ConditionalOnClass实践

两个测试方向 #

方向1：两个maven项目 #

详见git上的 conditional_on_class_main 项目以及 conditional_on_class2 项目

  1. 基础maven项目 conditional_on_class2
    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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>conditional_on_class_2</artifactId>
    <version>1.0-SNAPSHOT</version>

</project>

    java类

    package com;

public class LyReferenceImpl  {
    public String sayWord() {
        return "hello one";
    }
}

  2. 简单的SpringBoot项目 conditional_on_class_main

    <!--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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>conditional_on_class_main</artifactId>
    <version>1.0-SNAPSHOT</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.7.8</version>
    </parent>
    <dependencies>

        <!--把1配置的bean引用进来-->
        <dependency>
            <groupId>org.example</groupId>
            <artifactId>conditional_on_class_2</artifactId>
            <version>1.0-SNAPSHOT</version>
            <scope>provided</scope>
            <optional>true</optional>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <excludes>
                        <!-- 默认会将conditional_on_class_2 打包进去,现在会配置SayExist
						如果放开注释,那么会配置SayNotExist-->
                        <!--<dependency>
                            <groupId>org.example</groupId>
                            <artifactId>conditional_on_class_2</artifactId>
                        </dependency>-->
                    </excludes>
                    <jvmArguments>-Dfile.encoding=UTF-8</jvmArguments>
                </configuration>
                <executions>
                    <execution>
                        <goals>
                            <goal>repackage</goal><!--可以把依赖的包都打包到生成的Jar包中 -->
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

</project>

    //两个配置类  
//配置类1
package com.config;

import com.service.ISay;
import com.service.SayExist;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
//不要放在方法里面,否则会报错"java.lang.ArrayStoreException: sun.reflect.annotation.TypeNotPresentExceptionProxy"
@ConditionalOnClass(value = com.LyReferenceImpl.class)
public class ExistConfiguration {

    @Bean
    public ISay getISay1(){
        return new SayExist();
    }
}

    //配置类2
package com.config;

import com.service.ISay;
import com.service.SayNotExist;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingClass;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
@ConditionalOnMissingClass("com.LyReferenceImpl")
public class NotExistConfiguration {

    @Bean
    public ISay getISay1(){
        return new SayNotExist();
    }
}

方向2：3个maven项目(建议用这个理解) #

注意，这里可能还漏了一个问题，那就是 这个conditional_on_class1 的configuration之所以能够被自动装配，是因为和 conditional_on_class_main1的Application类是同一个包，所以不用特殊处理。如果是其他包名的话，那么是需要用到spring boot的自动装配机制的：在conditional_on_class1 工程的 resources 包下创建META-INF/spring.factories，并写上Config类的全类名

详见 git上的 conditional_on_class_main1, conditional_on_class1 项目以及 conditional_on_class2 项目

  1. 基础 conditional_on_class2
    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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>conditional_on_class_2</artifactId>
    <version>1.0-SNAPSHOT</version>

</project>

    java类

    package com;

public class LyReferenceImpl  {
    public String sayWord() {
        return "hello one";
    }
}

    以LyReferenceImpl.class存不存在，决定创建哪个bean

  2. conditional_on_class_1 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>org.example</groupId>
    <artifactId>conditional_on_class_1</artifactId>
    <version>1.0-SNAPSHOT</version>
    <dependencies>
        <!--引入被引用的类，只在编译期存在-->
        <dependency>
            <groupId>org.example</groupId>
            <artifactId>conditional_on_class_2</artifactId>
            <version>1.0-SNAPSHOT</version>
            <scope>provided</scope>
            <optional>true</optional>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-autoconfigure -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-autoconfigure</artifactId>
            <version>2.7.8</version>
        </dependency>

    </dependencies>
</project>

    //根据是否存在class_2中的类，进行自动装配  
@Configuration
//不要放在方法里面,否则会报错"java.lang.ArrayStoreException: sun.reflect.annotation.TypeNotPresentExceptionProxy"
@ConditionalOnClass(value = com.LyReferenceImpl.class)
public class ExistConfiguration {

    @Bean
    public LyEntity lyEntity1(){
        return new LyEntity("存在");
    }
}

    @Configuration
@ConditionalOnMissingClass("com.LyReferenceImpl")
public class NotExistConfiguration {

    @Bean
    public LyEntity lyEntity1(){
        return new LyEntity("不存在");
    }
}

    //基础类  

public class LyEntity {
    private String name;
    private Integer age;

    public LyEntity(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

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

    public Integer getAge() {
        return age;
    }

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

  3. 使用 在_main项目中 pom.xml

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.7.8</version>
    </parent>
    <dependencies>

        <!--把1配置的bean引用进来-->
        <dependency>
            <groupId>org.example</groupId>
            <artifactId>conditional_on_class_1</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency>


        <!--加上这个则会提示存在-->
       <!-- <dependency>
            <groupId>org.example</groupId>
            <artifactId>conditional_on_class_2</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency> -->

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

    如果不存在class_2中的类，则提示不存在；如果存在则提示存在

    
@SpringBootApplication
@RestController
public class MyApplication {

    @Autowired
    private LyEntity lyEntity;

    @RequestMapping("hello")
    public String hello(){
        return lyEntity.getName();
    }

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