springboot實現自己的starter

實現一個簡單的對象格式化starter

新建一個maven工程，引入spring-boot-starter和json

pom.xml

<?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.david</groupId>
  <artifactId>my-spring-boot-starter</artifactId>
  <version>1.0-SNAPSHOT</version>

  <name>my-spring-boot-starter</name>
  <!-- FIXME change it to the project's website -->
  <url>http://www.example.com</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compiler.source>1.7</maven.compiler.source>
    <maven.compiler.target>1.7</maven.compiler.target>
  </properties>

  <dependencies>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter</artifactId>
      <version>2.1.6.RELEASE</version>
    </dependency>
    <!--可選-->
    <dependency>
      <groupId>com.alibaba</groupId>
      <artifactId>fastjson</artifactId>
      <version>1.2.56</version>
      <optional>true</optional>
    </dependency>
    <!-- spring默認支持yaml,如果需要支持配置文件格式properties或xml需要添加這個依賴-->
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-configuration-processor</artifactId>
      <optional>true</optional>
      <version>2.1.6.RELEASE</version>
    </dependency>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.11</version>
      <scope>test</scope>
    </dependency>
  </dependencies>

  <build>
    <pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) -->
      <plugins>
        <!-- clean lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#clean_Lifecycle -->
        <plugin>
          <artifactId>maven-clean-plugin</artifactId>
          <version>3.1.0</version>
        </plugin>
        <!-- default lifecycle, jar packaging: see https://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_jar_packaging -->
        <plugin>
          <artifactId>maven-resources-plugin</artifactId>
          <version>3.0.2</version>
        </plugin>
        <plugin>
          <artifactId>maven-compiler-plugin</artifactId>
          <version>3.8.0</version>
        </plugin>
        <plugin>
          <artifactId>maven-surefire-plugin</artifactId>
          <version>2.22.1</version>
        </plugin>
        <plugin>
          <artifactId>maven-jar-plugin</artifactId>
          <version>3.0.2</version>
        </plugin>
        <plugin>
          <artifactId>maven-install-plugin</artifactId>
          <version>2.5.2</version>
        </plugin>
        <plugin>
          <artifactId>maven-deploy-plugin</artifactId>
          <version>2.8.2</version>
        </plugin>
        <!-- site lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#site_Lifecycle -->
        <plugin>
          <artifactId>maven-site-plugin</artifactId>
          <version>3.7.1</version>
        </plugin>
        <plugin>
          <artifactId>maven-project-info-reports-plugin</artifactId>
          <version>3.0.0</version>
        </plugin>
      </plugins>
    </pluginManagement>
  </build>
</project>

定義一個接口類IFormat，並實現2個不同的類，一個字符串一個json

public interface IFormat {

    <T> String doFormat(T obj);
}

實現類

json實現類

import com.alibaba.fastjson.JSON;

public class JsonFormat implements IFormat {

    @Override
    public <T> String doFormat(T obj) {
        return "Json Format:"+ JSON.toJSONString(obj);
    }
}



字符串實現類

public class StringFormat implements IFormat {

    @Override
    public <T> String doFormat(T obj) {
        return "String Format:"+obj.toString();
    }
}

 創建spring配置類

import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingClass;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;

@Configuration
public class FormatAutoConfiguration{

    @ConditionalOnMissingClass("com.alibaba.fastjson.JSON")// 當沒有json這個類時會加載這個bean，並交給spring容器管理
    @Primary // 設置一個首選項，不然會提示找到2個bean
    @Bean
    public IFormat stringFormat(){
        return new StringFormat();
    }

    @ConditionalOnClass(name = "com.alibaba.fastjson.JSON")// 當有json這個類時會加載這個bean，並交給spring容器管理
    @Bean
    public IFormat jsonFormat(){
        return new JsonFormat();
    }
}

創建springboot中可以在properties自動提示的類，這樣就可以動態的配置一些屬性，這裏只定義了一個屬性

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

@ConfigurationProperties(prefix = "com.david.format")// 自動提示的配置前綴
public class FormatProperties {

    private String info;

    public String getInfo() {
        return info;
    }

    public void setInfo(String info) {
        this.info = info;
    }
}

接着定義裝配的模板

public class FormatTemplate {

    private IFormat format;

    private FormatProperties formatProperties;

    public FormatTemplate(IFormat format, FormatProperties formatProperties) {
        this.format = format;
        this.formatProperties = formatProperties;
    }

    public <T> String doFormat(T obj){

        return "properties info:"+formatProperties.getInfo()+";"+format.doFormat(obj);
    }
}

然後定義自動裝配模板的配置類，spring會自動注入兩個bean創建FormatTemplate並交由spring容器管理

import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;

@Import(FormatAutoConfiguration.class)// 導入其他bean的配置
@EnableConfigurationProperties(FormatProperties.class)// 啓用配置文件
@Configuration
public class FormatTemplateAutoConfiguration {

    @Bean
    public FormatTemplate formatTemplate(IFormat format, FormatProperties formatProperties){
        return new FormatTemplate(format,formatProperties);
    }

}

最後一步就是整個自動裝配的核心了，在resources目錄下創建一個META-INF文件夾，然後在META-INF文件夾下創建一個spring.factories文件，文件內容如下：

org.springframework.boot.autoconfigure.EnableAutoConfiguration=com.david.FormatTemplateAutoConfiguration

springboot預留了擴展點（SPI），通過在資源路徑下創建META-INF文件夾，在META-INF下創建spring.factories文件，spring啓動時會掃描所有資源文件下的這個文件，並根據文件配置內容加載對應bean的信息交由spring管理，這樣我們就能使用autowired的註解實現快速注入使用，starter就是根據這個原理實現的。

項目結構如下圖

接着把這個項目install成jar，在創建一個新的springboot工程引用這個jar

新工程pom.xml，目前還沒有依賴json的jar包

<?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>2.2.4.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.david</groupId>
    <artifactId>my-web</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>my-web</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-web</artifactId>
        </dependency>
        <dependency>
            <groupId>com.david.my</groupId>
            <artifactId>mycode</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency>
        <dependency>
            <groupId>com.david</groupId>
            <artifactId>my-spring-boot-starter</artifactId>
            <version>1.0-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>

創建一個user類，user類裏面有name和age屬性並重寫toString方法

public class User {

    private String name;
    private int age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

創建一個controller並自動注入FormatTemplate

import com.david.FormatTemplate;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class MyController {

    @Autowired
    FormatTemplate formatTemplate;

    @RequestMapping("/format")
    public String format(){
        User user = new User();
        user.setName("David");
        user.setAge(27);
        return formatTemplate.doFormat(user);
    }
}

在application.properties中輸入會有自動提示

啓動運行項目，目前輸出會是string格式化對象，配置的屬性也有輸出

加上json的jar的pom.xml

<?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>2.2.4.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.david</groupId>
    <artifactId>my-web</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>my-web</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-web</artifactId>
        </dependency>
        <dependency>
            <groupId>com.david.my</groupId>
            <artifactId>mycode</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency>
        <dependency>
            <groupId>com.david</groupId>
            <artifactId>my-spring-boot-starter</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency>
        <!-- json jar 包-->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.56</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>

重啓並訪問