springboot 自定义转换器（converter）

忘是亡心i 2023-02-25 07:24 16阅读 0赞

--------------------

### springboot 自定义转换器（converter） ###

**应用：实现一对一转换，如将字符串转换为pojo、枚举等**

### \*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\* ###

**相关类与接口**

**Converter**

@FunctionalInterface
    public interface Converter<S, T> {
    
    	@Nullable
    	T convert(S source);  //将类型S的对象转换为类型T的对象
    
    }

**ConverterFactory**

public interface ConverterFactory<S, R> {
    
    	<T extends R> Converter<S, T> getConverter(Class<T> targetType);
    
    }

**\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\***

**部分内置converter、converterFactory**

**EnumToStringConverter：将枚举字面量转换为字符串**

final class EnumToStringConverter extends AbstractConditionalEnumConverter implements Converter<Enum<?>, String> {
    
    	public EnumToStringConverter(ConversionService conversionService) {
    		super(conversionService);
    	}
    
    	@Override
    	public String convert(Enum<?> source) {
    		return source.name();
    	}
    
    }

**StringToNumerConverterFactory：字符串转换为数字**

final class StringToNumberConverterFactory implements ConverterFactory<String, Number> {
    
    	@Override
    	public <T extends Number> Converter<String, T> getConverter(Class<T> targetType) {
    		return new StringToNumber<>(targetType);
    	}
    
    
    	private static final class StringToNumber<T extends Number> implements Converter<String, T> {
    
    		private final Class<T> targetType;
    
    		public StringToNumber(Class<T> targetType) {
    			this.targetType = targetType;
    		}
    
    		@Override
    		public T convert(String source) {
    			if (source.isEmpty()) {
    				return null;
    			}
    			return NumberUtils.parseNumber(source, this.targetType);
    		}
    	}
    
    }

**StringToEnumConverterFactory：****根据枚举字面量将字符串转换为枚举对象**

final class StringToEnumConverterFactory implements ConverterFactory<String, Enum> {
    
    	@Override
    	public <T extends Enum> Converter<String, T> getConverter(Class<T> targetType) {
    		return new StringToEnum(ConversionUtils.getEnumType(targetType));
    	}
    
    
    	private static class StringToEnum<T extends Enum> implements Converter<String, T> {
    
    		private final Class<T> enumType;
    
    		public StringToEnum(Class<T> enumType) {
    			this.enumType = enumType;
    		}
    
    		@Override
    		public T convert(String source) {  //根据枚举的字面量进行转换
    			if (source.isEmpty()) {
    				// It's an empty enum identifier: reset the enum value to null.
    				return null;
    			}
    			return (T) Enum.valueOf(this.enumType, source.trim());
    		}
    	}
    
    }

### \*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\* ###

**示例：自定义枚举转换器，根据枚举属性进行转换**

**\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\***

**myenum 层**

**Sex**

public enum Sex {
    
        Male(1,"男"),Female(2,"女");
    
        private Integer id;
        private String name;
    
        Sex(Integer id,String name){
            this.id=id;
            this.name=name;
        }
    
        public Integer getId() {
            return id;
        }
    
        public void setId(Integer id) {
            this.id = id;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        @Override
        public String toString() {
            return "Sex{" +
                    "id=" + id +
                    ", name='" + name + '\'' +
                    '}';
        }
    }

**\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\***

**pojo 层**

**Person**

@Data
    public class Person {
    
        private String name;
        private Integer age;
        private Sex sex;
    }

**\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\***

**config 层**

**StringToEnumConverter：根据属性name将字符串转换为枚举对象**

@Component
    public class StringToEnumConverter implements Converter<String, Sex> {
    
        @Override
        public Sex convert(String source) {
            Sex sex=Sex.Male;
            if ("女".equals(source)){
                sex=Sex.Female;
            }
    
            return sex;
        }
    }

**说明：将转换器注册为容器bean后，可自动注册，不需要使用WebMvcConfigurer**

**WebConfig：注册converter**

@Component
    public class WebConfig implements WebMvcConfigurer {
    
        @Resource
        private StringToEnumConverter stringToEnumConverter;
    
        @Override
        public void addFormatters(FormatterRegistry registry) {
            registry.addConverter(stringToEnumConverter);
        }
    }

**\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\***

**controller 层**

**HelloController**

@RestController
    public class HelloController {
    
        @RequestMapping("/hello")
        public String hello(Sex sex){
            System.out.println(sex);
    
            return "success";
    
        }
    
        @RequestMapping("/hello2")
        public String hello2(Person person){
            System.out.println(person);
    
            return "success";
        }
    }

### \*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\* ###

**默认枚举转换器测试**

**localhost:8080/hello?sex=Male**

2020-07-11 10:09:53.896  INFO 6652 --- [nio-8080-exec-2] o.s.web.servlet.DispatcherServlet        : Initializing Servlet 'dispatcherServlet'
    2020-07-11 10:09:53.908  INFO 6652 --- [nio-8080-exec-2] o.s.web.servlet.DispatcherServlet        : Completed initialization in 12 ms
    Sex{id=1, name='男'}

**localhost:8080/hello?sex=男**

2020-07-11 10:08:33.021  INFO 14848 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : Completed initialization in 5 ms
    2020-07-11 10:08:33.056  WARN 14848 --- [nio-8080-exec-1] .w.s.m.s.DefaultHandlerExceptionResolver : Resolved [org.springframework.web.method.annotation.MethodArgumentTypeMismatchException: Failed to convert value of type 'java.lang.String' to required type 'com.example.demo.myenum.Sex'; nested exception is org.springframework.core.convert.ConversionFailedException: Failed to convert from type [java.lang.String] to type [com.example.demo.myenum.Sex] for value '男'; nested exception is java.lang.IllegalArgumentException: No enum constant com.example.demo.myenum.Sex.男]

** 说明：默认的枚举转换器根据字面量进行转换，使用属性转换会报错**

### \*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\* ###

**自定义枚举转换器测试**

**localhost:8080/hello?sex=女**

2020-07-11 10:00:03.110  INFO 13032 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : Initializing Servlet 'dispatcherServlet'
    2020-07-11 10:00:03.119  INFO 13032 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : Completed initialization in 9 ms
    Sex{id=2, name='女'}

**localhost:8080/hello2?name=瓜田李下&age=20&sex=女**

Person(name=瓜田李下, age=20, sex=Sex{id=2, name='女'})

**说明：自定义枚举转换器生效，可根据枚举属性进行转换**