第二个参数为file2目录内的文件名
		File file4=new File("D:"+File.separator+"IO", "IOTest.java");//目录和文件的字符串类型
		
	}
}

File的常用方法

	file1.createNewFile();
		System.out.println("file1.isFile():  " + file1.isFile());
		System.out.println("file1.isDirectory():  " + file1.isDirectory());
		System.out.println("file1.getName():  " + file1.getName());
		System.out.println("file1.getAbsolutePath  " + file1.getAbsolutePath());
		file2.mkdir();
		System.out.println("file2.isDirectory():  " + file1.isDirectory());
		String[] list = file2.list();//返回String[]类型的文件 只含文件名
		File[] listFile=file2.listFiles();//返回File[]类型的文件 包含完整的文件对象

其他相关方法的总结如下：

• String getName():返回文件名或路径名（若是路径，返回最后一级子路径名）
• String getPath():返回对象对应的路径名
• File  getAbsoluteFile():返回绝对路径
• String getAbsolutePath():返回对象对应的绝对路径
• String getParent():返回文件目录的上一级目录名
• boolean renameTo(File newName):重命名此File对象对应的文件或目录，若重命名成功返回true;
• boolean exists():判断对象对应的文件或目录是否存在；
• boolean canWrite():判断对象对应文件或目录是否可写；
• boolean canRead():判断对象对应文件或目录是否可读；
• boolean isFile():判断对象是文件，不是目录；
• boolean isDirectory()  判断对象的文件是否是一个目录； 
• boolean isAbsolute() 判断对象对应文件或目录是否为绝对路径名； 
• boolean createNewFile() 当且仅当不存在，该方法创建一个该File对象所指定的新文件，创建成功返回true。 
• boolean delete():删除File对象所对应的文件或路径；
• boolean mkdir() 创建File对象所对应的目录，调用该方法的File对象必须对应路径，而不是文件。
• String[] list():列出File对象的所有子文件名和路径名。
• File[] listFiles():列出File对象的所有子文件和路径。
• static File[] listRoots():列出系统所有的根路径；

对文件的操作前要判断文件是否存在，再做进一步io操作。

练习列出一个目录下所有文件及目录(利用递归)：

public class IOTest {
	public static void main(String[] args) throws Exception {
	
		File file = new File("C:\\Users\\Mr\\Desktop\\源码");
		scan(file);

	}

	private static void scan(File file) {
		// TODO Auto-generated method stub
		File[] files = file.listFiles();
		for (int i = 0; i < files.length; i++) {
			File newfile = files[i];
			if (newfile.isFile()) {
				System.out.println("文件：" + newfile.getName());
			} else {
				System.out.println("目录：" + newfile.getName());
				scan(newfile);
			}
		}
	}
}

文件过滤器，根据文件名或路径获得想要的文件对象

	private static void scan(File file) {
		// TODO Auto-generated method stub
		File[] files = file.listFiles(new FilenameFilter() {

			@Override
			public boolean accept(File dir, String name) {
				// TODO Auto-generated method stub
				return name.contains(".java");
			}
			
		});
		System.out.println(Arrays.toString(files));

	}

通过listfile方法传入一个FilenameFilter接口的实例，复写accept方法，控制想要得到的文件。

三、流

• 字符流

FileReader(直接读取)

import java.io.File;
import java.io.FileReader;

public class FileReaderTest   {
	public static void main(String[] args) throws Exception{
		File file=new File("d:"+File.separator+"test4.txt");
		FileReader reader=new FileReader(file);
		int ch=0;
		while((ch=reader.read())!=-1){
			System.out.print((char)ch);
		}
		reader.close();
	}
}

利用字符数组读取以提高效率

import java.io.File;
import java.io.FileReader;

public class FileReaderTest {
	public static void main(String[] args) throws Exception {
		File file = new File("d:" + File.separator + "test4.txt");
		FileReader reader = new FileReader(file);
		char[] buf = new char[1024];
		int len = 0;
		while ((len = reader.read(buf)) != -1) {
			System.out.print(new String(buf, 0, len));
		}
		reader.close();
	}
}

