Simple IO flow

2019-01-10 • Java

This is the back-end small class of the monastery. Each article is shared from

[background introduction] [knowledge analysis] [common problems] [solutions] [coding practice] [extended thinking] [more discussion] [References]

Eight aspects of in-depth analysis of back-end knowledge / skills. This article shares:

[simple IO stream]

Hello, I'm the 9th java student of Shenzhen Branch of it Academy. I'm an honest and kind java programmer. Today, I'd like to share with you the simple IO stream of Java.

1. Background introduction

Stream is a set of sequential bytes with starting point and ending point. It is the general name or abstraction of data transmission.

The transmission of data between two devices is called stream. The essence of stream is data transmission. According to the characteristics of data transmission, the stream is abstracted into various types to facilitate more intuitive data operation.

2. Knowledge analysis

IO overview:

File class

IO stream classification

InputStream&Reader

OutPutStream&Writer

RandomAccessFile class: random reading;

Byte stream input and output

Byte stream

Learn the main classes and methods.

Q: Accept command line input:

Q: Accept keyboard input

Q: How do I know which directories and subdirectories are in the file system

How to know the attributes of the file, readable | writable;

Q: How to read and write files? (byte file, character file, sequential read, random read, object serialization and reconstruction, etc.)

summary:

Input: read

Output: disk, CD, database, node, etc. (very wide)

IO stream: input, output stream.

Byte stream: processes input and output operations in bytes

Character stream: processes input and output operations in character units

File class

The file class represents platform independent files and directories (it shields the difference of the underlying file system and is a platform independent file class)

Generalized classes, including methods, and files, folders, and platform independent.

Functions: create, delete and rename files and directories* You cannot read yourself through a file class. Need IO stream access.

Common methods:

Access file name: file detection directory operation related file operation related obtain general file information

getName() -exists() -mkDir() -createNewFile() -lastModify()

create folder

- getPath() -canWrite -list( ) -delete( ) -Length( )

Get the path of the construction parameter () and list all subdirectories

(return whatever the construction parameter is written)

- getAbsoluteFile -canRead -ListFile( )

() list all documents

Returns the absolute pathname form of the file object

- getAbsolutePath -isFile

( ) ( )

Get absolute path

(full path)

- getParent( ) -isDirectory

( )

- renameTo

(File newName)

According to different construction methods, files with different paths and files can be created.

eg：1:

File myfile = new file("xx","xxx.test)

File myfile = new file("xxx.test")

Eg: 2:

File mydic = new = new file ("XXX") / / create a folder in the current path

Mydic = new file (mydic, "XXX. Test") / / call this folder directly and let XXX Test is placed under XXX folder;

————————————

Console I/O

System. Out standard output is a printstream. There are many overloaded methods in it

system. In standard input is an InputStream~

System. Err standard error is a printstream~

In Java util

Scanner provides a standard (formatted) input function.

------------------------------------

Advanced I/O Streams

Def: input / output stream:

Input / output stream: it refers to data stream, and data stream is a set of bytes with sequence, starting point and ending point.

Java IO through Java A series of classes and interfaces of IO package;

Java developers provide standard input and output stream classes to shield the differences between underlying hardware or programs;

- Java cannot directly operate I / O devices, but establishes channels between programs and devices through streams as intermediate media;

The flow closes the differences between the underlying I / O devices.

- To establish a stream is actually to establish a data transmission channel to link the starting point and the ending point.

- Stream is an abstract expression of output transmission, which is independent of specific devices. Once the program has established the flow, it can ignore the device at the beginning or end.

- Input stream: load from file, standard input, input of other peripherals into memory;

- Output stream: save the data in memory to a file or transfer it to the output device;

File learning:

File: I:

1: Before I / O operator needs to get this file to basic information

Path File name read or write permission (Create time) (file size)

2: The file itself does not involve the specific contents inside the file, but processes the file as a whole, such as

Operations provided by the above common methods;

Pass: can operate on file name and path (is a generalized class)

3: Files and directories are abstracted into files;

If "file" is a directory, it has a list method.

