I have a Servlet that sends back a JSON Object and I would like to use this servlet in another Java project. I have this method that gets me the results:
public JSONArray getSQL(String aServletURL)
{
JSONArray toReturn = null;
String returnString = "";
try
{
URL myUrl = new URL(aServletURL);
URLConnection conn = myUrl.openConnection();
conn.setDoOutput(true);
BufferedReader in = new BufferedReader( new InputStreamReader( conn.getInputStream() ) );
String s;
while ((s = in.readLine()) != null )
returnString += s;
in.close();
toReturn = new JSONArray(returnString);
}
catch(Exception e)
{
return new JSONArray();
}
return toReturn;
}
This works pretty will, but the problem I am facing is the following:
When I do several simultaneous requests, the results get mixed up and I sometimes get a Response that does not match the request I send.
I suspect the problem to be related to the way I get the response back: The Reader reading a String from the InputStream of the connection.
How can I make sure that I get one reques -> one corresponding reply ?
Is there a better way to retrieve my JSON object from my servlet ?
Cheers,
Tim
When I do several simultaneous requests, the results get mixed up and I sometimes get a Response that does not match the request I send.
Your servlet is not thread safe. I'd bet that you've improperly assigned request scoped data either directly or indirectly as instance or class variables of the servlet. This is a common beginner's mistake.
Carefully read this How do servlets work? Instantiation, sessions, shared variables and multithreading and fix your servlet code accordingly. The problem is not in the URLConnection code shown so far, although it indicates that you're doing exactly the same job in both doGet() and doPost(), which in turn is already a smell as to how the servlet is designed.
Try removing setDoOutput(true), you are using the connection only for input and so you shouldn't use it.
Edit: alternatively try using HttpClient, it's much nicer that using "raw" Java.
Related
I have a dialogflow project that I'm trying to access from Java with a rest call.
It is giving me an authentication issue.
I have followed all online instructions (and many forum suggestions) to no avail.
I have tried generating the key json, as per the instructions here:
https://dialogflow.com/docs/reference/v2-auth-setup
and setting my environment variable as described, but nothing seems to work.
I have checked my projectID, and am running off the same machine with the environment variable, and have double, triple and quadruple checked it's name and location, but I still get the following error:
java.net.HttpRetryException: cannot retry due to server authentication, in streaming mode
Here is my code (though it's a REST call, so I don't know if it's so relevant):
String url = https://dialogflow.googleapis.com/v2/projects/MYPROJECT/agent/sessions/SESSION_NUM:detectIntent
URL url = new URL(full_url);
String inText = "Hello World";
String outText = "";
HttpURLConnection con = (HttpURLConnection) url.openConnection();
try {
con.setDoOutput(true);
con.setRequestMethod("POST");
// set body of http post
Map<String,String> arguments = new HashMap<>();
JSONObject inTextJsn = new JSONObject();
inTextJsn.append("text",inText);
inTextJsn.append("languageCode","en");
JSONObject fieldJsn = new JSONObject();
fieldJsn.append("text", inTextJsn);
arguments.put("queryInput", fieldJsn.toString());
StringJoiner sj = new StringJoiner("&");
for(Map.Entry<String,String> entry : arguments.entrySet())
sj.add(URLEncoder.encode(entry.getKey(), "UTF-8") + "="
+ URLEncoder.encode(entry.getValue(), "UTF-8"));
// post http post as bytes
byte[] bytes_out = sj.toString().getBytes(StandardCharsets.UTF_8);
con.setFixedLengthStreamingMode(bytes_out.length);
con.connect();
try (OutputStream os = con.getOutputStream()) {
os.write(bytes_out);
}
BufferedReader reader = new BufferedReader(new InputStreamReader(con.getInputStream(),
"UTF-8"));
// read all lines to a string
String line;
String response = "";
while ((line = reader.readLine()) != null) {
response += line;
}
JSONObject responseJsn = new JSONObject(response);
outText = responseJsn.get("fulfillmentText").toString();
} catch (Exception e) {
System.err.println(e);
} finally {
con.disconnect();
}
return restResponse;
The gist of the code is to simply send a message ("Hello World!") to my dialogflow, and get back my agent's response (the code may have bugs - it's a bit hard to test when I can't get passed this authentication issue, so please help with the authentication, not code bugs).
Thanks all!
The directions at that page assume you're going to use the gcloud program to generate a currently valid bearer token, which is then sent along with the HTTP headers. That page illustrates
Your code doesn't seem to be generating an Authorization HTTP header at all, which is why you're getting the error you do.
Since you're using Java, you should look at the google-auth-library-java library, which will give you the tools to generate the token you need to provide in the Authorization header.
You may also wish to check out the google-cloud-java library. This contains Java classes to directly perform operations against Dialogflow instead of coding the REST/HTTP calls yourself. (However, it is still at an Alpha level for Dialogflow, so may not be stable or forwards compatible.)
Sorry for the very basic question, I am new to Java.
To get data from an URL I use code like this
URL url = new URL(BaseURL+"login?name=foo");
URLConnection yc = url.openConnection();
BufferedReader in = new BufferedReader(new InputStreamReader(yc.getInputStream()));
while ((inputLine = in.readLine()) != null)
...