FileWriter(现有文件追加一行)

import java.io.File;
import java.io.FileWriter;

public class FileWriterTest {
	public static void main(String[] args) throws Exception{
		File file = new File("d:" + File.separator + "test4.txt");
		if(!file.exists())file.createNewFile();
		FileWriter writer=new FileWriter(file,true);//可追加设为true
		writer.write("\r\n-------新追加一行--------");
		writer.close();
	}
}

文本文件复制

import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;

public class Copy {
	public static void main(String[] args) throws Exception {
		File source = new File("d:" + File.separator + "test4.txt");
		File target = new File("d:" + File.separator + "test5.txt");
		if (!target.exists())
			target.createNewFile();
		FileReader reader = new FileReader(source);
		FileWriter writer = new FileWriter(target, true);
		char[] buf = new char[1024];
		int len = 0;
		while ((len = reader.read(buf)) != -1) {
			writer.write(buf, 0, len);
			writer.flush();
		}
		writer.close();
		reader.close();
	}
}

• 字符缓冲流

BufferedReader

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;

public class BufferedReaderTest {
	public static void main(String[] args) throws Exception {
		BufferedReader reader=new BufferedReader(new FileReader("d:" + File.separator + "test4.txt"));
		String line;
		while((line=reader.readLine())!=null){
			System.out.println(line);
		}
	}
}

BufferedWriter

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;

public class BufferedWriterTest {
	public static void main(String[] args) throws Exception {
		BufferedWriter writer=new BufferedWriter(new FileWriter("d:" + File.separator + "test5.txt",true));
		writer.newLine();
		writer.write("新追加一行");
		writer.flush();
		writer.close();
	}
}

文本文件复制(字符缓冲流)

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;

public class CopyByBuf {
	public static void main(String[] args) throws Exception {

		File source = new File("d:" + File.separator + "test4.txt");
		File target = new File("d:" + File.separator + "test6.txt");
		if (!target.exists())
			target.createNewFile();
		BufferedReader reader = new BufferedReader(new FileReader(source));
		BufferedWriter writer = new BufferedWriter(new FileWriter(target));
		String line;
		while ((line = reader.readLine()) != null) {
			writer.write(line);
			writer.newLine();
			writer.flush();
		}
		writer.close();
		reader.close();
	}
}

BufferedReader的子类LineNumberReader.setLineNumber(0)来设置初始行，默认0，getLineNumber()返回行号。

public class BufferedReaderTest {
	public static void main(String[] args) throws Exception {
		LineNumberReader reader=new LineNumberReader(new FileReader("d:" + File.separator + "test4.txt"));
		String line;
		//reader.setLineNumber(0);
		while((line=reader.readLine())!=null){
			System.out.println(reader.getLineNumber()+line);
		}
	}
}

• 字节流

FileInputStream直接读取

public class FileInputStreamTest {
	 public static void main(String[] args) throws Exception {
	 FileInputStream in = new FileInputStream("d:" + File.separator + "test4.txt");
		int ch = 0;
		while ((ch = in.read()) != -1) {
			System.out.print((char) ch);
		}
		in.close();
	}
}	

FileInputStream通过byte[]读取

public class FileInputStreamTest {
	
	public static void main(String[] args) throws Exception {
		FileInputStream in = new FileInputStream("d:" + File.separator + "test4.txt");
		byte[] buf = new byte[1024];
		int len = 0;
		while ((len = in.read(buf)) != -1) {
			System.out.print(new String(buf, 0, len));
		}
 		in.close();
	}
}	

FileOutputStream直接写入数据

public class FileInputStreamTest {
	public static void main(String[] args) throws Exception {
	FileOutputStream out=new FileOutputStream("d:" + File.separator + "test.txt");
	out.write("黑马你好".getBytes("UTF-8"));
	out.close();
 }
}

