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Where to declare the ArrayList, if I want dynamically to fill it

I have a Java Server, I want to store all IP, which send requests to Server, because I want to check, if user was here already, and if he was I want to send him another message.
There method sendStaticResource at the bottom should do it.
For this purpose I want to use ArrayList ips, which I will check every time, when request comes. My problem is that the values(IPs) won't be store - each time request is made, the old IP disappears ( so the length is always 1).
So the question is - where and how could I initialise the ArrayList, so each time request is made, ip goes in the Arraylist and the old won't disappear
public class Response {
Request request;
OutputStream output;
ArrayList<String> ips = new ArrayList<String>();
public Response(OutputStream output) {
this.output = output;
}
public void setRequest(Request request) {
this.request = request;
}
public String getIp() {
InetAddress thisIp = null;
try {
thisIp = InetAddress.getLocalHost();
} catch (Exception e) {
System.out.println(e.toString() );
}
return thisIp.getHostAddress();
}
public void content(String header, int contentLength, String msg ) throws IOException {
System.out.println(msg);
String message = "HTTP/1.1" + header + "\r\n" +
"Content-Type: text/html\r\n" +
"Content-Length: "+ contentLength + "\r\n" +
"\r\n" +
"<h1>" + msg + "</h1>";
try {
output.write(message.getBytes());
output.flush();
} catch (Exception e) {
System.out.println(e.toString());
}
}
public void sendStaticResource() throws IOException {
if(request.getUri().equals("/")) {
content("200 OK", 20, "Hello world");
ips.add (getIp());
System.out.println(ips.size());
}
}
}

I suppose that each a request comes in you create a new Response object. Since the ips list is an instance member of the Response object, each time you create a new instance of it you also create a new list of ips.
If you want to have a list of strings storing all the ips of the requests you have received, I suggest you modify your code in such manner that the ip list is a static field of the Response object.
This way you'll end up with something that is shared between all the objects of the Response class and not something unique to each instance. For more information I would suggest to check on the differences between instance and static members of a class. For more you can check here: https://docs.oracle.com/javase/tutorial/java/javaOO/classvars.html
Finally a small hint concerning code style and best practices revolves around this line:
ArrayList<String> ips = new ArrayList<String>();
I would strongly suggest to user something like this:
List<String> ips = new ArrayList<String>();
In my honest opinion it's much better to code to and interface rather than the concrete implementation.

ChunkedInput not working in jersey

Can anyone help me why the java code is having issue and printing all data in one go instead of prinitng each chunk as javascript code
Java Code :
import org.glassfish.jersey.client.ChunkedInput;
import javax.ws.rs.client.Client;
import javax.ws.rs.client.ClientBuilder;
import javax.ws.rs.core.GenericType;
import javax.ws.rs.core.Response;
public class RunClient {
public static void main(String args[]) throws InterruptedException {
Client client = ClientBuilder.newClient();
//2 is to increase amount of data and 3(seconds) is for time b/w chunked output ,can be changed
final Response response = client.target("http://jerseyexample-ravikant.rhcloud.com/rest/jws/streaming/2/3").request()
.get();
final ChunkedInput<String> chunkedInput = response.readEntity(new GenericType<ChunkedInput<String>>() {
});
String chunk;
while ((chunk = chunkedInput.read()) != null) {
System.err.println("Next chunk received: " );
System.out.println(chunk);
}
}
}
JavaScript : (Open Page http://jerseyexample-ravikant.rhcloud.com/rest/jws and then press F12 and run below in console as javascript call not allowed from other domain)
//2 is to increase amount of data and 3(seconds) is for time b/w chunked output ,can be changed
var xhr = new XMLHttpRequest()
xhr.open("GET", "http://jerseyexample-ravikant.rhcloud.com/rest/jws/streaming/2/3", true)
xhr.onprogress = function () {
console.log("PROGRESS:", xhr.responseText) ;console.log("\n");
}
xhr.send()
EDIT : Just for help it also works will normal java connection
String uri = "http://jerseyexample-ravikant.rhcloud.com/rest/jws/streaming/3/1";
URL url = new URL(uri);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("GET");
connection.setDoOutput(true);
BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
String line;
while ((line = in.readLine()) != null) {
System.out.println(line);
}
in.close();
My WebService Code
#Path("streaming/{param}/{sleepTime}")
#GET
#Produces(MediaType.TEXT_PLAIN)
public ChunkedOutput<String> getChunkedStream(#PathParam("param") String loopcount,#PathParam("sleepTime") String sleepTime) throws Exception {
final ChunkedOutput<String> output = new ChunkedOutput<>(String.class);
final Integer val=Integer.parseInt(loopcount);
final Integer isleepTime=Integer.parseInt(sleepTime)*1000;
new Thread(new Runnable() {
#Override
public void run() {
try {
StringBuffer chunk = null;
for (int i = 0; i < 10; i++) {
chunk = new StringBuffer();
for (int j = 0; j < val; j++) {
chunk.append(" Message #" + i+ "#"+j);
}
output.write(chunk.toString()+"\n");
System.out.println("write");
Thread.sleep(isleepTime);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
System.out.println("output.close();");
output.close();
} catch (IOException ex) {
ex.printStackTrace();
}
}
}
}).start();
return output;
}

