Implement a middleware from -1

Everyone else writes from 0 Start implementation xxx, Let me start with -1 At the beginning, it seems more awesome .

today , Let's start , To teach you how to implement a middleware .

New projects

First , Let's create a new one  module  Project for testing .

The project consists of two modules ,

test-infra

Development of user middleware module ,

demo

Used for testing .

<?xml version=&quot;1.0&quot; encoding=&quot;UTF-8&quot;?>
<project xmlns=&quot;http://maven.apache.org/POM/4.0.0&quot; xmlns:xsi=&quot;http://www.w3.org/2001/XMLSchema-instance&quot;
 xsi:schemaLocation=&quot;http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd&quot;>
 <modelVersion>4.0.0</modelVersion>
 <parent>
 <groupId>org.springframework.boot</groupId>
 <artifactId>spring-boot-starter-parent</artifactId>
 <version>2.7.0</version>
 <relativePath/> <!-- lookup parent from repository -->
 </parent>
 <groupId>com.aixiaoxian.infra</groupId>
 <artifactId>aixiaoxian-infra</artifactId>
 <version>0.0.1-SNAPSHOT</version>

 <name>aixiaoxian-infra</name>
 <description>aixiaoxian-infra</description>
 <packaging>pom</packaging>

 <properties>
 <java.version>1.8</java.version>
 </properties>

 <modules>
 <module>demo</module>
 <module>test-infra</module>
 </modules>

 <dependencies>

 </dependencies>

 <build>
 <plugins>
 <!-- Source -->
 <plugin>
 <artifactId>maven-source-plugin</artifactId>
 <inherited>true</inherited>
 <executions>
 <execution>
 <phase>package</phase>
 <goals>
 <goal>jar-no-fork</goal>
 </goals>
 </execution>
 </executions>
 </plugin>
 </plugins>
 </build>

</project>


Developing middleware

Project creation  OK  了 , Then start to develop the simplest middleware .

stay

resources

Create under directory

META-INFA/spring.factories

file , For automatic assembly , Don't ask me what is automatic assembly , Then configure an auto assembly class .

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.aixiaoxian.testInfra.config.TestConfiguration


Realization  

TestConfiguration

, The easiest way , Use it directly

@Bean

Annotations declare a  Bean  hand  Spring  management .

@Configuration
public class TestConfiguration implements BeanDefinitionRegistryPostProcessor, EnvironmentAware {
 private Environment environment;

 @Bean
 public TestManager getTestManager() {
 return new TestManager();
 }
 
 @Override
 public void setEnvironment(Environment environment) {
 this.environment = environment;
 }

}


Then implement the processing part of the real middleware logic

TestManager

.

@Slf4j
public class TestManager {

 public TestManager() {
 init();
 }

 public void init(){
 log.info("TestManager start");
 }
}


In this case , The simplest middleware will be developed , Add it directly to

demo

Module , Just start the test .

 <dependency>
 <groupId>com.aixiaoxian.infra</groupId>
 <artifactId>test-infra</artifactId>
 <version>0.0.1-SNAPSHOT</version>
 </dependency>


Change position

Let's change our posture to create  

Bean

, Use

BeanDefinitionRegistryPostProcessor

, Give Way  

TestConfiguration

  To achieve it , rewrite

postProcessBeanDefinitionRegistry

, Sign up for a new  Bean 

aiManager

, This is also  OK Of , There are many ways to write it , I won't repeat .

@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry beanDefinitionRegistry) throws BeansException {
 BeanDefinitionBuilder beanDefinitionBuilder = BeanDefinitionBuilder.genericBeanDefinition(AiManager.class);
 beanDefinitionBuilder.addConstructorArgValue(this.environment);
 beanDefinitionRegistry.registerBeanDefinition("aiManager", beanDefinitionBuilder.getBeanDefinition());
}

@Slf4j
public class AiManager {
 private Environment environment;

 public AiManager(Environment environment) {
 this.environment = environment;

 init();
 }

 public void init(){
 log.info("AiManager start");
 }
}


Another pose

For automatic assembly creation  Bean  With a basic understanding of , What should I do if I want to declare an annotation for others to use ？

First create an annotation , Notice that I used

@Import

annotation ,

TestImportSelector

  Realization

TestImportSelector

Interface .

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Import({TestImportSelector.class})
@Documented
public @interface TestAnnotation {
}

public class TestImportSelector implements DeferredImportSelector {
 @Override
 public String[] selectImports(AnnotationMetadata annotationMetadata) {
 return new String[]{AnnotationConfiguration.class.getName()};
 }
}


AnnotationConfiguration

  The writing method is also very simple , This also realizes automatic assembly , Of course, if you use the above writing method, you can achieve the same effect , But it is suggested to write , Don't ask , That's it .

public class AnnotationConfiguration implements BeanDefinitionRegistryPostProcessor {

 @Override
 public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry beanDefinitionRegistry) throws BeansException {
 BeanDefinitionBuilder beanDefinitionBuilder = BeanDefinitionBuilder.genericBeanDefinition(AnnotationManager.class);
 beanDefinitionRegistry.registerBeanDefinition("annotationManager", beanDefinitionBuilder.getBeanDefinition());
 }

 @Override
 public void postProcessBeanFactory(ConfigurableListableBeanFactory configurableListableBeanFactory) throws BeansException {

 }
}

@Slf4j
public class AnnotationManager {

 public AnnotationManager() {
 init();
 }

 public void init(){
 log.info("AnnotationManager start");
 }
}


Last in

demo

Put our annotation on the startup class .

@SpringBootApplication
@TestAnnotation
public class DemoApplication {

 public static void main(String[] args) {
 SpringApplication.run(DemoApplication.class, args);
 }
}


Finally we can see the output ：

2022-06-21 19:05:07.433 INFO 4598 --- [ main] c.a.testInfra.manager.TestManager : TestManager start
2022-06-21 19:05:07.456 INFO 4598 --- [ main] c.a.testInfra.manager.AiManager : AiManager start
2022-06-21 19:05:07.456 INFO 4598 --- [ main] c.a.testInfra.manager.AnnotationManager : AnnotationManager start


Okay , That's it , I guess , No one needs this source code ？ For the following article , First write this to pave the way , end .