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};   // 赵
        out.write(b);
        out.close();

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　　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();

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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();

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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
    */

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