Java IO 练习Demo

Posted 2022-12-11 HardyDragon_CC

package com.cwl;

import org.junit.Test;

import java.io.*;
import java.net.URL;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;


public class iostreamTest 

    private static class A implements Serializable 
        private int x;
        private String y;

        A(int x, String y) 
            this.x = x;
            this.y = y;
        

        @Override
        public String toString() 
            return "x = " + x + "  " + "y = " + y;
        
    

    @Test
    public void network() throws IOException 

        URL url = new URL("http://www.baidu.com");

        /* 字节流 */
        InputStream is = url.openStream();

        /* 字符流 */
        InputStreamReader isr = new InputStreamReader(is, "utf-8");

        /* 提供缓存功能 */
        BufferedReader br = new BufferedReader(isr);

        String line;
        while ((line = br.readLine()) != null) 
            System.out.println(line);
        

        br.close();
    

    @Test
    public void serializableTest() throws IOException, ClassNotFoundException 
        A a1 = new A(123, "abc");
        String objectFile = "resource/a.txt";
        ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(objectFile));
        objectOutputStream.writeObject(a1);
        objectOutputStream.close();

        ObjectInputStream objectInputStream = new ObjectInputStream(new FileInputStream(objectFile));
        A a2 = (A) objectInputStream.readObject();
        objectInputStream.close();
        System.out.println(a2);
    

    /**
     * 递归地列出一个目录下所有文件
     *
     * @param dir
     */
    public static void listAllFiles(File dir) 
        if (dir == null || !dir.exists()) 
            return;
        
        if (dir.isFile()) 
            System.out.println(dir.getName());
            return;
        
        for (File file : dir.listFiles()) 
            listAllFiles(file);
        
    

    /**
     * 复制文件内容
     *
     * @param src
     * @param dist
     * @throws IOException
     */
    public static void copyFile(String src, String dist) throws IOException 

        FileInputStream in = new FileInputStream(src);
        FileOutputStream out = new FileOutputStream(dist);
        byte[] buffer = new byte[20 * 1024];

        // read() 最多读取 buffer.length 个字节
        // 返回的是实际读取的个数
        // 返回 -1 的时候表示读到 eof，即文件尾
        while (in.read(buffer, 0, buffer.length) != -1) 
            out.write(buffer);
        

        in.close();
        out.close();
    

    public static void readFileContent(String filePath) throws IOException 

        FileReader fileReader = new FileReader(filePath);
        BufferedReader bufferedReader = new BufferedReader(fileReader);

        String line;
        while ((line = bufferedReader.readLine()) != null) 
            System.out.println(line);
        

        // 装饰者模式使得 BufferedReader 组合了一个 Reader 对象
        // 在调用 BufferedReader 的 close() 方法时会去调用 Reader 的 close() 方法
        // 因此只要一个 close() 调用即可
        bufferedReader.close();
    

    @Test
    public void test() throws IOException 
        String s1 = "resource/a.txt";
        String s2 = "resource/b.txt";
        fastCopy(s1, s2);
    


    /**
     * 使用 NIO 快速复制文件的实例
     *
     * @param src
     * @param dist
     * @throws IOException
     */
    public static void fastCopy(String src, String dist) throws IOException 

        /* 获得源文件的输入字节流 */
        FileInputStream fin = new FileInputStream(src);

        /* 获取输入字节流的文件通道 */
        FileChannel fcin = fin.getChannel();

        /* 获取目标文件的输出字节流 */
        FileOutputStream fout = new FileOutputStream(dist);

        /* 获取输出字节流的通道 */
        FileChannel fcout = fout.getChannel();

        /* 为缓冲区分配 1024 个字节 */
        ByteBuffer buffer = ByteBuffer.allocateDirect(1024);

        while (true) 

            /* 从输入通道中读取数据到缓冲区中 */
            int r = fcin.read(buffer);

            /* read() 返回 -1 表示 EOF */
            if (r == -1) 
                break;
            

            /* 切换读写 */
            buffer.flip();

            /* 把缓冲区的内容写入输出文件中 */
            fcout.write(buffer);

            /* 清空缓冲区 */
            buffer.clear();
        
    

https://pdai.tech/md/java/io/java-io-basic-usage.html