Java summarizes the principles of IO streams and the classification of streams-javaTutorial-php.cn

This article brings you relevant knowledge about java, which mainly organizes issues related to O flow principles and flow classification, including node flow, buffer flow, conversion flow, and output. Streaming and other content, let’s take a look at it below, I hope it will be helpful to everyone.

Java summarizes the principles of IO streams and the classification of streams

Recommended learning: "java Video Tutorial"

## 1. Overview

I/O is the abbreviation of Input/Output, I/O technology is a very practical technology for processing Data transfer between devices. Such as reading/writing files, network communication, etc.

Input
input: Read external data (data from storage devices such as disks and optical disks) into the program (memory).
Output
output: Output program (memory) data to storage devices such as disks and optical disks.

In Java programs, data input/output operations are performed in the form of "stream (
stream)".

java.io package provides various "stream" classes and interfaces to obtain different types of data and input or output through standard methods data.

Java summarizes the principles of IO streams and the classification of streams

2. Classification of streams

1. Overview

According to different operation data units, it is divided into: words Throttling (8
bit), character stream (16 bit)

## According to the different flow directions of the data stream, it is divided into: input stream, output stream Stream

According to the different roles of the stream, it is divided into: node stream, processing stream

Node stream: read directly from the data source or destination Write data

Processing flow: not directly connected to the data source or destination, but "connected" to an existing flow (node flow or processing flow) On top of that, it provides the program with more powerful reading and writing functions through data processing.

Java’s IO stream involves more than 40 classes, which are actually very regular and are derived from the above 4 abstract base classes. Yes, the names of subclasses derived from these four classes are all suffixed with the name of the parent class.

(Abstract base class)InputStreamInputStreamReaderOutputStreamOutputStreamWriter

Byte stream	Character stream

IO stream system: Java summarizes the principles of IO streams and the classification of streams

2. InputStream

Overview

Typical implementation:

FileInputStream

Method

Methodint read()intint read(byte[] b)b.lengthint read(byte[] b, int off,int len)public void close() throws IOException

Typical implementation class: FileInputStream

Code demonstration:

@Test
    public void testFileInputStream() {
        FileInputStream fis = null;
        try {
            //1. 造文件
            File file = new File("hello.txt");

            //2.造流
            fis = new FileInputStream(file);

            //3.读数据
            byte[] buffer = new byte[5];
            int len;//记录每次读取的字节的个数
            while((len = fis.read(buffer)) != -1){

                String str = new String(buffer,0,len);
                System.out.print(str);

            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if(fis != null){
                //4.关闭资源
                try {
                    fis.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }

            }
        }
    }

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3. Reader

Overview

Typical implementation class: FileReader

Method

Description
Read the next byte of data from the input stream. Returns an	byte value in the range 0 to 255. If no bytes are available because the end of the stream has been reached, the value -1 is returned.
Will read up to	bytes from this input stream The data is read into a byte array. If no bytes are available because the end of the stream has been reached, the value -1 is returned. Otherwise the actual number of bytes read is returned as an integer.
Read up to len data bytes from the input stream byte array. An attempt is made to read len bytes, but the number of bytes read may be smaller than this value. Returns the actual number of bytes read as an integer. If no bytes are available because the stream is at the end of the file, the value -1 is returned.
Close this input stream and release all system resources associated with the stream

# if the end of the stream has been reached Read characters into an array. If the end of the stream has been reached, -1 is returned. Otherwise, return the number of characters read this time. Read characters into a certain part of the array. Store it in the array cbuf, starting from off, and read up to len characters. If the end of the stream has been reached, -1 is returned. Otherwise, return the number of characters read this time. Closes this input stream and releases all system resources associated with the stream.

