Spring/json:转换类型化集合，如 List<MyPojo> [英] Spring/json: Convert a typed collection like List&lt;MyPojo&gt;

问题描述

我正在尝试通过 Spring Rest 模板编组一个列表:List 对象.

I'm trying to marshal a list: List<Pojo> objects via the Spring Rest Template.

我可以传递简单的 Pojo 对象，但我找不到任何描述如何发送 List 对象的文档.

I can pass along simple Pojo objects, but I can't find any documentation that describes how to send a List<Pojo> objects.

Spring 使用 Jackson JSON 来实现 HttpMessageConverter.杰克逊文档涵盖了这一点:

Spring is using Jackson JSON to implement the HttpMessageConverter. The jackson documentation covers this:

除了绑定到 POJO 和简单"类型，有一种附加变体:绑定到通用(类型化)容器.这个案例由于需要特殊处理所谓的类型擦除(Java 使用在某种程度上实现泛型向后兼容的方式)，其中阻止你使用类似的东西Collection.class(不编译).

In addition to binding to POJOs and "simple" types, there is one additional variant: that of binding to generic (typed) containers. This case requires special handling due to so-called Type Erasure (used by Java to implement generics in somewhat backwards compatible way), which prevents you from using something like Collection<String>.class (which does not compile).

所以如果你想把数据绑定到一个Map 你需要使用:

So if you want to bind data into a Map<String,User> you will need to use:

Mapresult = mapper.readValue(src, new TypeReference>() {});

其中 TypeReference 只需要传递泛型类型定义(通过在这种情况下是任意内部类):重要的部分是> 定义类型绑定到.

where TypeReference is only needed to pass generic type definition (via anynomous inner class in this case): the important part is <Map<String,User>> which defines type to bind to.

这可以在 Spring 模板中完成吗?我看了一眼代码，这让我不以为然，但也许我只是不知道一些技巧.

Can this be accomplished in the Spring template? I took a glance at the code and it makes me thing not, but maybe I just don't know some trick.

解决方案

最终的解决方案，感谢以下有用的答案，不是发送列表，而是发送一个简单扩展列表的对象，例如:class PojoList extends ArrayList.Spring 可以成功地封送这个对象，它完成与发送 List 相同的事情，尽管它的解决方案不那么干净.我还在春季发布了一个 JIRA，让他们在 HttpMessageConverter 接口中解决这个缺点.

The ultimate solution, thanks to the helpful answers below, was to not send a List, but rather send a single object which simply extends a List, such as: class PojoList extends ArrayList<Pojo>. Spring can successfully marshal this Object, and it accomplishes the same thing as sending a List<Pojo>, though it be a little less clean of a solution. I also posted a JIRA in spring for them to address this shortcoming in their HttpMessageConverter interface.

推荐答案

如果我阅读了 docs for MappingJacksonHttpMessageConverter 对，您必须创建并注册 MappingJacksonHttpMessageConverter 的子类code> 并覆盖 getJavaType(Class) 方法:

If I read the docs for MappingJacksonHttpMessageConverter right, you will have to create and register a subclass of MappingJacksonHttpMessageConverter and override the getJavaType(Class<?>) method:

返回 Jackson JavaType具体类.默认实现回报TypeFactory.type(java.lang.reflect.Type),但这可以在子类，允许自定义通用集合处理.为了实例:

Returns the Jackson JavaType for the specific class. Default implementation returns TypeFactory.type(java.lang.reflect.Type), but this can be overridden in subclasses, to allow for custom generic collection handling. For instance:

protected JavaType getJavaType(Class<?> clazz) {
   if (List.class.isAssignableFrom(clazz)) {
     return TypeFactory.collectionType(ArrayList.class, MyBean.class);
   } else {
     return super.getJavaType(clazz);
   }
}

这篇关于Spring/json:转换类型化集合，如 List<MyPojo>的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！