<> Singleton mode

Characteristics of singleton model :

A singleton class can only have one instance
Singleton classes must create their own unique instances
Singleton classes must provide this object instance to all other objects

<> Slouch style

characteristic :

Lazy singletons are initialized on the first call
Lazy singletons are thread unsafe , In the case of concurrency , There may be more than one Singleton example
To achieve thread safety, you need to getInstance() Carry out transformation , To ensure thread safety .

<> A single example of starving Han style

characteristic :

A single example of starving Han style :
The starving singleton is instantiated at the beginning of the class
Thread safety

The difference between the hungry and the lazy
By name , The hungry and the lazy ,

A hungry man is a class once loaded , Just initialize the singleton , ensure getInstance When I was young , The singleton already exists ,

Lazy people are lazy , Only when called getInstance When I was young , Just go back to initialize this singleton .

In addition, the following two ways can be distinguished from each other :

1, Thread safety :

Starvation is inherently thread safe , Can be directly used for multithreading without problems ,

Laziness itself is not thread safe , There are several ways to write for thread safety , They are above 1,2,3, These three implementations differ in resource loading and performance .

2, Resource loading and performance :

When creating a class, we instantiate a static object , Whether or not this singleton will be used later , Will occupy a certain amount of memory , But correspondingly , It's also faster on the first call , Because its resource has been initialized ,

And the sluggard style, as the name suggests , Load will be delayed , The object is instantiated only when the singleton is used for the first time , Initialization should be done on the first call , If there is more work to be done , There will be some delay in performance , After that, it's the same as the hungry man style .

as for 1,2,3 There are some differences among the three implementations ,

The third 1 species , Method calls are synchronized , Although the thread is safe , But synchronize every time , Can affect performance , after all 99% In this case, synchronization is not required ,

The third 2 species , stay getInstance I did it twice null inspect , It ensures that synchronization is only done when the singleton is called for the first time , This is also thread safe , At the same time, the performance loss of every synchronization is avoided

The third 3 species , Took advantage of classloader To ensure initialization instance There is only one thread when running , So it's also thread safe , At the same time, there is no performance loss .

<> build Spring MVC+Spring+JDBC frame

The previous chapters have been mastered Spigvc Start with this section ,
Let's transform the control layer of supermarket order management system (orolel Part of the code implementation , Combined with the source code of the materials provided and the software we have built SinovCc frame , Complete the transformation of the project framework , Finally, it was transformed into JSP+Spring
Performance based Considerations in the future ,Spring MVC+Spring+JDBC The framework is also used more frequently in some Internet projects
high , Therefore, this chapter will be in the original material of this book (SMBMS) On the basis of , use Spring
MVC Research on the framework transformation of supermarket order management system Contoller layer ,DAO Layer temporarily used JDBC realization . On page 12 chapter SSM Framework integration , Let's reinvent it DAO Layer is MyBatis The realization of , Complete the three frameworks (Spring
MWtSpingnMyBai) The integration of .

1. join Spring. Soring MNC. Database driver, etc jar file .

2.Spring configuration file

3. to configure web.xml file

©2019-2020 Toolsou All rights reserved,
Huawei 2021 session Hardware Engineer Logical post (FPGA) Super detailed surface !!!Vue-element-admin upgrade ui edition virtual machine VMware Download and install the most detailed tutorial !C++ Move constructor and copy constructor sound of dripping water java Backstage interview pygame Realize full screen mode and adjustable window size mysql Database setting character set configuration modification my.ini file (windows)30 What's the experience of being a junior programmer at the age of 20 C++ Multithreading programming ( Summary of common functions and parameters )python_ cherry tree