Method	Description
`int read()`	Read a single character. Character read as an integer in the range 0 to 65535 (0x00-0xffff) (2-byte Unicode code), or -1
##int read(char[] cbuf)
int read(char[] cbuf,int off,int len)
public void close() throws IOException

Typical implementation class: FileReader

@Test
    public void testFileReader(){
        FileReader fr = null;
        try {
            //1.实例化File类的对象，指明要操作的文件
            File file = new File("hello.txt");//相较于当前Module
            //2.提供具体的流
            fr = new FileReader(file);

            //3.数据的读入
            //read():返回读入的一个字符。如果达到文件末尾，返回-1
            //方式一：//        int data = fr.read();//        while(data != -1){//            System.out.print((char)data);//            data = fr.read();//        }

            //方式二：语法上针对于方式一的修改
            int data;
            while((data = fr.read()) != -1){
                System.out.print((char)data);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            //4.流的关闭操作//            try {//                if(fr != null)//                    fr.close();//            } catch (IOException e) {//                e.printStackTrace();//            }
            //或
            if(fr != null){
                try {
                    fr.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

    }

    //对read()操作升级：使用read的重载方法
    @Test
    public void testFileReader1()  {
        FileReader fr = null;
        try {
            //1.File类的实例化
            File file = new File("hello.txt");

            //2.FileReader流的实例化
            fr = new FileReader(file);

            //3.读入的操作
            //read(char[] cbuf):返回每次读入cbuf数组中的字符的个数。如果达到文件末尾，返回-1
            char[] cbuf = new char[5];
            int len;
            while((len = fr.read(cbuf)) != -1){
                //方式一：
                //错误的写法//                for(int i = 0;i 4. OutputStream<h3></h3><p> Overview<strong></strong></p><blockquote>Typical implementation: <p>FileOutputStream<code></code></p>
</blockquote><p> Method <strong></strong></p>

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Method DescriptionWrite the specified bytes this output stream. The general contract of write is: write one byte to the output stream. The bytes to be written are the eight low-order bits of parameter b. The 24 high-order bits of b are ignored. That is, the range of 0~255 is written. Write b.length bytes from the specified byte array to this output stream. The general contract of write(b) is that it should have exactly the same effect as calling write(b, 0, b.length). Will start from offset off in the specified byte array len bytes are written to this output stream. Flushes this output stream and forces all buffered output bytes to be written out. Call this method to indicate These bytes should be written immediately to their intended destination. Closes this output stream and releases all system resources associated with the stream.


void write(int b)
void write(byte[] b)
void write(byte[] b,int off,int len)
public void flush()throws IOException
public void close() throws IOException

Main implementation class: FileInputOutputStream

/*
    实现对图片的复制操作
     */
    @Test
    public void testFileInputOutputStream()  {
        FileInputStream fis = null;
        FileOutputStream fos = null;
        try {
            //
            File srcFile = new File("爱情与友情.jpg");
            File destFile = new File("爱情与友情2.jpg");

            //
            fis = new FileInputStream(srcFile);
            fos = new FileOutputStream(destFile);

            //复制的过程
            byte[] buffer = new byte[5];
            int len;
            while((len = fis.read(buffer)) != -1){
                fos.write(buffer,0,len);
            }

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if(fos != null){
                //
                try {
                    fos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(fis != null){
                try {
                    fis.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }

            }
        }

    }

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5. Writer

Overview

Typical implementation:
FileWriter

Method

Method DescriptionWrite a single character. The character to be written is contained in the 16 low-order bits of the given integer value, the high-order 16 bits are ignored. That is, write a Unicode code between 0 and 65535. Write character array. Write a certain part of the character array. Starting from off, write len characters Write string. Write a certain part of the string. Flushes the buffers for this stream, immediately writing them to the intended destination. Closes this output stream and releases all system resources associated with the stream.

主要实现类：FileWriter

概述

输出操作，对应的File可以不存在的。并不会报异常

File对应的硬盘中的文件如果不存在，在输出的过程中，会自动创建此文件。
File对应的硬盘中的文件如果存在：

如果流使用的构造器是：FileWriter(file,false) / FileWriter(file):对原有文件的覆盖

如果流使用的构造器是：FileWriter(file,true):不会对原有文件覆盖，而是在原有文件基础上追加内容

代码演示

//从内存中写出数据到硬盘的文件里。
    @Test
    public void testFileWriter() {
        FileWriter fw = null;
        try {
            //1.提供File类的对象，指明写出到的文件
            File file = new File("hello1.txt");

            //2.提供FileWriter的对象，用于数据的写出
            fw = new FileWriter(file,false);

