Spring Boot 2.0 配置属性自定义转换

迷南。 2021-09-18 13:56 277阅读 0赞

### 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();
            }
    }