将JSON数据映射到Java对象

Question

我一直在尝试使用PC上的JSON文件将JSON数据映射到Java对象，但是它总是抛出异常：

org.codehaus.jackson.map.exc.UnrecognizedPropertyException: Unrecognized field "title" (Class MovieResponse), not marked as ignorable at [Source: C:\M.json; line: 2, column: 13] (through reference chain: MovieResponse["title"])

我的数据类：

import org.codehaus.jackson.annotate.JsonProperty;

public class MovieResponse{
  private String title;
  private Integer year;
  @JsonProperty("mpaa_rating")
  private String mpaaRating;
  private Integer runtime;
  @JsonProperty("critics_consensus")
  private String criticsConsensus;

  public String getTitle(){
    return title;
  }
  public String setTitle(String t){
    return title = t;
  }

  public Integer getYear(){
    return year;
  }
  public Integer setYear(Integer y){
    return year = y;
  }

  public String getMpaa(){
    return mpaaRating;
  }
  public String setMpaa(String mp){
    return mpaaRating = mp;
  }

  public Integer getRuntime(){
    return runtime;
  }
  public Integer setRuntime(Integer r){
    return runtime = r;
  }

  public String getCritics(){
    return criticsConsensus;
  }
  public String setCritics(String c){
    return criticsConsensus = c;
  }

  @Override
  public String toString(){
    return "MovieResponse[title="+title+",year="+year+",mpaa_Rating="+mpaaRating+",runtime="+runtime+",critics_Consensus="+criticsConsensus
            +"]";
  }
}

我的映射器类：

import java.io.File;
import java.io.IOException;
import org.codehaus.jackson.JsonGenerationException;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;
import java.net.*;
import org.codehaus.jackson.annotate.JsonIgnoreProperties;
@JsonIgnoreProperties
public class Movie{
 public static void main(String[] args) throws MalformedURLException, URISyntaxException, IOException {
 MovieResponse a = new MovieResponse();
 ObjectMapper mapper = new ObjectMapper();
 try{

     MovieResponse response = new ObjectMapper().readValue(new File("C:\\M.json"), MovieResponse.class);
 }catch(MalformedURLException u){
    u.printStackTrace();
 }
 catch(IOException i){
    i.printStackTrace();
 }
 }

json文件包含以下数据：

{
  "title": "Toy Story 3",
  "year": 2010,
  "mpaa_rating": "G",
  "runtime": 103,
  "critics_consensus": "Deftly blending comedy, adventure, and honest emotion, Toy Story 3 is a rare second sequel that really works."
}

我究竟做错了什么？我正在使用Jackson图书馆。

Answer 1

这是我在您的代码中看到的问题列表：

1. 该@JsonIgnoreProperties属性应放在MovieResponse类之上，而不是Movie类之上。查阅文档，最值得注意的是有关“ ignoreUnknown”属性的说法，默认为false：

公共抽象布尔值 ignoreUnknown

定义可以在反序列化期间忽略任何无法识别的属性的属性。如果为true，则所有无法识别的属性（即 没有设置器或创建者接受它们
）都将在没有警告的情况下被忽略（尽管仍会调用未知属性的处理程序）。

1. 您的设置员不应返回任何值，这可以解释为什么杰克逊没有看到“标题”设置员。这是“ title”的设置方法：

   public void setTitle(String t) {
   title = t;
   

   }

2. 这不是使其不起作用的原因，但是您要两次声明对象映射器，请考虑使用映射器，而不是实例化一个新的映射器：

   MovieResponse response = mapper.readValue(new File("C:\\M.json"), MovieResponse.class);
   

编辑：这是我认为的固定代码：

import java.io.File;
import org.codehaus.jackson.map.ObjectMapper;
import java.net.*;
import org.codehaus.jackson.annotate.JsonIgnoreProperties;

public class Movie {
    public static void main(String[] args) throws Exception {
        MovieResponse response;
        ObjectMapper mapper = new ObjectMapper();

        response = mapper.readValue(new File("C:\\M.json"), MovieResponse.class);
        System.out.println(response);
    }
}