• OutputStream、InputStream 、FileOutputStream、FileInputStream,字节流API


    OutputStream、InputStream是所有字节流的超类,所谓字节流就是一个字节一个字节的读取,类似于c中的二进制读取方法

    java.io.OutputStream

    Method

      void write(int b)

        Writes the specified byte to this output stream

      void write(byte[] b)    //   String 类的方法,  byte[] b = "中国".getBytes();   

        Writes b.length bytes from the specified byte array to this output stream.

      void write(byte[], int offset, int len)

        Writes len bytes from the specified byte array starting at offset off to this output stream.

            OutputStream out = new FileOutputStream("E:/a.txt");
            out.write(97);   // 写下二进制的97,文本编辑器读出二进制97,查询本机编码表,得出a
            
            byte[] b = {-43,-44};   //
            out.write(b);
            out.close();
    View Code

      void flush()

        Flushes this output stream and forces any buffered output bytes to be written out.

      void close()

    子类 FileOutputStream

    构造函数

      FileOutputStream(File file, boolean append)     //  append 参数不写默认为false,即每次都会创建一个新文件(不管文件是否存在)

        Creates a file output stream to write to the file represented by the specified File object.

      FileOutputStream(String name, boolean append)   // @name  the file path @append 同上

    其余方法暂时略,大部分与父类相同

    java.io.InputStream

      int read()

        Reads the next byte of data from the input stream

      int read(byte[] b)

        Reads some number of bytes from the input stream and stores them into the buffer array b.

      int read(byte[] b, int off, int len)

        Reads up to len bytes of data from the input stream into an array of bytes.

      

            InputStream in = new FileInputStream("E:/a.txt");  //文件内容 abcde
            //int a = in.read();   // 97 
            byte[] b = new byte[2];
            int a = in.read(b);   // a值 2   b值 ab
            a = in.read(b);   //  a值  2     b值 cd
            a = in.read(b);   // a值 1       b值 ed
            a = in.read(b);   // a值 -1      b值 ed 
            
            // a 为读出的字节数, 读到文件末尾时为 -1
            in.close();
    View Code

    子类 FileInputStream

    构造函数

      FileInputStream(File file, boolean append)

      FileInputStream(String name, boolean append)  // 同上

    二进制文件复制

            InputStream in = new FileInputStream("E:/test.avi");
            OutputStream out = new FileOutputStream("E:/copy.avi");
            
            int len;
            byte[] b = new byte[1024];
            while((len = in.read(b)) != -1)
            {
                out.write(b, 0, len);
                // out.flush();
            }
            
            in.close();
            out.close();
    View Code

    BufferedOutputStream、BufferedInputStream 提高程序读取效率

    构造函数 BufferedOutputStream(OutputStream out)

    下面是一个对比,复制102M的文件耗时

    public static void copy_4(String desPath, String srcPath) throws IOException{
            
             BufferedInputStream in = new BufferedInputStream(new FileInputStream(srcPath));
       
            BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(desPath));
            
            int len;
            byte[] b = new byte[1024];
            while((len = in.read(b)) != -1)
            {
                out.write(b, 0, len);         
            }
            
            in.close();
            out.close();
    }
    
    /*
         * 一个字节一个的读,没缓冲     408,891
         * 一个字节一个的读,有缓冲       4979
         * 每次读 1024字节, 没缓冲      898
         * 每次读 1024字节, 有缓冲      236
        */
    View Code
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  • 原文地址:https://www.cnblogs.com/YKang/p/7283333.html
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