Java 输入输出流，Java InputStream FileInputStream OutputStream FileOutputStream

Java 输入输出流，Java InputStream FileInputStream OutputStream FileOutputStream

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©Copyright 蕃薯耀 2021-04-20

https://www.cnblogs.com/fanshuyao/

一、字节流和文件流使用，实现文件（适用所有文件）复制

InputStream、FileInputStream ：获取源文件

OutputStream、FileOutputStream：输出目标文件

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

public class Stream1FileStream {

    
    public static void fileInputStream() throws IOException {
        InputStream is = new FileInputStream("c:/img/0.png");
        OutputStream os = new FileOutputStream("c:/img/1.png");
        
        byte[] buffer = new byte[1024];
        int length;
        while((length = is.read(buffer)) != -1) {
            os.write(buffer, 0, length);
        }
        
        os.close();
        is.close();
        System.out.println("执行完成。");
    }
    
    public static void main(String[] args) throws IOException {
        fileInputStream();
    }
}

二、字节流和文件流使用，实现文件（文本文件）复制，无中文乱码问题

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

public class Stream1FileStreamTxt {

    
    public static void fileInputStream() throws IOException {
        
        //字节流读取文件不会有中文乱码的问题
        InputStream is = new FileInputStream("c:/img/0.txt");
        OutputStream os = new FileOutputStream("c:/img/1-2.txt");
        
        byte[] buffer = new byte[20];
        int length;
        while((length = is.read(buffer)) != -1) {
            //System.out.println(new String(buffer, "GBK"));//这里直接输出会有中文乱码的问题（因为每次读取的字节数组存在将汉字分开的情况，这样就出现乱码，汉字不被分开就不会有乱码），但生成文件是没有中文乱码问题的
            os.write(buffer, 0, length);
        }
        
        os.close();
        is.close();
        System.out.println("执行完成。");
    }
    
    public static void main(String[] args) throws IOException {
        fileInputStream();
    }
}

三、ByteArrayOutputStream字节数组使用

ByteArrayOutputStream的作用就是将多次读取到的所有字节都缓存起来，最后一起输入，能解决中文被截断后出现乱码的问题

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

public class Stream1FileStreamTxtByteArray {

    
    public static void fileInputStream() throws IOException {
        
        //字节流读取文件不会有中文乱码的问题
        InputStream is = new FileInputStream("c:/img/0.txt");//0.txt为GBK编码
        OutputStream os = new FileOutputStream("c:/img/1-3.txt");
        
        //将字节存储在ByteArrayOutputStream中，解决中文汉字截断后在控制台输出存在中文乱码的问题
        ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
        
        byte[] buffer = new byte[20];
        int length;
        while((length = is.read(buffer)) != -1) {
            os.write(buffer, 0, length);
            byteArrayOutputStream.write(buffer, 0, length);
        }
        
        //System.out.println(byteArrayOutputStream.toString("GBK"));
        System.out.println(new String(byteArrayOutputStream.toByteArray(), "GBK"));//处理中文乱码，GBK编码设置，取决于文件的编码，如果不是UTF-8，就必须设置，不然会有乱码
        
        byteArrayOutputStream.close();
        
        os.close();
        is.close();
        System.out.println("执行完成。");
    }
    
    
    public static void fileInputStreamUtf8() throws IOException {
        
        //字节流读取文件不会有中文乱码的问题，但文件的编码一定要是UTF-8，不然在输出时就要指定相应的编码
        InputStream is = new FileInputStream("c:/img/utf8.txt");//utf8.txt为UTF-8编码
        OutputStream os = new FileOutputStream("c:/img/utf8-2.txt");
        
        //将字节存储在ByteArrayOutputStream中，解决中文汉字截断后在控制台输出存在中文乱码的问题
        ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
        
        byte[] buffer = new byte[20];
        int length;
        while((length = is.read(buffer)) != -1) {
            os.write(buffer, 0, length);
            byteArrayOutputStream.write(buffer, 0, length);
        }
        
        System.out.println(byteArrayOutputStream.toString());
        
        byteArrayOutputStream.close();
        
        os.close();
        is.close();
        System.out.println("执行完成。");
    }
    
    public static void main(String[] args) throws IOException {
        //fileInputStream();
        fileInputStreamUtf8();
    }
}

四、字符流

字符流就是用来读取文件内容的，如txt，但这个一般都会有中文乱码

Reader、FileReader：输入

Writer、FileWriter：输出

import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.Reader;
import java.io.Writer;

public class Stream2FileReader {

    
    public static void fileInputStream() throws IOException {
        
        Reader r = new FileReader("c:/img/0.txt");//FileReader：直接使用会有中文乱码
        Writer w = new FileWriter("c:/img/2.txt");
        
        char[] buffer = new char[1024];
        int length = 0;
        while((length = r.read(buffer)) != -1) {
            System.out.println(new String(buffer));
            w.write(buffer, 0, length);
        }
        
        r.close();
        w.close();
        System.out.println("执行完成。");
    }
    
    public static void main(String[] args) throws IOException {
        fileInputStream();
    }
}