Form jersey docs:
Writing chunks with ChunkedOutput is simple, you only call method write() which writes exactly one chunk to the output. With the input reading it is slightly more complicated. The ChunkedInput does not know how to distinguish chunks in the byte stream unless being told by the developer. In order to define custom chunks boundaries, the ChunkedInput offers possibility to register a ChunkParser which reads chunks from the input stream and separates them. Jersey provides several chunk parser implementation and you can implement your own parser to separate your chunks if you need. In our example above the default parser provided by Jersey is used that separates chunks based on presence of a \r\n delimiting character sequence.
So your server has to separate chunks with \r\n, or you have to register a ChunkParser.
Assuming you have a constant finalising each chunk you could try:
Client client = ClientBuilder.newClient();
//2 is to increase amount of data and 3(seconds) is for time b/w chunked output ,can be changed
final Response response = client.target("http://jerseyexample-ravikant.rhcloud.com/rest/jws/streaming/2/3").request()
.get();
final ChunkedInput<String> chunkedInput = response.readEntity(new GenericType<ChunkedInput<String>>() {
});
chunkedInput.setParser(ChunkedInput.createParser(BOUNDARY));
String chunk;
while ((chunk = chunkedInput.read()) != null) {
System.err.println("Next chunk received: " );
System.out.println(chunk);
}
While BOUNDARY is a finalizing string for each chunk.
The in.readLine solution in your edit will break down "chunks" by every newline, even if one chunk consist a \n, it will be interpreted as 2 chunks.

how to get a value by key from an json (or xml) string?

In the android app I get an xml or json string returned, However, I cant seem to figure out any way on how to get an value from the string in any way by entering an key.
In PHP you just use something like $myArray['parent']['child'] but I have no clue on how this works in java.
Any idea's would be greatly appreciated! (an example for both XML and JSON even more ;) )

Here's what I would do:
locate an XML/JSON library (there's tons) (google-gson for json)
read the documentation to find a parse method ((new JsonParser()).parse(text))
read the documentation to find out what the return value is (JsonElement)
decide what you want to do with the parsed data (myJsonObj.get(...))
write the code

