手寫Spring Boot Starter起步依賴demo

以下例子代碼在github中，代碼鏈接

Spring Boot起步依賴（starter）大大簡化了項(xiàng)目構(gòu)建中的依賴配置，利用了傳遞依賴解析，把常用庫聚合在一起，組成了幾個為特定功能而定制的依賴，這些依賴項(xiàng)是使項(xiàng)目快速啟動和運(yùn)行所需的依賴項(xiàng)，如spring-boot-starter-web起步依賴，聚合了spring-boot-starter、spring-boot-starter-json、spring-boot-starter-tomcat、spring-web、spring-webmvc等依賴，使得我們的web項(xiàng)目無需引入多個web相關(guān)的依賴項(xiàng)以及為了解決版本沖突等問題。

官方starter命名的格式是spring-boot-starter-*，如spring-boot-starter-actuator、spring-boot-starter-web、spring-boot-starter-test等官方starter，平常我們自己定義的starter一般命名格式是thirdProject-spring-boot-starter

  • 本文示例代碼項(xiàng)目結(jié)構(gòu)是寫一個自定義的demo-spring-boot-starter引入兩個jar包demo1和demo2，然后在project項(xiàng)目中引入demo-spring-boot-starter，項(xiàng)目結(jié)構(gòu)如圖所示：


    項(xiàng)目結(jié)構(gòu).png
一、demo1項(xiàng)目

（1）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>

    <groupId>com.fiuty</groupId>
    <artifactId>demo1</artifactId>
    <version>1.0-SNAPSHOT</version>

</project>

（2）demo1只有一個Student類：

@Data
public class Student {

    private String name;

    private Integer age;
}
二、demo2

（1）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>

    <groupId>com.fiuty</groupId>
    <artifactId>demo2</artifactId>
    <version>1.0-SNAPSHOT</version>

</project>

（2）同樣，demo2也只有一個類Teacher：

@Data
public class Teacher {

    private String name;

    private Integer age;

}
三、demo-spring-boot-starter項(xiàng)目

（1）定義starter需要引入spring-boot-starter依賴、spring-boot-autoconfigure依賴以及第三方j(luò)ar demo1和demo2的依賴，如果需要配置元信息的話，還需引入spring-boot-configuration-processor依賴。
（2）引入demo1和demo2的pom文件：

        <dependency>
            <groupId>com.fiuty</groupId>
            <artifactId>demo1</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency>

        <dependency>
            <groupId>com.fiuty</groupId>
            <artifactId>demo2</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency>

完整的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 https://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>2.4.0</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.fiuty</groupId>
    <artifactId>demo-spring-boot-starter</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>demo-spring-boot-starter</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>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </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>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-configuration-processor</artifactId>
            <optional>true</optional>
        </dependency>

        <dependency>
            <groupId>com.fiuty</groupId>
            <artifactId>demo1</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency>

        <dependency>
            <groupId>com.fiuty</groupId>
            <artifactId>demo2</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency>
    </dependencies>

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

</project>

（3）demo-spring-boot-starter的代碼結(jié)構(gòu)如下圖所示，有一個DemoConfiguration配置類（注入了兩個bean，demo1的student和demo2的teacher），還有兩個properties配置類用于讀取yaml文件的配置值，還有自動裝配類DemoAutoConfiguration和自動裝配配置文件spring.factories，用于項(xiàng)目啟動時(shí)初始化bean并且被spring容器管理：

demo-spring-boot-starter的代碼結(jié)構(gòu).png
  • TeacherProperties配置類：
@ConfigurationProperties(prefix = "com.demo2")
@Configuration
@Data
public class TeacherProperties {

    private String name = "defaultTeacher";

    private Integer age = 30;
}
  • StudentProperties配置類
@ConfigurationProperties(prefix = "com.demo1")
@Configuration
@Data
public class StudentProperties {

    private String name = "defaultStudent";

    private Integer age = 10;
}
  • DemoConfiguration配置類，將yaml文件的配置值賦值到兩個bean，demo1的student和demo2的teacher：
@Configuration
//允許導(dǎo)入配置類,配置類bean被spring容器管理
@EnableConfigurationProperties({StudentProperties.class, TeacherProperties.class})
@Slf4j
public class DemoConfiguration {

    @Bean
    public Student getStudent(StudentProperties studentProperties) {
        Student student = new Student();
        log.info("初始化student");
        student.setName(studentProperties.getName());
        student.setAge(studentProperties.getAge());
        return student;
    }

    @Bean
    public Teacher getTeacher(TeacherProperties teacherProperties) {
        Teacher teacher = new Teacher();
        teacher.setName(teacherProperties.getName());
        teacher.setAge(teacherProperties.getAge());
        return teacher;
    }
}
  • DemoAutoConfiguration自動裝配類
//自動裝配,項(xiàng)目啟動即在spring容器中注冊管理相關(guān)bean
@Import(DemoConfiguration.class)
@Configuration
public class DemoAutoConfiguration {
}
  • META-INF spring.factories配置自動裝配類，需要注意的是spring.factories需放在resource
    的目錄下，在引入starter的時(shí)候spring容器會注冊相關(guān)自動裝配bean。
# Auto Confiure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.fiuty.demo.spring.boot.starter.configure.DemoAutoConfiguration,\
com.fiuty.demo.spring.boot.auto.assemble.AssembleAutoConfiguration
四、project項(xiàng)目

（1）project項(xiàng)目結(jié)構(gòu)如下，引入自定義starter，在yaml文件配置starter的兩個配置類，最后注入demo1的student bean和demo2的teacher bean，獲取其name和age的值：


project項(xiàng)目結(jié)構(gòu).png

（2）引入自定義的starter的pom文件如下：

        <dependency>
            <groupId>com.fiuty</groupId>
            <artifactId>demo-spring-boot-starter</artifactId>
            <version>0.0.1-SNAPSHOT</version>
        </dependency>

完整的pom文件：

<?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 https://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>2.4.0</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.fiuty</groupId>
    <artifactId>project</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>project</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>

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

        <dependency>
            <groupId>com.fiuty</groupId>
            <artifactId>demo-spring-boot-starter</artifactId>
            <version>0.0.1-SNAPSHOT</version>
        </dependency>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </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>

（3）代碼如下

  • DemoController
@RestController
@RequestMapping("/api")
public class DemoController {

    @Autowired
    private DemoService demoService;

    @GetMapping("/student/info")
    public String studentInfo() {
        return demoService.studentInfo();
    }

    @GetMapping("/teacher/info")
    public String info() {
        return demoService.teacherInfo();
    }
}
  • DemoService
public interface DemoService {

    String studentInfo();

    String teacherInfo();

}
  • DemoServiceImpl
@Service
public class DemoServiceImpl implements DemoService {

    @Autowired
    private Student student;

    @Autowired
    private Teacher teacher;

    @Override
    public String studentInfo() {
        return student.getName() + ":" + student.getAge();
    }

    @Override
    public String teacherInfo() {
        return teacher.getName() + ":" + teacher.getAge();
    }
}
  • application.yaml
com:
  demo1:
    age: 18
    name: zhangsan
  demo2:
    name: lili
    age: 25

在寫yaml文件的時(shí)候可以看到有相關(guān)提示，如下圖所示：

發(fā)現(xiàn)配置前綴.gif
發(fā)現(xiàn)配置1.png
發(fā)現(xiàn)配置2.png

  • 最后項(xiàng)目跑起來，瀏覽器訪問：


    瀏覽器1.png
瀏覽器2.png
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