泛型静态方法中的Jackson ObjectMapper [英] Jackson ObjectMapper in Static Method with Generics
问题描述
我有一个静态方法,该方法旨在使用ObjectMapper读取JSON并解析为Class(在运行时指定).我想返回一个'N'类型的对象,但是我在使用泛型时遇到了一个错误.
I have a static method that is intended to read JSON and Parse to a Class (specified at runtime) with ObjectMapper. I would like to return an Object of the 'N' type, but I'm getting an error about using Generics.
如何使以下代码完成此任务?
How can I make the following code accomplish this?
public static <N, T extends AbstractRESTApplication> N GET_PAYLOAD( T app, String urlString, REQUEST_TYPE requestType) throws JsonProcessingException, MalformedURLException, IOException, NoSuchAlgorithmException, KeyManagementException {
HttpsURLConnection con = null;
try {
RSSFeedParser.disableCertificateValidation();
URL url = new URL(urlString);
con = (HttpsURLConnection) url.openConnection();
String encoding = Base64.getEncoder().encodeToString((app.getUser() + ":" + app.getPassword()).getBytes("UTF-8"));
con.setRequestProperty("Authorization", String.format("Basic %s", encoding));
//con.setDoOutput(true);//only used for writing to.
con.setDoInput(true);
con.setRequestProperty("Content-Type", "application/json; charset=UTF-8");
con.setRequestMethod(requestType.toString());
con.setRequestProperty("User-Agent", "Java client");
DataOutputStream wr = new DataOutputStream(con.getOutputStream());
// wr.write(val);
StringBuilder content;
try (BufferedReader in = new BufferedReader(
new InputStreamReader(con.getInputStream()))) {
String line;
content = new StringBuilder();
while ((line = in.readLine()) != null) {
content.append(line);
content.append(System.lineSeparator());
}
System.out.println(Class.class.getName() + ".GET_PAYLOAD= " + content);
//Map Content to Class.
ObjectMapper om = new ObjectMapper();
return om.readValue(content.toString(),N);//Doesn't Like N type. How do i fix?
}
} finally {
con.disconnect();
}
}
推荐答案
Java泛型使用类型擦除"实现.这意味着编译器可以检查类型安全性,并在运行时将其删除.
Java Generics are implemented using "type erasure". That means the compiler can check the type safety and the types get removed at run time.
因此,您不能像这样使用类型变量("N").您必须将实际的类作为参数传递:
So you can't use your type variables ("N") like that. You have to pass the actual class as an argument:
public static <N, T extends AbstractRESTApplication> N GET_PAYLOAD( T app,
String urlString, REQUEST_TYPE requestType,
Class<N> nClass) throws ... {
return om.readValue(content.toString(), nClass);
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