spring之类型转换

spring之类型转换

  • PropertyEditor
    • 普通用法
    • spring中用法
  • ConditionalGenericConverter
    • 普通用法
    • spring中用法
  • TypeConverter
    • 用法

在spting中,会遇到很多将String类型转换为其他类型的场景。Spring源码中提供了一些技术来更方便的做对象的类型转化。

PropertyEditor

在JDK中,给我们提供了PropertyEditor用来将String转换为指定类型。

普通用法

User :

import lombok.Data;

@Data
public class User {
    public User() {
        System.out.println("无参构造");
    }
    private String name;
}

StringToUserPropertyEditor :

import java.beans.PropertyEditor;
import java.beans.PropertyEditorSupport;

public class StringToUserPropertyEditor extends PropertyEditorSupport implements PropertyEditor {
    @Override
    public void setAsText(String text) throws IllegalArgumentException {
        User user = new User();
        user.setName(text);
        this.setValue(user);
    }
}

Main:

    public static void main(String[] args) {
        StringToUserPropertyEditor propertyEditor = new StringToUserPropertyEditor();
        propertyEditor.setAsText("1");
        User value = (User) propertyEditor.getValue();
        System.out.println(value);
    }

spring中用法

import org.springframework.beans.factory.config.CustomEditorConfigurer;
import org.springframework.context.annotation.Bean;
import top.mingempty.spring.service.StringToUserPropertyEditor;
import top.mingempty.spring.service.User;

import java.beans.PropertyEditor;
import java.util.HashMap;
import java.util.Map;

public class AppConfig {

    @Bean
    public CustomEditorConfigurer customEditorConfigurer() {
        CustomEditorConfigurer customEditorConfigurer = new CustomEditorConfigurer();
        Map<Class<?>, Class<? extends PropertyEditor>> propertyEditorMap = new HashMap<>();

        // 表示StringToUserPropertyEditor可以将String转化成User类型,在Spring源码中,如果发现当前对象是String,而需要的类型是User,就会使用该PropertyEditor来做类型转化
        propertyEditorMap.put(User.class, StringToUserPropertyEditor.class);
        customEditorConfigurer.setCustomEditors(propertyEditorMap);
        return customEditorConfigurer;
    }

}

UserService:

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

@Component
public class UserService {


    @Value("demo")
    private User user;

    public void test() {
        System.out.println("demo");
        System.out.println(user);
    }
}

Main:

    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);
        ClassPathBeanDefinitionScanner scanner = new ClassPathBeanDefinitionScanner(context);
        scanner.scan("com.ming.spring");
        context.getBean("userService", UserService.class).test();
    }

ConditionalGenericConverter

在spring中,也给我们提供了一个类型转化服务,它比PropertyEditor更强大。

普通用法

StringToUserConverter :

import org.springframework.core.convert.TypeDescriptor;
import org.springframework.core.convert.converter.ConditionalGenericConverter;

import java.util.Collections;
import java.util.Set;

public class StringToUserConverter implements ConditionalGenericConverter {


    /**
     * 判断是否要使用该类型转换器
     *
     * @param sourceType 原始类型
     * @param targetType 目标类型
     * @return
     */
    @Override
    public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType) {
        return sourceType.getType().equals(String.class) && targetType.getType().equals(User.class);
    }

    /**
     * 此转换器可以转换的目标类型和原始类型的集合
     *
     * @return
     */
    @Override
    public Set<ConvertiblePair> getConvertibleTypes() {
        return Collections.singleton(new ConvertiblePair(String.class, User.class));
    }

    /**
     * 转换方法
     *
     * @param source     要被转换的数据
     * @param sourceType 原始类型
     * @param targetType 目标类型
     * @return
     */
    @Override
    public Object convert(Object source, TypeDescriptor sourceType, TypeDescriptor targetType) {
        User user = new User();
        user.setName((String) source);
        return user;
    }
}

Main:

    public static void main(String[] args) {
        DefaultConversionService conversionService = new DefaultConversionService();
        conversionService.addConverter(new StringToUserConverter());
        User value = conversionService.convert("1", User.class);
        System.out.println(value);

    }

spring中用法

import org.springframework.context.annotation.Bean;
import org.springframework.context.support.ConversionServiceFactoryBean;
import top.mingempty.spring.service.StringToUserConverter;

import java.util.Collections;

public class AppConfig {

    @Bean
    public ConversionServiceFactoryBean conversionService() {
        ConversionServiceFactoryBean conversionServiceFactoryBean = new ConversionServiceFactoryBean();
        conversionServiceFactoryBean.setConverters(Collections.singleton(new StringToUserConverter()));

        return conversionServiceFactoryBean;
    }

}

UserService:

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

@Component
public class UserService {


    @Value("demo")
    private User user;

    public void test() {
        System.out.println("demo");
        System.out.println(user);
    }
}

Main:

    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);
        ClassPathBeanDefinitionScanner scanner = new ClassPathBeanDefinitionScanner(context);
        scanner.scan("com.ming.spring");
        context.getBean("userService", UserService.class).test();
    }

TypeConverter

整合了PropertyEditor和ConversionService的功能,是Spring内部用的。

用法

    public static void main(String[] args) {

        SimpleTypeConverter typeConverter = new SimpleTypeConverter();
        typeConverter.registerCustomEditor(User.class, new StringToUserPropertyEditor());

        DefaultConversionService conversionService = new DefaultConversionService();
        conversionService.addConverter(new StringToUserConverter());
        typeConverter.setConversionService(conversionService);

        User value = typeConverter.convertIfNecessary("1000", User.class);
        System.out.println(value);

    }

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