I want to make an Http request and store the result in a JSONObject. I haven't worked much with servlets, so I am unsure as to whether I am 1) Making the request properly, and 2) supposed to create the JSONObject. I have imported the JSONObject and JSONArray classes, but I don't know where I ought to use them. Here's what I have:
public void doGet(HttpServletRequest req, HttpServletResponse resp)
throws IOException {
//create URL
try {
// With a single string.
URL url = new URL(FEED_URL);
// Read all the text returned by the server
BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));
String str;
while ((str = in.readLine()) != null) {
// str is one line of text; readLine() strips the newline character(s)
}
in.close();
} catch (MalformedURLException e) {
}
catch (IOException e) {
}
My FEED_URL is already written so that it will return a feed formatted for JSON.
This has been getting to me for hours. Thank you very much, you guys are an invaluable resource!
First gather the response into a String:
BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));
StringBuilder fullResponse = new StringBuilder();
String str;
while ((str = in.readLine()) != null) {
fullResponse.append(str);
}
Then, if the string starts with "{", you can use:
JSONObject obj = new JSONObject(fullResponse.toString()); //[1]
and if it starts with "[", you can use:
JSONArray arr = new JSONArray(fullResponse.toStrin()); //[2]
[1] http://json.org/javadoc/org/json/JSONObject.html#JSONObject%28java.lang.String%29
[2] http://json.org/javadoc/org/json/JSONArray.html#JSONArray%28java.lang.String%29
Firstly, this is actually not a servlet problem. You don't have any problems with javax.servlet API. You just have problems with java.net API and the JSON API.
For parsing and formatting JSON strings, I would recommend to use Gson (Google JSON) instead of the legacy JSON API's. It has much better support for generics and nested properties and can convert a JSON string to a fullworthy javabean in a single call.
I've posted a complete code example before here. Hope you find it useful.
Related
I am now working on making get current order book of crypto currencies.
my codes are as shown below.
public static void bid_ask () {
HttpClient client = HttpClientBuilder.create().build();
HttpGet request = new HttpGet("https://api.binance.com//api/v1/depth?symbol=ETHUSDT");
System.out.println("Binance ETHUSDT");
try {
HttpResponse response = client.execute(request);
HttpEntity entity = response.getEntity();
if (entity != null) {
try (InputStream stream = entity.getContent()) {
BufferedReader reader =
new BufferedReader(new InputStreamReader(stream));
String line;
while ((line = reader.readLine()) != null) {
System.out.println(line);
}
}
}
} catch (IOException e) {
e.printStackTrace();
}
}
result of this code is as follows..
Binance ETHUSDT
"lastUpdateId":236998360,"bids":[["88.98000000","2.30400000",[]]..........,"asks":[["89.04000000","16.06458000",[]],.......
What I want to make is a kind of price array..
Double Binance[][] = [88.98000000][2.30400000][89.04000000][6.06458000]
How can I extract just Price and Qty from the HTTP/GET response?
If the response is a JSON, use a parser like Jackson and extract the values. This can be then added to array.
This link will help you.
You will need to parse those values out of the variable line:
There are many ways to do that including using regular expressions or simply using String functions. You'd need to create an ArrayList just before the loop and add each price into it. I highly recommend that you use the Money class from java 9 rather than a double or a float. See -> https://www.baeldung.com/java-money-and-currency
I did a http client and I'm getting a response. I am using a JSONObject to parse the data and when I execute the code below it prints out all of the JSON just fine
HttpResponse response = httpclient.execute(httppost);
HttpEntity entity = response.getEntity();
if(entity!=null){
try(InputStream instream = entity.getContent()) {
String responseString = readInputStream(instream);
JSONObject job = new JSONObject(responseString);
statusLabel.setText("Command Result: " + job.toString());
Here is the readInputSream function:
static private String readInputStream(InputStream inputStream) throws IOException {
BufferedReader reader = new BufferedReader(new InputStreamReader(
inputStream, "UTF-8"));
String tmp;
StringBuilder sb = new StringBuilder();
while ((tmp = reader.readLine()) != null) {
sb.append(tmp).append("\n");
}
if (sb.length() > 0 && sb.charAt(sb.length() - 1) == '\n') {
sb.setLength(sb.length() - 1);
}
reader.close();
return sb.toString();
}
If I change it from job.toString() to:
statusLabel.setText("Command Result: " + job.get("result"));
it prints a 1 which is correct, it works all the way up to my_list. I'm not sure how to parse the list. I put a snippet of the response below. Ive tried "my_list", "my_list[]", my_list[0]" which none have worked. I get JSONObject "blank" not found
{"result":1, "ver":1,"total":2,"catch":true,"my_list":[{"id":3,"mid":0,"format":3,"user":4,"property":1,"type":0,"title":"hello","start":146,"end":1464,"hid":3,"bid":1,"reason":1,"time":0,"creator":"1","hello":0,"my":0,"year":"0","ggg":614,"name":"","ch":"0","attr":0,"type":1,"vtype":1,"tm_log": {"fr":4,"action":0,"vr":"82","started":1,"av_ended":2,"tr":1}}
The element you trying to retrieve is parsed into a JSONArray, not a JSONObject. Try:
JSONArray my_list = job.getJSONArray("my_list");
Assuming that you are using json parser project JSON-java to parse your JSON you need to retrieve a JSONArray instance - this is how arrays are storred in JSONObject. so do the following: JSONArray my_list = job.getJSONArray("my_list"); and then use methods of JSONArray class to access your array. The Javadoc to JSON-java package can be found here: http://stleary.github.io/JSON-java/index.html. Also note that JSON-java is very simple and easy to use JSON parser project but it is not very efficient for any serious project. Common recommendation for commercial use is Jackson JSON Processor which is one of the fastest and powerful JSON parsers. Here are some links to read about it: https://github.com/FasterXML/jackson, http://wiki.fasterxml.com/JacksonHome
I have a servlet in which the from InputStream I am getting the my form data in XML format. I am able to get retrieve the form data in XML format and able to write the same in file. If I open the file I am able to see my form data.