            //3.写出的操作
            fw.write("I have a dream!\n");
            fw.write("you need to have a dream!");
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            //4.流资源的关闭
            if(fw != null){

                try {
                    fw.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

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6. 练习：复制操作

代码演示：

实现对文本的复制操作

 @Test
    public void testFileReaderFileWriter() {
        FileReader fr = null;
        FileWriter fw = null;
        try {
            //1.创建File类的对象，指明读入和写出的文件
            File srcFile = new File("hello.txt");
            File destFile = new File("hello2.txt");

            //不能使用字符流来处理图片等字节数据//            File srcFile = new File("爱情与友情.jpg");//            File destFile = new File("爱情与友情1.jpg");


            //2.创建输入流和输出流的对象
            fr = new FileReader(srcFile);
            fw = new FileWriter(destFile);


            //3.数据的读入和写出操作
            char[] cbuf = new char[5];
            int len;//记录每次读入到cbuf数组中的字符的个数
            while((len = fr.read(cbuf)) != -1){
                //每次写出len个字符
                fw.write(cbuf,0,len);

            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            //4.关闭流资源
            //方式一：//            try {//                if(fw != null)//                    fw.close();//            } catch (IOException e) {//                e.printStackTrace();//            }finally{//                try {//                    if(fr != null)//                        fr.close();//                } catch (IOException e) {//                    e.printStackTrace();//                }//            }
            //方式二：
            try {
                if(fw != null)
                    fw.close();
            } catch (IOException e) {
                e.printStackTrace();
            }

            try {
                if(fr != null)
                    fr.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }}

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实现对图片的复制操作

    @Test
    public void testFileInputOutputStream()  {
        FileInputStream fis = null;
        FileOutputStream fos = null;
        try {
            //
            File srcFile = new File("爱情与友情.jpg");
            File destFile = new File("爱情与友情2.jpg");

            //
            fis = new FileInputStream(srcFile);
            fos = new FileOutputStream(destFile);

            //复制的过程
            byte[] buffer = new byte[5];
            int len;
            while((len = fis.read(buffer)) != -1){
                fos.write(buffer,0,len);
            }

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if(fos != null){
                //
                try {
                    fos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(fis != null){
                try {
                    fis.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }

            }
        }

    }

    //指定路径下文件的复制
    public void copyFile(String srcPath,String destPath){
        FileInputStream fis = null;
        FileOutputStream fos = null;
        try {
            //
            File srcFile = new File(srcPath);
            File destFile = new File(destPath);

            //
            fis = new FileInputStream(srcFile);
            fos = new FileOutputStream(destFile);

            //复制的过程
            byte[] buffer = new byte[1024];
            int len;
            while((len = fis.read(buffer)) != -1){
                fos.write(buffer,0,len);
            }

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if(fos != null){
                //
                try {
                    fos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(fis != null){
                try {
                    fis.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }

            }
        }


    }

    @Test
    public void testCopyFile(){

        long start = System.currentTimeMillis();

        String srcPath = "C:\\Users\\Administrator\\Desktop\\01-视频.avi";
        String destPath = "C:\\Users\\Administrator\\Desktop\\02-视频.avi";//        String srcPath = "hello.txt";//        String destPath = "hello3.txt";

        copyFile(srcPath,destPath);


        long end = System.currentTimeMillis();

        System.out.println("复制操作花费的时间为：" + (end - start));//618
    }}

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三、节点流(或文件流)

1. 概述

定义文件路径时，注意：可以用“/”或者“\\”。

在写入一个文件时，如果使用构造器FileOutputStream(file)，则目录下有同名文件将被覆盖。如果使用构造器FileOutputStream(file,true)，则目录下的同名文件不会被覆盖，在文件内容末尾追加内容。

在读取文件时，必须保证该文件已存在，否则报异常。

字节流操作字节，比如：.mp3，.avi，.rmvb，.mp4，.jpg，.doc，.ppt

字符流操作字符，只能操作普通文本文件。最常见的文本文件：txt，.java，.c，.cpp等语言的源代码。尤其注意.doc,excel,ppt这些不是文本文件。

2. 读取文件

概述

1.建立一个流对象，将已存在的一个文件加载进流。

java FileReader fr = new FileReader(new File(“Test.txt”));

