引言

当我们通过@ConfigurationProperties注解实现配置 bean的时候,如果默认的配置属性转换无法满足我们的需求的时候,我们可以根据自己的需求通过以下扩展方式对配置属性进行转换

PropertyEditorSupport实现

下面的例子是把属性中定义的字符串转换成Movie,并且把name的值大写

• 继承PropertyEditorSupport并且实现PropertyEditorRegistrar接口

package com.paderlol.spring.practice.properties.editor;

import com.paderlol.spring.practice.properties.pojo.Movie;
import java.beans.PropertyEditorSupport;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.PropertyEditorRegistrar;
import org.springframework.beans.PropertyEditorRegistry;

/**
  * @author pader PropertyEditor 在不同的包下面
  */
@Slf4j
public class CustomMovieEditor extends PropertyEditorSupport
implements PropertyEditorRegistrar {

    @Override
    public String getAsText() {
        Movie movie = (Movie) getValue();
        return movie == null ? "" : movie.getName();
    }

    @Override
    public void setAsText(String text) throws IllegalArgumentException {
        log.info("继承[PropertyEditorSupport]类,转换数据={}", text);
        String[] data = text.split("-");
        Movie movie = Movie.builder().name(data[0]
        .toUpperCase()).seat(Integer.parseInt(data[1]))
        .build();
        setValue(movie);
    }


    @Override
    public void registerCustomEditors(PropertyEditorRegistry registry) {
        registry.registerCustomEditor(Movie.class,this);
    }
}

• 注册自定义的PropertyEditor

@Bean
public CustomEditorConfigurer customEditorConfigurer() {
    CustomEditorConfigurer customEditorConfigurer = new CustomEditorConfigurer();      
      // 有两种注册方式 这是第一种
    customEditorConfigurer.setPropertyEditorRegistrars(  
        new PropertyEditorRegistrar[]{ new CustomMovieEditor() });
          //  第二 种
        Map<Class<?>,Class<? extends PropertyEditor>> maps = new HashMap<>();
        maps.put(Movie.class,CustomMovieEditor.class);

    return customEditorConfigurer;
}

Converter接口+@ConfigurationPropertiesBinding注解

//注意
@Component
@ConfigurationPropertiesBinding
public class StringToPersonConverter implements Converter<String, Person> {

    @Override
    public Person convert(String from) {
        log.info("使用[Converter]接口,转换数据={}", from);
        String[] data = from.split(",");
        return Person.builder().name(data[0]).age(Integer.parseInt(data[1])).build();
    }
}

总结

• 以上两种实现方式结果,但是Converter接口相比PropertyEditor接口更加灵活一些,PropertyEditor接口仅限于String转换,Converter可以自定义别的,并且PropertyEditor接口通常用于Controller中的接收参数的转换。
• @ConfigurationPropertiesBinding是限定符注解@Qualifier的派生类而已,参考org.springframework.boot.context.properties.ConversionServiceDeducer，以下是源代码片段

@Autowired(required = false)
@ConfigurationPropertiesBinding
public void setConverters(List<Converter<?, ?>> converters) {
      this.converters = converters;
}

/**
* A list of custom converters (in addition to the defaults) to use when
* converting properties for binding.
* @param converters the converters to set
*/
@Autowired(required = false)
@ConfigurationPropertiesBinding
public void setGenericConverters(List<GenericConverter> converters) {
this.genericConverters = converters;
  }

• Formatter接口是不能对属性完成转换的,因为ConversionServiceDeducer初始化的时候只获取GenericConverter和Converter接口
• 官方文档上还介绍了可以使用实现org.springframework.core.convert.ConversionService并且Bean名称也必须叫conversionService，不过大部分情况不推荐自己通过这种方式去实现这个接口,因为自己实现的ConversionService会替代默认的。具体参考ConversionServiceDeducer源码：

public ConversionService getConversionService() {
        try {
            //默认首先寻找Bean名称叫conversionService的ConversionService的Bean类
            return this.applicationContext.getBean(
                    ConfigurableApplicationContext.CONVERSION_SERVICE_BEAN_NAME,
                    ConversionService.class);
        }
        catch (NoSuchBeanDefinitionException ex) {
            //找不到就默认生成ApplicationConversionService类
            return this.applicationContext.getAutowireCapableBeanFactory()
                    .createBean(Factory.class).create();
        }
}