我使用过Gson库，但可以看到我的输出

Question

这是我的主类。可以告诉我为什么它在System.print（）中返回null。我使用了Gson外部库。我在这里做错了。如何显示所有包含

public class PostsActivity extends Activity {

    private static final String TAG = "PostsActivity";
    private List<Post> posts;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_posts);
        PostFetcher fetcher = new PostFetcher();
        fetcher.execute();
    }


    private void handlePostsList(List<Post> posts) {
        this.posts = posts;

        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                for(Post post : PostsActivity.this.posts) {
                    Toast.makeText(PostsActivity.this, post.TITLE, Toast.LENGTH_SHORT).show();
                }
            }
        });
    }

    private void failedLoadingPosts() {
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                Toast.makeText(PostsActivity.this, "Failed to load Posts. Have a look at LogCat.", Toast.LENGTH_SHORT).show();
            }
        });
    }


    private class PostFetcher extends AsyncTask<Void, Void, String> {
        private static final String TAG = "PostFetcher";
        public static final String SERVER_URL = "http://indianpoliticalleadersmap.com/android/DemoSchool/json/json_item.php";

        @Override
        protected String doInBackground(Void... params) {
            try {
                //Create an HTTP client
                HttpClient client = new DefaultHttpClient();
                HttpPost post = new HttpPost(SERVER_URL);

                //Perform the request and check the status code
                HttpResponse response = client.execute(post);
                StatusLine statusLine = response.getStatusLine();
                if(statusLine.getStatusCode() == 200) {
                    HttpEntity entity = response.getEntity();
                    InputStream content = entity.getContent();

                    try {
                        //Read the server response and attempt to parse it as JSON
                        Reader reader = new InputStreamReader(content);

                        GsonBuilder gsonBuilder = new GsonBuilder();
                        gsonBuilder.setDateFormat("M/d/yy hh:mm a");
                        Gson gson = gsonBuilder.create();
                        Post po = gson.fromJson(reader, Post.class);
                        List<Post> posts = Arrays.asList(po);
                        System.out.println("ID:"+po);
                        content.close();

                        handlePostsList(posts);
                    } catch (Exception ex) {
                        Log.e(TAG, "Failed to parse JSON due to: " + ex);
                        failedLoadingPosts();
                    }
                } else {
                    Log.e(TAG, "Server responded with status code: " + statusLine.getStatusCode());
                    failedLoadingPosts();
                }
            } catch(Exception ex) {
                Log.e(TAG, "Failed to send HTTP POST request due to: " + ex);
                failedLoadingPosts();
            }
            return null;
        } 
    }
}

// Post.java

public class Post {

    @SerializedName("id")
    public long ID;
    public String TITLE;
    public String AUTHOR;
    public String URL;
    @SerializedName("date")
    public Date dateCreated;
    public String body;

    public List<Tag> tags;

    public Post() {

    }
     public String toString() {
            return "Student [id=" + ID + ", title="
                    + TITLE + ", thumb_url=" + URL
                    + ", dt=" + AUTHOR + "]";
        } 
}

Answer 1

您需要考虑一些事项。首先，您的字段需要具有正确的 @SerializedName（“”）注释。它表示属性名称（如thumb_url，dt）与JSON中的字段名称不匹配。如果两个名称匹配，则不需要注释。

其次，您需要“解析”从服务器获取的响应到JsonObject，然后读取JsonElement。

以下是您需要的代码：

GsonBuilder gsonBuilder = new GsonBuilder();
gsonBuilder.setDateFormat("yy-d-M hh:mm");
//2014-06-14 02:39:24
//yy-d-M hh:mm
Gson gson = gsonBuilder.create();
List<Post> posts = new ArrayList<Post>();
JsonParser jsonParser = new JsonParser();
JsonObject details = jsonParser.parse(reader).getAsJsonObject();
JsonArray array = details.getAsJsonArray("veg_food");
for ( JsonElement element : array ){
     Post post = gson.fromJson(element, Post.class);
     posts.add(post);
}
System.out.println("ID:"+ posts);

另外，请务必将Post.java课程更改为：

@SerializedName("id")
public long ID;
@SerializedName("title")
public String TITLE;
@SerializedName("thumb_url")
public String URL;
@SerializedName("dt")
public Date dateCreated;

希望它有所帮助。

<强> [编辑]

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