2.创建一个临时存放数据的数组。

java char[] ch = new char[1024];

3.调用流对象的读取方法将流中的数据读入到数组中。

java fr.read(ch);

4.关闭资源。

java fr.close();

代码演示

FileReader fr = null;try {fr = new FileReader(new File("c:\\test.txt"));char[] buf = new char[1024];int len;while ((len = fr.read(buf)) != -1) {System.out.print(new String(buf, 0, len));}} catch (IOException e) {System.out.println("read-Exception :" + e.getMessage());} finally {if (fr != null) {try {fr.close();} catch (IOException e) {System.out.println("close-Exception :" + e.getMessage());} } }

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3. 写入文件

概述

1.创建流对象，建立数据存放文件
FileWriter fw = new FileWriter(new File(“Test.txt”));
2.调用流对象的写入方法，将数据写入流
fw.write(“atguigu-songhongkang”);
3.关闭流资源，并将流中的数据清空到文件中。
fw.close();

代码演示

FileWriter fw = null;try {fw = new FileWriter(new File("Test.txt"));fw.write("atguigu-songhongkang");} catch (IOException e) {e.printStackTrace();} finally {if (fw != null)try {fw.close();} catch (IOException e) {e.printStackTrace();} }

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四、缓冲流

1. 概述

为了提高数据读写的速度，Java API提供了带缓冲功能的流类，在使用这些流类时，会创建一个内部缓冲区数组，缺省使用8192个字节(8Kb)的缓冲区。

缓冲流要“套接”在相应的节点流之上，根据数据操作单位可以把缓冲流分为：

BufferedInputStream 和 BufferedOutputStream

BufferedReader 和BufferedWriter

当读取数据时，数据按块读入缓冲区，其后的读操作则直接访问缓冲区

当使用BufferedInputStream读取字节文件时，BufferedInputStream会一次性从文件中读取8192个(8Kb)，存在缓冲区中，直到缓冲区装满了，才重新从文件中读取下一个8192个字节数组。

向流中写入字节时，不会直接写到文件，先写到缓冲区中直到缓冲区写满，BufferedOutputStream才会把缓冲区中的数据一次性写到文件里。使用方法 flush()可以强制将缓冲区的内容全部写入输出流

关闭流的顺序和打开流的顺序相反。只要关闭最外层流即可，关闭最外层流也会相应关闭内层节点流

flush()方法的使用：手动将buffer中内容写入文件
如果是带缓冲区的流对象的close()方法，不但会关闭流，还会在关闭流之前刷新缓冲区，关闭后不能再写出

2. 实现非文本文件的复制

    @Test
    public void BufferedStreamTest() throws FileNotFoundException {
        BufferedInputStream bis = null;
        BufferedOutputStream bos = null;

        try {
            //1.造文件
            File srcFile = new File("爱情与友情.jpg");
            File destFile = new File("爱情与友情3.jpg");
            //2.造流
            //2.1 造节点流
            FileInputStream fis = new FileInputStream((srcFile));
            FileOutputStream fos = new FileOutputStream(destFile);
            //2.2 造缓冲流
            bis = new BufferedInputStream(fis);
            bos = new BufferedOutputStream(fos);

            //3.复制的细节：读取、写入
            byte[] buffer = new byte[10];
            int len;
            while((len = bis.read(buffer)) != -1){
                bos.write(buffer,0,len);//                bos.flush();//刷新缓冲区

            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            //4.资源关闭
            //要求：先关闭外层的流，再关闭内层的流
            if(bos != null){
                try {
                    bos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }

            }
            if(bis != null){
                try {
                    bis.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }

            }
            //说明：关闭外层流的同时，内层流也会自动的进行关闭。关于内层流的关闭，我们可以省略.//        fos.close();//        fis.close();
        }



    }

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3. 实现文件复制

    @Test
    public void testCopyFileWithBuffered(){
        long start = System.currentTimeMillis();

        String srcPath = "C:\\Users\\Administrator\\Desktop\\01-视频.avi";
        String destPath = "C:\\Users\\Administrator\\Desktop\\03-视频.avi";


        copyFileWithBuffered(srcPath,destPath);


        long end = System.currentTimeMillis();

        System.out.println("复制操作花费的时间为：" + (end - start));//618 - 176
    }

 //实现文件复制的方法
    public void copyFileWithBuffered(String srcPath,String destPath){
        BufferedInputStream bis = null;
        BufferedOutputStream bos = null;

        try {
            //1.造文件
            File srcFile = new File(srcPath);
            File destFile = new File(destPath);
            //2.造流
            //2.1 造节点流
            FileInputStream fis = new FileInputStream((srcFile));
            FileOutputStream fos = new FileOutputStream(destFile);
            //2.2 造缓冲流
            bis = new BufferedInputStream(fis);
            bos = new BufferedOutputStream(fos);

            //3.复制的细节：读取、写入
            byte[] buffer = new byte[1024];
            int len;
            while((len = bis.read(buffer)) != -1){
                bos.write(buffer,0,len);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            //4.资源关闭
            //要求：先关闭外层的流，再关闭内层的流
            if(bos != null){
                try {
                    bos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }

            }
            if(bis != null){
                try {
                    bis.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }

            }
            //说明：关闭外层流的同时，内层流也会自动的进行关闭。关于内层流的关闭，我们可以省略.//        fos.close();//        fis.close();
        }
    }

 /*
    使用BufferedReader和BufferedWriter实现文本文件的复制

     */
    @Test
    public void testBufferedReaderBufferedWriter(){
        BufferedReader br = null;
        BufferedWriter bw = null;
        try {
            //创建文件和相应的流
            br = new BufferedReader(new FileReader(new File("dbcp.txt")));
            bw = new BufferedWriter(new FileWriter(new File("dbcp1.txt")));

            //读写操作
            //方式一：使用char[]数组//            char[] cbuf = new char[1024];//            int len;//            while((len = br.read(cbuf)) != -1){//                bw.write(cbuf,0,len);//    //            bw.flush();//            }

            //方式二：使用String
            String data;
            while((data = br.readLine()) != null){
                //方法一：//                bw.write(data + "\n");//data中不包含换行符
                //方法二：
                bw.write(data);//data中不包含换行符
                bw.newLine();//提供换行的操作

            }


        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            //关闭资源
            if(bw != null){

                try {
                    bw.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(br != null){
                try {
                    br.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }

            }
        }

    }}

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五、转换流

1. 概述

转换流提供了在字节流和字符流之间的转换

Java API提供了两个转换流：

InputStreamReader：将InputStream转换为Reader

OutputStreamWriter：将Writer转换为OutputStream

字节流中的数据都是字符时，转成字符流操作更高效。

很多时候我们使用转换流来处理文件乱码问题。实现编码和解码的功能。

2. InputStreamReader

概述

实现将字节的输入流按指定字符集转换为字符的输入流。

需要和InputStream“套接”。

构造器


void write(int c)
void write(char[] cbuf)
void write(char[] cbuf,int off,int len)
void write(String str)
void write(String str,int off,int len)
void flush()
public void close() throws IOException


`public InputStreamReader(InputStream in)`
`public InputSreamReader(InputStream in,String charsetName)`

3. OutputStreamWriter

概述

实现将字符的输出流按指定字符集转换为字节的输出流。

需要和OutputStream“套接”。

（2）构造器


`public OutputStreamWriter(OutputStream out)`
`public OutputSreamWriter(OutputStream out,String charsetName)`

4. 代码演示

代码演示1：

  @Test
    public void test1() throws IOException {

        FileInputStream fis = new FileInputStream("dbcp.txt");//        InputStreamReader isr = new InputStreamReader(fis);//使用系统默认的字符集
        //参数2指明了字符集，具体使用哪个字符集，取决于文件dbcp.txt保存时使用的字符集
        InputStreamReader isr = new InputStreamReader(fis,"UTF-8");//使用系统默认的字符集

        char[] cbuf = new char[20];
        int len;
        while((len = isr.read(cbuf)) != -1){
            String str = new String(cbuf,0,len);
            System.out.print(str);
        }

        isr.close();

