FileInputStream文件字节输入流

一.概念

二.构造器

三.方法

四.执行

方法一：一个一个字节读

1.代码

package org.example;

import java.io.*;

public class day05 {
    public static void main(String[] args) throws IOException {
        //1.创建文件字节输入流管道与源文件接通:两种方法都行
        InputStream f1 = new FileInputStream(new File("D:\\temp\\day05\\a.txt"));
        InputStream f2 = new FileInputStream("D:\\temp\\day05\\a.txt");
        //2.读取文件的字节数据
        int b1 = f1.read();
        System.out.println(b1);
        System.out.println((char) b1);
        int b2 = f1.read();
        System.out.println(b2);
        System.out.println((char) b2);
        int b3 = f1.read();
        System.out.println(b3);
    }
}

2.结果

方法二：循环读

1.代码

package org.example;

import java.io.*;

public class day05 {
    public static void main(String[] args) throws IOException {

        InputStream f1 = new FileInputStream("D:\\temp\\day05\\b.txt");
        int b; //用于记住读取的字节
        while((b = f1.read()) != -1){
            System.out.print((char)b);
        }
        f1.close();
    }
}

2.结果

方法三：每次读取多个字节

1.代码

package org.example;

import java.io.*;

public class day05 {
    public static void main(String[] args) throws IOException {
        //b.txt内容：abcdefg
        InputStream f1 = new FileInputStream("D:\\temp\\day05\\b.txt");
        //开始读取文件中的字节数据，每次读取多个字节
         byte[] buffer = new byte[4];
         int len = f1.read(buffer);
         String s = new String(buffer);
        System.out.println(s);
        System.out.println("读取的字节数"+len);
        int len2 = f1.read(buffer);
        String s2 = new String(buffer);
        System.out.println(s2);
        System.out.println("读取的字节数"+len2);
        f1.close();
    }
}

2.结果

3.改进

package org.example;

import java.io.*;

public class day05 {
    public static void main(String[] args) throws IOException {
        //b.txt内容：abcdefg
        InputStream f1 = new FileInputStream("D:\\temp\\day05\\b.txt");
        //开始读取文件中的字节数据，每次读取多个字节
         byte[] buffer = new byte[4];
         int len = f1.read(buffer);
         String s = new String(buffer);
        System.out.println(s);
        System.out.println("读取的字节数"+len);
        int len2 = f1.read(buffer);
        String s2 = new String(buffer,0,len2);
        System.out.println(s2);
        System.out.println("读取的字节数"+len2);
        f1.close();
    }
}

4.结果 

 方法四：循环读取

1.代码

package org.example;

import java.io.*;

public class day05 {
    public static void main(String[] args) throws IOException {
        //b.txt内容：abcdefg
        InputStream f1 = new FileInputStream("D:\\temp\\day05\\b.txt");
        //开始读取文件中的字节数据，每次读取多个字节
        byte[] buffer = new byte[4];
        int len;
        while ((len = f1.read(buffer)) != -1) {
            String s = new String(buffer, 0, len);
            System.out.print(s);
        }
        f1.close();
    }
}

2.结果

五.问题 

 方法1

1.代码

package org.example;

import java.io.*;

public class day05 {
    public static void main(String[] args) throws IOException {
        //c.txt内容：我们在一起abcd
        InputStream f1 = new FileInputStream("D:\\temp\\day05\\c.txt");
        //这里的19可以用f1.length()获取
        byte[] buffer = new byte[19];
        int len;
        while ((len = f1.read(buffer)) != -1) {
            String s = new String(buffer, 0, len);
            System.out.print(s);
        }
        f1.close();
    }
}

2.结果

 方法2

1.代码

package org.example;

import java.io.*;

public class day05 {
    public static void main(String[] args) throws IOException {
        //c.txt内容：我们在一起abcd
        InputStream f1 = new FileInputStream("D:\\temp\\day05\\c.txt");
        final byte[] bytes = f1.readAllBytes();
        System.out.println(new String(bytes));
    }
}

2.结果