java 获取文件大小

java 中如何获取文件的大小呢?

有两种方式

方式一:使用File 的length()方法;

方式二:使用FileInputStream的available()方法;

实例:

@Test
	public void test01() throws IOException {
		String filepath = "d:\\bin\\pushpoxy-0.0.1-SNAPSHOT.jar";
		System.out.println("File has " + new File(filepath).length()+ " bytes");
		FileInputStream fis = null;  
        fis = new FileInputStream(filepath);  
        System.out.println("File has " + fis.available() + " bytes");

	}

运行结果 :

File has 29061936 bytes

File has 29061936 bytes

其实这两个方法时有区别的;

File 的length()方法 是获取文件所占硬盘空间大小;

FileInputStream的available()方法是还有多少字节可以读取.

available()方法的说明如下:

Returns an estimate of the number of remaining bytes that can be read (or skipped over) from this input stream without blocking by the next invocation of a method for this input stream. The next invocation might be the same thread or another thread. A single read or skip of this many bytes will not block, but may read or skip fewer bytes. 

 

我们把上面的程序稍微修改一下:

@Test
	public void test01() throws IOException {
		String filepath = "d:\\bin\\pushpoxy-0.0.1-SNAPSHOT.jar";
		System.out.println("File has " + new File(filepath).length()+ " bytes");
		FileInputStream fis = null;  
        fis = new FileInputStream(filepath);
        byte[]bytes=new byte[10];
        fis.read(bytes);
        System.out.println("File has " + fis.available() + " bytes");
        fis.skip(-10);
        System.out.println("File has " + fis.available() + " bytes");

	}

 执行结果如下:

File has 29061936 bytes

File has 29061926 bytes

File has 29061936 bytes

 

总结:获取文件大小时建议使用File 的length()方法