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This article mainly introduces the SpringBoot how to achieve automatic code execution at startup related knowledge, the content is detailed and easy to understand, the operation is simple and fast, has a certain reference value, I believe that everyone after reading this SpringBoot how to achieve automatic code execution at startup article will have a harvest, let's take a look.

Preface

The currently developed SpringBoot project needs to preload some resources when it starts. There are many ways to execute the code during startup or after successful startup. We can implement it in the static code block, in the constructor, or using the @ PostConstruct annotation.

Of course, you can also implement the ApplicationRunner and CommandLineRunner interfaces of Spring to realize the function that runs after startup. Sort out the differences in execution at these locations and the loading order here.

The startup loading mode of java itself static code block

Static static code block, which is automatically executed when the class is loaded.

Construction method

Executes when the object is initialized. The order of execution comes after the static static code block.

Spring loading mode at startup

@ PostConstruct comment

PostConstruct annotations are used on methods, which are executed after object dependency injection initialization.

ApplicationRunner and CommandLineRunner

SpringBoot provides two interfaces, CommandLineRunner and ApplicationRunner, to implement the functions that the Spring container executes after startup.

These two interfaces need to implement a run method, which can be implemented in run. The functions of the two interfaces are basically the same, and the difference lies in the input parameters of the run method. The input parameter of run method for ApplicationRunner is ApplicationArguments, and the input parameter of run method for CommandLineRunner is String array.

What is ApplicationArguments

The official document is interpreted as:

"Provides access to the arguments that were used to run a SpringApplication.

Access application parameters used when the Spring application is running. That is, we can get SpringApplication.run (…) The application parameters of the.

Order comments

When multiple classes implement the CommandLineRunner and ApplicationRunner interfaces, you can set the running order by adding @ Order annotations to the classes.

Code testing

To test the effect and order of running at startup, write some test code to run it.

TestPostConstruct

Componentpublic class TestPostConstruct {static {System.out.println ("static");} public TestPostConstruct () {System.out.println ("constructer");} @ PostConstruct public void init () {System.out.println ("PostConstruct");}}

TestApplicationRunner

@ Component@Order (1) public class TestApplicationRunner implements ApplicationRunner {@ Override public void run (ApplicationArguments applicationArguments) throws Exception {System.out.println ("order1:TestApplicationRunner");}}

TestCommandLineRunner

@ Component@Order (2) public class TestCommandLineRunner implements CommandLineRunner {@ Override public void run (String...) Strings) throws Exception {System.out.println ("order2:TestCommandLineRunner");}}

Execution result

This is the end of the article on "how to automatically execute code at startup in SpringBoot". Thank you for reading! I believe that everyone has a certain understanding of the knowledge of "how to automatically execute code when SpringBoot starts". If you want to learn more, you are welcome to follow the industry information channel.

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