Spring MVC 类型转换:PropertyEditor 还是 Converter? [英] Spring MVC type conversion : PropertyEditor or Converter?

问题描述

我正在寻找在 Spring MVC 中绑定和转换数据的最简单和最简单的方法.如果可能，不做任何 xml 配置.

I am looking for the easiest and simplest way to bind and convert data in Spring MVC. If possible, without doing any xml configuration.

到目前为止我一直在使用 PropertyEditors 像这样:

So far I've been using PropertyEditors like so :

public class CategoryEditor extends PropertyEditorSupport {

    // Converts a String to a Category (when submitting form)
    @Override
    public void setAsText(String text) {
        Category c = new Category(text);
        this.setValue(c);
    }

    // Converts a Category to a String (when displaying form)
    @Override
    public String getAsText() {
        Category c = (Category) this.getValue();
        return c.getName();
    }

}

和

...
public class MyController {

    @InitBinder
    public void initBinder(WebDataBinder binder) {
        binder.registerCustomEditor(Category.class, new CategoryEditor());
    }

    ...

}

很简单:两个转换都定义在同一个类中，绑定很简单.如果我想对所有控制器进行通用绑定，我仍然可以添加 我的 xml 配置中的 3 行.

It is simple : both conversion are defined in the same class, and the binding is straightforward. If I wanted to do a general binding across all my controllers, I could still add 3 lines in my xml config.

但是 Spring 3.x 引入了一种新方法，使用 转换器 :

But Spring 3.x introduced a new way to do it, using Converters :

在一个 Spring 容器中，这个系统可以作为一个替代方案给属性编辑器

Within a Spring container, this system can be used as an alternative to PropertyEditors

所以假设我想使用转换器，因为它是最新的替代方案".我必须创建两个转换器:

So let's say I want to use Converters because it is "the latest alternative". I would have to create two converters :

public class StringToCategory implements Converter<String, Category> {

    @Override
    public Category convert(String source) {
        Category c = new Category(source);
        return c;
    }

}

public class CategoryToString implements Converter<Category, String> {

    @Override
    public String convert(Category source) {
        return source.getName();
    }

}

第一个缺点:我必须创建两个类.好处:由于通用性，无需强制转换.

First drawback : I have to make two classes. Benefit : no need to cast thanks to genericity.

那么，我如何简单地对转换器进行数据绑定?

Then, how do I simply data bind the converters ?

第二个缺点:我还没有找到任何简单的方法(注释或其他编程工具)在控制器中做到这一点:没有像 someSpringObject.registerCustomConverter(...);.

Second drawback : I haven't found any simple way (annotations or other programmatic facilities) to do it in a controller : nothing like someSpringObject.registerCustomConverter(...);.

我发现的唯一方法是乏味的，不简单的，而且只是关于通用的跨控制器绑定:

The only ways I've found would be tedious, not simple, and only about general cross-controller binding :

• XML 配置 :

<bean id="conversionService"
  class="org.springframework.context.support.ConversionServiceFactoryBean">
    <property name="converters">
        <set>
            <bean class="somepackage.StringToCategory"/>
            <bean class="somepackage.CategoryToString"/>
        </set>
    </property>
</bean>

Java 配置(仅在 Spring 3.1+ 中):

@EnableWebMvc
@Configuration
public class WebConfig extends WebMvcConfigurerAdapter {

    @Override
    protected void addFormatters(FormatterRegistry registry) {
        registry.addConverter(new StringToCategory());
        registry.addConverter(new CategoryToString());
    }

}

有所有这些缺点，为什么要使用转换器?我错过了什么吗?还有其他我不知道的技巧吗?

With all these drawbacks, why using Converters ? Am I missing something ? Are there other tricks that I am not aware of ?

我很想继续使用 PropertyEditors...绑定更容易、更快捷.

I am tempted to go on using PropertyEditors... Binding is much easier and quicker.

推荐答案

有所有这些缺点，为什么要使用转换器?我失踪了吗某物 ?还有其他我不知道的技巧吗?

With all these drawbacks, why using Converters ? Am I missing something ? Are there other tricks that I am not aware of ?

不，我认为您已经非常全面地描述了 PropertyEditor 和 Converter，它们是如何声明和注册的.

No, I think you have very comprehensively described both PropertyEditor and Converter, how each one is declared and registered.

在我看来，PropertyEditor 的范围是有限的——它们帮助将 String 转换为类型，并且这个字符串通常来自 UI，因此使用 @InitBinder 和使用 WebDataBinder 注册一个 PropertyEditor 是有意义的.

In my mind, PropertyEditors are limited in scope - they help convert String to a type, and this string typically comes from UI, and so registering a PropertyEditor using @InitBinder and using WebDataBinder makes sense.

另一方面，Converter 更通用，它用于系统中的任何转换——不仅仅是 UI 相关的转换(字符串到目标类型).例如，Spring Integration 广泛使用转换器将消息有效负载转换为所需类型.

Converter on the other hand is more generic, it is intended for ANY conversion in the system - not just for UI related conversions(String to target type). For eg, Spring Integration uses a converter extensively for converting a message payload to a desired type.

我认为对于 UI 相关的流程，PropertyEditor 仍然适用，尤其是在您需要为特定命令属性做一些自定义的情况下.对于其他情况，我会接受 Spring 参考中的建议并编写一个转换器(例如，将 Long id 转换为实体，例如作为示例).

I think for UI related flows PropertyEditors are still appropriate especially for the case where you need to do something custom for a specific command property. For other cases, I would take the recommendation from Spring reference and write a converter instead(for eg, to convert from a Long id to an entity say, as a sample).

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