I'm using google volley for networking in android. I will make a http GET request and need to return a response header value. I found some answers on stack overflow to access the header fields, but don't know how to return it to my calling spot. Please have a look at my code, I put four numbers in it to explain my problem.
At (1) I can print out the value which I need. Than I've tried to save it in a class attribute (2) and there is no error in the IDE. If I want to return it from there (3), I got a NullPointerException at (4). Maybe its a read before write problem there. So how can I get the value from (1) to (4)? Thanks a lot!
public class Login {
String phpsessid = null;
public Login() {}
public String getSessionId(Context context) {
RequestQueue queue = Volley.newRequestQueue(context);
StringRequest sr = new StringRequest(Request.Method.GET, "any url",
new Response.Listener<String>() {
@Override
public void onResponse(String response) {
System.out.println(response);
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
}
}) {
@Override
protected Response<String> parseNetworkResponse(NetworkResponse response) {
System.out.println(response.headers.get("Set-Cookie")); (1)
phpsessid = response.headers.get("Set-Cookie"); (2)
return super.parseNetworkResponse(response);
}
};
queue.add(sr);
return phpsessid; (3)
}
}
in main:
Login login = new Login();
String result = login.getSessionId(this.getContext);
System.out.println(result); (4)
When you add a request to the queue, that request is executed asynchronously. This means it is not executed in the same order as you're reading it - it happens on another thread, and will return eventually when it's done.
protected Response<String> parseNetworkResponse(NetworkResponse response) {
System.out.println(response.headers.get("Set-Cookie")); (1)
phpsessid = response.headers.get("Set-Cookie"); (2)
return super.parseNetworkResponse(response);
}
This returns the body of the response - from what I'm reading in your code, it looks like you want to return the value of the "Set-Cookie" header. You can do this like this:
protected Response<String> parseNetworkResponse(NetworkResponse networkResponse) {
String sessionId = response.headers.get("Set-Cookie");
com.android.volley.Response<String> result = com.android.volley.Response.success(sessionId,
HttpHeaderParser.parseCacheHeaders(networkResponse));
return result;
}
This will return the value of the "Set-Cookie" header to your onResponse
method:
new Response.Listener<String>() {
@Override
public void onResponse(String response) {
System.out.println(response);
}
}
A better idea may be to pass a success/failure listener in when making your getSessionId
call. In this way, you can then easily get access to the result in the calling class:
public void getSessionId(Context context, final Response.Listener<String> successListener, Response.ErrorListener failureListener) {
RequestQueue queue = Volley.newRequestQueue(context); // This should be a singleton!
StringRequest sr = new StringRequest(Request.Method.GET, "any url",
successListener,
failureListener) {
@Override
protected Response<String> parseNetworkResponse(NetworkResponse networkResponse) {
String sessionId = response.headers.get("Set-Cookie");
com.android.volley.Response<String> result = com.android.volley.Response.success(sessionId,
HttpHeaderParser.parseCacheHeaders(networkResponse));
return result;
}
};
queue.add(sr);
}
Edit:
Now, you can call this as follows:
Login login = new Login();
login.getSessionId(this, new Response.Listener<String>() {
@Override
public void onResponse(String response) {
// You can access member variables from here.
// This will only get called after the network activity has happened!
phpsessid = response;
// All the work you need to do after your session ID has updated, you can put into a method and call it from here
// In your original example, this would be (4)
onSessionIdUpdated();
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
// We'll just ignore these for now - you should handle errors though!
}
});
// Anything you put here will happen immediately after the getSessionId call above, and notably *before* onResponse or onErrorResponse is called (ignoring potential race conditions here for now).