Table of contents
Register the Bean object with Spring
3. Take out the bean object from Spring
4. Related interview questions
After the previous blog, we already know that Spring is an IoC container with many tools and methods, since it is a container. Then there are these two basic functions.
- store the object in the container
- remove the object from the container
In Spring, objects are also called Beans, so we will call them Beans when we encounter objects later.
Therefore, the creation and use of the entire project has the following three steps:
1. Create a Spring project
2. Store beans
3. Take Bean
1. Create a Spring project
1. Create a new normal Maven project
2. Add dependencies - Spring framework support (spring-context, spring-beans)
3. Add the startup class (because we are a Spring core project here, not a web project, we need to manually create the startup class by ourselves)
1. Create a Maven project
The essence of Spring is actually a Maven project. Creating a Maven project is somewhat similar to the creation of our previous servlet project.
2. Add Spring dependency
Add Spring dependency in pom.xml in the project (can be copied directly, dependency can be obtained from Maven central warehouse)
<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
<version>5.2.3.RELEASE</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-beans</artifactId>
<version>5.2.3.RELEASE</version>
</dependency>
</dependencies>
3. Add startup class
2. Store objects in Spring
Overview:
1. Create a Bean object
2. Register the Bean object with Spring (using the Spring configuration file for registration)
Create a Bean object
The so-called Bean is an ordinary object in the Java language
Register the Bean object with Spring
First of all, we register the configuration file to use Spring, and register in the configuration file.
spirng configuration file (can be copied directly)
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
</beans>But note that our configuration file here is not the final version - when we use annotations to access Bean objects more efficiently later, our configuration file will change.
As shown below
3. Take out the bean object from Spring
Case Analysis
getBean method analysis
It can be seen from the above figure that the getBean method can pass multiple parameter types.
So is there any difference between these different parameter types? Let's take a look together!
method one:
Sometimes there may be some problems due to the need for forced transfer
Method Two:
Method 3 (This is also the method I recommend everyone to use)
some supplements
The same User class is registered twice in spring
singleton pattern
4. Related interview questions
In addition to ApplicationContext, we can also use BeanFactory as the context of Spring
ApplicationContext and BeanFactory have the same effect, and ApplicationContext belongs to the subclass of BeanFactory .
Their differences are as follows.
V. Summary