Now the issue is, When i try to append the form data to the string buffer it is not happening. I tried buffer.append(). After that method When I try to print the string buffer value nothing is showing/printing in the console.
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
response.setContentType("html/text");
PrintWriter out = response.getWriter();
out.println("doPost Method is excecuting");
DataInputStream in = new DataInputStream (request.getInputStream());
StringBuffer buffer = new StringBuffer();
File file = new File("reqOutput.txt");
file.createNewFile();
FileWriter writer = new FileWriter(file);
int value;
while ((value=in.read()) != -1) {
buffer.append(value);
writer.write(value);
}
System.out.println("Value is : "+ buffer.toString()); // Nothing is printing
writer.flush();
writer.close();
}
What's wrong with my code.Any suggestions please.
Here is your code modified to read from a file:
public static void main(final String[] args) throws Exception {
BufferedReader in = null;
try {
in = new BufferedReader(new FileReader("test"));
final StringBuilder sb = new StringBuilder();
String line;
while ((line = in.readLine()) != null) {
sb.append(line);
}
System.out.println("Value is : " + sb.toString());
} finally {
if (in != null) {
in.close();
}
}
}
I added a BufferedReader around the FileReader to optimize the reading.
I switched from reading one character at a time to reading line by line.
This also gives you the results as String so you don't have to convert the int.
Furthermore I added resource handling (pre-7 style and without exception handling) and switched to StringBuilder.
Output:
hello world! -> Value is : hello world!
I think there is another problem, not in this part of your code.
Additional comments on your code (not related to the question):
StringBuffer is a thread-safe implementation. If you have no need for this (like in your servlet example) you'd better use StringBuilder.
Don't close resources within the code block, use a try-finally (or since Java 7 try-with-resources) to guarantee resources are always closed, even when exceptions occur in the block somewhere.
This question already has answers here:
Retrieving JSON from URL on Android
(6 answers)
Closed 9 years ago.
I am given a URL from World Bank and I was told to get data from it. I checked the JSON api pages but did not understand where to start. It is an Android app that I am practicing and I have to choose some indicators and get data by that URL. I need to know where to start and some basic advice about using JSON. So as a programmer, if you are given a url to get data from, how would you start ?
String myDataString = "URL STRING";
String dataString = new String();
I did a android project recently fetching data from a json file on a remote server. I used something like this.
public void getData(String URL) {
AsyncTask<String,String,String> getTask = new AsyncTask<String,String,String>(){
#Override
protected String doInBackground(String... params) {
String response = "";
try{
URL url = new URL(params[0]);
HttpURLConnection urlConnection = (HttpURLConnection)
url.openConnection();
BufferedReader
reader = new
BufferedReader(new InputStreamReader(urlConnection.getInputStream()));
String line = "";
while((line = reader.readLine()) != null){
response += line + "\n";
}
} catch (Exception e){
}
return response;
}
protected void onPostExecute(String result) {
System.out.println(result);
}
};
getTask.execute(URL);
}
So you wanna do an AsyncTask to avoid the activity from crashing when it is waiting for response. It opens a urlConnection, initiates a bufferedReader and keeps reading when more lines are to be found. When it is done, it prints the result to console.
I found that this way seemed the most common when fetching data from JSON to an android app. How you manipulate the data is up to you, some use strings some use JSON objects..
You may want to start with a tutorial on how to parse a remote JSON : Android JSON Parsing from URL – Example
I use the code below which in my http get request,but what I get from return is a null.I don't know why.
public static String getResponseFromGetUrl(String url) throws Exception {
StringBuffer sb = new StringBuffer();
try {
HttpResponse httpResponse = httpclient.execute(httpRequest);
String inputLine = "";
if (httpResponse.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
InputStreamReader is = new InputStreamReader(httpResponse
.getEntity().getContent());
BufferedReader in = new BufferedReader(is);
while ((inputLine = in.readLine()) != null) {
sb.append(inputLine);
}
in.close();
}
} catch (Exception e) {
e.printStackTrace();
return "net_error";
} finally {
httpclient.getConnectionManager().shutdown();
}
return sb.toString();
}
And what I have use the function is
String json_str = HttpUtils.getResponseFromGetUrl("www.xxx.com/start");
if ((json_str == null)) Log.d("Chen", "lastestTimestap----" + "json_str == null");
And sometimes the Log will be printed.Not always,in fact like 1%.But I don't know why it caused.
This code will not produce a "null". There must be more code you are not showing.
If this is all the code you have I suggest you remove the StringBuffer and replace it with
return "";
More likely you have forgetten to mention some code which is doing something like
Object o = null;
sb.append(o); // appears as "null"
EDIT: Based on your update, I would have to assume you are reading a line like "null"
It is highly unlikely you want to discard the newline between each line. I suggest either you append("\n") as well or just record all the text you get without regard for new lines.
BTW Please don't use StringBuffer as its replacement StringBuilder has been around for almost ten years. There is a common misconception that using StringBuffer helps with multi-threading but more often it results in incorrect code because it is very harder, if not impossible to use StringBuffer correctly in a multi-threaded context