spring mvc 空字符转换为null

最新推荐文章于 2023-10-09 02:52:27 发布

Willy__QI

最新推荐文章于 2023-10-09 02:52:27 发布

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分类专栏： Java

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DataBinder

继承自ExtendedServletRequestDataBinder，主要用来自定义数据绑定处理

public class EmptyStringToNullRequestDataBinder extends ExtendedServletRequestDataBinder {
    
    public EmptyStringToNullRequestDataBinder(Object target, String objectName) {
        super(target, objectName);
    }

    protected void addBindValues(MutablePropertyValues mpvs, ServletRequest request) {
        super.addBindValues(mpvs, request);
        for (PropertyValue propertyValue : mpvs.getPropertyValueList()) {
                //转换处理
                if (propertyValue.getValue().equals(""))
                propertyValue.setConvertedValue(null);
        }
    }
}

参数处理器

我们需要写一个自定义的请求参数处理器，然后把这个处理器放到HandlerAdapter中，这样我们的处理器就可以被拿来处理请求了。

public class EmptyStringToNullModelAttributeMethodProcessor extends ServletModelAttributeMethodProcessor implements ApplicationContextAware {

    ApplicationContext applicationContext;

    public EmptyStringToNullModelAttributeMethodProcessor(boolean annotationNotRequired) {
        super(annotationNotRequired);
    }

    @Override
    protected void bindRequestParameters(WebDataBinder binder, NativeWebRequest request) {
        EmptyStringToNullRequestDataBinder toNullRequestDataBinderBinder = new EmptyStringToNullRequestDataBinder(binder.getTarget(), binder.getObjectName());
        RequestMappingHandlerAdapter requestMappingHandlerAdapter = applicationContext.getBean(RequestMappingHandlerAdapter.class);
        requestMappingHandlerAdapter.getWebBindingInitializer().initBinder(toNullRequestDataBinderBinder, request);
        toNullRequestDataBinderBinder.bind(request.getNativeRequest(ServletRequest.class));
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.applicationContext = applicationContext;
    }
}

注册器

SpringMVC有自带的处理器。SpringMVC处理请求参数是轮询每一个处理器，看是否支持，也就是supportsParameter方法，如果返回true，就交给对应的处理器处理，并不会问下面的处理器。这就导致了如果我们简单的把我们的自定义处理器加到HandlerAdapter的Resolver列中是不行的，需要加到第一个去。

public class EmptyStringToNullProcessorRegistry implements ApplicationContextAware, BeanFactoryPostProcessor {

    private ApplicationContext applicationContext;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.applicationContext = applicationContext;
    }

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {

        RequestMappingHandlerAdapter requestMappingHandlerAdapter = applicationContext.getBean(RequestMappingHandlerAdapter.class);

        List<HandlerMethodArgumentResolver> resolvers = requestMappingHandlerAdapter.getArgumentResolvers();


        List<HandlerMethodArgumentResolver> newResolvers = new ArrayList<HandlerMethodArgumentResolver>();

        for (HandlerMethodArgumentResolver resolver : resolvers) {
            newResolvers.add(resolver);
        }
        EmptyStringToNullModelAttributeMethodProcessor processor = new EmptyStringToNullModelAttributeMethodProcessor(true);
        processor.setApplicationContext(applicationContext);
        newResolvers.add(0, processor);
        requestMappingHandlerAdapter.setArgumentResolvers(Collections.unmodifiableList(newResolvers));
    }
}

XML配置

    <mvc:annotation-driven>
        <mvc:argument-resolvers>
            <bean class="studio.geek.databind.EmptyStringToNullModelAttributeMethodProcessor">
                <constructor-arg name="annotationNotRequired" value="true"/>
            </bean>
        </mvc:argument-resolvers>
    </mvc:annotation-driven>

参考文档：

https://blog.youkuaiyun.com/zgzczzw/article/details/53912966