public class parsingjsontest2 extends Activity {
/** Called when the activity is first created. */
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(main);
String str = connect("http://rentopoly.com/ajax.php?query=Bo"));
System.out.println("String::"+str);
}
}
private String connect(String url)
{
// Create the httpclient
HttpClient httpclient = new DefaultHttpClient();
// Prepare a request object
HttpGet httpget = new HttpGet(url);
// Execute the request
HttpResponse response;
// return string
String returnString = null;
try {
// Open the webpage.
response = httpclient.execute(httpget);
if(response.getStatusLine().getStatusCode() == 200){
// Connection was established. Get the content.
HttpEntity entity = response.getEntity();
// If the response does not enclose an entity, there is no need
// to worry about connection release
if (entity != null) {
// A Simple JSON Response Read
InputStream instream = entity.getContent();
// Load the requested page converted to a string into a JSONObject.
JSONObject myAwway = new JSONObject(convertStreamToString(instream));
// Get the query value'
String query = myAwway.getString("query");
**// Make array of the suggestions
JSONArray suggestions = myAwway.getJSONArray("suggestions");
// Build the return string.
returnString = "Found: " + suggestions.length() + " locations for " + query;
for (int i = 0; i < suggestions.length(); i++) {
returnString += "\n\t" + suggestions.getString(i);
}
// Cose the stream.
instream.close();
}
}
else {
// code here for a response othet than 200. A response 200 means the webpage was ok
// Other codes include 404 - not found, 301 - redirect etc...
// Display the response line.
returnString = "Unable to load page - " + response.getStatusLine();
}
}
catch (IOException ex) {
// thrown by line 80 - getContent();
// Connection was not established
returnString = "Connection failed; " + ex.getMessage();
}
catch (JSONException ex){
// JSON errors
returnString = "JSON failed; " + ex.getMessage();
}
return returnString;
}
private static String convertStreamToString(InputStream is) {
/*
* To convert the InputStream to String we use the BufferedReader.readLine()
* method. We iterate until the BufferedReader return null which means
* there's no more data to read. Each line will appended to a StringBuilder
* and returned as String.
*/
BufferedReader reader = new BufferedReader(new InputStreamReader(is));
StringBuilder sb = new StringBuilder();
String line = null;
try {
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
is.close();
} catch (IOException e) {
e.printStackTrace();
}
}
return sb.toString();
}
}

As you didn't specify what kind of xml you are trying to read, I'm answering based on what I know.
In Android, if you were talking about the layout and strings.xml files, you use a dot (.) operator, like R.string.appname.
Please post more details about your specific problem, if this is not what you were looking for.

How do you access posted form data in a servlet?

If I have a servlet running JVM1.4.2, and it is receiving a POST request with form data fields. I use req.getParameterNames() to get, what I would expect, all the query string and form data. However, all I ever get are the querystring parameters.
Literature I am reading from various sources says that getParameterNames() and getParameterValues(String) should be the way to get all query string and posted form data sent by the browser for JDK 1.4. Here is the method I use to extract all the parameters, which I expect would include posted form data :
public Map getParameterMap(HttpServletRequest req) {
Map params= new HashMap();
String name = null;
System.out.println("<< Getting Parameter Map.>>");
Enumeration enumParams = req.getParameterNames();
for (; enumParams.hasMoreElements(); ) {
// Get the name of the request parameter
name = (String)enumParams.nextElement();
// Get the value of the request parameters
// If the request parameter can appear more than once
// in the query string, get all values
String[] values = req.getParameterValues(name);
params.put(name, values);
String sValues = "";
for(int i=0;i<values.length;i++){
if(0<i) {
sValues+=",";
}
sValues +=values[i];
}
System.out.println("Param " + name + ": " + sValues);
}
System.out.println("<< END >>");
return params;
}
This question also agrees with my expectations, but the servlet is not picking up the form data. Obviously I am missing something....
Update: The post data is very straight forward and is not a Multipart form or rich media. Just plain'ol text submitted via an AJAX POST that looks like this in post body
c1=Value%20A&c2=Value%20B&c3=Value%20C

