将JSON数据映射到Java对象 [英] Mapping JSON data to Java objects
问题描述
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.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:
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 theMovieResponse
class, not theMovie
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.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);
}
}
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