I have a small test application I'm writing in Java to parse some JSON from the Reddit API. Some sample JSON I'm looking to parse would be like this:
[
{
"kind": "Listing",
"data": {
"modhash": "1jq62oyvwe15aaba7eb18b0b4363b567a00750766351e03dcc",
"children": [
{
"kind": "t3",
"data": {
"domain": "businessinsider.com",
"media_embed": {},
"levenshtein": null,
"subreddit": "Android",
"selftext_html": null,
"selftext": "",
"likes": null,
"saved": false,
"id": "n17u2",
"clicked": false,
"title": "CONFESSION OF A NON-APPLE-FANBOY: Even If The Samsung Galaxy Nexus Is Better, I'm Still Buying An iPhone",
"media": null,
"score": 0,
"over_18": false,
"hidden": false,
"thumbnail": "http://e.thumbs.redditmedia.com/sL0dCwGAvWqnY_sd.jpg",
"subreddit_id": "t5_2qlqh",
"author_flair_css_class": null,
"downs": 2,
"is_self": false,
"permalink": "/r/Android/comments/n17u2/confession_of_a_nonapplefanboy_even_if_the/",
"name": "t3_n17u2",
"created": 1323127132,
"url": "http://www.businessinsider.com/apple-iphone-versus-samsung-galaxy-nexus-2011-12",
"author_flair_text": null,
"author": "FormulaT",
"created_utc": 1323101932,
"num_comments": 0,
"ups": 1
}
}
],
"after": null,
"before": null
}
},
{
"kind": "Listing",
"data": {
"modhash": "1jq62oyvwe15aaba7eb18b0b4363b567a00750766351e03dcc",
"children": [],
"after": null,
"before": null
}
}
]
What I'm trying to accomplish is to get just a few values out of this JSON, eg the title and the author. I'm using Jackson to handle the JSON, and the code I'm using looks like this:
URLConnection conn = redditURL.openConnection();
BufferedReader buf = new BufferedReader(new InputStreamReader(conn.getInputStream()));
ObjectMapper mapper = new ObjectMapper();
RedditComment comment = mapper.readValue(buf, RedditComment.class);
Iterator itr = comment.getData().getChildren().listIterator();
I created the RedditComment and other needed classes using the JSONGen website (http://jsongen.byingtondesign.com/). However, when parsing the JSON from the BufferedReader, Jackson throws this exception:
org.codehaus.jackson.map.JsonMappingException: Can not deserialize instance of com.test.RedditAPI.RedditComment out of START_ARRAY token
at [Source: java.io.BufferedReader@3ebfbbe3; line: 1, column: 1]
at org.codehaus.jackson.map.JsonMappingException.from(JsonMappingException.java:163)
at org.codehaus.jackson.map.deser.StdDeserializationContext.mappingException(StdDeserializationContext.java:219)
at org.codehaus.jackson.map.deser.StdDeserializationContext.mappingException(StdDeserializationContext.java:212)
at org.codehaus.jackson.map.deser.BeanDeserializer.deserializeFromArray(BeanDeserializer.java:869)
at org.codehaus.jackson.map.deser.BeanDeserializer.deserialize(BeanDeserializer.java:597)
at org.codehaus.jackson.map.ObjectMapper._readMapAndClose(ObjectMapper.java:2723)
at org.codehaus.jackson.map.ObjectMapper.readValue(ObjectMapper.java:1877)
at com.test.RedditAPI.main.returnRedditComment(Main.java:17)
Does anyone have any ideas? I've been scratching my head for a few hours now.
EDIT: Thanks to @Chin Boon and @Chris, I came up with the following (after switching to GSON):
Gson gson = new Gson();
List<RedditComment> comment = gson.fromJson(buf, new TypeToken<List<RedditComment>>() {}.getType());
List<RedditChildren> children = comment.get(1).getData().getChildren();
System.out.println(children.get(1).getData().getAuthor());
but that throws the following exception:
java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to com.test.RedditAPI.RedditChildren
Apologies if I'm being a bother, I've looked around the API and there isn't any reference of LinkedHashMaps, so I don't know why it's popping up here.
The problem is that the response is an array of entries. Try:
List<RedditComment> comment = mapper.readValue(buf,new TypeReference<List<RedditComment>>(){});
if you have not already invested too much time into Jackson, may i recommend you looking at GSON, here is a tutorial that should have you started.
Google GSON API maps your JSON string into a domain object.
http://java.sg/parsing-a-json-string-into-an-object-with-gson-easily/
Also, you can use a JSON parser to see your JSON.
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