FileOutputStream和FileInputStream通过byte[]图片

public class FileInputStreamTest {
	public static void main(String[] args) throws Exception {
	FileInputStream in = new FileInputStream("d:" + File.separator + "heima.jpg");
	FileOutputStream out=new FileOutputStream("d:" + File.separator + "heima_copy.jpg");
	byte[] buf = new byte[1024];
	int len = 0;
	while ((len = in.read(buf)) != -1) {
		out.write(buf, 0, len);
	}
	in.close();
	out.close();
}
}	

FileOutputStream和FileInputStream通过BufferedOutputStream和BufferedInputStream复制图片

public class FileInputStreamTest {
	public static void main(String[] args) throws Exception {
		BufferedInputStream in=new BufferedInputStream(new FileInputStream("d:" + File.separator + "heima.jpg"));
		BufferedOutputStream out=new BufferedOutputStream(new FileOutputStream("d:" + File.separator + "heima_copy1.jpg"));
		int data = 0;
		while ((data = in.read()) != -1) {
			out.write(data);
		}
		in.close();
		out.close();
	}
}

• 转换流

System.out:对应的是标准输出设备，控制台。
System.in:对应的标准输入设备：键盘。

而它们都是属于字节流，现在要实现对控制台输入的字符串打印或其他操作，由于是对文本进行操作，FileReader和FileWriter更为方便，怎样将要操作的字节流转换为字符流然后进行操作呢？这里可以用转换流InputStreamReader和OutputStreamReader：

package Blog;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;

public class ConsoleTest {
	public static void main(String[] args) throws Exception {
		BufferedReader reader = new BufferedReader(new InputStreamReader(
				System.in));
		BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(
				System.out));
		String line = null;
		while (!"stop".equals(line) && (line = reader.readLine()) != null) {
			writer.write(line);
			writer.newLine();
			writer.flush();
		}
		writer.close();
		reader.close();
	}
}

• 字符流与字节流的总结

字节流和字符流在处理数据时代码和流程大致相同，字符流其根本也是用的字节流，但是为了处理文字方便加入了类似缓冲块的概念，使其字符流可以对文字的编码进行操作，避免乱码的出现，正因为有了缓冲，所以每次写入后需要flush操作将其刷进目标中，而字节流则不需要。并且字符流读取后close方法时也会对缓冲区进行刷新操作。字符流和字节流两者相比，字节流通用可以处理任何类型数据，但处理处理文本时，由于字符流的编码特性是最为合适的，并且字符流提供了专门处理文本的方便方法，而处理非文本时，一定要使用字节流，如果使用字符流可能复制成功后文件仍无法读取。

• 用流对目录复制

将C盘下目录复制到D盘

package Blog;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;

public class CopyDir {
	public static void main(String[] args) throws Exception {
		File dir_s = new File("c:" + File.separator + "heima");//源目录
		File dir_d = new File("d:" + File.separator + dir_s.getName());//目标目录
		dir_d.mkdir();//创建目录
		DoCopy(dir_s, dir_d);
	}

	private static void DoCopy(File dir_s, File dir_d) throws Exception {
		// TODO Auto-generated method stub

		File[] files = dir_s.listFiles();
		for (File file : files) {
			if (file.isFile()) {//如果是文件 复制
				BufferedInputStream in = new BufferedInputStream(new FileInputStream(file));
				File file_new=new File(dir_d, file.getName());
				file_new.createNewFile();
				BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(file_new));
				int data = 0;
				while ((data = in.read()) != -1) {
					out.write(data);
				}
				in.close();
				out.close();
			} else {//如果是目录 递归
				File dir_new=new File(dir_d,file.getName());
				dir_new.mkdir();
				DoCopy(file,dir_new);//
			}
		}
	}

