Java学习_20220616

IO框架

1. FileInputStream（文件字节输入流）

（1）创建FileInputStream，并指定文件路径

FileInputStream fileInputStream = new FileInputStream("e:\\aaa.txt");

（2）读取文件

1. FileInputStream.read()，只能返回一个字节,读取结束后返回-1.

int re = 0;
while((re = fileInputStream.read())!=-1){
  //  System.out.println(re); //返回的是每个字符的ASCII
    System.out.println((char)re);//a b c d .....
}

  b. FileInputStream.read(byte[])，一次读取多个字节

byte[] bytes = new byte[10]; //一次读取10个字节
 //第一次读
int count = fileInputStream.read(bytes);
System.out.println(new String(bytes));//abcdefghij
System.out.println(count);//10
//第二次读
int count1 = fileInputStream.read(bytes);
System.out.println(new String(bytes));//klmnopqrst
System.out.println(count1);//10
//第三次读
int count2 = fileInputStream.read(bytes);
System.out.println(new String(bytes,0,count2));//uvwxyz
System.out.println(count2);//6

  c. FileInputStream.read(byte[])+while语句

byte[] bytes = new byte[100];
int co = 0;
while ((co=fileInputStream.read(bytes))!=-1){
    System.out.println(new String(bytes,0,co));//abcdefghijklmnopqrstuvwxyz
}

（3）关闭

fileInputStream.close();

2. FileOutputStream（文件字节输出流）

（1）创建文件字节输出流对象

FileOutputStream fileOutputStream = new FileOutputStream("e:\\bbb.txt");
//new FileOutputStream("e:\\bbb.txt",true);后面＋true表示在后面追加而不是覆盖。

（2）写入文件

1. FileOutputStream.write()，一次写入一个字节

   fileOutputStream.write(97);//a
   fileOutputStream.write('b');
   fileOutputStream.write('c'); //打开文件后 有 abc三个字符

   b.  FileOutputStream.write(byte[] )，使用字节数组传值  

String string = "qwertyuiop";
fileOutputStream.write(string.getBytes());//string.getBytes()获取字符串对应的字节数组

（3）关闭

fileOutputStream.close();

（4）将文件复制一份（先将存储设备中的文件读到内存，后将内存中的内容写到存储设备中）

FileInputStream fileInputStream = new FileInputStream("e:\\001.jpg");
FileOutputStream fileOutputStream = new FileOutputStream("e:\\002.jpg");
byte[] bytes = new byte[1024];
int count = 0;
//边读边写
while((count = fileInputStream.read(bytes))!=-1){
    fileOutputStream.write(bytes,0,count);
}
fileInputStream.close();
fileOutputStream.close();