Javaでjsonレスポンスから配列を取得する方法

Question

私はinstagram REST APIを使用しています。JSONレスポンスから画像リンクを取得する必要があります。

JSONは次のようになります。

{ 
    "meta": 
    { 
     "code": 200 
    }, 
    "data": 
    { 
     "attribution": null, 
     "tags": 
     [ 
      "tag" 
     ], 
     "type": "image", 
     "location": null, 
     "comments": 
     { 
      "count": 7 
     }, 
     "filter": "Normal", 
     "created_time": "1451066377", 
     "link": "https://www.instagram.com/p/at3rg7uj_9/", 
     "likes": 
     { 
      "count": 39 
     }, 
     "images": 
     { 
      "low_resolution": 
      { 
       "url": "https://url.jpg", 
       "width": 320, 
       "height": 320 
      }, 
      "thumbnail": 
      { 
       "url": "https://url.jpg", 
       "width": 150, 
       "height": 150 
      }, 
      "standard_resolution": 
      { 
       "url": "https://url.jpg?ig_cache_key=key", 
       "width": 640, 
       "height": 640 
      } 
     }, 
     "users_in_photo": 
     [ 
     ], 
     "caption": 
     { 
      "created_time": "1451066377", 
      "text": "caption", 
      "from": 
      { 
       "username": "f", 
       "profile_picture": "https://profilepic.jpg", 
       "id": "185333924", 
       "full_name": "name" 
      }, 
      "id": "17852020759022520" 
     }, 
     "user_has_liked": false, 
     "id": "1147950432085956322_185333924", 
     "user": 
     { 
      "username": "", 
      "profile_picture": "https://prifilepic.jpg", 
      "id": "185333924", 
      "full_name": "name" 
     } 
    } 
} 

私はJavaで「画像」オブジェクトを参照するだろうか？

JSONObject object = (JSONObject) new JSONTokener(s).nextValue(); 
JSONObject images = object.getJSONObject("images"); 
JSONObject image = images.getJSONObject("standard_resolution"); 
String url = image.getString("url"); 

と、この：

JSONObject object = (JSONObject) new JSONTokener(s).nextValue(); 
JSONArray images = object.getJSONArray("images"); 
JSONObject standardRes = images.getJSONObject(2); 
String url = standardRes.getString("url"); 

Sがそうのように文字列として保存されたJSONレスポンスです：

try { 
     URL url = new URL(link); 
     HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection(); 
     try { 
      BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(urlConnection.getInputStream())); 
      StringBuilder stringBuilder = new StringBuilder(); 
      String line; 
      while ((line = bufferedReader.readLine()) != null) { 
       stringBuilder.append(line).append("\n"); 
      } 
      bufferedReader.close(); 
      return stringBuilder.toString(); // s 
     } finally { 
      urlConnection.disconnect(); 
     } 
    } catch (Exception e) { 
     Log.e("ERROR", e.getMessage(), e); 
     return null; 
    } 

が、両方のケースでは、私が受け取る

は、私はこれを試してみました'画像に値がありません'というエラーです。

JSONObject object = (JSONObject) new JSONTokener(s).nextValue(); 
JSONObject data = object.getJSONObject("data"); 
JSONObject images = object.getJSONObject("images"); 
JSONObject stan_res = object.getJSONObject("standard_resolution"); 
String url = stan_res.getString("url"); 

問題は、あなたがしたいURLを取得するので、あなたが唯一持っていた、と思ったかもしれないことをあまり毛深いた：

Answer 1

imagesは、このコードを試してみてくださいdata

JSONObject object = (JSONObject) new JSONTokener(s).nextValue(); 
JSONObject data = object.getJSONObject("data"); 
JSONObject images = data.getJSONObject("images"); 
... 