}

输入两个目录，作为源和目的，将源目录中所有.java文件复制到目的目录中同时将扩展名修改为txt

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;



public class Copy {
	
	public static void main(String[] args) throws Exception {
		System.out.println("请输入一个源目录");
		String SourceDir = getDir();
		System.out.println("请输入一个目的目录");
		String dtDir = getDir();
		mainJob(SourceDir, dtDir);
		System.out.println("-------------已完成-------------");
	}

	static String getDir() throws Exception {
		BufferedReader reader = new BufferedReader(new InputStreamReader(
				System.in));
		String str = reader.readLine();
		//reader.close();
		return str;
	}

	static void mainJob(String S, String D) throws Exception {
		File source = new File(S);
		File dest = new File(D);
		dest.mkdir();
		List<File> javaList = new ArrayList<File>();
		javaList = scanDir(source, javaList);
		for (File file : javaList) {
			File newFile = new File(dest,FileUtil.getHeadName(file)+".txt");
			int n = 0;
			String head=FileUtil.getHeadName(newFile);
			String tail=FileUtil.getExtendName(newFile);
			while (newFile.exists()) {
				//判断 若有同名文件出现时 防止覆盖
				newFile=new File(dest,head+"("+(++n)+")."+tail);
			}
			newFile.createNewFile();
			copy2dest(file, newFile);

		}

	}

	/**
	 * @param source
	 * @param javaList
	 * @return
	 * @throws Exception
	 * 扫描目录筛选java文件   返回File集合
	 */
	static List<File> scanDir(File source, List<File> javaList)
			throws Exception {
		File[] javas = source.listFiles();
		for (File file : javas) {
			if (file.isDirectory()) {
				scanDir(file, javaList);
			} else {
				if (file.getName().endsWith(".java"))
					javaList.add(file);
			}
		}
		return javaList;

	}

	/**
	 * @param file
	 * @param dest
	 * @throws Exception
	 * 主要复制动作
	 */
	static void copy2dest(File file, File dest) throws Exception {
		BufferedInputStream in = new BufferedInputStream(new FileInputStream(
				file));
		BufferedOutputStream out = new BufferedOutputStream(
				new FileOutputStream(dest));
		int data = 0;
		System.out.println("正在复制  "+dest.getName());
		while ((data = in.read()) != -1) {
			out.write(data);
		}
		in.close();
		out.close();

		 
	}
	
	
 
}
/**
 * @author Mr
 *	自定义文件工具类
 */
class FileUtil{
	/**
	 * @param file
	 * @return
	 * 获取文件名不带扩展名
	 */
	public static String getHeadName(File file){
		return file.getName().substring(0,file.getName().lastIndexOf("."));
	}
	/**
	 * @param file
	 * @return
	 * 获取扩展名
	 */
	public static String getExtendName(File file){
		
		return file.getName().substring(file.getName().lastIndexOf(".")+1);
	}
	/**
	 * @param file
	 * @param extendName
	 * @return
	 * 修改扩展名
	 */
	public static File trExtendName(File file,String extendName){
		return new File(file.getParent(),getHeadName(file)+"."+extendName);
	}
}

四、其它重要IO相关

1.可接收字符输出流和字节输出流的打印流PrintWriter，PrintWriter功能十分强大也比较常用，同时可直接接受File类型文件或String文件路径，具有自动flush的特点。

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.PrintWriter;

public class PrintWriterTest  {
	public static void main(String[] args) throws Exception{
		BufferedReader reader=new BufferedReader(new FileReader("d:" + File.separator + "test4.txt"));
		PrintWriter printer=new PrintWriter(System.out,true);//true 自动刷新， system.out是输出流 也可以是文件File或文件路径
		String data=null;
		while((data=reader.readLine())!=null){
			printer.println(data);
		}
		printer.close();
		reader.close();
	}
}

