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This article mainly introduces "the introduction of control inversion in Spring framework and the way to create objects". In daily operation, I believe that many people have doubts about the introduction of control inversion in Spring framework and the way of creating objects. Xiaobian consulted all kinds of materials and sorted out simple and easy-to-use operation methods. I hope it will be helpful to answer the doubts about "introduction of control inversion in Spring framework and the way to create objects". Next, please follow the editor to study!

Spring framework

Inversion of control (Inversion on Control) in the spring framework is usually handed over to the Spring container. This is called inversion of control.

What is a reversal of control?

First of all, let's talk about the positive control.

Class Demo {Student student = new Student ();}

To put it simply, it is to create your own objects and create whatever objects you need, which are actually created in the current file and new by yourself. This is called "control forward".

So what is the inversion of control:

It is the opposite of control, which is the object I need. I don't need to create it on my own new, I just need to go to one place to get it and use it, which is equivalent to letting others create the object we need. In addition, there are two ways for someone else to create an object: the first is to call the parameterized constructor directly, and the other is to call the constructor and then implement it using the set method.

The first way is to write in the configuration file (applicationContext.xml) of spring

ApplicationContext.xml

Demo.class

Public class Demo {public static void main (String [] args) {ApplicationContext context = new ClassPathXmlApplicationCOntext ("applicationContext.xml"); Student student = (Student) context.getBean ("student"); / / find the name you want to create}} based on your name in applicationContext.xml

The second way is to call the no-parameter constructor in the configuration file of spring, and then put the element in by using the set method

ApplicationContext.xml

This method is to build a no-parameter construction method, then take out the corresponding elements and use the set method to put them in. As for the corresponding class file, it is also used for the Demo.class above.

For optimization of the second method:

It is embodied in the three-tier structure.

StudentController.class

/ / the previous comment is equivalent to @ Controller At other levels, the corresponding @ service @ Repository annotation is / / equivalent to / / @ Controller (name= "studentController") public class StudentController {/ / @ Resource (name= "studnetService") in the ApplicationContext.xml file, which is equivalent to calling the setStudentService () method to put the following corresponding elements into the Controller object / / / then ref calls / / @ Resource (name= "studentService") private StudentService studentService Public void selectAll () {studentService.selectAll ();} public void setStudnetService (StudentService studnetService) {this.studnetService = studentService;}}

After the sub-optimization becomes

StudentController.class

@ Controllerpublic class StudnetController {@ Autowired / / this will automatically perform dependency injection, and it is convenient without writing a set method, but pay attention to the configuration file, configure it, scan the comment private StudentService studentService; public void selectAll () {studentService.selectAll ();}}

ApplicationContext.xml

The problem is that Autowried is injected based on type, but if there are multiple implementation subclasses of an interface, which one is injected by Autowried? Or will it make a mistake?

Answer: the reason for Error create bean with 'studnetController', is not because Autowired is used in StudentController, but because Autowired is used for injection in StudentController, and there are several expected single matching bean but found 2: banjiServiceImpl,banjiServiceImpl2 for multiple implementations, so the solution is:

@ Controllerpublic class StudnetController {@ Autowired / / add the following note to make it clear that the injection @ Qualifier (value= "studentServiceImpl2") private StudentService studentService; public void selectAll () {studentService.selectAll ();}} ends the study of "introduction to inversion of control in the Spring framework and how to create objects", hoping to solve everyone's doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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