Java基础 IO & NIO file操作总结（详细）

前言

IO操作比较繁琐，容易忘记，再加上NIO的一些基本操作，一段时间内居然混淆，这里做一下记录，以后直接拿来用，忘了方便查阅。还有，这里直接贴代码，运行结果就不放上去了。:open_mouth:

1. 原生IO对File读写复制

1.1 读取控制台中的输入  

public void test1() throws IOException {
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));
        System.out.println("请输入一个字符");
        char c;
        c = (char) bufferedReader.read();
        System.out.println("你输入的字符为"+c);
}
复制代码

public void test2() throws IOException {
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));
        System.out.println("请输入一行字符");
        String str = bufferedReader.readLine();
        System.out.println("你输入的字符为" + str);
}

复制代码

1.2 二进制文件的写入和读取  FileOutputStream+FileInputStream

public void test04() throws IOException {
        byte[] bytes = {12,21,34,11,21};
        FileOutputStream fileOutputStream = new FileOutputStream(new File(""));
        fileOutputStream.write(bytes);
        fileOutputStream.close();
}复制代码

public void test05() throws IOException {
        FileInputStream fileInputStream = new FileInputStream(new File(""));
        int c;
        // 读取写入的二进制文件，输出字节数组
        while ((c = fileInputStream.read()) != -1) {
            System.out.print(c);
        }
 }复制代码

1.3 文本文件的写入和读取   FileReader + FileWriter

public void test1() throws IOException {
        FileReader fileReader = new FileReader(new File(""));
        BufferedReader bufferedReader = new BufferedReader(fileReader);
        String str;
        while ((str = bufferedReader.readLine()) != null) {
            System.out.println(str);
        }
        fileReader.close();
        bufferedReader.close();
}



public void test2() throws IOException {
        FileReader fileReader = new FileReader(new File(""));
        int c;
//      读取字符
        while ((c = fileReader.read()) != -1) {
            System.out.print((char) c);
        }
    }复制代码

// 开启追加模式
public static void test1() throws IOException {        FileWriter fileWriter = new FileWriter(new File("D://1.txt"), true); // 开启追加模式
        fileWriter.write("----1----");
        fileWriter.write("----2----"); // 不会覆盖文件原本的内容
//        fileWriter.write(null); 不能直接写入 null
        fileWriter.append("----3----"); // 直接追加的内容
        fileWriter.append(null);
        fileWriter.flush();
        fileWriter.close();
    }

    // 关闭追加模式
    public void test2() throws IOException {
        FileWriter fileWriter = new FileWriter(new File("").getAbsolutePath()+"/io/test.txt", false); // 关闭追加模式，变为覆盖模式
        fileWriter.write("----1----");
        fileWriter.write("----2----");  // 覆盖掉前面的内容
        fileWriter.append("----3----");  // 追加的内容
        fileWriter.flush();
        fileWriter.close();
    }
复制代码

1.4 文本文件的写入和读取 OutputStreamWriter+ InputStreamReader

public void test1() throws IOException {
        FileOutputStream fileOutputStream = new FileOutputStream(new File(""));
        OutputStreamWriter outputStreamWriter = new OutputStreamWriter(fileOutputStream, "utf-8"); // 使用 GBK 编码文件
        outputStreamWriter.write("----1----");
        outputStreamWriter.append("----2----"); // 追加内容
        outputStreamWriter.flush();
        outputStreamWriter.close();
        fileOutputStream.close();
    }

  
    public void test2() throws IOException {
        FileInputStream fileInputStream = new FileInputStream(new File("").getAbsolutePath()+"/io/test2.txt");
        InputStreamReader inputStreamReader = new InputStreamReader(fileInputStream, "GBK"); // 使用 GBK 解码文件
        BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
        String str;
        while ((str = bufferedReader.readLine()) != null) {
            System.out.println(str);
        }
        bufferedReader.close();
        inputStreamReader.close();
    }复制代码

