Java I/O flow

1, Classification of flow

• According to different operation data units, it is divided into byte stream (8 bit) and character stream (16 bit)
• According to the flow direction of data, it can be divided into input flow and output flow

Abstract base class	Byte stream	Character stream
Input stream	InputStream	Reader
Output stream	OutputStream	Writer

The names of subclasses derived from these four classes (abstract classes) are suffixed by their parent class names

IO stream system

classification	Byte input stream	Byte output stream	Character input stream	Character output stream
Abstract base class	InputStream	OutputStream	Reader	Writer
access files	FileInputStream	FileOutputStream	FileReader	FileWriter
Access array	ByteArrayInputStream	ByteArrayOutputStream	CharArrayReader	CharArrayWriter
Access pipeline	PipedInputStream	PipedOutStream	PipedReader	PipedWriter
Access string			StringReader	StringWriter
Buffer stream	BufferedInputStream	BufferedOutputStream	BufferdReadier	BufferWriter
Conversion flow			InputStreamReader	OutputStreamWriter
Object flow	ObjectInputStream	ObjectOutput Stream
	FilterInputStream	FilterOutputStream	FilterReader	FilterWriter
Print stream		PrintStream		PrintWriter
Push back input stream	PushbackInputStream		PushbackReader
Special flow	DataInputStream	DataOutputStream

The difference between character stream and byte stream

• The basic unit of byte stream operation is byte; The basic unit of character stream operation is Unicode symbol.
• The byte stream will not use the buffer during operation, while the character stream will use the buffer during operation
• Byte stream can be used for any type of object, including binary objects, while character stream can only process characters or strings

2, File operation

2.1 FileReader

Construction method

FileReader(File file)				//Construct a FileReader object according to the given File object.
FileReader(FileDescriptor fd) 		//Construct a FileReader object according to the given file name.
FileReader(String fileName)			//Construct a FileReader object according to the given FileDescriptor

use

int read() throws IOException	//Read a single character and return an int variable to represent the read character. The return value of - 1 is equivalent to reading it
int read(char [] c, int offset, int len)//Read characters to c array and return the number of characters read    
void close() throw IOException	//Close flow

2.2 FileWriter

Construction method

FileWriter(String fileName) throws IOException	//Construct a FileWriter object according to the given file name.
FileWriter(String fileName,boolean append) throws IOException//The FileWriter object is constructed based on the given file name and a boolean value indicating whether to attach write data. append: a boolean value. If true, the data will be written to the end of the file instead of the beginning of the file.
FileWriter(File file) throws IOException	//Construct a FileWriter object according to the given File object.

common method

void write(int c) 		//Write a character 
void write(String str)//Write string
void write(String str, int off, int len) 	//Write part of a string. 
void write(char[] cbuf, int off, int len) 	//Writes part of a character array. 
void flush() throws IOException //Refresh the stream. 
void close() throws IOException		//Refresh before closing the stream

2.3 FileInputStream

Construction method

FileInputStream(File file) throws FileNotFoundException //Construct a FileInputStream object according to the given File object.
FileInputStream(String name) throws FileNotFoundException //Construct a FileInputStream object according to the given file name.
FileInputStream(FileDescriptor fd)	//Construct a FileInputStream object according to the given FileDescriptor

common method

int read() throws IOException	//Convert the read byte type 8-bit binary into hexadecimal int type and return, - 1 indicates that the reading is completed
int read(byte[] b) throws IOException//Read b.length bytes from the input stream into the byte array, and return the total number of bytes read into the buffer - 1 indicates that the reading is complete
int read(byte[] b,int off,int len) throws IOException  //Read up to len bytes from the input stream into the byte array, and store bytes from the off position of the array  
void close() throws IOException	//Close flow

2.4 FileOutputStream

Construction method

FileOutputStream(File file) throws FileNotFoundException	//Construct a FileOutputStream object according to the given File object.
FileOutputStream(File file,boolean append) throws FileNotFoundException{}	//If the second parameter is true, the byte will be written to the end of the file instead of the beginning. When the second parameter is false, the original content will be overwritten
FileOutputStream(String name) throws FileNotFoundException{}//Construct a FileOutputStream object according to the given file name object.
FileOutputStream(String name,boolean append) throws FileNotFoundException   

common method

void write(int b) throws IOException	//Writes a specified byte to the output stream of the file
void write(byte[] b) throws IOException	//Writes the b.length bytes in the specified byte array to the output stream
void write(byte[] b,int off,int len) throws IOException	//Writes len bytes in the specified byte array starting from offset off to the output stream
void close() throws IOException			//Close flow

The getBytes method under the common String class converts the String into a byte array

3, Buffer stream

The difference between Buffered and FIle in FIle operation

• BufferedReader and BufferedWriter will carry an 8kb byte buffer in memory
• BufferedReader provides the readLine() method
• The BufferedReader class will try to extract more bytes than the current operation needs, so as to improve the efficiency in more cases

3.1 BufferedReader

Construction method

BufferedReader br = new BufferedReader(new FileReader("FileName"));//First, create a FileReader object and pass the FileReader to BufferedReader
BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream("FileName"), "utf-8"));//Create a BufferedReader object using the wrapped InputStream class

common method

int read() throws IOException;	//Read one or more bytes and return a character. When reading to the end of the file, return - 1
int read(byte[] b,int off,int len) throws IOException  //Read up to len bytes from the input stream into the byte array, and store bytes from the off position of the array  
String readline()		//Read a line of data, store it in the string and return it, excluding line breaks
void close()			//Close flow

Garbled code problem

When the BufferedReader packaging FileReader reads a file, if the file code is different from the project code, there will be garbled code

resolvent:

Use the BufferedReader that wraps the InputStreamReader to read the file

BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream("FileName"), "utf-8"));
//BufferedReader is only responsible for reading into its internal buffer, and the decoding is completed by InputStreamReader.

3.2 BufferedWriter

Construction method

BufferedWriter bw = new BufferedWriter(new FileWriter("FileName"));//First, create a FileWriter object and pass the FileWriter to BufferedWriter

common method

void write(int c) 		//Write a single character.
void write(char[] c, int off, int len) //Write a part of the character array with the length of len from off
void write(String s, int off, int len) //Write a part of the string with length len from off.
void newLine() 			//Write a line separator.
void flush() throws IOException			//Flush the buffer of the stream.
void close() throws IOException			//Refresh before closing the stream

3.3 BufferedInputStream

Construction method

 BufferedInputStream input = new BufferedInputStream(new FileInputStream("FileName"));//Create a bufferedinputstream object using the wrapped InputStream class

common method

 int read() throws IOException 			 // Read next byte
 int read( byte [] b, int off, int len) throws IOException   // Writes the data in the buffer to the byte array b. off is the starting position of byte array b, and len is the write length
 void mark(int readlimit)				//Mark the current position in the buffer. readlimit is the maximum number of bytes that can be read after mark
 void reset() throws IOException 		// Resets the current position in the buffer to the position marked by mark()
 void close() throws IOException		//Close flow

3.4 BufferedOutputStream

Construction method

BufferedOutputStream output = new BufferedOutputStream(new FileOutputStream("FileName"));//Create a bufferedoutputstream object using the wrapped OutputStream class

common method

void write(int b)throws IOException		//Write one byte at a time
void write(byte[] b,int off,int len) throws IOException    //Write a byte string with length len from byte array off
void flush() throws IOException			//Refresh buffer
void close() throws IOException			//Refresh before closing the stream