java：【@Import】和【ImportSelector】的简单示例

# 代码结构

# 项目【myBeanBranch】

【pom.xml】

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-context</artifactId>
    <version>5.2.15.RELEASE</version>
</dependency>
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-web</artifactId>
    <version>5.2.15.RELEASE</version>
</dependency>
<dependency>
    <groupId>ch.qos.logback</groupId>
    <artifactId>logback-classic</artifactId>
    <version>1.2.11</version>
</dependency>
<dependency>
    <groupId>jakarta.annotation</groupId>
    <artifactId>jakarta.annotation-api</artifactId>
    <version>1.3.5</version>
</dependency>

【BranchBean.java】

package com.chz.myBeanBranch.bean;

@Slf4j
@Getter
@Setter
// 被【ImportSelector】指过来的类不需要添加【@Component】
public class BranchBean {

    private String name;

    @PostConstruct
    public void init()
    {
        name = "BranchBeanName put in from @PostConstruct";
    }
}

【BranchController.java】

package com.chz.myBeanBranch.controller;

// 被【ImportSelector】指过来的类不需要添加【@RestController】，但要加【@ResponseBody】
@Slf4j
@ResponseBody
@RequestMapping("/branch")
public class BranchController {

    @Autowired
    private BranchBean branchBean;

    @GetMapping("/test1")
    public String test1() {
        return "test1: " + branchBean.getName();
    }
}

【BranchImportBean.java】

package com.chz.myBeanBranch.importSelector;

// 被【@Bean】指过来的类不需要添加【@Component】
@Getter
@Setter
public class BranchImportBean 
{
    private Integer id = 1;
    private String name = "BranchImportBeanName";
}

【BranchImportConfiguration.java】

package com.chz.myBeanBranch.importSelector;

// 被【ImportSelector】指过来的类不需要添加【@Configuration】
public class BranchImportConfiguration 
{
    @Bean
    public BranchImportBean branchImportBean() {
        BranchImportBean branchBean = new BranchImportBean();
        branchBean.setId(19);
        branchBean.setName("I am branchImportBean!!!");
        return branchBean;
    }
}

【BranchImportSelector.java】

package com.chz.myBeanBranch.importSelector;

public class BranchImportSelector implements ImportSelector
{
    @Override
    public String[] selectImports(AnnotationMetadata annotationMetadata)
    {
        // 这里想让哪个类变成bean就在返回值里面返回，所以ImportSelector可以用来做为动态添加bean的一个方法，
        // 比如扫描某一个自定义注解，然后返回类名，变成bean
        return new String[]{
                BranchImportConfiguration.class.getName(),
                BranchController.class.getName(),
                BranchBean.class.getName()
        };
    }
}

【EnableBranchImportSelector.java】

package com.chz.myBeanBranch.importSelector;

@Retention(RetentionPolicy.RUNTIME)
@Documented
@Target(ElementType.TYPE)
@Import(BranchImportSelector.class)   // 这里使用了@ImportSelector
public @interface EnableBranchImportSelector {
}

# 项目【myBeanMain】

【pom.xm】

<dependency>
    <groupId>com.chz</groupId>
    <artifactId>myBeanBranch</artifactId>
    <version>${project.version}</version>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <version>2.3.12.RELEASE</version>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-actuator</artifactId>
    <version>2.3.12.RELEASE</version>
</dependency>
<dependency>
    <groupId>ch.qos.logback</groupId>
    <artifactId>logback-classic</artifactId>
    <version>1.2.11</version>
</dependency>

【application.properties】

server.port=8080
spring.application.name=myBeanMain

management.server.port=7001
management.endpoints.web.exposure.include=*

【MainBean.java】

package com.chz.myBeanMain.bean;

@Getter
@Setter
@Component
public class MainBean
{
    @Autowired
    private NotAnnotatedBean notAnnotatedBean;

    @Autowired
    private BranchBean branchBean;

    @Autowired
    private BranchImportBean branchImportBean;
}

【NotAnnotatedBean.java】

package com.chz.myBeanMain.bean;

// 被【@Import】指过来的bean不需要添加【@Component】
@Getter
@Setter
public class NotAnnotatedBean 
{
    private String name = "I am " + this.getClass().getSimpleName();
}

【MainController.java】

package com.chz.myBeanMain.controller;

@Slf4j
@RestController
@RequestMapping("/main")
public class MainController 
{
    @Autowired
    private MainBean mainBean;

    @GetMapping("/notAnnotatedBean")
    public String notAnnotatedBean() {
        return "notAnnotatedBean: " + mainBean.getNotAnnotatedBean().getName();
    }

    @GetMapping("/branchBean")
    public String branchBean() {
        return "branchBean: " + mainBean.getBranchBean().getName();
    }

    @GetMapping("/branchImportBean")
    public String branchImportBean() {
        return "branchImportBean: " + mainBean.getBranchImportBean().getName();
    }
}

【MyBeanMainTest.java】

package com.chz.myBeanMain;

@Import(NotAnnotatedBean.class)         // 这里使用了@Import
@EnableBranchImportSelector             // 这里使用了@ImportSelector
@SpringBootApplication
public class MyBeanMainTest 
{
    public static void main(String[] args) {
        SpringApplication.run(MyBeanMainTest.class, args);
    }
}

# 测试

启动【MyBeanMainTest】，然后：

访问【http://localhost:8080/branch/test1】

访问【http://localhost:8080/main/branchBean】

访问【http://localhost:8080/main/branchImportBean】

访问【http://localhost:8080/main/notAnnotatedBean】