Write a starter

Preface

To make up for it java Defects of the upward class loading mechanism ： The upper layer provides interfaces , The specific implementation is provided by subclasses ; In order to load this method into java In the virtual machine ,java Provides a SPI Mechanism （service provider interface）, It can be loaded into implementation classes that cannot be loaded by the class loading mechanism , There are many schemes for class loading using this mechanism , Such as jdbc load Driver,Dubbo Of SPI Mechanism ,Spring Automatic assembly, etc ; Next, we will package a Starter, Then it is referenced by another service , When the service starts, it will pass SpringBoot Of SpringBootApplication Medium EnableAutoConfiguration Under the @Import(AutoConfigurationImportSelector.class) Annotations automatically assemble a Starter.

Writing a Starter

First, we need to build a multi moudle engineering , Under this project, two module, One redission-spring-boot-starter The other is the quotation change starter Of spring-boot-demo, The specific project structure is shown in the figure below , The following describes how to establish these two projects ;

redission-spring-boot-starter

1、pom file

pom In file redisson rely on , The details are as follows

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter</artifactId>
</dependency>
<dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.11</version>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter</artifactId>
    <version>2.1.6.RELEASE</version>
    <optional>true</optional>
</dependency>
<dependency>
    <groupId>org.redisson</groupId>
    <artifactId>redisson</artifactId>
    <version>3.13.2</version>
</dependency>

2、 stay resource Create one in the directory META-INF The catalog of , And create a spring-factories The file of , The content of the document is composed of two parts , It's actually equivalent to a key structure ,

key yes ：org.springframework.boot.autoconfigure.EnableAutoConfiguration

value It is a specific class that is automatically configured ：com.yangfan.redissionspringbootstarter.RedissonAutoConfiguration

key and value In between =\ Segmentation , The details are as follows

org.springframework.boot.autoconfigure.EnableAutoConfiguration =\
com.yangfan.redissionspringbootstarter.RedissonAutoConfiguration

3、RedissonProperties

RedissonProperties It's a read yml perhaps apollo Inside the configuration information class , The details are as follows ：

@ConfigurationProperties(prefix = "yang.redisson")
public class RedissonProperties {
    private String host = "localhost";
    private int port = 6379;
    private int timeout;//  Timeout time 
    private boolean ssl;

    public String getHost() {
        return host;
    }

    public void setHost(String host) {
        this.host = host;
    }

    public int getPort() {
        return port;
    }

    public void setPort(int port) {
        this.port = port;
    }

    public int getTimeout() {
        return timeout;
    }

    public void setTimeout(int timeout) {
        this.timeout = timeout;
    }

    public boolean isSsl() {
        return ssl;
    }

    public void setSsl(boolean ssl) {
        this.ssl = ssl;
    }
}

4、RedissonAutoConfiguration Is an automatic assembly redission Configuration class , The details are as follows

@Configuration
// Conditions for assembly , Used to control the bean Is it loaded 
@ConditionalOnClass(Redisson.class)
//RedissonProperties Injection into Spring ioc In the container 
@EnableConfigurationProperties(RedissonProperties.class)
public class RedissonAutoConfiguration {

    @Bean
    public RedissonClient redissonClient(RedissonProperties redissonProperties){
        Config config =  new Config();
        String prefix = "redis://";
        if (redissonProperties.isSsl()){
            prefix = "rediss://";
        }
        config.useSingleServer().setAddress(prefix+redissonProperties.getHost()+":"+redissonProperties.getPort()).setConnectTimeout(redissonProperties.getTimeout());
        return Redisson.create(config);
    }
}

spring-boot-demo

1、 In the first pom Introduce in the file redission-spring-boot-starter,pom The specific contents of the document are as follows

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <version>2.3.1.RELEASE</version>
</dependency>

<dependency>
    <groupId>com.example</groupId>
    <artifactId>redission-spring-boot-starter</artifactId>
    <version>0.0.1-SNAPSHOT</version>
</dependency>

2、 stay application.properties Configuration in file redis Required domain name and port

yang.redisson.host=127.0.0.1
yang.redisson.port=6379

3、 Write a controller Verify whether the automatic assembly is successful

@RestController
@RequestMapping
public class RedisController {

    @Autowired
    private RedissonClient redissonClient;

    @GetMapping("/test")
    public String test(){
        RBucket bucket = redissonClient.getBucket("name");
        if(bucket.get() == null){
            bucket.set("com.yang.redisson");
        }else {
            bucket.expire(1, TimeUnit.SECONDS);
        }
        return bucket.get()+"";
    }

}

Before enabling the service, you need to check redission-spring-boot-starter Conduct install once , In this way, it can be referenced by the second service , If install times Unable to find main class, So you need to redission-spring-boot-starter Of build Get rid of ;

  adopt http Request to see the following information to prove that the automatic assembly is successful

SPI Principle analysis

First, let's look at this method ：getAutoConfigurationEntry The way is to get META-INF/spring.factories Load the contents of java In the virtual machine ;

org.springframework.boot.autoconfigure.AutoConfigurationImportSelector#getAutoConfigurationEntry

Let's take a look getCandidateConfigurations This method , The core is this loading method ：loadSpringFactories