问题描述
我收到来自 URL 的响应，如下所示:
I have a response from URL which looks like:
{"seq":1,"id":"Test1","changes":[{"rev":"1-52f5cdf008ecfbadf621c2939af7bd80"}]}
{"seq":2,"id":"Test2","changes":[{"rev":"1-8ce403a89dc5e7cb4187a16941b3fb7d"}]}
{"seq":3,"id":"Test3","changes":[{"rev":"1-52as7ddfd8ecfbadf621c2939af7bd80"}]}
{"seq":4,"id":"Test4","changes":[{"rev":"1-6yy03a89dc5e7cb45677a16941b3fb7d"}]}
如果映射对象是字符串，则获取所有更改提要.
If the mapped object is String, then getting all the changes feed.
ResponseEntity<String> responseEntity = restTemplate.exchange(URL, HttpMethod.GET, requestEntity, String.class);
然而，如果我碰巧使用自定义 Value 对象，例如:
Whereas, if I happen to use a custom Value object, somethings like:
public class KnChanges {
private long seq;
private String id;
private List changes;
使用 getter 和 setter 方法，那么我只能获得第一个文档更改详细信息.即使使用了 KnChanges[](数组)，也只能得到第一个变化.
with getter and setter methods, then I'm getting only the first doc change details. Even if the KnChanges[] (array) is used, only the first change is obtained.
你能帮忙看看上面提到的 JSON 列表结构如何映射到一个对象吗?
Can you please help as to how the JSON list structure mentioned above can be mapped to an object?
谢谢哈莎
推荐答案
有些人要求得到更好的答案并进行一些解释.所以这里是:
Some people asked for a better answer with some explaination. So here it is:
正如sujim 提到的:你需要
ParameterizedTypeReference<List<KnChanges>> responseType = new ParameterizedTypeReference<List<KnChanges>>() {};
ResponseEntity<List<KnChanges>> resp = restTemplate.exchange(URL, HttpMethod.GET, requestEntity, responseType);
List<KnChanges> list = resp.getBody();
说明:
exchange 方法调用的最后一个参数定义了在收到响应时实例化的类.然后将响应数据映射到结果对象.所以你首先需要一个 List.class .因为您需要一个 JSON 数组.现在您需要定义该List 的内容类型.这里Java 的类型擦除会给您带来一些障碍.由于 Java 在编译时删除了泛型类型信息，因此您不能仅将预期的 List 定义为 List.class.幸运的是"有一个 hack ;) 而那个 hack 是 new ParameterizedTypeReference.如果该对象应用程序能够在运行时读取泛型类型信息.因此能够将接收到的数据映射到您的 Java 对象.() {}
The last parameter of the exchange method call defines the class that gets instantiated when the response is received. The response data will then be mapped to the resulting object. So you need a List.class in fist place. Because you expect a JSON array. Now you need to define the type of the content of that List. Here Java's type erasure throws some stones in your way. As Java removes generic type information at compile-time, you can't just define the expected List to be a List<KnChanges>.class. "Luckily" there is a hack ;) And that hack is new ParameterizedTypeReference<List<KnChanges>>() {}. Provided that object the application is able to read the generic type information at runtime. And therefore is able to map the received data to your Java objects.
附带说明:该 hack 有多种实现方式.它通常用于依赖注入或映射器系统，其中类型擦除有时可能是一个问题.Googles Guava 也提供了一个实现.查看代码想要查询更多的信息.如果您愿意，您还可以在那里了解它是如何完成的.
As a side-note: There a several implementations of that hack. It's commonly used for dependency injection or mapper systems, where type erasure can sometimes be an issue. Also Googles Guava offers an implementation. See the code for more information. There you can also learn how it's done, if you like.
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