[英]Using Jackson ObjectMapper with Generics to POJO instead of LinkedHashMap
[英]Jackson ObjectMapper in Static Method with Generics
我有一個 static 方法,旨在讀取 JSON 並使用 ObjectMapper 解析為 Class(在運行時指定)。 我想返回一個“N”類型的 Object,但在使用 Generics 時出現錯誤。
我怎樣才能讓下面的代碼完成這個?
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();
}
}
Java Generics 是使用“類型擦除”實現的。 這意味着編譯器可以檢查類型安全並在運行時刪除類型。
所以你不能像那樣使用你的類型變量(“N”)。 您必須將實際的 class 作為參數傳遞:
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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