Inputstream/outputstream (input and output of file)

We have already talked about File Some common methods of class , For file systems , There must be input and output of file content

One 、InputStream

1. About file reading

There are two ways ： Direct reading and text reading
No matter what kind of reading , All need to use java.io.InputStream
Indicates the input stream
InputStream Itself is an abstract class , What we use in real use is its implementation class FileInputStream
For the degree of the file , We can abstract it into getting water from the tap , We need to prepare a container , Go and get the water from the tap

Be careful ： There are two situations in water connection ：1. There is water at present 2. There is no water at present , But there will be water behind 3. There is currently no water , There will be no water behind .
In the code , about 1. This situation , Directly return a number greater than zero , Indicates the current amount of water flowing about 2 Returns the 0, It means there is no water at present , But there will be about
3 Return to one -1, It means there is no water at present , There will be no more water after full .

Use InputStream when , We need to prepare a container in advance ( Usually a byte[])

1. Direct reading

Read as binary data , That's in the code byte In units of
When using read , We use InputStream Implementation class read（） Method
such as ： stay D：/IO There is a world.txt file ,

We need to read his content
a. Read one at a time

b. Read more than one at a time

Such a result is meaningless to us , So what we need is to read the text directly

2、 Text reading

The so-called text reading , The content we get is the original content of the document .
When reading, we should pay attention to the original encoding format of the file , And whether the codes when we escape are consistent , If it's not consistent , There may be garbled code , Problems such as unrecognized file content .
Common coding rules are

On the basis of obtaining file data , We can use Scanner Class, the data we get , Escape according to the coding rules , Finally get the content of the source text , But the premise is that the coding rules we give should be consistent with the coding rules of the source text
For example, we need to read D:/IO In the catalog world.txt file

We can see that his coding rule is ：UTF-8
Next, write code to read the contents of this file
Use Scanner Construction method of class

We can see , In this way, the content of the source text is read

Two 、OutputStream

There are also two cases for writing documents , Direct write , Write as original
When we write , Need to pass in the file path written , The file itself may not exist （ If it doesn't exist, it will be created automatically ）, But his ancestral path must exist , when written , The original data in the file will be cleared

1、 Direct write

Direct write call write（） When the method is used , You can only import byte perhaps byte[]
We're going straight to D:/IO/world.txt Write in file “a”
here world.txt Already exist

Now let's write the code directly

Such input must be very inconvenient

2、 Text writing

There are two common writing methods
All the way to world.txt write in “ Hello China ”

3、 buffer

Be careful ： When the file is written , The reading and writing speed of memory is much higher than that of hard disk , therefore , There's a buffer , Data is written to the buffer first , When （1、 The buffer is full or reaches a certain threshold 2、 After a while 3、 The process takes the initiative to brush the disk ）, The data in the buffer is written to the hard disk , To prevent the remaining data in the buffer from being brushed into the hard disk , Write the data at the end , We should call flush() Methods manually brush the disc