If "file" is a file, there is no list method;

File: II:

The file class has four constructors:

The object of file can be: directory, file, existing specific file, and file that does not exist (it will be created automatically after the construction is completed)

——————————————————————————————————————————

I / O Basics

Byte : in. out

Character : Reader writer

InputStream:

Except for filterinputstream, all the others are read according to bytes (function stream), which is very inefficient and can only read one byte at a time

FileInputStream read file - the starting point is the file; Read local file

Objectinputstream distributed programming transfers objects (between nodes) on two virtual machines

Pipeinputstream transmits data between multiple threads;

It is used to read data from the pipeline during pipeline input / output

The sequenceinputsteam stream is from multiple nodes, and the nodes are read in turn

(used by converting to a single InputStream input stream object)

FileterInputStream DataInputStream

Format the data, which can be used to read the basic data types in Java

Pushbackinputstream for reading data from local files

(first read a part to determine the attribute, and then press the data back,

Pushback ~ ~ then read the entire file)

Buffered~~ BufferedInputStream

Multiple data can be buffered during reading (cached streams are added)

LineNumberInputStream

(read line by line)

Stringbufferinputstream reads from memory and starts from memory

Bytearrayinputstream is a stream of byte arrays in memory

Audioinputstream audio input / output

OutputStream

fileOutputStream DataOutPutStream

Write data to local file bufferdoutputstream

PrintStream

Provides many ways to output formatted data to the screen

ObjectOutPutStream

PipedOutPutStream

Output data to a pipeline (in pairs)

ByteArrayOutPutStream

Dataoutputstream provides support for basic data types of Java

Reader

BufferdReader LineNumberReader

CharArrayReader

StringReader

InputStreamReader FilerReader

Byte to character conversion Bridge

PipedReader

FilterReader pushbackReader

Writer:

BufferedWriter

CharArrayWriter

StringWriter

OutputStreamWriter fileWriter

PrintWriter

PipeWriter

FilterWriter

Judge the end point of reading and writing; Judge the reading mode. You can select the corresponding function implementation; file. jia buff

____

InputStream methods -- abstract methods

Int read(). Abstract methods; Read one at a time

Int read (byte buffer) -- specific method; Read several at a time, in the method byte []

Int read (byte buffer, int offset, int length) the specific method reads several times at a time, where to start reading and how long to read

Other methods include:

Void close( )

How many bytes does int avaliable() have, and then facilitate subsequent memory development

Long skip (long n) how many byte reads are skipped

Boolean makSupported ( )

Void mark (int readlimit)

Void reset() returns to the last tag and reads it repeatedly

OutputStream Methods __ Abstract method

Void write (int c) abstract method

Specific method of void write (byte buffer)

Specific method of void write (byte buffer, int length)

Void close() concrete method

The last stream of the void flush() method is pushed by itself;

The Reader Methods

Int read() Abstract

Int read (char cbuf)

Other data declared by InputStream is not byte, but char

The Writer Methods

Void write(int c)

Void write(char cbuf)

Void write(char cbuf,int length )

Void write(String string )

Void write(String string,int length)

Void close( )

Void flush( )

3. Frequently asked questions

Character stream and byte stream conversion characteristics, when to convert, specific embodiment?

4. Solutions

Characteristics of conversion flow:

It is a bridge between character stream and byte stream

The read byte data can be converted into characters through specified encoding

The read character data can be converted into bytes through specified encoding

When to use a transformation stream?

When there is conversion between bytes and characters;

When the data of stream operation needs to be encoded or decoded.

Specific objects:

Inputstreamreader: byte to character Bridge

Outputstreamwriter: character to byte Bridge

These two stream objects are members of the character system. They have the function of conversion. They are also character streams, so they need to pass in byte stream objects during construction.

5. Coding practice

。。。

6. Expand thinking

When to use byte stream and character stream?

Whenever dealing with plain text data, character streams are preferred. In addition, byte streams are used.

7. References

Baidu CSDN

8. More discussion

Q1:

of InputStream What is the basic media flow:

A1:

Bytearrayinputstream, stringbufferinputstream and FileInputStream are three basic media streams,

They read data from byte arrays, stringbuffers, and local files, respectively.

Pipedinputstream reads data from a pipe shared with other threads.

Objectinputstream and all subclasses of filterinputstream are decorating streams (the protagonist of decorator pattern).

Q2:

Basic of OutputStream What is a media stream:

A2:

Utputstream is the parent class of all output byte streams. It is an abstract class.

Bytearrayoutputstream and fileoutputstream are two basic media streams,

They write data to byte arrays, and local files, respectively. Pipedoutputstream writes data to a pipeline shared with other threads,

Objectoutputstream and all subclasses of filteroutputstream are decorative streams.

Q3:

What is serialization of objects?

A3:

Convert the object into a series of bytes and record the state of the bytes so that the object can be reconstructed on another machine.

Ppt link: stamp here

Tencent Video: poke here

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