Answer 2

内にネストされますJSONObjectとJSONArrayではなくJSONObjectを処理します。私のコードは、standard_resolution JSONオブジェクトに当たるまでJSON構造体に潜り込み、URLを抽出します。

Answer 3

とにかく、GSONを使用する方が良い方法です。 JSONオブジェクト（POJO）に対応するオブジェクトを作成します。 Uオンラインhttp://www.jsonschema2pojo.orgを使用できます。あなたのJSONは次のように変換されます。

public class Caption { 

@SerializedName("created_time") 
@Expose 
private String createdTime; 
@SerializedName("text") 
@Expose 
private String text; 
@SerializedName("from") 
@Expose 
private From from; 
@SerializedName("id") 
@Expose 
private String id; 

/** 
* 
* @return 
* The createdTime 
*/ 
public String getCreatedTime() { 
return createdTime; 
} 

/** 
* 
* @param createdTime 
* The created_time 
*/ 
public void setCreatedTime(String createdTime) { 
this.createdTime = createdTime; 
} 

/** 
* 
* @return 
* The text 
*/ 
public String getText() { 
return text; 
} 

/** 
* 
* @param text 
* The text 
*/ 
public void setText(String text) { 
this.text = text; 
} 

/** 
* 
* @return 
* The from 
*/ 
public From getFrom() { 
return from; 
} 

/** 
* 
* @param from 
* The from 
*/ 
public void setFrom(From from) { 
this.from = from; 
} 

/** 
* 
* @return 
* The id 
*/ 
public String getId() { 
return id; 
} 

/** 
* 
* @param id 
* The id 
*/ 
public void setId(String id) { 
this.id = id; 
} 

} 
-----------------------------------com.example.Comments.java----------------------------------- 

package com.example; 

import javax.annotation.Generated; 
import com.google.gson.annotations.Expose; 
import com.google.gson.annotations.SerializedName; 

@Generated("org.jsonschema2pojo") 
public class Comments { 

@SerializedName("count") 
@Expose 
private Integer count; 

/** 
* 
* @return 
* The count 
*/ 
public Integer getCount() { 
return count; 
} 

/** 
* 
* @param count 
* The count 
*/ 
public void setCount(Integer count) { 
this.count = count; 
} 

} 
-----------------------------------com.example.Data.java----------------------------------- 

package com.example; 

import java.util.ArrayList; 
import java.util.List; 
import javax.annotation.Generated; 
import com.google.gson.annotations.Expose; 
import com.google.gson.annotations.SerializedName; 

@Generated("org.jsonschema2pojo") 
public class Data { 

@SerializedName("attribution") 
@Expose 
private Object attribution; 
@SerializedName("tags") 
@Expose 
private List<String> tags = new ArrayList<String>(); 
@SerializedName("type") 
@Expose 
private String type; 
@SerializedName("location") 
@Expose 
private Object location; 
@SerializedName("comments") 
@Expose 
private Comments comments; 
@SerializedName("filter") 
@Expose 
private String filter; 
@SerializedName("created_time") 
@Expose 
private String createdTime; 
@SerializedName("link") 
@Expose 
private String link; 
@SerializedName("likes") 
@Expose 
private Likes likes; 
@SerializedName("images") 
@Expose 
private Images images; 
@SerializedName("users_in_photo") 
@Expose 
private List<Object> usersInPhoto = new ArrayList<Object>(); 
@SerializedName("caption") 
@Expose 
private Caption caption; 
@SerializedName("user_has_liked") 
@Expose 
private Boolean userHasLiked; 
@SerializedName("id") 
@Expose 
private String id; 
@SerializedName("user") 
@Expose 
private User user; 

/** 
* 
* @return 
* The attribution 
*/ 
public Object getAttribution() { 
return attribution; 
} 

/** 
* 
* @param attribution 
* The attribution 
*/ 
public void setAttribution(Object attribution) { 
this.attribution = attribution; 
} 

/** 
* 
* @return 
* The tags 
*/ 
public List<String> getTags() { 
return tags; 
} 

/** 
* 
* @param tags 
* The tags 
*/ 
public void setTags(List<String> tags) { 
this.tags = tags; 
} 

/** 
* 
* @return 
* The type 
*/ 
public String getType() { 
return type; 
} 

/** 
* 
* @param type 
* The type 
*/ 
public void setType(String type) { 
this.type = type; 
} 

/** 
* 
* @return 
* The location 
*/ 
public Object getLocation() { 
return location; 
} 

/** 
* 
* @param location 
* The location 
*/ 
public void setLocation(Object location) { 
this.location = location; 
} 

/** 
* 
* @return 
* The comments 
*/ 
public Comments getComments() { 
return comments; 
} 

/** 
* 
* @param comments 
* The comments 
*/ 
public void setComments(Comments comments) { 
this.comments = comments; 
} 

/** 
* 
* @return 
* The filter 
*/ 
public String getFilter() { 
return filter; 
} 

/** 
* 
* @param filter 
* The filter 
*/ 
public void setFilter(String filter) { 
this.filter = filter; 
} 

