Error on converting json to list of strings java play framework

Question

I am trying to convert a json file to a list of strings, but it is throwing expected -> error

I've already tried TypeReference<List<String>> List<String> but it throws a different error each time. Look at line 28 for the error location.

Error Message:

[error] /home/willroy/Code/playframework/database/app/controllers/HomeController.java:28:1: -> expected [error] return mapper.readValue(new File("/tmp/notes.json"), List(){}); [error] (Compile / compileIncremental) javac returned non-zero exit code [error] Total time: 0 s, completed 12-Jun-2019 11:05:01

public class HomeController extends Controller {
  public Result get() {
    return ok("")
    WS.url("localhost:9000")
      .seteContentType("/")
      .post(getJson());
  } 

  public Result post(String text) { 
    List<String> noteJson = getJson();
    noteJson.append(text);
    return ok("");  
  }

  private List<String> getJson() {
    ObjectMapper mapper = new ObjectMapper();
    return mapper.readValue(new File("/tmp/notes.json"), List<String>(){});
  }    

  private void saveJson(List<String> noteJson) {
    FileWriter file = new FileWriter("/tmp/notes.json");
    file.write(notJson.toJSONString());
  } 

}

SOLVED:

Did not import enough at the top of the file (File, List, etc...) XD.

Answer 1

您必须在第二个参数中指定Class，

return mapper.readValue(new File("/tmp/notes.json"), new TypeReference<List<String>>(){});

Answer 2

Just change your code by using this example below :

private List<String> getJson() {
    List<String> texts = new ArrayList<String>();
    ObjectMapper mapper = new ObjectMapper();
    final JsonNode nodes = objectMapper.readTree(new File("/tmp/notes.json")).get("list");
    if (nodes.isArray()) {
        for (final JsonNode node : nodes) {
            texts.add(node.get("property").asText());
        }
    }
    return texts;
}