The most powerful Introduction to Java NIO ever: Worried about getting started and giving up, please read this article!

The original title of this article is “Introduction to NIO” by Gregory M. Travis, author of JDK 1.4 Tutorial and other books.

1, the introduction

2. About the author

Travis: Gregory m.













JDK 1.4 Tutoria

3. Before you start

3.1 About this tutorial

NIO


















java.io.*

3.2 How do I run the Code

4. Input/Output: Conceptual description

4.1 I/O profile

4.2 Why use NIO?

4.3 Comparison of streams and blocks

java.io.*

4.4 Integrated I/O

java.io.*
java.io.*

5. Channels and buffers

5.1 an overview of the

5.2 What is a buffer?

Buffer

5.3 Buffer Types

ByteBuffer












In fact, there is a buffer type for every basic Java type:

• ByteBuffer
• CharBuffer
• ShortBuffer
• IntBuffer
• LongBuffer
• FloatBuffer
• DoubleBuffer
  
  

5.4 What is a Channel?

5.5 Channel Types

InputStream
OutputStream

6. From Theory to Practice: Reading and writing in NIO

6.1 an overview of the

6.2 Reading Data from a File

FileInputStream
Channel












So reading a file involves three steps:

6.3 Three easy steps

FileInputStream fin = new FileInputStream( "readandshow.txt" );
FileChannel fc = fin.getChannel();Copy the code

ByteBuffer buffer = ByteBuffer.allocate( 1024 );Copy the code

fc.read( buffer );Copy the code

6.4 Writing a File

FileOutputStream fout = new FileOutputStream( "writesomebytes.txt" );
FileChannel fc = fout.getChannel();Copy the code

ByteBuffer buffer = ByteBuffer.allocate( 1024 );
 
for (int ii=0; ii<message.length; ++ii) {
     buffer.put( message[ii] );
}
buffer.flip();Copy the code

fc.write( buffer );Copy the code

6.5 Combining Read and Write

6.6 Example of Running CopyFile

fcin.read( buffer );
fcout.write( buffer );Copy the code

6.7 Checking The Status

int r = fcin.read( buffer );
 
if (r==-1) {
     break;
}Copy the code

6.8 Resetting the Buffer

buffer.clear();
int r = fcin.read( buffer );
 
if (r==-1) {
     break;
}
 
buffer.flip();
fcout.write( buffer );Copy the code

7. Details inside the buffer zone

7.1 an overview of the

7.2 Status Variables

Three values can be used to specify the state of the buffer at any time:

• position
• limit
• capacity
  
  

7.3 the Position

7.4 Limit

7.5 Capacity

7.6 Observed Variables

The state of the Buffer looks like this:





























The position Settings are as follows:

7.7 First Read

After reading this, position increases to 3, as shown below:

7.8 Second Read

These two bytes are stored at the position specified by position, which increases position by 2:

7.9 the flip

This method does two very important things:

• 1) It sets limit to the current position;
• 2) It sets position to 0.

Here is the buffer after flip:

7.10 First Write

This increases position to 4 while limit remains the same, as shown below:

7.11 Write Second Time

This increases position to 5 and leaves limit unchanged, as shown below:

7.12 the clear

Clear does two very important things:

• 1) It sets limit to the same as capacity;
• 2) It sets position to 0.

The following figure shows the state of the buffer after clear() is called:

7.13 Access Methods

7.14 the get () method

The ByteBuffer class has four get() methods:

• 1) byte the get ();
• 2）ByteBuffer get( byte dst[] );
• 3）ByteBuffer get( byte dst[], int offset, int length );
• 4) byte get(int index);

7.15 the put () method

There are five put() methods in the ByteBuffer class:

• 1) ByteBuffer put(byte B);
• 2）ByteBuffer put( byte src[] );
• 3）ByteBuffer put( byte src[], int offset, int length );
• 4) ByteBuffer put(ByteBuffer SRC);
• 5) ByteBuffer put(int index, byte B);

7.16 Typed get() and PUT () methods

As follows:

• getByte()
• getChar()
• getShort()
• getInt()
• getLong()
• getFloat()
• getDouble()
• putByte()
• putChar()
• putShort()
• putInt()
• putLong()
• putFloat()
• putDouble()
  
  

7.17 Buffer usage: An internal loop

while (true) {
     buffer.clear();
     int r = fcin.read( buffer );
  
     if (r==-1) {
       break;
     }
  
     buffer.flip();
     fcout.write( buffer );
}Copy the code

More on buffers

8.1 an overview of the

8.2 Buffer allocation and packaging

ByteBuffer buffer = ByteBuffer.allocate( 1024 );Copy the code

byte array[] = new byte[1024];
ByteBuffer buffer = ByteBuffer.wrap( array );Copy the code

