Java FileInputStream available()用法及代码示例

FileInputStream 类的 available() 方法用于返回可以从输入流中读取而不会阻塞的估计剩余字节数。此方法返回要从文件中读取的剩余字节数。当一个文件被完全读取时，这个函数返回零。

用法:

FileInputStream available() 

返回值：该方法返回并估计从该输入流中读取的剩余字节数而不阻塞。

异常：该方法可以产生IOException或FileNotFoundException等异常。这些异常如下所述。

• IOException -如果文件输入流已通过调用 close 关闭或发生任何 I/O 错误。
• FileNotFoundException -如果该目录不可用，那么我们将得到 FileNotFoundException。

如何调用 available() 方法？

第 1 步：将文件附加到 FileInputStream，因为这将使我们能够从文件中读取数据，如下所示：

FileInputStream fileInputStream = new FileInputStream(“file.txt”);

第 2 步：现在，要从文件中读取有多少数据可供读取的数据，我们应该使用 FileInputStream 对象调用一个可用的方法，如下所示；

int ch = fileInputStream.available(); 

Step 3(a)：当没有更多数据可供进一步读取时，available()方法返回0；

步骤 3(b)：然后，我们应该将监视器附加到输出流。为了显示数据，我们可以使用 System.out.print。

System.out.print(ch);

Implementation

原始文件内容：file.txt

GeeksforGeeks

该程序将读取一个文件并返回每次读取的字符数。

// Java program to demonstrate the working
// of the FileInputStream available() method
import java.io.File;
import java.io.FileInputStream;
public class abc {
    public static void main(String[] args)
    {
        // Creating file object and specifying path
        File file = new File("file.txt");
        try {
            FileInputStream input = new FileInputStream(file);
            int character;
            // read character by character by default
            // read() function return int between 0 and 255.
            while ((character = input.read()) != -1) {
                int ch = input.available();
                System.out.print("Currently Reading:"
                                 + (char)character);
                System.out.print(" Remaining character:"
                                 + ch);
                System.out.println();
            }
            input.close();
        }
        catch (Exception e) {
            e.printStackTrace();
        }
    }
}

输出

Currently Reading:G Remaining character:12
Currently Reading:e Remaining character:11
Currently Reading:e Remaining character:10
Currently Reading:k Remaining character:9
Currently Reading:s Remaining character:8
Currently Reading:f Remaining character:7
Currently Reading:o Remaining character:6
Currently Reading:r Remaining character:5
Currently Reading:G Remaining character:4
Currently Reading:e Remaining character:3
Currently Reading:e Remaining character:2
Currently Reading:k Remaining character:1
Currently Reading:s Remaining character:0