/** 
* 
* @return 
* The createdTime 
*/ 
public String getCreatedTime() { 
return createdTime; 
} 

/** 
* 
* @param createdTime 
* The created_time 
*/ 
public void setCreatedTime(String createdTime) { 
this.createdTime = createdTime; 
} 

/** 
* 
* @return 
* The link 
*/ 
public String getLink() { 
return link; 
} 

/** 
* 
* @param link 
* The link 
*/ 
public void setLink(String link) { 
this.link = link; 
} 

/** 
* 
* @return 
* The likes 
*/ 
public Likes getLikes() { 
return likes; 
} 

/** 
* 
* @param likes 
* The likes 
*/ 
public void setLikes(Likes likes) { 
this.likes = likes; 
} 

/** 
* 
* @return 
* The images 
*/ 
public Images getImages() { 
return images; 
} 

/** 
* 
* @param images 
* The images 
*/ 
public void setImages(Images images) { 
this.images = images; 
} 

/** 
* 
* @return 
* The usersInPhoto 
*/ 
public List<Object> getUsersInPhoto() { 
return usersInPhoto; 
} 

/** 
* 
* @param usersInPhoto 
* The users_in_photo 
*/ 
public void setUsersInPhoto(List<Object> usersInPhoto) { 
this.usersInPhoto = usersInPhoto; 
} 

/** 
* 
* @return 
* The caption 
*/ 
public Caption getCaption() { 
return caption; 
} 

/** 
* 
* @param caption 
* The caption 
*/ 
public void setCaption(Caption caption) { 
this.caption = caption; 
} 

/** 
* 
* @return 
* The userHasLiked 
*/ 
public Boolean getUserHasLiked() { 
return userHasLiked; 
} 

/** 
* 
* @param userHasLiked 
* The user_has_liked 
*/ 
public void setUserHasLiked(Boolean userHasLiked) { 
this.userHasLiked = userHasLiked; 
} 

/** 
* 
* @return 
* The id 
*/ 
public String getId() { 
return id; 
} 

/** 
* 
* @param id 
* The id 
*/ 
public void setId(String id) { 
this.id = id; 
} 

/** 
* 
* @return 
* The user 
*/ 
public User getUser() { 
return user; 
} 

/** 
* 
* @param user 
* The user 
*/ 
public void setUser(User user) { 
this.user = user; 
} 

} 
-----------------------------------com.example.Example.java----------------------------------- 

package com.example; 

import javax.annotation.Generated; 
import com.google.gson.annotations.Expose; 
import com.google.gson.annotations.SerializedName; 

@Generated("org.jsonschema2pojo") 
public class Example { 

@SerializedName("meta") 
@Expose 
private Meta meta; 
@SerializedName("data") 
@Expose 
private Data data; 

/** 
* 
* @return 
* The meta 
*/ 
public Meta getMeta() { 
return meta; 
} 

/** 
* 
* @param meta 
* The meta 
*/ 
public void setMeta(Meta meta) { 
this.meta = meta; 
} 

/** 
* 
* @return 
* The data 
*/ 
public Data getData() { 
return data; 
} 

/** 
* 
* @param data 
* The data 
*/ 
public void setData(Data data) { 
this.data = data; 
} 

} 
-----------------------------------com.example.From.java----------------------------------- 

package com.example; 

import javax.annotation.Generated; 
import com.google.gson.annotations.Expose; 
import com.google.gson.annotations.SerializedName; 

@Generated("org.jsonschema2pojo") 
public class From { 

@SerializedName("username") 
@Expose 
private String username; 
@SerializedName("profile_picture") 
@Expose 
private String profilePicture; 
@SerializedName("id") 
@Expose 
private String id; 
@SerializedName("full_name") 
@Expose 
private String fullName; 

/** 
* 
* @return 
* The username 
*/ 
public String getUsername() { 
return username; 
} 

/** 
* 
* @param username 
* The username 
*/ 
public void setUsername(String username) { 
this.username = username; 
} 

/** 
* 
* @return 
* The profilePicture 
*/ 
public String getProfilePicture() { 
return profilePicture; 
} 

/** 
* 
* @param profilePicture 
* The profile_picture 
*/ 
public void setProfilePicture(String profilePicture) { 
this.profilePicture = profilePicture; 
} 

