如何使用ObjectMapper Jackson反序列化泛型类型(How to deserialize a generic type with ObjectMapper Jackson)

 我正在努力尝试简化我的代码。 我有一个常见的操作，它向API发出请求并获取JSON对象。 这个json可以是Categories ， Products等。我使用的是jackson ObjectMapper 。 
 
 目前我有一个方法用于每个请求，但我想在一个方法中简化它。 例如。 
 
myMethod(String Path, Here The class Type)
 
 其中一种常见方法是： 
 
public List<Category> showCategories() {

    HttpClient client = HttpClientBuilder.create().build();
    HttpGet getRequest = new HttpGet(Constants.GET_CATEGORY);
    getRequest.setHeader(HttpHeaders.ACCEPT, MediaType.APPLICATION_JSON);
    getRequest.setHeader(HttpHeaders.COOKIE, Login.getInstance().getToken());

    List<Category> data = null;

    HttpResponse response;
    try {
        response = client.execute(getRequest);
        data = Constants.JSON_MAPPER.readValue(response.getEntity().getContent(), new TypeReference<List<Category>>() {
        });
    } catch (IOException ex) {
        LOGGER.error("Error retrieving categories, " + ex.toString());
    }
    // TODO: Replace List<category> with Observable?
    return data;
}
 
 在所有方法中改变的一件事是要检索的对象的类型。 
 
 可以概括该线 
 
Constants.JSON_MAPPER.readValue(response.getEntity().getContent(), new TypeReference<List<Category>>() {
        });
 
 成为 
 
Constants.JSON_MAPPER.readValue(response.getEntity().getContent(), new TypeReference<List<T>>() {
        });
 
 我试图添加为方法Class<T> class ，如此处所示，但我得到错误Cannot find symbol T 

I am struggling trying to simplify my code. I have a common oppperation that makes a request to an API and gets a JSON object. This json can be Categories, Products etc. I am using jackson ObjectMapper.
 
Currently I have a method for each request, but I want to simplify it in one method. For example.
 
myMethod(String Path, Here The class Type)
 
One of this common methods is:
 
public List<Category> showCategories() {

    HttpClient client = HttpClientBuilder.create().build();
    HttpGet getRequest = new HttpGet(Constants.GET_CATEGORY);
    getRequest.setHeader(HttpHeaders.ACCEPT, MediaType.APPLICATION_JSON);
    getRequest.setHeader(HttpHeaders.COOKIE, Login.getInstance().getToken());

    List<Category> data = null;

    HttpResponse response;
    try {
        response = client.execute(getRequest);
        data = Constants.JSON_MAPPER.readValue(response.getEntity().getContent(), new TypeReference<List<Category>>() {
        });
    } catch (IOException ex) {
        LOGGER.error("Error retrieving categories, " + ex.toString());
    }
    // TODO: Replace List<category> with Observable?
    return data;
}
 
The one thing that changes across all methods is the type of object to retrieve.
 
It is possible to generalize the line
 
Constants.JSON_MAPPER.readValue(response.getEntity().getContent(), new TypeReference<List<Category>>() {
        });
 
To be
 
Constants.JSON_MAPPER.readValue(response.getEntity().getContent(), new TypeReference<List<T>>() {
        });
 
I've tried to add as a param to the method Class<T> class, as shown here, but I get the error Cannot find symbol T

原文：https://stackoverflow.com/questions/28895088