java io读取数据

1.字节流读取数据 

2.字节流读取数据： read（）

package wwx;
 
import jdk.swing.interop.SwingInterOpUtils;
 
import java.io.*;
import java.nio.charset.StandardCharsets;
 
public class Test {
    public static void main(String[] args) {
        FileInputStream fileInputStream = null;
 
 
        try {
            fileInputStream = new FileInputStream("E:\\wwx\\xx\\wx.txt");
 
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
        try {
 
            int read = fileInputStream.read();
            System.out.println((char)read);
            int read1 = fileInputStream.read();
            System.out.println((char)read1);
            int read2 = fileInputStream.read();
            System.out.println((char)read2);
 
        } catch (IOException e) {
            e.printStackTrace();
        }
        finally {
            try {
                fileInputStream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
 
 
 
 
    }
 
}
 
 

 

 优化：

package wwx;
 
import jdk.swing.interop.SwingInterOpUtils;
 
import java.io.*;
import java.nio.charset.StandardCharsets;
 
public class Test {
    public static void main(String[] args) {
        FileInputStream fileInputStream = null;
 
 
        try {
            fileInputStream = new FileInputStream("E:\\wwx\\xx\\wx.txt");
 
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
        try {
 
            int read ;
 
//            System.out.println((char)read);
//            int read1 = fileInputStream.read();
//            System.out.println((char)read1);
//            int read2 = fileInputStream.read();
//            System.out.println((char)read2);
 
//            while (read != -1) {
//                System.out.println((char) read);
//                read = fileInputStream.read();
//            }
            //优化
            while ((read = fileInputStream.read()) != -1) {
                System.out.print((char) read);
 
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                fileInputStream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
 
 
    }
 
}
 
 

3.字节流复制文件：

package wwx;
 
import jdk.swing.interop.SwingInterOpUtils;
 
import java.io.*;
import java.nio.charset.StandardCharsets;
 
public class Test {
 
    public static void main(String[] args) throws IOException {
        FileInputStream fileInputStream = new FileInputStream("E:\\Test\\wwx.txt");
 
        FileOutputStream fileOutputStream = new FileOutputStream("E:\\cTest\\wwx.txt");
       
        int by;
        while ((by = fileInputStream.read()) != -1) {
            fileOutputStream.write(by);
        }
        fileInputStream.close();
        fileOutputStream.close();
    }
 
 
}
 
 

 4.byte数组转为字符串：new String(byte)方法

package wwx;
public class Test {
    public static void main(String[] args) {
 
        byte[] bytesArray={97,98,99};
 
        String s = new String(bytesArray);//用构造方法创建的，值为正常值
 
        System.out.println("byte数组转为字符串形式："+s);
 
 
       String str1="3,4,5,67";
 
       byte[] bytes1=str1.getBytes();//该方法返回值为内存地址
 
       System.out.println("字符串转为byte数组"+bytes1);
 
    }
 
}
 
 

 

5.字节流以字节数组形式读取数据：

用idea读取该记事本的数据 

该记事本f之后换行，换行为一个\n,占两个字节 

package wwx;
 
import jdk.swing.interop.SwingInterOpUtils;
 
import java.io.*;
import java.nio.charset.StandardCharsets;
 
public class Test {
    public static void main(String[] args) throws IOException {
 
        FileInputStream input = new FileInputStream("E:\\wwx\\xx\\wx.txt");
 
        byte[] bytes = new byte[5];
        System.out.println("第1次读取数据");
        int bytesLen = input.read(bytes);
        System.out.println("byte数组长度:"+bytesLen);
        System.out.println(new String(bytes));
 
        System.out.println("第2次读取数据");
        bytesLen = input.read(bytes);
        System.out.println("byte数组长度:"+bytesLen);
        System.out.println(new String(bytes));
 
 
        System.out.println("第3次读取数据");
        bytesLen = input.read(bytes);
        System.out.println("byte数组长度:"+bytesLen);
        System.out.println(new String(bytes));
 
        input.close();
 
    }
 
}

6.要求一次性读取wx.txt 中13个字节数据 ：

package wwx;
 
import jdk.swing.interop.SwingInterOpUtils;
 
import java.io.*;
import java.nio.charset.StandardCharsets;
/*
要求一次性读取wx.txt 中13个字节数据
 */
public class Test {
    public static void main(String[] args) throws IOException {
 
        FileInputStream inputStream = new FileInputStream("E:\\wwx\\xx\\wx.txt");
 
        byte[] bytes = new byte[13];
 
        int len = inputStream.read(bytes);
 
        System.out.println("byte数组字节长度："+len);
 
        System.out.println(new String(bytes));
 
        inputStream.close();
 
    }
}

7.字节流以1024字节读取数据：

 

package wwx;
import java.io.*;
/*
要求一次性读取wx.txt 中13个字节数据
 */
public class Test {
    public static void main(String[] args) throws IOException {
        FileInputStream inputStream = new FileInputStream("E:\\wwx\\xx\\wx.txt");
 
        byte[] bytes = new byte[1024];
 
        int len;
        while ((len = inputStream.read(bytes)) != -1) {
            System.out.println("byte数组字节长度：" + len);
            System.out.println(new String(bytes,0,len));
        }
        inputStream.close();
    }
}