spring学习笔记（六）自定义spring-boot-starter（2）

上篇文章我们主要讲了spring自动装配的原理，我们知道了springboot在启动的时候会自动去读.factories文件，在factories文件中，autoConfiguration对应的就是我们程序启动时自己预加载的类，另外我也提到了另外一个比较核心的注解，即@ConditionOnxxx。详情点击https://blog.csdn.net/qq_41907991/article/details/88704448。

---

这篇文章我们主要分析下@ConditionOnxxx注解，以及自己实现一个starter。下面开始分析我们的@ConditionOnxxx注解。先看代码：

我们以@ConditionalOnMissingBean这个注解来分析原理：

@Target({ ElementType.TYPE, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Conditional(OnBeanCondition.class)
public @interface ConditionalOnMissingBean {....}

很明显，上面的核心注解就是@Conditional注解，我们接下来分析这个注解，直接上代码看效果

package com.study.spring.condition.condition;

import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.core.type.AnnotatedTypeMetadata;

/**
 * @Author: dmz
 * @Description:
 * @Date: Create in 23:16 2019/3/25
 */
public class CatCondition implements Condition {
    @Override
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        return context.getEnvironment().getProperty("what").equals("cat");
    }
}

package com.study.spring.condition.condition;

import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.core.type.AnnotatedTypeMetadata;

/**
 * @Author: dmz
 * @Description:
 * @Date: Create in 23:16 2019/3/25
 */
public class DogCondition implements Condition {
    @Override
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        return context.getEnvironment().getProperty("what").equals("dog");
    }
}

上面这两个类，是我自定义的两个条件

package com.study.spring.condition.model;

import com.study.spring.condition.condition.CatCondition;
import org.springframework.context.annotation.Conditional;
import org.springframework.stereotype.Component;

/**
 * @Author: dmz
 * @Description:
 * @Date: Create in 23:19 2019/3/25
 */
@Component
@Conditional({CatCondition.class})
public class Cat {
    public Cat(){
        System.out.println("猫来了，喵喵喵~~");
    }
}

package com.study.spring.condition.model;

import com.study.spring.condition.condition.DogCondition;
import org.springframework.context.annotation.Conditional;
import org.springframework.stereotype.Component;

/**
 * @Author: dmz
 * @Description:
 * @Date: Create in 23:18 2019/3/25
 */
@Component
@Conditional({DogCondition.class})
public class Dog {
    public Dog(){
        System.out.println("dog 来了，汪汪汪~~~");
    }
}

主要是为了通过条件控制我们这两个类的加载

what:cat

这是配置文件中的内容

package com.study.spring.condition;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class ConditionApplication {

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

}

这是启动类

启动程序，可以看到程序打印：

猫来了，喵喵喵~~

经过上面的程序我相信大家对这个@conditional注解已经有了一定的了解

接下来我们来实现我们的自定义starter

pom文件如下：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.3.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.study.spring</groupId>
    <artifactId>starter</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>myAutoconfig-spring-boot-starter</name>
    <description>Demo project for Spring Boot</description>
    <packaging>jar</packaging>
    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-autoconfigure</artifactId>
        </dependency>

        <!--为了生成spring-configuration-metadata.json-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-configuration-processor</artifactId>
        </dependency>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

整体项目结构如下

package com.study.spring.starter.AutoConfig;

import lombok.Data;
import org.springframework.boot.context.properties.ConfigurationProperties;

/**
 * @author dmz
 * @date Create in 22:06 2019/3/23
 */
@Data
@ConfigurationProperties(prefix = "config")
public class Config {
    private String name;
    private Integer age;
}

package com.study.spring.starter.AutoConfig;

import com.study.spring.starter.service.MyService;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

/**
 * @author dmz
 * @date Create in 21:24 2019/3/23
 */
@Configuration
@EnableConfigurationProperties(Config.class)
@ConditionalOnClass(MyService.class)
public class MyAutoConfig {

    @Bean
    @ConditionalOnMissingBean(MyService.class)
    public MyService getMyService() {
        return new MyService();
    }
}

package com.study.spring.starter.service;

import com.study.spring.starter.AutoConfig.Config;
import org.springframework.beans.factory.annotation.Autowired;

/**
 * @author dmz
 * @date Create in 21:53 2019/3/23
 */
public class MyService {

    @Autowired
    private Config config;

    public void say() {
        System.out.println("自定义的starter来了,say:" + config.getName());
    }
}

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
/**
 *保留启动类，主要是为了执行maven的命令，
 * 打包到我们的本地仓库
 */
@SpringBootApplication
public class StarterApplication{
    public static void main(String[] args) {
        SpringApplication.run(StarterApplication.class, args);
    }

}

spring.factories文件如下：

org.springframework.boot.autoconfigure.EnableAutoConfiguration=
com.study.spring.starter.AutoConfig.MyAutoConfig

测试代码如下：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.3.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.study.spring</groupId>
    <artifactId>starter-test</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>starter-test</name>
    <description>Demo project for Spring Boot</description>

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

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>
         <!--引入我们的依赖-->
        <dependency>
            <groupId>com.study.spring</groupId>
            <artifactId>starter</artifactId>
            <version>0.0.1-SNAPSHOT</version>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>

    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

启动类：

package com.study.spring.startertest;

import com.study.spring.starter.service.MyService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.ApplicationArguments;
import org.springframework.boot.ApplicationRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class StarterTestApplication implements ApplicationRunner {

    @Autowired
    private MyService myService;

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

    @Override
    public void run(ApplicationArguments args) throws Exception {
        myService.say();
    }
}

我们在测试项目中加了配置信息

config.name=zhangsan

运行结果如下：

  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.1.3.RELEASE)

2019-03-27 00:09:52.995  INFO 19468 --- [           main] c.s.s.s.StarterTestApplication           : Starting StarterTestApplication on DESKTOP-N88SU6M with PID 19468 (C:UsersdellDesktopspring-masterstarter-test	argetclasses started by dell in C:UsersdellDesktopspring-master)
2019-03-27 00:09:52.999  INFO 19468 --- [           main] c.s.s.s.StarterTestApplication           : No active profile set, falling back to default profiles: default
2019-03-27 00:09:53.416  INFO 19468 --- [           main] c.s.s.s.StarterTestApplication           : Started StarterTestApplication in 0.722 seconds (JVM running for 1.243)
自定义的starter来了,say:zhangsan

Process finished with exit code 0

验证成功~~

项目github地址：https://github.com/daimingzhi/spring.git