/** 
* 
* @return 
* The id 
*/ 
public String getId() { 
return id; 
} 

/** 
* 
* @param id 
* The id 
*/ 
public void setId(String id) { 
this.id = id; 
} 

/** 
* 
* @return 
* The fullName 
*/ 
public String getFullName() { 
return fullName; 
} 

/** 
* 
* @param fullName 
* The full_name 
*/ 
public void setFullName(String fullName) { 
this.fullName = fullName; 
} 

} 
-----------------------------------com.example.Images.java----------------------------------- 

package com.example; 

import javax.annotation.Generated; 
import com.google.gson.annotations.Expose; 
import com.google.gson.annotations.SerializedName; 

@Generated("org.jsonschema2pojo") 
public class Images { 

@SerializedName("low_resolution") 
@Expose 
private LowResolution lowResolution; 
@SerializedName("thumbnail") 
@Expose 
private Thumbnail thumbnail; 
@SerializedName("standard_resolution") 
@Expose 
private StandardResolution standardResolution; 

/** 
* 
* @return 
* The lowResolution 
*/ 
public LowResolution getLowResolution() { 
return lowResolution; 
} 

/** 
* 
* @param lowResolution 
* The low_resolution 
*/ 
public void setLowResolution(LowResolution lowResolution) { 
this.lowResolution = lowResolution; 
} 

/** 
* 
* @return 
* The thumbnail 
*/ 
public Thumbnail getThumbnail() { 
return thumbnail; 
} 

/** 
* 
* @param thumbnail 
* The thumbnail 
*/ 
public void setThumbnail(Thumbnail thumbnail) { 
this.thumbnail = thumbnail; 
} 

/** 
* 
* @return 
* The standardResolution 
*/ 
public StandardResolution getStandardResolution() { 
return standardResolution; 
} 

/** 
* 
* @param standardResolution 
* The standard_resolution 
*/ 
public void setStandardResolution(StandardResolution standardResolution) { 
this.standardResolution = standardResolution; 
} 

} 
-----------------------------------com.example.Likes.java----------------------------------- 

package com.example; 

import javax.annotation.Generated; 
import com.google.gson.annotations.Expose; 
import com.google.gson.annotations.SerializedName; 

@Generated("org.jsonschema2pojo") 
public class Likes { 

@SerializedName("count") 
@Expose 
private Integer count; 

/** 
* 
* @return 
* The count 
*/ 
public Integer getCount() { 
return count; 
} 

/** 
* 
* @param count 
* The count 
*/ 
public void setCount(Integer count) { 
this.count = count; 
} 

} 
-----------------------------------com.example.LowResolution.java----------------------------------- 

package com.example; 

import javax.annotation.Generated; 
import com.google.gson.annotations.Expose; 
import com.google.gson.annotations.SerializedName; 

@Generated("org.jsonschema2pojo") 
public class LowResolution { 

@SerializedName("url") 
@Expose 
private String url; 
@SerializedName("width") 
@Expose 
private Integer width; 
@SerializedName("height") 
@Expose 
private Integer height; 

/** 
* 
* @return 
* The url 
*/ 
public String getUrl() { 
return url; 
} 

/** 
* 
* @param url 
* The url 
*/ 
public void setUrl(String url) { 
this.url = url; 
} 

/** 
* 
* @return 
* The width 
*/ 
public Integer getWidth() { 
return width; 
} 

/** 
* 
* @param width 
* The width 
*/ 
public void setWidth(Integer width) { 
this.width = width; 
} 

/** 
* 
* @return 
* The height 
*/ 
public Integer getHeight() { 
return height; 
} 

/** 
* 
* @param height 
* The height 
*/ 
public void setHeight(Integer height) { 
this.height = height; 
} 

} 
-----------------------------------com.example.Meta.java----------------------------------- 

package com.example; 

import javax.annotation.Generated; 
import com.google.gson.annotations.Expose; 
import com.google.gson.annotations.SerializedName; 

@Generated("org.jsonschema2pojo") 
public class Meta { 

@SerializedName("code") 
@Expose 
private Integer code; 

/** 
* 
* @return 
* The code 
*/ 
public Integer getCode() { 
return code; 
} 

/** 
* 
* @param code 
* The code 
*/ 
public void setCode(Integer code) { 
this.code = code; 
} 

} 
-----------------------------------com.example.StandardResolution.java----------------------------------- 

package com.example; 

import javax.annotation.Generated; 
import com.google.gson.annotations.Expose; 
import com.google.gson.annotations.SerializedName; 

