使用JsonReader使用Java中的Neo4j REST API解析来自Cypher查询的JSON结果

Question

我目前编写了一个程序，该程序使用REST API检索对Neo4j数据库进行的Cypher查询的JSON结果。 该项目是用Android Studio编写的，其代码如下：

public class MainActivity extends AppCompatActivity {

private TextView userText;
private Button clicker;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    userText = (TextView) findViewById(R.id.txtUsername);
    clicker = (Button) findViewById(R.id.btnClick);
    clicker.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            //The REST API needs it's own thread for Neo4j connection. Read up on this documentation.
            AsyncTask.execute(new Runnable() {
                @Override
                public void run() {
                    try {
                        //The URL will change based on what is needed for the documentations.
                        //Provides the address for the HTTP communication.
                        String neo4jURL = "http://ec2-35-176-79-15.eu-west-2.compute.amazonaws.com:7474/db/data/cypher";
                        //Helps to create the JSON object used by the query.
                        //QueryData neo4jqueryData = new QueryData();
                        //Creates the client used for the connection.
                        HttpClient neo4jClient = new DefaultHttpClient();
                        //Assigns the address to either the HttpGet or HttpPost request.
                        HttpPost neo4jRequest = new HttpPost(neo4jURL);
                        //Creates the JSON Attributes that will be used as part of the query.
                        String query = "MATCH (n:Student) WHERE n.Username=\'cs16thm\' RETURN n.StudentID";
                        JSONObject neo4jJSON = new JSONObject();
                        neo4jJSON.put("query",query);
                        //neo4jJSON.put("params","");
                        String check = neo4jJSON.toString();
                        Log.d("JSON",check);
                        StringEntity queryString = new StringEntity(check,"UTF-8");
                        //Ensures that the application type is JSON.
                        queryString.setContentType("application/json");
                        //Adds the Attribute data to the JSON query.
                        neo4jRequest.setEntity(queryString);
                        //Adds the Headers to the query.
                        //bmVvNGo6Z3JvdXAzNw== is the Base64 encoding of the username and password.
                        neo4jRequest.setHeader("Authorization","Basic bmVvNGo6Z3JvdXAzNw==");
                        //Shows the data types that would be accepted by the query result.
                        neo4jRequest.setHeader("Accept", "application/json; charset=UTF-8");
                        //Used to show the data type being sent to the server.
                        neo4jRequest.setHeader("Content-Type", "application/json");
                        //Performs the neo4j query.
                        HttpResponse queryResult = neo4jClient.execute(neo4jRequest);
                        //Checks the status code of the request.
                        int statusCode = queryResult.getStatusLine().getStatusCode();
                        if (statusCode == 200){
                            Log.d("CONNECT","Query Made " + Integer.toString(statusCode));
                            //Gets the results stream from the connection. Results is returned as a JSON which needs to be parsed.
                            InputStreamReader resultsReader = new InputStreamReader(queryResult.getEntity().getContent());
                            JsonReader JsonReader = new JsonReader(resultsReader);
                            //Begins processing of the JSON results.
                            JsonReader.beginObject();
                            //Checks all of the parameter keys returned by the document.
                            Log.d("PARSE","Begin JSON Parse");
                            while(JsonReader.hasNext()){
                                //Gathers the name of the current key.
                                String resultKey = JsonReader.nextName();
                                Log.d("RESULT","Entered Loop " + resultKey);
                                //Checks if it's the data we're looking for, and if it contains a value.
                                if(resultKey.equals("data") && JsonReader.peek() != JsonToken.NULL){
                                    Log.d("RESULT","Entered IF Block");
                                    //Begin array needs to go here.
                                    JsonReader.beginArray();
                                    //Gathers the String value that we require.
                                    String result = JsonReader.nextString();
                                    //Shows the result in the application.
                                    Log.d("RESULT","Result=" + result);
                                    //Prevents further loop execution now that our data is retrieved.
                                    JsonReader.endArray();
                                    break;
                                } else {
                                    //Skips to the next value if the current one contains nothing of interest.
                                    JsonReader.skipValue();
                                }
                            }
                            Log.d("PARSE","End JSON Parse");
                            JsonReader.endObject();
                            //JsonReader.endObject();
                            //Closes the JSON reader after task to prevent resource hogging.
                            JsonReader.close();
                        } else {
                            Log.d("ERROR", "Request not made " + Integer.toString(statusCode));
                        }


                    } catch (MalformedURLException e) {
                        e.printStackTrace();
                        Log.d("ERROR", "Bad URL");
                    } catch (IOException ioe) {
                        ioe.printStackTrace();
                        Log.d("ERROR", "Cannot Connect");
                    } catch (Exception par){
                        par.printStackTrace();
                        Log.d("ERROR", "Parse Fail");
                    }
                }
            });
        }
    });
}
}

查询成功，生成HTTP 200代码，并且代码正确运行，直到错误消息“ Expected a string but was BEGIN_ARRAY String result = JsonReader.nextString();行中引发了Expected a string but was BEGIN_ARRAY和IllegalStateException String result = JsonReader.nextString(); 。 为了尝试解决此错误，我在JsonReader.beginArray()添加了JsonReader.beginArray()和JsonReader.endArray()行到代码中。 但是，对于同一行代码仍会产生相同的错误消息。 基于Neo4j文档， 网址为：（ https://neo4j.com/docs/rest-docs/current/ ，第3.6节），我要解析的JSON结果应采用与本示例类似的格式：

 {
  "columns" : ["n.StudentID"],
  "data" : [ ["1607174"] ]
}

最后，当前代码使用Apache Http Client和Google Simple JSON库，以防影响任何东西。 对于此问题的任何见解或解决方案都将非常有用，如果您还有其他问题，请随时提出。 同样，任何其他允许我正确解析此JSON结果的建议也将受到欢迎。

Answer 1

数据具有嵌套数组： [[]]

"data" : [ ["1607174"] ]

因此，您需要开始内部数组。

JsonReader.beginArray(); // outer
 JsonReader.beginArray(); // inner
 String result = JsonReader.nextString();

PS可能会遍历内部数组（如果可能具有多个值）