2.通过InputStream下的SequenceInputStream类实现合并多个字节输入流

该类有两个构造方法，也就是两种不同的实现方式：

通过传入Enumeration<? extends InputStream>对多个流的封装

public class SequenceInputStreamTest {
	public static void main(String[] args) throws Exception {
		FileInputStream in1 = new FileInputStream("d:" + File.separator
				+ "test4.txt");
		FileInputStream in2 = new FileInputStream("d:" + File.separator
				+ "test5.txt");
		FileInputStream in3 = new FileInputStream("d:" + File.separator
				+ "test6.txt");
		Vector<InputStream> vector = new Vector<InputStream>();
		vector.add(in1);
		vector.add(in2);
		vector.add(in3);//将三个inputStream添加进Vector集合
		Enumeration<InputStream> enumeration = vector.elements();//获取Enumeration对象
		SequenceInputStream in_all = new SequenceInputStream(enumeration);
		PrintWriter printer = new PrintWriter(System.out, true);
		BufferedReader reader = new BufferedReader(
				new InputStreamReader(in_all));
		String data = null;
		while ((data = reader.readLine()) != null) {
			printer.println(data);
		}
		reader.close();
		in1.close();
		in2.close();
		in2.close();
		in_all.close();
		printer.close();
	}
}

传入两个inputStream实例对象，并且只能是两个，不常用

public class SequenceInputStreamTest {
	public static void main(String[] args) throws Exception {
		FileInputStream in1 = new FileInputStream("d:" + File.separator
				+ "test4.txt");
		FileInputStream in2 = new FileInputStream("d:" + File.separator
				+ "test5.txt");
		SequenceInputStream in_all = new SequenceInputStream(in1, in2);
		PrintWriter printer = new PrintWriter(System.out, true);
		BufferedReader reader = new BufferedReader(
				new InputStreamReader(in_all));
		String data = null;
		while ((data = reader.readLine()) != null) {
			printer.println(data);
		}
		reader.close();
		in1.close();
		in2.close();
		in_all.close();
		printer.close();
	}
}

3.切割流

public class SplitFile {
	public static void main(String[] args) throws Exception{
		BufferedInputStream in=new BufferedInputStream(new FileInputStream("d:" + File.separator + "梁心颐 - 小树.mp3"));
		BufferedOutputStream out=null;
		byte[] data=new byte[1024*1024];
		int len=0;
		int count=0;
		while((len=in.read(data))!=-1){
			out=new BufferedOutputStream(new FileOutputStream("d:" + File.separator + "梁心颐 - 小树"+(++count)+".part"));
			out.write(data, 0, len);
			out.close();
		}
		in.close();
	}
}

4.ObjectInputStream和ObjectOutStream实现对象持久化

要想通过该方法持久化的实例对象，该类必须实现Serializable接口

import java.io.Serializable;

public class Person implements Serializable{
	
	private static final long serialVersionUID = -4102534291757583600L;
	private String name;
	private Integer age;
	public String add;
	public Person(String name, Integer age, String add) {
		super();
		this.name = name;
		this.age = age;
		this.add = add;
	}
	public Person() {
		// TODO Auto-generated constructor stub
	}
}

并声明UID，如果不实现该接口则在ObjectOutputStream写出对象时会报“未序列化的对象”异常

下面开始对一个Person对象进行持久化即写入一个文件中，随后读出该文件

public class ObjectStream {
	public static void main(String[] args) throws Exception, IOException {
		Person p1=new Person("liuli", 25, "china");
		//写
		ObjectOutputStream out=new ObjectOutputStream(new FileOutputStream("D:"+File.separator+"test.obj"));
		out.writeObject(p1);
		out.close();
		//读
		ObjectInputStream in=new ObjectInputStream(new FileInputStream("D:"+File.separator+"test.obj"));
		Person p2=(Person)in.readObject();
		System.out.println(p2.getName()+p2.getAdd()+p2.getAge());
	}
}