I managed to identify the problem. Because there is so much chatter from JDK 1.5+ and talk of getParameterMaps() method for 1.5, info on how 1.4 handles form post data was scarce and ambiguous. (Please post a comment if you find something that is specific for 1.4).
Pre-1.5 you have to manually get the form data via getInputStream, and then parse it out. I found this method, (posted below), from the java sun site that does a nice job using a Hashtable. I had to make a minor mod for deprecated methods. But seems to work quite robustly, "out of the box", so you should able to just cut-n-paste. I know it's "old tech" but I thought it worthwhile for those who may be in the same situation as me who are stuck on solving (what seems to be) straight forward problems.
public Hashtable parsePostData(int length, ServletInputStream instream) {
String valArray[] = null;
int inputLen, offset;
byte[] postedBytes = null;
boolean dataRemaining=true;
String postedBody;
Hashtable ht = new Hashtable();
//Vector paramOrder = new Vector(10);
StringBuffer sb = new StringBuffer();
if (length <=0) {
return null;
}
postedBytes = new byte[length];
try {
offset = 0;
while(dataRemaining) {
inputLen = instream.read (postedBytes, offset, length - offset);
if (inputLen <= 0) {
throw new IOException ("read error");
}
offset += inputLen;
if((length-offset) ==0) {
dataRemaining=false;
}
}
} catch (IOException e) {
System.out.println("Exception ="+e);
return null;
}
postedBody = new String (postedBytes);
StringTokenizer st = new StringTokenizer(postedBody, "&");
String key=null;
String val=null;
while (st.hasMoreTokens()) {
String pair = (String)st.nextToken();
int pos = pair.indexOf('=');
if (pos == -1) {
throw new IllegalArgumentException();
}
try {
key = URLDecoder.decode(pair.substring(0, pos),"UTF8");
val = java.net.URLDecoder.decode(pair.substring(pos+1,pair.length()),"UTF8");
} catch (Exception e) {
throw new IllegalArgumentException();
}
if (ht.containsKey(key)) {
String oldVals[] = (String []) ht.get(key);
valArray = new String[oldVals.length + 1];
for (int i = 0; i < oldVals.length; i++) {
valArray[i] = oldVals[i];
}
valArray[oldVals.length] = val;
} else {
valArray = new String[1];
valArray[0] = val;
}
ht.put(key, valArray);
String sValues = "";
for(int i=0;i<valArray.length;i++) {
if (0<i) {
sValues+=",";
}
sValues = valArray[i];
}
System.out.println("Form data field " + key + ":" +sValues);
//paramOrder.addElement(key);
}
return ht;
}

That's true. The getParameterNames(), getParameterValues(), and getParameter() methods are the way to access form data unless it's a multipart form, in which case you'll have to use something like Commons Fileupload to parse the multipart request before all the parameters are accessible to you.
Edit: You're probably not encoding the POST data properly in your AJAX call. POST data must carry a Content-Type of application/x-www-form-urlencoded or else multipart/form-data. If you're sending it as something else, it doesn't qualify as a request parameter, and I expect you'd see the behavior you're describing. The solution you've engineered essentially consists of setting up custom parsing of custom content.

How efficient it is to return a string in Java

All sample function I've seen so far avoid, for some reason, returning a string. I am a total rookie as far as Java goes, so I am not sure whether this is intentional. I know that in C++ for example, returning a reference to a string is way more efficient than returning a copy of that string.
How does this work in Java?
I am particularly interested in Java for Android, in which resources are more limited than desktop/server environment.
To help this question be more focused, I am providing a code snippet in which I am interested in returning (to the caller) the string page:
public class TestHttpGet {
private static final String TAG = "TestHttpGet";
public void executeHttpGet() throws Exception {
BufferedReader in = null;
try {
HttpClient client = new DefaultHttpClient();
HttpGet request = new HttpGet();
request.setURI(new URI("http://www.google.com/"));
HttpResponse response = client.execute(request); // actual HTTP request
// read entire response into a string object
in = new BufferedReader(new InputStreamReader(response.getEntity().getContent()));
StringBuffer sb = new StringBuffer("");
String line = "";
String NL = System.getProperty("line.separator");
while ((line = in.readLine()) != null) {
sb.append(line + NL);
}
in.close();
String page = sb.toString();
Log.v(TAG, page); // instead of System.out.println(page);
}
// a 'finally' clause will always be executed, no matter how the program leaves the try clause
// (whether by falling through the bottom, executing a return, break, or continue, or throwing an exception).
finally {
if (in != null) {
try {
in.close(); // BufferedReader must be closed, also closes underlying HTTP connection
}
catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
In the example above, can I just define:
public String executeHttpGet() throws Exception {
instead of:
public void executeHttpGet() throws Exception {
and return:
return (page); // Log.v(TAG, page);

A String in java corresponds more or less to std::string const * in c++. So, it's cheap to pass around, and can't be modified after it's created (String is immutable).

String is a reference type - so when you return a string, you're really just returning a reference. It's dirt cheap. It's not copying the contents of the string.

In java most of the time you return something, you return it by reference. There's no object copying or cloning of any kind. So it is fast.
Also, Strings in Java are immutable. No need to worry about that either.