Doing HTTP Post with Android

plusminus · by **plusminus** » Thu Jan 10, 2008 10:26 pm

What you will learn: You will learn how to do HTTP Post from within Android.

:?:

Problems/Questions: Write them right below...

Difficulty: 2 of 5

What it will look like:

Description:
0.) HTTP is a request-response protocol. Various types of requests are possible, each identified by a different HTTP method. Here we will use the POST-Method.

1.) So we will once again start, where all Activities start. We will do some simple preparation first:

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        @Override
        public void onCreate(Bundle icicle) {
                super.onCreate(icicle);
 
                /* Create a new HTTP-RequestQueue. */ 
                android.net.http.RequestQueue rQueue = new RequestQueue(this);
                
                /* Prepare the Post-Text we are going to send. */
                String POSTText = null;
                try {
                        POSTText = "mydata=" + URLEncoder.encode("HELLO, ANDROID HTTPPostExample - by anddev.org", "UTF-8");
                } catch (UnsupportedEncodingException e) {
                        return;
                }
                /* And put the encoded bytes into an BAIS,
                 * where a function later can READ bytes from. */
                byte[] POSTbytes = POSTText.getBytes();
                ByteArrayInputStream baos = new ByteArrayInputStream(POSTbytes);
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2.) Preparation is done now, now we will do the interesting stuff:

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                /* Create a header-hashmap */
                Map<String, String> headers = new HashMap<String, String>();
                /* and put the Default-Encoding for html-forms to it. */
                headers.put("Content-Type", "application/x-www-form-urlencoded");
                
                /* Create a new EventHandler defined above, to handle what gets returned. */
                MyEventHandler myEvH = new MyEventHandler(this);
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:idea: MyEventHandler is described in step 5.)

3.) I prepared a very simple php-file on my server, which will simply echo the 'mydata' variable posted to it:

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                 <?php
                                echo "POSTed data: '".$_POST['mydata']."'";
                 ?>
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4.) So we will call the queueRequest of our RequestQueue with the following parameters:

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"http://www.anddev.org/postresponse.php",  // The location of the php-file
"POST", // The Request-'Mode'
headers, // The Header which tells we will have some POST-vars
myEvH, // our eventhandler
baos, // our POST-String(converted to bytes) and ready to be sent
POSTbytes.length, // amount of the bytes in 'baos' to be sent
false // dunno <img src="http://www.anddev.org/images/smilies/hmm.png" alt=":?" title="Confused" />
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So as a real implementated call it looks like this:

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                /* Calls a php-file I prepared. It looks like:
                 * <?php
                 *              echo "POSTed data: '".$_POST['data']."'";
                 * ?>*/
                rQueue.queueRequest("http://www.anddev.org/postresponse.php", "POST",
                                headers, myEvH, baos, POSTbytes.length,false);
 
                /* Wait until the request is complete.*/
                rQueue.waitUntilComplete();
        }
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5.) The last thing we have is a small nearly dummy-class, the MyEventHandler, which simple reacts on events that occur during the "answer" of the requested url called. There basically are just two functions that actually do something:

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                public void data(byte[] bytes, int len) {
                        baf.append(bytes, 0, len); // Add received data to a buffer }
 
                public void endData() {
                        String text = new String(baf.toByteArray()); // Conert Buffer to String
                        myShowNotificationAndLog("Data loaded: n" + text); // Log what was returned }
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Thats it

The Full Source:

"/src/your_package_structure/HTTPPostExample.java"

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package org.anddev.android.webstuff;
 
import java.io.ByteArrayInputStream;
import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
 
import org.apache.http.util.ByteArrayBuffer;
 
import android.app.Activity;
import android.app.NotificationManager;
import android.net.http.EventHandler;
import android.net.http.Headers;
import android.net.http.RequestQueue;
import android.net.http.SslCertificate;
import android.os.Bundle;
import android.util.Log;
 
public class HTTPPostExample extends Activity {
 
        // ===========================================================
        // Fields
        // ===========================================================
        
        private final String DEBUG_TAG = "httpPostExample";
 
        // ===========================================================
        // 'Constructors'
        // ===========================================================
 
        @Override
        public void onCreate(Bundle icicle) {
                super.onCreate(icicle);
 
                /* Create a new HTTP-RequestQueue. */ 
                android.net.http.RequestQueue rQueue = new RequestQueue(this);
                
                /* Prepare the Post-Text we are going to send. */
                String POSTText = null;
                try {
                        POSTText = "mydata=" + URLEncoder.encode("HELLO, ANDROID HTTPPostExample - by anddev.org", "UTF-8");
                } catch (UnsupportedEncodingException e) {
                        return;
                }
                /* And put the encoded bytes into an BAIS,
                 * where a function later can read bytes from. */
                byte[] POSTbytes = POSTText.getBytes();
                ByteArrayInputStream baos = new ByteArrayInputStream(POSTbytes);
                
                /* Create a header-hashmap */
                Map<String, String> headers = new HashMap<String, String>();
                /* and put the Default-Encoding for html-forms to it. */
                headers.put("Content-Type", "application/x-www-form-urlencoded");
                
                /* Create a new EventHandler defined above, to handle what gets returned. */
                MyEventHandler myEvH = new MyEventHandler(this);
 
                /* