[英]How to resolve neo4j error (Parameters Must be a JSON Map) when attempting to make an REST API Cypher query in Java
I am currently attempting to perform a Cypher query with my neo4j database as part of an Android Studio application I have made to get started and practise using the REST API. 我目前正在尝试对我的neo4j数据库执行Cypher查询,作为开始并练习使用REST API的Android Studio应用程序的一部分。 The code for which is shown below: 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");
}
}
});
}
});
}
}
While my program does successfully receive a response from my neo4j Amazon EC2 server, it replies with an HTTP 400 error and provides the following error messages, present within the output JSON string: Result=Parameters must be a JSON map
, Result=IllegalArgumentException
, Result=java.lang.IllegalArgumentException
当我的程序确实从我的neo4j Amazon EC2服务器成功接收到响应时,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
Due to these messages, I tried to ensure that my query entity is in the valid JSON format, but despite this, the error message still seems to appear. 由于这些消息,我试图确保我的查询实体采用有效的JSON格式,但是尽管如此,错误消息似乎仍然出现。 Despite a significant amount of searching throughout internet sources, I have been unable to find a solution to this problem. 尽管在整个Internet资源中进行了大量搜索,但我仍无法找到解决该问题的方法。 I am currently using the Apache HttpClient and Google's Simple JSON external libraries. 我目前正在使用Apache HttpClient和Google的Simple JSON外部库。
I would be grateful if anyone could offer any insight or solutions that would help me solve this problem. 如果有人可以提供任何能帮助我解决此问题的见解或解决方案,我将不胜感激。 I would also be interested in seeing any other Java code that could make my REST API connection. 我还将对看到任何其他可以建立我的REST API连接的Java代码感兴趣。 However, I can confirm that many of the official drivers offered by Neo4j, eg Neo4j-Java-Driver don't seem to be compatible with Android Studio when trying to connect through the Bolt protocol. 但是,我可以确认Neo4j提供的许多官方驱动程序,例如Neo4j-Java-Driver在尝试通过Bolt协议进行连接时似乎与Android Studio不兼容。 Finally, if you have any further questions for me please feel free to ask. 最后,如果您还有其他疑问,请随时提出。
UPDATED: 更新:
Omitting the 'params' value as suggested by cybersam does solve the error and produce an HTTP 200 code for a successful query. 取消Cybersam建议的'params'值确实可以解决该错误,并为成功查询生成HTTP 200代码。 However when I try to read the JSON file provided by Neo4j as a query result by changing the line if(resultKey.equals("message")) to if(resultKey.equals("data")), I receive the following error message: java.lang.IllegalStateException: Expected a string but was BEGIN_ARRAY thrown on the line String result = JsonReader.nextString(); 但是,当我尝试通过将if(resultKey.equals(“ message”))行更改为if(resultKey.equals(“ data”))来读取Neo4j提供的JSON文件作为查询结果时,收到以下错误消息:java.lang.IllegalStateException:需要一个字符串,但是在行String result = JsonReader.nextString();上引发了BEGIN_ARRAY along with a ParseException. 以及ParseException。 Neo4j docs say, the JSON file should take a format similar to this: { "columns" : [ "n.StudentID" ], "data" : ["1607174"] } Neo4j文档说,JSON文件应采用类似于以下格式:{“ columns”:[“ n.StudentID”],“ data”:[“ 1607174”]}
You are currently setting ""
as the value of params
. 您当前正在将""
设置为params
的值。 Since ""
is not a JSON map, you are getting that error. 由于""
不是JSON映射,因此您会收到该错误。
You can either set {}
as the value of params
, or, even better, just omit the entire put
statement for the params
field since that field is optional. 您可以将{}
设置为params
的值,或者甚至更好,因为params
字段是可选的,所以只需省略整个put
语句。
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.