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Summary of I / O knowledge points

2022-04-23 02:04:00 【Fu Sheng Ruo Meng 521】

I/O Flow of knowledge
·I/O The basic concept of
·I/O Application of stream knowledge
· A practical example
Basic knowledge of , What is flow
· Simply speaking , Stream is a unified management of data input and output .
· The system helps us define how to write the contents of the stream to different external devices , When programming , All we need to consider is how to write the data in memory to the stream
· Determination of the direction of flow ：
The reference is our own memory space
· Output stream ：FileOutputStream, Is to store memory space data Write To external devices
· Input stream ：FileInputStream, Is to transfer external data read Into memory .
· The output stream is write
· The read stream is the input stream
The type of flow
· Character stream , Is to transmit in character units , Character streams can be processed directly Unicode But it can only handle characters or strings
· Byte stream , Is to transmit in bytes , Byte stream can be used for any object , But you can't deal with it directly Unicode character
When to use what stream
· If you're dealing with plain text , Then use the character stream
· If it's dealing with pictures 、 Video etc. , Then use byte stream
Byte stream
· Byte stream operations are inherited from abstract classes
InputStream And OutputStream
· Generally, you can operate on files , Will use
FileInoutStream And FileOutputStream
·FileIutputStream Input stream
String path = "D:/test.txt";
File file = new Path();
FileInputStream fis = new FileInputStream(file);
if(!file.exists()){
// If not, create a file
file.createNewFile();
}
//1024 Is the maximum space that can be created , To avoid not knowing how big the file is
byte[] in = new byte[1024];
// Read the contents of the file
fis.read(in);
System.out.prinln(new String(in));
·FileOutputStream Output stream
String path = "D:/test.txt";
File file = new Path();
if(!file.exists()){
// If not, create a file
file.createNewFile();
}
FileOutputStream fos = new FileOutputStream(file);
byte[] out = {'1','2','3'};
fos.write(out);
· If you want to save objects , You can use
ObjectInputStream And ObjectOutputStream
· among ,input Indicates input , Read ;output Identify the output , The write ;
· Operations on objects ObjectInputStream And ObjectOutputStream
Character stream
· Character stream operations inherit from abstract classes
Reader And Writer
· Generally operate on files , Will use FileReader And FileWriter
How to improve byte stream efficiency
·BufferedInputStream And BufferedOutputStream
· Because the byte stream is through byte To transmit , and byte The maximum transmission is 1024,1024byte=1kb, The file transferred is very small , So how do we optimize it ,
Then we need to use BufferedInputStream And BufferedOutputStream To transmit ,byte It's similar to that every time we transmit, it's in bytes , It's like a string,
Then through the String【】 Every time we transmit an array, we transmit it group by group , therefore Buffered That's how it works , We go through Buffered The blessing , We are a group byte A group of byte The transmission of .
InputStream is = new FileInputStream(sourcePath);
BufferedInputStream bis = new BufferedInputStream(is);
OutputStream os = new FileOutputStream(desPath);
BufferedOutputStream bos = new BufferedOutputStream(os);
byte[] in = new byte[1024];
int count= 0;
while ((count = bis.read(in)) != -1) {
bos.write(in, 0, count);
}
bis.close();
bos.close();

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https://yzsam.com/2022/04/202204220842001974.html

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