    }

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代码演示2：

    @Test
    public void test2() throws Exception {
        //1.造文件、造流
        File file1 = new File("dbcp.txt");
        File file2 = new File("dbcp_gbk.txt");

        FileInputStream fis = new FileInputStream(file1);
        FileOutputStream fos = new FileOutputStream(file2);

        InputStreamReader isr = new InputStreamReader(fis,"utf-8");
        OutputStreamWriter osw = new OutputStreamWriter(fos,"gbk");

        //2.读写过程
        char[] cbuf = new char[20];
        int len;
        while((len = isr.read(cbuf)) != -1){
            osw.write(cbuf,0,len);
        }

        //3.关闭资源
        isr.close();
        osw.close();


    }}

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六、标准输入、输出流

1. 概述

System.in和System.out分别代表了系统标准的输入和输出设备

默认输入设备是：键盘，输出设备是：显示器

System.in的类型是InputStream，System.out的类型是PrintStream，其是OutputStream的子类，FilterOutputStream 的子类

重定向：通过System类的setIn，setOut方法对默认设备进行改变。

public static void setIn(InputStream in)

public static void setOut(PrintStream out)

2. 代码演示

/*
从键盘输入字符串，要求将读取到的整行字符串转成大写输出。然后继续进行输入操作，
直至当输入“e”或者“exit”时，退出程序。
 方法一：使用Scanner实现，调用next()返回一个字符串
 方法二：使用System.in实现。System.in  --->  转换流 ---> BufferedReader的readLine()

     */
    public static void main(String[] args) {
        BufferedReader br = null;
        try {
            InputStreamReader isr = new InputStreamReader(System.in);
            br = new BufferedReader(isr);

            while (true) {
                System.out.println("请输入字符串：");
                String data = br.readLine();
                if ("e".equalsIgnoreCase(data) || "exit".equalsIgnoreCase(data)) {
                    System.out.println("程序结束");
                    break;
                }

                String upperCase = data.toUpperCase();
                System.out.println(upperCase);

            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (br != null) {
                try {
                    br.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

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七. 打印流

1. 概述

实现将基本数据类型的数据格式转化为字符串输出

打印流：PrintStream和PrintWriter

提供了一系列重载的print()和println()方法，用于多种数据类型的输出

PrintStream和PrintWriter的输出不会抛出IOException异常

PrintStream和PrintWriter有自动flush功能

PrintStream打印的所有字符都使用平台的默认字符编码转换为字节。在需要写入字符而不是写入字节的情况下，应该使用 PrintWriter 类。

System.out返回的是PrintStream的实例

2. 代码演示

 /*
    2. 打印流：PrintStream 和PrintWriter

    2.1 提供了一系列重载的print() 和 println()
    2.2 练习：



     */

    @Test
    public void test2() {
        PrintStream ps = null;
        try {
            FileOutputStream fos = new FileOutputStream(new File("D:\\IO\\text.txt"));
            // 创建打印输出流,设置为自动刷新模式(写入换行符或字节 '\n' 时都会刷新输出缓冲区)
            ps = new PrintStream(fos, true);
            if (ps != null) {// 把标准输出流(控制台输出)改成文件
                System.setOut(ps);
            }


            for (int i = 0; i <h2>八、数据流</h2><blockquote><p> 为了方便地操作Java语言的基本数据类型和String的数据，可以使用数据流。</p></blockquote><blockquote>
<p> 数据流有两个类：(用于读取和写出基本数据类型、String类的数据）</p>
<ol>
<li><code>DataInputStream</code></li>
<li><code>DataOutputStream</code></li>
</ol>
<p>分别“套接”在 <code>InputStream</code> 和 <code>OutputStream</code> 子类的流上</p>
</blockquote><blockquote><p><code>DataInputStream</code>中的方法：</p></blockquote>

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`boolean readBoolean()`
`byte readByte() char`
`readChar()`
`float readFloat()`
`double readDouble()`
`long readLong()`
`int readInt()`
`short readShort()`
`String readUTF()`
`void readFully(byte[] b)`

Supplement: Method in DataOutputStream: Change the read of the above method to the corresponding write

Recommended learning: "java video tutorial"

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