@Generated("org.jsonschema2pojo") 
public class StandardResolution { 

@SerializedName("url") 
@Expose 
private String url; 
@SerializedName("width") 
@Expose 
private Integer width; 
@SerializedName("height") 
@Expose 
private Integer height; 

/** 
* 
* @return 
* The url 
*/ 
public String getUrl() { 
return url; 
} 

/** 
* 
* @param url 
* The url 
*/ 
public void setUrl(String url) { 
this.url = url; 
} 

/** 
* 
* @return 
* The width 
*/ 
public Integer getWidth() { 
return width; 
} 

/** 
* 
* @param width 
* The width 
*/ 
public void setWidth(Integer width) { 
this.width = width; 
} 

/** 
* 
* @return 
* The height 
*/ 
public Integer getHeight() { 
return height; 
} 

/** 
* 
* @param height 
* The height 
*/ 
public void setHeight(Integer height) { 
this.height = height; 
} 

} 
-----------------------------------com.example.Thumbnail.java----------------------------------- 

package com.example; 

import javax.annotation.Generated; 
import com.google.gson.annotations.Expose; 
import com.google.gson.annotations.SerializedName; 

@Generated("org.jsonschema2pojo") 
public class Thumbnail { 

@SerializedName("url") 
@Expose 
private String url; 
@SerializedName("width") 
@Expose 
private Integer width; 
@SerializedName("height") 
@Expose 
private Integer height; 

/** 
* 
* @return 
* The url 
*/ 
public String getUrl() { 
return url; 
} 

/** 
* 
* @param url 
* The url 
*/ 
public void setUrl(String url) { 
this.url = url; 
} 

/** 
* 
* @return 
* The width 
*/ 
public Integer getWidth() { 
return width; 
} 

/** 
* 
* @param width 
* The width 
*/ 
public void setWidth(Integer width) { 
this.width = width; 
} 

/** 
* 
* @return 
* The height 
*/ 
public Integer getHeight() { 
return height; 
} 

/** 
* 
* @param height 
* The height 
*/ 
public void setHeight(Integer height) { 
this.height = height; 
} 

} 
-----------------------------------com.example.User.java----------------------------------- 

package com.example; 

import javax.annotation.Generated; 
import com.google.gson.annotations.Expose; 
import com.google.gson.annotations.SerializedName; 

@Generated("org.jsonschema2pojo") 
public class User { 

@SerializedName("username") 
@Expose 
private String username; 
@SerializedName("profile_picture") 
@Expose 
private String profilePicture; 
@SerializedName("id") 
@Expose 
private String id; 
@SerializedName("full_name") 
@Expose 
private String fullName; 

/** 
* 
* @return 
* The username 
*/ 
public String getUsername() { 
return username; 
} 

/** 
* 
* @param username 
* The username 
*/ 
public void setUsername(String username) { 
this.username = username; 
} 

/** 
* 
* @return 
* The profilePicture 
*/ 
public String getProfilePicture() { 
return profilePicture; 
} 

/** 
* 
* @param profilePicture 
* The profile_picture 
*/ 
public void setProfilePicture(String profilePicture) { 
this.profilePicture = profilePicture; 
} 

/** 
* 
* @return 
* The id 
*/ 
public String getId() { 
return id; 
} 

/** 
* 
* @param id 
* The id 
*/ 
public void setId(String id) { 
this.id = id; 
} 

/** 
* 
* @return 
* The fullName 
*/ 
public String getFullName() { 
return fullName; 
} 

/** 
* 
* @param fullName 
* The full_name 
*/ 
public void setFullName(String fullName) { 
this.fullName = fullName; 
} 

} 

は今UはJSONから、あなたのオブジェクトを作成することができます。それ

Example exampleObj = new GSON().fromJson(yourJSON, Example.class); 
    Data dataObj = exampleObj.getData(); 
    Images imagesObj = dataObj.getImages(); 
    //now U can fetch any of your images 
    String imageUrl = imagesObj.getThumbnail().getUrl(); 

であること。 また、Retrofit for REST（似たようなトピックについては、ここで答えられるかもしれません：How to use ProgressDialog to show JSON parsing progress?）と一緒に使用することを強くお勧めします。 Uさんがあなたの画像を表示するときは、グライドやピカソのライブラリを使って、簡単で素敵な方法でダウンロードできます。