Java基础IO流（五）RandomAccessFile

RandomAccessFile支持随机访问文件，可以访问文件的任意位置

(1)java文件模型：
    在硬盘上的文件是byte byte byte存储的，是数据的集合
(2)打开文件：
    有两种模式“rw"（读写） ”r"(只读)
    RandomAccessFile raf = new RandomAccessFile(file,"rw")
    文件指针，打开文件时指针在开头 pointer = 0;
(3)写方法
    raf.write(int) -->只写一个字节（后8位),同时指针指向下一个位置,准备再次写入
(4)读方法
    int b = raf.read() --->读一个字节
(5) 文件读写完以后一定要关闭(Oracle官方说明)

<span style="font-size: 16px"><span style="color: #0000ff">package</span><span style="color: #000000"> Blog;

</span><span style="color: #0000ff">import</span><span style="color: #000000"> java.io.File;
</span><span style="color: #0000ff">import</span><span style="color: #000000"> java.io.IOException;
</span><span style="color: #0000ff">import</span><span style="color: #000000"> java.io.RandomAccessFile;
</span><span style="color: #0000ff">import</span><span style="color: #000000"> java.util.Arrays;

</span><span style="color: #0000ff">public</span> <span style="color: #0000ff">class</span><span style="color: #000000"> RafDemo {
    </span><span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">void</span> main(String[] args) <span style="color: #0000ff">throws</span><span style="color: #000000"> IOException {
        File demo </span>= <span style="color: #0000ff">new</span> File("demo"<span style="color: #000000">);
        </span><span style="color: #0000ff">if</span> (!<span style="color: #000000">demo.exists()){
            demo.mkdir();
        }
        File file </span>= <span style="color: #0000ff">new</span> File(demo,"raf.dat"<span style="color: #000000">);
        </span><span style="color: #0000ff">if</span> (!<span style="color: #000000">file.exists()) {
            file.createNewFile();
        }
        RandomAccessFile raf </span>= <span style="color: #0000ff">new</span> RandomAccessFile(file, "rw"<span style="color: #000000">);
        </span><span style="color: #008000">//</span><span style="color: #008000">指针的位置</span>
<span style="color: #000000">        System.out.println(raf.getFilePointer());
        
        raf.write(</span>‘A‘);<span style="color: #008000">//</span><span style="color: #008000">只写了一个字节</span>
<span style="color: #000000">        System.out.println(raf.getFilePointer());
        raf.write(</span>‘B‘<span style="color: #000000">);
        
        </span><span style="color: #0000ff">int</span> i = 0x7fffffff<span style="color: #000000">;
        </span><span style="color: #008000">//</span><span style="color: #008000">用write方法每次只能写一个字节,如果要把i写进去就得写4次</span>
        raf.write(i >>> 24);<span style="color: #008000">//</span><span style="color: #008000">高8位</span>
        raf.write(i >>> 16<span style="color: #000000">);
        raf.write(i </span>>>> 8<span style="color: #000000">);
        raf.write(i);
        System.out.println(raf.getFilePointer());
        
        </span><span style="color: #008000">//</span><span style="color: #008000">可以直接写一个int</span>
<span style="color: #000000">        raf.writeInt(i);
        
        String s </span>= "中"<span style="color: #000000">;
        </span><span style="color: #0000ff">byte</span>[] gbk = s.getBytes("gbk"<span style="color: #000000">);
        raf.write(gbk);
        System.out.println(raf.length());
        
        </span><span style="color: #008000">//</span><span style="color: #008000">读文件,必须把指针移到头部</span>
        raf.seek(0<span style="color: #000000">);
        </span><span style="color: #008000">//</span><span style="color: #008000">一次性读取,把文件中的内容都读到字节数组中</span>
        <span style="color: #0000ff">byte</span>[] buf = <span style="color: #0000ff">new</span> <span style="color: #0000ff">byte</span>[(<span style="color: #0000ff">int</span><span style="color: #000000">)raf.length()];
        raf.read(buf);
        System.out.println(Arrays.toString(buf));
    
        String s1 </span>= <span style="color: #0000ff">new</span><span style="color: #000000"> String(buf);
        System.out.println(s1);
        
        </span><span style="color: #0000ff">for</span> (<span style="color: #0000ff">byte</span><span style="color: #000000"> b : buf){
            System.out.println(Integer.toHexString(b </span>& 0xff) + " "<span style="color: #000000">);
        }
        raf.close();
    }
}</span></span>

 

Java基础IO流（五）RandomAccessFile

标签：string   sts   size   集合   ESS   开头   oracle   poi   字节数组   

本文系统来源：https://www.cnblogs.com/deepSleeping/p/10111341.html

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