文件流之字节缓冲流(BufferedInputStream BufferedOutputStream)

Posted 2020-10-06

• 缓冲流的优势是: 

　　BufferedInputStream: 输入缓冲流：先从磁盘中将要读取的内容放入到内存中，再一次性从内存中取出来，避免了读一段取一段；

　　BufferedOutputStream: 输出缓冲流：先将要输出的内容放入到内存中，再一次性全都输出。

• 缓冲流的构造函数:

public BufferedInputStream(InputStream in) {
            this (in, DEFAULT_BUFFER_SIZE); 
    }

public BufferedInputStream(InputStream in, int size) {
            super (in);
            if (size <= 0 ) {
                throw  new IllegalArgumentException("Buffer size <= 0" ); 
        } 
        buf = new  byte [size]; 
    }

public BufferedOutputStream(OutputStream out) {
            this (out, 8192 ); 
    }

public BufferedOutputStream(OutputStream out, int size) {
            super (out);
            if (size <= 0 ) {
                throw  new IllegalArgumentException("Buffer size <= 0" ); 
        } 
        buf = new  byte [size]; 
    }

• 缓冲流关闭:

只需将缓冲流关闭，无需将节点流关闭，因为缓冲流内部会自动调用节点流关闭。

• 缓冲流需要调用flush()方法才能将内容输入或输出出来，或者调用close()方法时，也会调用flush()方法。
• 注意：

　　　　new FileOutputStream("***"); 如果参数中的路径有目录不存在，并不会自动创建目录；

　　　　此外：调用File 类的mkdir()或mkdirs()可能出现错误“Access is denied”，暂时还没解决。

• 缓冲流的应用

public class BufferedStream {

    public static void main(String[] args) {
        //BufferedStream fbs = new BufferedStream();
        // fbs.writeFileWithBufferedStream("HelloBufferedOutputStream",
        // "/home/rding/bufferd.txt");
        // fbs.readFileWithBufferedStream("/home/rding/bufferd.txt");
        //fbs.writeFileWithBufferedStream("HelloWorld", "d:/rding/rding/buffered.txt");
        
        String str = "c:\\cc\\cc";
        System.out.println(str.lastIndexOf("\\"));
    }

    public void readFileWithBufferedStream(String srcPath, int size) {
        InputStream inputStream = null;
        BufferedInputStream bufferedInputStream = null;
        StringBuffer sb = new StringBuffer();
        try {
            inputStream = new FileInputStream(srcPath);
            bufferedInputStream = new BufferedInputStream(inputStream);
            byte[] byteArr = new byte[size];
            int len = 0;
            while ((len = bufferedInputStream.read(byteArr)) != -1) {
                sb.append(new String(byteArr), 0, len);
            }
            System.out.println(sb);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (bufferedInputStream != null) {
                try {
                    bufferedInputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    public void readFileWithBufferedStream(String srcPath) {
        InputStream inputStream = null;
        BufferedInputStream bufferedInputStream = null;
        try {
            inputStream = new FileInputStream(srcPath);
            bufferedInputStream = new BufferedInputStream(inputStream);
            int size = bufferedInputStream.available();
            byte[] byteArr = new byte[size];
            bufferedInputStream.read(byteArr);
            String str = new String(byteArr);
            System.out.println(str);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (bufferedInputStream != null) {
                try {
                    bufferedInputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    public void writeFileWithBufferedStream(String content, String destPath) {
        OutputStream outputStream = null;
        BufferedOutputStream bufferedOutputStream = null;
        try {

            // 下面的语句中，如果destPath中的目录不存在，不会自动创建目录，因此，建议使用下面的代码
            // outputStream = new FileOutputStream(destPath);
　　　　　　　// 前提是输出的路径是"/"而不是"\\"

            File tmp = new File(destPath.substring(0, destPath.lastIndexOf("/")));
            if(!tmp.exists()){
                tmp.mkdirs();
            }
            outputStream = new FileOutputStream(destPath);
            bufferedOutputStream = new BufferedOutputStream(outputStream);

            byte[] byteArr = content.getBytes();
            bufferedOutputStream.write(byteArr);
            bufferedOutputStream.flush();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (bufferedOutputStream != null) {
                try {
                    bufferedOutputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

    }

    public void copyFileWithBufferedStream(String srcPath, String destPath, int size) {
        InputStream inputStream = null;
        BufferedInputStream bufferedInputStream = null;

        OutputStream outputStream = null;
        BufferedOutputStream bufferedOutputStream = null;

        try {
            inputStream = new FileInputStream(srcPath);

            // 下面的语句中，如果destPath中的目录不存在，不会自动创建目录，因此，建议使用下面的代码
            // outputStream = new FileOutputStream(destPath);

            File tmp = new File(destPath.substring(0, destPath.lastIndexOf("/")));
            if(!tmp.exists()){
                tmp.mkdirs();
            }
            
            outputStream = new FileOutputStream(tmp);

            bufferedInputStream = new BufferedInputStream(inputStream);

            bufferedOutputStream = new BufferedOutputStream(outputStream);

            byte[] byteArr = new byte[size];

            int len = 0;
            while ((len = bufferedInputStream.read(byteArr)) != -1) {
                bufferedOutputStream.write(byteArr, 0, len);
            }
            bufferedOutputStream.flush();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (bufferedOutputStream != null) {
                try {
                    bufferedOutputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (bufferedInputStream != null) {
                try {
                    bufferedInputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

    }

}