1.IO and NIO The difference between

NIO Namely New IO stay JDK1.4 Introduction in .

IO and NIO Have the same function and purpose , But the implementation is different ,NIO The main use is block , therefore NIO Is more efficient than IO Much faster .

stay Java API Two sets of NIO, A set for standard input and output NIO, The other is network programming IO.

① Stream oriented and buffer oriented

1. Java IO It's flow oriented and Java NIO It's buffer oriented , Just as the focus of one is on the process , Another key point is that there is a stage .

   stay Java IO Reading and writing data in is stream oriented （Stream） Of , Like a river . All the data keeps flowing forward , We can only touch the current water .

   If you need to get the data before or after a data, you must cache the data yourself （ Pump water out of the river ）, Not directly from the stream （ Because flow orientation means that we only have one aspect of data flow ）

2. Java NIO The reading and writing of data in is buffer oriented （Buffer） Of , When reading, the whole block of data can be read into the buffer , When writing, the data in the whole buffer can be written together .

   It's like building a dam on a river , Stream oriented data reading and writing only provides a data stream aspect , Buffer oriented IO Then we can see all the water （ Context of data ）, In other words, it is very convenient to get the previous data or the latter data of a certain data in the buffer . This convenience comes at a price , Because we Buffers must be managed , This includes not allowing new data to overwrite useful data in the buffer that has not yet been processed ; Block the data in the buffer correctly , Distinguish what has been handled and what hasn't, etc .

② Blocking and non-blocking

1. Java IO It's blocked , If the data is not ready for a read-write data call , Or it can't be written at present , that Read and write operations will be blocked until the data is ready or the target is writable .

2. Java NIO It's non blocking , Every time the data Read and write calls will return immediately , And will now be readable （ Or writable ） The contents of are written to or output from the buffer , Even if no data is currently available , The call still returns immediately and does nothing to the buffer .

   for instance ：

   IO and NIO Go shopping in the supermarket , If the supermarket does not have the required goods or the quantity is not enough , IO We will wait until the quantity of goods needed in the supermarket is enough, and then bring back all the goods we need .Java NIO Is different , No matter how many goods are needed in the supermarket , It will have the goods it needs , Buy it all immediately and return , Even goods that are not needed will be returned immediately .

   IO Ask to complete the task at one time ,NIO Allow multiple tasks

2.IO and NIO The applicable scenarios of

NIO To make up for tradition IO Born of a lack of , however NIO It's also flawed , Should be NIO It's a buffer oriented operation , Every time data processing is done on the buffer , Then we must pay attention to ： Before data processing, it is necessary to determine whether the data in the buffer is complete or has been read . without , Suppose the data only reads a part of it , So there's no point in incomplete data processing . Therefore, the buffer should be detected before each data processing .

Be careful ： Every time you want to process data, you must ensure that the data has been prepared , But data processing can be done many times .

IO and NIO Each use scenario ：

IO： A small amount of connection , These connections send a lot of data every time .

NIO： You need to manage thousands of connections that are open at the same time , These links only send a small amount of data at a time , For example, chat server

IO and NIO workflow

Java IO Workflow

because Java IO It's blocked , Therefore, when reading and writing to multiple streams, multiple threads are required . For example, on the Internet IO in ,Server The end uses a thread to listen on a port , Once a connection is accept, Create a new thread to handle the newly established connection .

among read/write It's blocked .

Java NIO Workflow

Java NIO Provide Selector Realize a single thread to manage multiple channel The function of .

among select The call may be blocked , It can also be non blocking . however read/write It's non blocking ！

Learn from the article - Knowing and doing wandering

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author ： Xiaofeifei
source ：CSDN
original text ：https://blog.csdn.net/weixin_42988712/article/details/109036394
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