为什么Jersey / JAX-RS客户端无法处理泛型？ [英] Why is Jersey/JAX-RS client unable to handle generics?

问题描述

我有一个Jersery / JAX-RS客户端，它打击了一个RESTful API（JSON），它应该返回一个我的POJO列表：

I have a Jersery/JAX-RS client that hits a RESTful API (JSON) that is supposed to return a list of my POJOs:

// Hits: GET localhost:8080/myapp/fizz/widget/{widget_id}
@Override
public List<Widget> getWidgetsByUser(Long id) {
    return webResource.path("fizz").path("widget").path(id.toString()).get(List.class);
}

另外还有一个驱动程序用以测试客户端：

And a driver to test the client with:

public class Driver {
    public static void main(String[] args) {
        Driver d = new Driver();
        d.run();
    }

    public void run() {
        MyAppService myService = getSomehow();

        List<Widget> widgets = myService.getWidgetResource().getWidgetsByUser(2L);
        for(Widget widget : widgets) {
            System.out.println("\t...and it found Widget #" + widget.getCaseId());
        }
    }
}

当我运行这个时，我get：

When I run this, I get:

Exception in thread "main" java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to com.me.myapp.Widget
    <stack trace omitted for brevity>

从for循环抛出异常：

The exception is being thrown from the for-loop:

for(Widget widget : widgets) {

这告诉我客户端有点工作，但我没有正确配置它。

Which tells me the client is sort of working, but that I don't have it configured correctly.

所以Jersey要么尝试返回纯JSON，要么不是试图将其映射回Widgets列表，或者我错误地调用了 get（Class<>）方法。任何想法？

So either Jersey is trying to return pure JSON and isn't attempting to map it back to a list of Widgets, or I am invoking the get(Class<?>) method incorrectly. Any ideas?

推荐答案

Pavel Horal的评论是正确的。如果没有已知的类型，Jackson（底层的deserilaizer）将映射到 LinkedHashMap ，所以它会返回 List< LinkedHashMap>

The comment by Pavel Horal is correct. Without a known type, Jackson (the underlying deserilaizer) will map to LinkedHashMap, so it will return List<LinkedHashMap>

修正：

对于泛型类型，我们应该使用其他的 get（）方法，它需要一个 GenericType 参数。所以我们应该做一些像

For generic types, we should use the other get() method, which takes a GenericType argument. So we should do something like

...get(new GenericType<List<Widget>>(){});

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