期望一个对象数组但在对象中得到一个对象 [英] Expected an array of objects but got an object in an object

问题描述

在我正在处理的项目中，我遇到了一个角度异常：错误：[$ resource：badcfg]资源配置出错。预期的响应包含一个数组但得到一个对象？

In a project I'm currently working on I got an angular exception: Error: [$resource:badcfg] Error in resource configuration. Expected response to contain an array but got an object?

在我寻找解决方案的搜索中，我直接输入了Web服务的URL我的浏览器，令人惊讶的是我没有按预期收到数组。

In my search to find a solution I entered the URL of the web service directly into my browser and surprisingly I did not receive an array as expected.

网络服务类：

@Path("/menu")
public class MenuHandler {
    @GET
    @Path("/cls")
    @Produces(MediaType.APPLICATION_JSON)
    public List<Clazz> getCLSs()    {
        Clazz clazz = new Clazz();
        Clazz.setFoo("foo");
        Clazz.setBar("bar");

        ArrayList<Clazz> clazzes = new ArrayList<>();
        clazzes.add(clazz);

        return clazzes;
    }
}

当我输入网址 http：// localhost：8080 / myProject / rest / menu / cls 我希望看到一个带有JSON对象的JSON数组：

When I enter the url http://localhost:8080/myProject/rest/menu/cls I would expect to see a JSON array with JSON objects:

[ {"foo": "foo", "bar": "bar"} ]

但是，我收到一个JSON对象，其中包含我期望的JSON对象属性而没有任何数组：

but instead, I receive an JSON object with a property the JSON object I was expecting without any array:

{
  "clazz": {
    "foo": "foo",
    "bar": "bar"
  }
}

所以我想知道为什么没有数组，当我添加另一个Clazz对象时会发生什么。在这种情况下，我仍然得到一个JSON对象，但这次参数之一是我希望从一开始就拥有的JSON数组。

So I wondered why there was no array and what would happen when I add another Clazz object. In that case I still get a JSON object but this time one of the parameters is the JSON array that I would expect to have from the start.

{
  "clazz": [
    {
      "foo": "foo",
      "bar": "bar"
    },
    {
      "foo": "foo2",
      "bar": "bar2"
    }
  ]
}

有人可以解释一下为什么会出现这种情况以及我的想法出错吗？

Can somebody explain me why this behavior is happening and where my thinking went wrong?

推荐答案

所以我发现了这个问题。我能够重现它。您似乎忘了启用POJOMappingFeature

So I spotted the problem. I was able to reproduce it. It seems you just forgot the enable the POJOMappingFeature

<init-param>
    <param-name>com.sun.jersey.api.json.POJOMappingFeature</param-name>
    <param-value>true</param-value>
</init-param>

这使用Jackson来反序列化/序列化。如果未设置，则使用Jersey的内部JSON提供程序进行反序列化/序列化。我不确定如何配置默认提供商，但我认为最好还是跟杰克逊一起去。

This uses Jackson to deserialize/serialize. If this is not set, it uses Jersey's internal JSON provider(s) to deserialize/serialize. I am not sure sure how to configure the default providers, but I think it's safer to just go with Jackson anyway.

另外，在我上面的评论中，我说要测试杰克逊是否被使用。一种轻松完成此任务的方法是只创建一个 ContextResolver 和一个s.o.p.在 getContext 方法中。需要映射器时调用此方法。因此，如果使用Jackson，则应打印s.o.p

Aside, in my comments above I was saying to test if Jackson is being used. One way to easily accomplish this is to just create a ContextResolver and and a s.o.p. inside the getContext method. This method is called when the mapper is needed. So if Jackson is being used, the s.o.p should print

@Provider
public class ObjectMapperContextResolver implements ContextResolver<ObjectMapper> {

    private final ObjectMapper defaultMapper;

    public ObjectMapperContextResolver() {
        defaultMapper = new ObjectMapper();
    }

    @Override
    public ObjectMapper getContext(Class<?> type) {
        System.out.println("--- getContext ---");
        return defaultMapper;
    }  
}

请注意，这也是一种进行任何配置的方法使用Jackson serization / deserialization（只需配置映射器）。

Note that this is also a way to make any configurations with the Jackson serization/deserialization (just configure the mapper).

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