8.3 Buffer Fragments

ByteBuffer buffer = ByteBuffer.allocate( 10 );Copy the code

for (int i=0; i<buffer.capacity(); ++i) {
     buffer.put( (byte)i );
}Copy the code

buffer.position( 3 );
buffer.limit( 7 );
ByteBuffer slice = buffer.slice();Copy the code

8.4 Buffer slices and data sharing

for (int i=0; i<slice.capacity(); ++i) {
     byte b = slice.get( i );
     b *= 11;
     slice.put( i, b );
}Copy the code

buffer.position( 0 );
buffer.limit( buffer.capacity() );
  
while (buffer.remaining()>0) {
     System.out.println( buffer.get() );
}Copy the code

$ java SliceBuffer
0
1
2
33
44
55
66
7
8
9Copy the code

8.5 Read-only Buffer

8.6 Direct and indirect buffers

The Sun (and now Oracle) documentation describes direct buffers like this:

Given a direct byte buffer, the Java VIRTUAL machine will do its best to perform native I/O operations directly on it. That is, it tries to avoid copying the contents of the buffer into an intermediate buffer (or copying data from an intermediate buffer) before (or after) each call to the native I/O operation of the underlying operating system.

8.7 Memory-mapped File I/O

8.8 Mapping a File to memory

MappedByteBuffer mbb = fc.map( FileChannel.MapMode.READ_WRITE, 0, 1024 );Copy the code

MappedByteBuffer

Scatter and gather

9.1 an overview of the

9.2 Scattered or Aggregated I/ OS

ScatteringByteChannel
GatheringByteChannel

long read( ByteBuffer[] dsts );
long read( ByteBuffer[] dsts, int offset, int length );Copy the code

9.3 Application of dispersion/aggregation

9.4 Clustered Write

long write( ByteBuffer[] srcs );
long write( ByteBuffer[] srcs, int offset, int length );Copy the code

10. File locking

10.1 an overview of the

10.2 Locking a File

RandomAccessFile raf = new RandomAccessFile( "usefilelocks.txt", "rw" );
FileChannel fc = raf.getChannel();
FileLock lock = fc.lock( start, end, false );Copy the code

lock.release();Copy the code

10.3 File Locking and Portability

The following guidelines will help you keep your code as portable as possible:

• 1) Use exclusive locks only;
• 2) Consider all locks to be advisory.

Networking and asynchronous I/O

11.1 an overview of the

11.2 the asynchronous I/O

11.3 Selectors

Selector

Selector selector = Selector.open();Copy the code

11.4 Opening a ServerSocketChannel

ServerSocketChannel

ServerSocketChannel ssc = ServerSocketChannel.open();
ssc.configureBlocking( false );
  
ServerSocket ss = ssc.socket();
InetSocketAddress address = new InetSocketAddress( ports[ii] );
ss.bind( address );Copy the code

11.5 select key

SelectionKey key = ssc.register( selector, SelectionKey.OP_ACCEPT );Copy the code

11.6 Internal Loop

int num = selector.select();
  
Set selectedKeys = selector.selectedKeys();
Iterator it = selectedKeys.iterator();
  
while (it.hasNext()) {
     SelectionKey key = (SelectionKey)it.next();
     // ... deal with I/O event ...
}Copy the code

11.7 Listening for New Connections

if ((key.readyOps() & SelectionKey.OP_ACCEPT)
     == SelectionKey.OP_ACCEPT) {
  
     // Accept the new connection
     // ...
}Copy the code

11.8 Accepting New Connections

ServerSocketChannel ssc = (ServerSocketChannel)key.channel();
SocketChannel sc = ssc.accept();Copy the code

sc.configureBlocking( false );
SelectionKey newKey = sc.register( selector, SelectionKey.OP_READ );Copy the code

11.9 Deleting the SelectionKey

it.remove();Copy the code

11.10 Incoming I/ OS

} else if ((key.readyOps() & SelectionKey.OP_READ)
     == SelectionKey.OP_READ) {
     // Read the data
     SocketChannel sc = (SocketChannel)key.channel();
     // ...
}Copy the code

11.11 Back to main Loop

Character set

12.1 an overview of the

12.2 Encoding/Decoding

CharsetDecoder
CharsetEncoder

12.3 The correct way to process text

In fact, every Java implementation requires full support for the following character encodings:

• US-ASCII
• ISO-8859-1
• UTF-8
• UTF-16BE
• UTF-16LE
• UTF-16
  
  

12.4 Sample program

Charset latin1 = Charset.forName( "ISO-8859-1" );Copy the code

CharsetDecoder decoder = latin1.newDecoder();
CharsetEncoder encoder = latin1.newEncoder();Copy the code

CharBuffer cb = decoder.decode( inputData );Copy the code

ByteBuffer outputData = encoder.encode( cb );Copy the code

13. Conclusion

14. Sample source code attachment download

nio-src(52im.net).zip
(7.96KB, download times: 0, price: 1 gold)

Appendix: More NIO related articles

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