Pooling idea: string constant pool, thread pool, database connection pool

Pool thought

Resources are reused , Return after use , Save a lot of time and resources wasted in building and destroying , There are still a lot of resources for establishment and destruction

String constant pool

Constant pools are independent of stacks and heaps , The following two creation methods are different

1, Save the contents of constant pool directly
String s1 = “ Save directly ”

2,new String Save indirectly
String s2 = new String(“ Save indirectly ”)

difference ：

• Save directly , No matter how many are created, they are the same
• Indirect saving actually saves the address value , Point to thread pool , This method produces two objects ; If you save indirectly for many times , for example ：
  String s3 = new String(“ Save indirectly ”)
  String s4 = new String(“ Save indirectly ”)
  String s5 = new String(“ Save indirectly ”)

In fact, only one is created in the constant pool " Save indirectly " The object of , The reference object creates 3 Time

Thread pool

Advantages compared with tradition

• Traditional thread implementation methods include thread creation Thread to destroy Time for , Threads can be reused , So the thread pool is introduced , Create and destroy threads Change it to Return after use , Not destroyed , Reuse resources , Improve thread utilization , Improve the response speed of the program
• Easy to manage Thread objects in a unified way
• You can control the maximum concurrency

Thread pool model —— Bank

Counter window ： Threads , Without destroying
Waiting area ： Waiting in line
When the window is not enough ： Add threads
When there are no seats in the waiting area ： Refusal strategy —— Report an exception or give it to a thread to go left
There are too many free windows ： Reduce threads

Thread pool creation

JUC The concurrency toolkit provides ThreadPoolExecutor Creating a thread pool ,ThreadPoolExecutor Yes 8 Parameters , Respectively ：

• corePoolSize： Number of core threads —— The number of counter windows that never close
• maximumPoolSize： Maximum number of threads —— The maximum number of windows
• keepAliveTime： Thread lifetime —— How long does it take for a non core thread to be destroyed without receiving a task —— You need to set the unit unit
• unit：TimeUnit.SECONDS or TimeUnit.MICROSECONDS You can wait
• BlockingQueue ： Waiting in line ,new ArrayBlockingQueue<>(capacity:10) here capacity The value of the set 10
• ThreadFactory： Thread factory —— No need to create , Call directly Executors.defaultThreadFactory()
• RejectedExecutionHandler： Refusal strategy ——new ThreadPoolExecutor.AbortPolicy() The handler of the rejected task , Throw a RejectedExecutionException

After creating it, use ExecutorService Class object to receive , Then you can directly call
for example ： utilize lambda expression

for(){
executorService.execute( ()->{  Thread business logic  } );
}// The thread pool will automatically adjust the current number of threads 
executorService.shutdown();// Close thread pool 

Reference resources ：

Thread pool details

Database connection pool

advantage

• Resource reuse
• Faster system response
• New means of resource allocation
• Unified connection management , Avoid database connection leaks

Reference resources 1

Reference resources 2

Excellent open source database connection pool agent

（1）DBCP yes Apache Database connection pool provided .tomcat The server comes with dbcp Database connection pool . Speed is relative to c3p0 Faster , But because of its own existence BUG,Hibernate3 Support is no longer available .

（2）C3P0 It is a database connection pool provided by an open source organization , Relatively slow , Stability is OK ,hibernate Official recommendation .

（3）Proxool yes sourceforge The next open source project database connection pool , It has the function of monitoring connection pool status , More stable c3p0 almost .

（4）BoneCP Is a database connection pool provided by an open source organization , Fast .

（5）Druid It is the database connection pool provided by Ali , It's said to be a collection DBCP 、C3P0 、Proxool All in one database connection pool , But the speed is not sure if there is BoneCP fast .