5.管道流

public class PipeTest {
	public static void main(String[] args) throws Exception {
		PipedInputStream pipeIn = new PipedInputStream();
		PipedOutputStream pipeOut = new PipedOutputStream();
		pipeIn.connect(pipeOut);//连接两个流
		In in = new In(pipeIn);
		Out out = new Out(pipeOut);
		Thread t1 = new Thread(in);
		Thread t2 = new Thread(out);
		t1.start();
		t2.start();
	}
}

class In implements Runnable {
	private PipedInputStream in;

	public In(PipedInputStream in) {
		// TODO Auto-generated constructor stub
		this.in = in;
	}

	@Override
	public void run() {
		// TODO Auto-generated method stub

		BufferedReader reader = new BufferedReader(new InputStreamReader(in));
		String line = null;
		try {
			while ((line = reader.readLine()) != null) {
				System.out.println(line);
			}
			reader.close();
			in.close();

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

		}
	}
}

class Out implements Runnable {
	private PipedOutputStream out;

	public Out(PipedOutputStream out) {
		// TODO Auto-generated constructor stub
		this.out = out;
	}

	@Override
	public void run() {
		// TODO Auto-generated method stub
		PrintWriter writer=new PrintWriter(out, true);
		try {
			writer.println("黑马程序员2015年1月9日18:51:42");
			writer.println("黑马程序员2015年1月9日18:51:45");
			writer.println("黑马程序员2015年1月9日18:51:47");
			writer.close();
			out.close();
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
}

由此可见管道流建立了两个不同线程的沟通桥梁，可以实现线程间的通讯，可以实现生产者消费者模型。

6.DataInputStream和DataOutputStream存储基本数据类型数据

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;

public class DataStream {
	public static void main(String[] args) throws Exception{
		DataOutputStream out=new DataOutputStream(new FileOutputStream("d:" + File.separator + "test.txt"));
		out.writeInt(2015);
		out.writeBoolean(true);
		out.writeDouble(2015.0109);
		out.close();
		
		DataInputStream in=new DataInputStream(new FileInputStream("d:" + File.separator + "test.txt"));
		System.out.println(in.readInt());
		System.out.println(in.readBoolean());
		System.out.println(in.readDouble());
		in.close();
	}
}

7.ByteArrayInputStream和ByteArrayOutputStream

public class ByteArrayOutputStreamTest {
	public static void main(String[] args) throws Exception {
		File file = new File("d:" + File.separator + "test4.txt");
		if (!file.exists())
			throw new RuntimeException("文件不存在");
		FileInputStream in;
		ByteArrayOutputStream arr = new ByteArrayOutputStream();

		in = new FileInputStream(file);
		byte[] data = new byte[5];
		int len = 0;

		while ((len = in.read(data)) != -1) {
			arr.write(data, 0, len);

		}
		System.out.println(arr.toString());
		in.close();
	}	
}	

8.StringReader和StringWriter

public class StringReader {
	public static void main(String[] args) throws Exception {
		
		BufferedReader reader2=new BufferedReader(new StringReader("黑马程序员"));
		StringWriter writer2=new StringWriter();
		writer2.append(reader2.readLine());
		writer2.append("------追加新文字");
		System.out.println(writer2.toString());
		
		BufferedReader reader3=new BufferedReader(new CharArrayReader("黑马程序员".toCharArray()));
		CharArrayWriter writer3=new CharArrayWriter();
		writer3.write(reader3.readLine().toCharArray());
		System.out.println(writer3.toString());
	}	
}	

9.CharArrayReader和CharArrayWriter

public class CharArray {
	public static void main(String[] args) throws Exception {
		BufferedReader reader3=new BufferedReader(new CharArrayReader("黑马程序员".toCharArray()));
		CharArrayWriter writer3=new CharArrayWriter();
		writer3.write(reader3.readLine().toCharArray());
		System.out.println(writer3.toString());
	}	
}

总结：ByteArrayInputStream和ByteArrayOutputStream、CharArrayReader和CharArrayWriter、StringReader和StringWriter都是用流的思想操作内存中的数据。