Spring instantiation bean process parsing and complete code example

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The instantiation of beans in spring is an important part of the bean life cycle. Usually, beans will not change after initialization.

So what is the process of spring instance bean?!

Spring instantiation bean process analysis

To obtain a bean object, you must first obtain it through the getBean () method of beanfactory, during which a series of steps will be taken to instantiate the bean object:

Step 1: call the default construction method of the bean (of course, it can also be other specified construction methods) to generate the bean instance: bean1.

Step 2: check whether the bean attribute value is injected into the bean configuration file. If so, inject its attribute based on the bean1 instance, overwrite the original bean1 and form a new bean instance: bean2.

Step 3: check whether the bean implements the initializingbean interface. If this interface is implemented, call the afterpropertieset() method to perform corresponding operations on bean2 and overwrite bean2 to form a new bean instance: bean3.

Step 4: check whether the attribute init method is specified in the bean configuration file. If it is specified, call the corresponding method of this attribute and perform corresponding operations on bean3, and finally overwrite bean3 to form a new instance: bean4.

Through the above steps, we find that when spring instantiates a bean, the bean is constantly changing!

Spring instantiation bean process code demonstration

To better explain the above steps, please see the following code:

Entity class:

Tools:

Spring bean configuration:

Test class:

Operation results:

From the running results, we should be clear about the specific process of bean instantiation.

Employee implements three interfaces:

Initializingbean: this interface provides the afterpropertieset () method, which is used to provide the function of defining initialization for beans. Disposablebean: this interface provides the destroy () method, which is used to provide the function of operation before the bean instance is destroyed. Beannameaware: this interface provides setbeanname() method, which is used to provide the function of setting bean name. It can be seen from the above running results that this method is carried out in step 2.

summary

The above is all about the spring bean instantiation process in this article. I hope it will be helpful to you. Interested friends can continue to refer to this website:

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