public class Test {
	public static void main(String[] args) throws IOException, InterruptedException {
	    test1();
//	    test2();
	    test3();
	}
	
	private static void test1() throws IOException{
	    
	    String filePath = "F:/shanch/temp/a.txt";
	    
	    //RandomAccessFile没有会自动创建文件
	    RandomAccessFile raFile = new RandomAccessFile(filePath,"rw");
	    System.out.println(raFile.getFilePointer());
	    
	    //setLength会往文件里面写入空白串 即byte 00
	    raFile.setLength(36);
	    
	    raFile.writeBytes("0123456789abcdefghijklmnopqrstuvwxyz1111");
	    
	    System.out.println(raFile.getFilePointer());
	    
	    //会将多出的1111截掉
	    raFile.setLength(36);
	    System.out.println(raFile.getFilePointer());
	    
	    raFile.seek(20);
	    System.out.println(raFile.getFilePointer());
	    
	    raFile.skipBytes(6);
	    System.out.println(raFile.getFilePointer());
	    
	    //skipbytes不会使指针将超过文件长度
	    raFile.skipBytes(20);
        System.out.println(raFile.getFilePointer());
	    
        //seek如果位置超过文件长度，会将文件扩大
        raFile.seek(50);
        System.out.println(raFile.getFilePointer());
        raFile.write(100);
        
        raFile.setLength(36);
        
	}
	
	private static void test2() throws IOException{
	    
	    String filePath = "F:/shanch/temp/a.txt";
        RandomAccessFile raFile = new RandomAccessFile(filePath,"rw");
        
        raFile.seek(10);
        //read读取当前指针的byte 读取之后指针下移一个byte
        System.out.println((char)raFile.read());
        System.out.println(raFile.getFilePointer());
        
        raFile.seek(10);
        raFile.write(0);//替换a 而非插入
        raFile.write(0);//替换b
        raFile.write(0);//替换c
	}
	
	private static void test3() throws IOException, InterruptedException{
	 
	    final String filePath = "F:/shanch/temp/a.txt";
        RandomAccessFile raFile = new RandomAccessFile(filePath,"rw");
        FileChannel fChannel = raFile.getChannel();

        //当文件锁住时，不可修改
//        fChannel.lock();
        //程序退出时会自动释放锁
        
        //position与FilePointer一致
        fChannel.position(10);
        System.out.println(raFile.getFilePointer());
        raFile.seek(20);
        System.out.println(fChannel.position());
        
        //清空文件,从文件头开始,只保留指定字节数 
        fChannel.truncate(50);
        
        fChannel.lock(10, 10, true);
        //FileChannel与RandomAccessFile的写方法是不同的实现
        //FileChannel锁住时,RandomAccessFile将不能写
//        raFile.seek(15); 
//        raFile.write(97); //此处会报异常
        
        Thread.currentThread().sleep(2000);
        new Thread() {
            public void run(){
                try
                {
                    RandomAccessFile raFile = new RandomAccessFile(filePath,"rw");
                    raFile.seek(15);
                    System.out.println((char)raFile.read());
                    raFile.write(26);//另一个程序已锁定文件的一部分，进程无法访问。
//                    raFile.read();
                }
                catch (IOException e1)
                {
                    e1.printStackTrace();
                }
            }
        }.start();
        
	}
}