The practical application of Java-based

I 流

java operations on the data stream by way of, for processing the data stream IO transfer between devices, file uploading and downloading files, Java objects for the operation of the flow in the IO package.

Base class byte stream	Inputstream	OutputStream
Byte stream file operation	FileInputStream	FileOutputStream
Byte buffer flow (high flow)	BufferedInputStream	BufferedOutputStream

NIO

Three major components: chanel, buffer, selector

 ###FileChannel和buffer的简单使用
 ​
 RandomAccessFile accessFile = null;
 try {
     accessFile = new RandomAccessFile("test.txt", "rw");
     FileChannel channel = accessFile.getChannel();
     ByteBuffer buffer = ByteBuffer.allocate(1024);
     int bytesRead;
     while ((bytesRead = channel.read(buffer)) != -1) {
         buffer.flip();
         while (buffer.hasRemaining()) {
             System.out.print((char) buffer.get());
         }
         buffer.compact();
     }
 } finally {
     accessFile.close();
 }

Use Buffer (buffer) of

buffer: Buffer, actually a container, continuous array. Channel provides read data from files, network channels, but reading and writing of data must pass through buffer.

The buffer can be simply understood as a set of elements of the list of basic data types, it is to save the state of the current position data by several variables: capacity, position, limit, mark.

index	Explanation
capacity	The total length of the array of buffers
position	The position of the next data element to be operated
limit	Position of the next element in the buffer array inoperable: limit <= capacity
mark	For recording the position of the current position of a front or a default -1

effect	Related Methods
Allocated space	ByteBuffer buffer = ByteBuffer.allocate(1024);
Data is written into buffer	int bytesRead = channel.read(buffer)
Analyzing the data in buffer	boolean b=buffer.hasRemaining()
Reading data from the Buffer	buffer.get()
starting time	buffer.flip()
When it ends	buffer.compact()

Methods of Using Arrays

1. The array into List:List<String> list = Arrays.asList(arr.split(","));

2. According to sort an array of ASCII code:Arrays.sort(arrayToSort, String.CASE_INSENSITIVE_ORDER);

Iterator of use

 【---list---】
 List<Integer> list = new ArrayList<>();
 //遍历
 while (iterator.hasNext()) {
     System.out.print(iterator.next() + " ");
 }
 //删除
 while (iterator.hasNext()) {
     iterator.remove();
 }
 ​
 【---map---】
 Map<Integer, String> map = new HashMap<>();
 Iterator<Integer> it = map.keySet().iterator();
 while(it.hasNext()) {
     Integer key = it.next();
     System.out.println(key+"->"+map.get(key));
 }

JVM-related

Memory Allocation

java -jar -Xms128m -Xmx256m xx.war

command	Explanation
Xms	When referring to the size of memory for the program set to start
Xmx	Is the maximum that can be consumed during the setup process is running on memory size
Xss	It refers to the set of each thread stack size

These three parameters are set to default Byte units may be added to [k / K] or [m / M] in the later figures to KB or MB.