springBoot按条件装配：Condition

编码格式转换器接口

package com.boot.condition.bootconditionconfig.converter;

/**
 * 编码格式转换器接口
 */
public interface EncodingConverter {
}

GBK转换器

package com.boot.condition.bootconditionconfig.converter;

public class GBKEncodingConverter implements EncodingConverter {
}

UTF-8转换器

package com.boot.condition.bootconditionconfig.converter;

public class UTF8EncodingConverter implements EncodingConverter {
}

装配配置类

package com.boot.condition.bootconditionconfig.config;

import com.boot.condition.bootconditionconfig.condition.GBKCondition;
import com.boot.condition.bootconditionconfig.condition.UTF8Condition;
import com.boot.condition.bootconditionconfig.converter.EncodingConverter;
import com.boot.condition.bootconditionconfig.converter.GBKEncodingConverter;
import com.boot.condition.bootconditionconfig.converter.UTF8EncodingConverter;
import org.springframework.boot.SpringBootConfiguration;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Conditional;

/**
 * 使用按照条件装配的过程:
 * 1、@Conditional [value值必须是实现Condition接口的类]
 * 2、根据接口中的matches方法的返回结果确定是否装配bean对象到spring容器中
 *    false 不装配 ， true 就会装配到spring容器中
 */
@SpringBootConfiguration
// @Conditional(UTF8Condition.class)
public class EncodingConverterConfig {

    @Bean
    @Conditional(UTF8Condition.class)
    public EncodingConverter createUTF8Converter() {
        return new UTF8EncodingConverter();
    }

    @Bean
    @Conditional(GBKCondition.class)
    public EncodingConverter createGBKConverter() {
        return new GBKEncodingConverter();
    }
}

GBK装配条件类

package com.boot.condition.bootconditionconfig.condition;

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

public class GBKCondition implements Condition {
    @Override
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        String encoding = System.getProperty("file.encoding");
        if ("gbk".equals(encoding.toLowerCase())) {
            return true;
        }
        return false;
    }
}

UTF-8装配条件类

package com.boot.condition.bootconditionconfig.condition;

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

public class UTF8Condition implements Condition {
    @Override
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        String encoding = System.getProperty("file.encoding");
        if ("utf-8".equals(encoding.toLowerCase())) {
            return true;
        }
        return false;
    }
}

测试类

package com.boot.condition.bootconditionconfig;

import com.boot.condition.bootconditionconfig.converter.EncodingConverter;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;

import java.util.Map;

@SpringBootApplication
public class BootConditionConfigApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext context =
                SpringApplication.run(BootConditionConfigApplication.class, args);

        Map<String, EncodingConverter> beansOfType = context.getBeansOfType(EncodingConverter.class);
        System.out.println(beansOfType);
        // 使用获取系统的编码格式的系统变量的key
        System.out.println(System.getProperty("file.encoding"));

        context.close();
    }
}

结果分析：

若file.encoding=’gbk’，则只装配GBKEncodingConverter

若file.encoding=’utf-8’，则只装配UTF8EncodingConverter