五、InputStreamReader：将字节流转换成字符流

将字节流转换成字符流，转换时，可以声明文件编码，解决中文乱码问题

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;

public class Stream3FileInputStreamReader {

    
    public static void fileInputStream() throws IOException {
        
        //使用转换流InputStreamReader解决中文乱码问题。InputStreamReader：将字节流inputStream转换成字符流Reader
        InputStreamReader inputStreamReader = new InputStreamReader(new FileInputStream("c:/img/0.txt"), "GB2312");//InputStreamReader中的GB2312为具体文件的编码，默认是UTF-8的编码，不一致就会出现中文乱码
        
        OutputStreamWriter outputStreamWriter = new OutputStreamWriter(new FileOutputStream("c:/img/3.txt"), "UTF-8");//生成新的文件，使用UTF-8编码
        
        char[] buffer = new char[1024];
        int length = 0;
        while((length = inputStreamReader.read(buffer)) != -1) {
            //System.out.println(new String(buffer));
            outputStreamWriter.write(buffer, 0, length);
        }
        
        outputStreamWriter.close();
        inputStreamReader.close();
        System.out.println("执行完成。");
    }
    
    public static void main(String[] args) throws IOException {
        fileInputStream();
    }
}

六、字节缓冲流

BufferedInputStream、BufferedOutputStream：加快文件输入输出，小文件影响不大，但大文件影响很明显。

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

public class Stream4FileStreamBufferStream {

    
    public static void fileInputStream() throws IOException {
        
        long start = System.currentTimeMillis();
        
        InputStream is = new FileInputStream("c:/img/00.mp4");
        OutputStream os = new FileOutputStream("c:/img/11.mp4");
        
        //缓冲流，加快文件输入输出
        BufferedInputStream bufferedInputStream = new BufferedInputStream(is);
        BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(os);
        
        
        byte[] buffer = new byte[1024];
        int length;
        while((length = bufferedInputStream.read(buffer)) != -1) {
            bufferedOutputStream.write(buffer, 0, length);
        }
        
        bufferedOutputStream.close();
        bufferedInputStream.close();
        os.close();
        is.close();
        
        long end = System.currentTimeMillis();
        System.out.println("end - start=" + (end - start));//307 12767 14004
        System.out.println("执行完成。");
    }
    
    public static void fileInputStreamBuffer() throws IOException {
        long start = System.currentTimeMillis();
        
        InputStream is = new FileInputStream("c:/img/00.mp4");
        OutputStream os = new FileOutputStream("c:/img/22.mp4");
        
        //缓冲流，加快文件输入输出
        BufferedInputStream bufferedInputStream = new BufferedInputStream(is);
        BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(os);
        
        
        byte[] buffer = new byte[1024];
        int length;
        while((length = bufferedInputStream.read(buffer)) != -1) {
            bufferedOutputStream.write(buffer, 0, length);
        }
        
        bufferedOutputStream.close();
        bufferedInputStream.close();
        os.close();
        is.close();
        
        long end = System.currentTimeMillis(); 
        System.out.println("end - start=" + (end - start));//276 4307 7262 7130
        System.out.println("执行完成。");
    }
    
    
    
    public static void main(String[] args) throws IOException {
        //fileInputStream();
        fileInputStreamBuffer();
    }
}

七、字符缓存流

BufferedReader、BufferedWriter

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;

public class Stream5BufferedReader {

    
    public static void fileInputStream() throws IOException {
        
        //使用转换流InputStreamReader解决中文乱码问题。InputStreamReader：将字节流inputStream转换成字符流Reader
        InputStreamReader inputStreamReader = new InputStreamReader(new FileInputStream("c:/img/0.txt"), "GB2312");//InputStreamReader中的GB2312为文件的编码，默认是UTF-8的编码，不一致就会出现中文乱码
        OutputStreamWriter outputStreamWriter = new OutputStreamWriter(new FileOutputStream("c:/img/5.txt"), "UTF-8");//生成新的文件，使用UTF-8编码
        
        BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
        BufferedWriter bufferedWriter = new BufferedWriter(outputStreamWriter);
        
        char[] buffer = new char[1024];
        int length = 0;
        while((length = bufferedReader.read(buffer)) != -1) {
            //System.out.println(new String(buffer));
            bufferedWriter.write(buffer, 0, length);
        }
        
        bufferedWriter.close();
        bufferedReader.close();
        outputStreamWriter.close();
        inputStreamReader.close();
        System.out.println("执行完成。");
    }
    
    public static void main(String[] args) throws IOException {
        fileInputStream();
    }
}

八、Java 数据流

DataInputStream、DataOutputStream

用于数据存储，类似map的键值对，而且读写顺序要一致。

省略。

九、Java 对象流

ObjectInputStream、ObjectOutputStream

用于在网络中实现对象的传输，对象需要实现序列化接口。

省略。

注：

示例代码只是往外抛异常，没有使用Try…Catch…Finally，是不对的，只是为了演示代码整洁，实际是要使用Try…Catch…Finally来关闭流。

（时间宝贵，分享不易，捐赠回馈，^_^）

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https://www.cnblogs.com/fanshuyao/

今天越懒，明天要做的事越多。

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原文地址：https://www.cnblogs.com/fanshuyao/p/14679868.html