java - 尝试在 Java 中进行 REST API Cypher 查询时如何解决 neo4j 错误(参数必须是 JSON 映射)

Question

我目前正在尝试使用 Neo4j 数据库执行 Cypher 查询，作为我为开始和练习使用 REST API 而制作的 Android Studio 应用程序的一部分。其代码如下所示:

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");
                        Log.d("Check-Type",neo4jRequest.getEntity().toString());
                        //Performs the neo4j query.
                        HttpResponse queryResult = neo4jClient.execute(neo4jRequest);
                        //Checks the status code of the request.
                        int statusCode = queryResult.getStatusLine().getStatusCode();
                        if (statusCode == 200 || statusCode == 400){
                            Log.d("CONNECT","Query Made");
                            //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("RESULT","Begin JSON Parse");
                            while(JsonReader.hasNext()){
                                //Gathers the name of the current key.
                                String resultKey = JsonReader.nextName();
                                //Checks if it's the data we're looking for.
                                if(resultKey.equals("message")){
                                    //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.
                                    break;
                                } else {
                                    //Skips to the next value if the current one contains nothing of interest.
                                    JsonReader.skipValue();
                                }
                            }
                            Log.d("RESULT","End JSON Parse");
                            //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");
                    }
                }
            });
        }
    });
}
}

虽然我的程序成功接收到来自 Neo4j Amazon EC2 服务器的响应，但它会回复 HTTP 400 错误并提供以下错误消息，这些消息出现在输出 JSON 字符串中:Result=Parameters must be a JSON map , Result=IllegalArgumentException , Result=java.lang.IllegalArgumentException

由于这些消息，我尝试确保我的查询实体采用有效的 JSON 格式，但尽管如此，错误消息似乎仍然出现。尽管在互联网资源中进行了大量搜索，但我一直无法找到该问题的解决方案。我目前正在使用 Apache HttpClient 和 Google 的 Simple JSON 外部库。

如果有人能够提供任何见解或解决方案来帮助我解决这个问题，我将不胜感激。我也有兴趣查看任何其他可以建立我的 REST API 连接的 Java 代码。但是，我可以确认 Neo4j 提供的许多官方驱动程序，例如当尝试通过 Bolt 协议(protocol)连接时，Neo4j-Java-Driver 似乎与 Android Studio 不兼容。最后，如果您还有其他问题想问我，请随时提问。

更新:
按照 cybersam 建议省略“params”值确实可以解决错误并为成功查询生成 HTTP 200 代码。但是，当我尝试通过将行 if(resultKey.equals("message")) 更改为 if(resultKey.equals("data")) 来读取 Neo4j 提供的 JSON 文件作为查询结果时，我收到以下错误消息: java.lang.IllegalStateException: Expected a string but was BEGIN_ARRAY throwed on the line String result = JsonReader.nextString();以及 ParseException。 Neo4j 文档说，JSON 文件应采用类似于以下的格式: { "columns": [ "n.​​StudentID"], "data": ["1607174"] }

Answer 1

您当前正在将 "" 设置为 params 的值。由于 "" 不是 JSON 映射，因此您会收到该错误。

您可以将 {} 设置为 params 的值，或者更好的是，直接省略 params 字段的整个 put 语句，因为该字段是可选的。