1.5 复制文件

输入和输出使用缓冲流 BufferedInputStream + BufferedInputStream

public void test1() throws IOException {        
        FileInputStream in = new FileInputStream("");
        BufferedInputStream inBuffer = new BufferedInputStream(in);
        FileOutputStream out = new FileOutputStream("");
        BufferedOutputStream outBuffer = new BufferedOutputStream(out);
        int len = 0;
        byte[] bs = new byte[1024];
        while ((len = inBuffer.read(bs)) != -1) {
            outBuffer.write(bs, 0, len);
        }
        in.close();
        outBuffer.close();
        out.close();
    }

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输入和输出都不使用缓冲流  FileInputStream + FileOutputStream 

public void test2() throws IOException {
        
        FileInputStream in = new FileInputStream("");
        FileOutputStream out = new FileOutputStream("");
        int len = 0;
        byte[] bs = new byte[1024];
        while ((len = in.read(bs)) != -1) {
            out.write(bs, 0, len);
        }
        in.close();
        out.close();
    }
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按字符拷贝 FileReader + FileWriter 

public void test3() throws IOException {
        File file=new File("");
        if(!file.isFile()){
            System.out.println("文件不存在，无法拷贝！");
            return;
        }
        FileReader fr=new FileReader(file);
        FileWriter fw=new FileWriter(""); 
        char chars[]=new char[512];
        int temp=0;
        while ((temp=fr.read(chars))!=-1){
            fw.write(chars,0,temp);
        }
        fw.flush();
        fw.close();
        fr.close();
        System.out.println("拷贝成功！");
    }
}
复制代码

2. NIO对File读写复制

2.1 写操作

public void test1() throws IOException {
        FileOutputStream fileOutputStream = new FileOutputStream("");
        FileChannel fileChannel = fileOutputStream.getChannel();
        // 创建一个缓冲区
        ByteBuffer byteBuffer = ByteBuffer.allocate(1024);
        byteBuffer.put("[内容]".getBytes());
        // 对byteBuffer进行flip
        byteBuffer.flip();
        // 将byteBuffer数据写入fileChannel
        fileChannel.write(byteBuffer);
        fileOutputStream.close();
    }复制代码

2.2 读操作

public void test1() throws IOException {
        File file = new File("");
        FileInputStream fileInputStream = new FileInputStream(file);
        // 获得inputStream对应的FileChannel
        FileChannel fileChannel = fileInputStream.getChannel();
        // 创建缓冲区
        ByteBuffer byteBuffer = ByteBuffer.allocate((int)file.length());
        // 从channel读数据到byteBuffer
        fileChannel.read(byteBuffer);
        // 将byteBuffer的字节数据转换成String
        System.out.println(new String(byteBuffer.array()));
        fileInputStream.close();
    }复制代码

2.3 复制操作

FileChannel 实现

public void test1() throws IOException {
        // 输入流
        FileInputStream fileInputStream = new FileInputStream("");
        FileChannel fileChannel1 = fileInputStream.getChannel();
        // 输出流
        FileOutputStream fileOutputStream = new FileOutputStream("");
        FileChannel fileChannel2 = fileOutputStream.getChannel();

        ByteBuffer byteBuffer = ByteBuffer.allocate(1024);

        while (true) {
            byteBuffer.clear();
            int read = fileChannel1.read(byteBuffer);
            if (read == -1) {
                break;
            }
            // flip一次byteBuffer
            byteBuffer.flip();
            fileChannel2.write(byteBuffer);
        }
        fileInputStream.close();
        fileOutputStream.close();
    }复制代码

transferFrom实现

public void test1() throws IOException {
        // 输入流
        FileInputStream fileInputStream = new FileInputStream("");
        FileChannel fileChannel1 = fileInputStream.getChannel();
        // 输出流
        FileOutputStream fileOutputStream = new FileOutputStream("");
        FileChannel fileChannel2 = fileOutputStream.getChannel();

        // 用transerFrom完成拷贝
        fileChannel2.transferFrom(fileChannel1, 0, fileChannel1.size());
        

        fileInputStream.close();
        fileOutputStream.close();
    }复制代码