Spring家族-自定义类型转换器

Spring家族-自定义类型转换器

        Spring最早是通过xml方式注入bean，但是xml文件本质是字符串，所以可想而知，底层spring是做了类型转换。

一、PropertyEditor

需要注意这个接口是jdk提供的接口，并非Spring提供的

1.1、继承PropertyEditorSupport

public class StringToObject extends PropertyEditorSupport {
    @Override
    public void setAsText(String text) throws IllegalArgumentException {
        if (text.startsWith("mem.")) {//需要以mem.开始字符串才可以
            MemberService service = new MemberService();
            service.setClusterName(text.substring(4));
            this.setValue(service);
        }
    }
}

1.2、注入CustomEditorConfigurer

定义好转换器后，需要作为bean注入到spring容器中，spring提供了一个类，用于收集所有的转换器，具体如下

@Configuration
public class AppConfig {
    @Bean
    public CustomEditorConfigurer getCustomPropertyToBean() {
        CustomEditorConfigurer customEditorConfigurer = new CustomEditorConfigurer();
        Map, Class> customEditors = new HashMap<>();
        customEditors.put(MemberService.class, StringToObject.class);
        customEditorConfigurer.setCustomEditors(customEditors);
        return customEditorConfigurer;
    }
}

1.3、应用

@Component
public class UserService {
    @Value("mem.beijingCluster")  //字符串 转成 MemberService对象
    private MemberService memberService;

    public UserService() {
        System.out.println("UserService constructor");
    }

    @Override
    public String toString() {
        return "UserService{" +
                "memberService=" + memberService +
                '}';
    }
}

public class App {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext("com.example");
        UserService userService = context.getBean("userService", UserService.class);
        System.out.println(userService);
    }
}

//输出结果：
// UserService{memberService=MemberService{clusterName='beijingCluster'}}
//

二、接口ConditionalGenericConverter

Spring提供有条件转换器，功能更强大一些，但是有一点需要注意：注入Bean的名字必须是conversionService否则不能注入。

public class CustomConvertService implements ConditionalGenericConverter {
    
    @Override
    public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType) {
        return sourceType.getType().equals(String.class) && targetType.getType().equals(MemberService.class);
    }

    
    @Override
    public Set getConvertibleTypes() {
        Set set = new HashSet<>();
        ConvertiblePair pair = new ConvertiblePair(String.class, MemberService.class);
        set.add(pair);
        return set;
    }

    
    @Override
    public Object convert(Object source, TypeDescriptor sourceType, TypeDescriptor targetType) {
        if (targetType.getType() == MemberService.class) {
            MemberService service = new MemberService();
            service.setClusterName((String)source);
            return service;
        } 
        return null;
    }
}

@Configuration
public class AppConfig {
    //注意这里的名字 方法名字必须是conversionService,否则不能注入
    @Bean
    public ConversionServiceFactoryBean conversionService() {
        ConversionServiceFactoryBean bean = new ConversionServiceFactoryBean();
        bean.setConverters(Collections.singleton(new CustomConvertService()));
        return bean;
    }
}

@Component
public class UserService {
    @Value("mem.beijingCluster")
    private MemberService memberService;

    public UserService() {
    }

    @Override
    public String toString() {
        return "UserService{" +
                "memberService=" + memberService +
                '}';
    }
}


public class App {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext("com.example");
        UserService userService = context.getBean("userService", UserService.class);
        System.out.println(userService);
    }
}

三、总结

通过上面总结，我们完全可以自定义类型转换器，完成更为复杂的业务处理，比如说json的转换。