将JSON数据映射到Java对象

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

I have been trying to map JSON data to Java objects, with the JSON file on my PC, but it always throws the exception:

org.codehaus.jackson.map.exc.UnrecognizedPropertyException：无法识别的字段title（类MovieResponse），未在[来源：C：\ M.json;上标记为可忽略的; line：2，column：13]（通过引用链：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.*; 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：

The json file contains following data:

{ "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." }

我做错了什么？我正在使用Jackson库。

What am I doing wrong? I am using the Jackson library.

推荐答案

以下是我在代码中看到的问题列表：

Here is a list of problems I see in your code:

@JsonIgnoreProperties 属性应该放在 MovieResponse上方 class，而不是 Movie 类。查看文档，最值得注意的是关于ignoreUnknown属性的说法，默认为false：

The @JsonIgnoreProperties attribute should be put above the MovieResponse class, not the Movie class. Check out the documentation, most notably what is said about the "ignoreUnknown" property, defaulted to false:

public abstract boolean ignoreUnknown

定义在反序列化期间是否可以忽略任何无法识别的属性的属性。如果为true，则无法识别无法识别的所有属性 - 即没有接受 的setter或创建者 - 会被忽略而不会发出警告（尽管处理程序为未知$ b） $ b属性（如果有的话）仍将被调用）无例外。

Property that defines whether it is ok to just ignore any unrecognized properties during deserialization. If true, all properties that are unrecognized -- that is, there are no setters or creators that accept them -- are ignored without warnings (although handlers for unknown properties, if any, will still be called) without exception.

你的setter不应该返回任何值，这个可以解释为什么杰克逊没有看到头衔的制定者。以下是标题的设置者应该如何：

Your setters should not return any value, this may explain why Jackson does not see a "title" setter. Here is how the setter for "title" should be:

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

不是它无法正常工作的理由，但你宣称你的对象映射器两次，考虑使用你的映射器而不是实例化一个新映射器：

Not a reason for it to NOT work, but you are declaring your object mapper twice, consider using your mapper instead of instanciating a new one:

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

编辑：这是我的固定代码我认为：

here's your fixed code I think:

import java.io.File; import org.codehaus.jackson.map.ObjectMapper; import java.*; 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); } }