That works perfectly fine. When I now want to continue and send the next command to the server (like ".../getStatus"), do I need to create these objects over and over again, or is there a smarter way?
Thanks!
You have to call openConnection again in order to get a new URLConnection. The HttpURLConnection does internal caching, though, so if the HTTP-server supports Connection: keep-alive the underlying connection to the server will be reused so it's not that bad as it originally might look. It's just hidden from you.
I looked into the Apache HttpComponents (HttpClient) and it still requires a lot of code. As I don't need cookie-handling (it's only a simple RESTful server giving json-blocks as responses) I'm going for a very simple solution:
public static String readStringFromURL(String requestURL) throws IOException
{
URL u = new URL(requestURL);
try (InputStream in = u.openStream()) {
return new String(in.readAllBytes(), StandardCharsets.UTF_8);
}
}
For me that looks like a perfect solution, but as mentioned, I am new to Java and open (and thankful) for hints...
I'm using HttpURLConnection to send JSON data from an Android Application to my Tomcat Server.
The POST works fine with small sized JSONs. On bigger data sets it fails with a FileNotFoundException.
What can it be?
Here's the code:
try {
URL url = new URL(urlIn);
strOut = "";
huc = (HttpURLConnection) url.openConnection();
huc.setRequestProperty("Connection", "Close");
huc.setRequestMethod("POST");
huc.setRequestProperty("User", userId);
huc.setRequestProperty("Action", action);
huc.setRequestProperty("JSON", jsonData);
huc.setConnectTimeout(10000);
in = new BufferedReader(new InputStreamReader(huc.getInputStream()));
while ((inputLine = in.readLine()) != null){
if (strOut.equalsIgnoreCase("")){
strOut = inputLine;
} else {
strOut = strOut + inputLine;
}
}
} catch (Exception e) {
strOut = "";
e.printStackTrace();
}
When jsonData get to a certain size (arround 10000 chars), the POST fails with the error mentioned. The content of the JSON does not have any special character.
Thanks in advance.
Best regards, Federico.
HTTPUrlConnection throws a FileNotFoundException if the server responds with a 404 response code, so the reason why this happens seems to be located on the server side rather than the client side. Most likely the server is configured to accept request headers up to a particular length and will return an error if that size is exceeded. A short Google-search brought up a couple of results, sizes of 16 KB are mentioned but shorter values are also reasonable.
As I mentioned in my comment to your question, you should change your process to receive the JSON-data (and the other values for User and Action as well BTW) as part of the request body, e.g. as url-encoded query string or as multipart formdata. Both ways are supported by HTTP client libraries you can use or are easily built manually.
After lots of reading and trying I gave up with configuring Tomcat to accept larger headers.
So I convinced the team in charge of the Tomcat app to make a servlet that is able to receive this data in the body, just as Lothar suggested.
Thanks!
i want to make an application which is based on a php page, sending to it parameters to obtain data from the remote db through the php page.
I will use jsons, but my question is:
assumed i use this code to send request:
URL url = new URL("http://www.francescorizzi.altervista.org/Main.php?Request=Login&UserName=mario&Password=lol");
URLConnection conn = url.openConnection();
// Get the response
BufferedReader rd = new BufferedReader(new InputStreamReader(conn.getInputStream()));
String line;
while ((line = rd.readLine()) != null) {
System.out.println(line);
}
Should i recreate the url object, conn, and rd at each new request? or is there a more efficient way to do this?
Please note: I'm new to http handling through java.
since it is an http request and you retrieving data from that particular url, there is a need to recreate the object because the site may get updated later. so creating new object again will dispose the previous object reference and also close connection after retrieving data.
I would like to upload files from java application/applet using POST http event. I would like to avoid to use any library not included in SE, unless there is no other (feasible) option.
So far I come up only with very simple solution.
- Create String (Buffer) and fill it with compatible header (http://www.ietf.org/rfc/rfc1867.txt)
- Open connection to server URL.openConnection() and write content of this file to OutputStream.
I also need to manually convert binary file into POST event.
I hope there is some better, simpler way to do this?
You need to use the java.net.URL and java.net.URLConnection classes.
There are some good examples at http://java.sun.com/docs/books/tutorial/networking/urls/readingWriting.html
Here's some quick and nasty code:
public void post(String url) throws Exception {
URL u = new URL(url);
URLConnection c = u.openConnection();
c.setDoOutput(true);
if (c instanceof HttpURLConnection) {
((HttpURLConnection)c).setRequestMethod("POST");
}
OutputStreamWriter out = new OutputStreamWriter(
c.getOutputStream());
// output your data here
out.close();
BufferedReader in = new BufferedReader(
new InputStreamReader(
c.getInputStream()));
String s = null;
while ((s = in.readLine()) != null) {
System.out.println(s);
}
in.close();
}
Note that you may still need to urlencode() your POST data before writing it to the connection.
You need to learn about the chunked encoding used in newer versions of HTTP. The Apache HttpClient library is a good reference implementation to learn from.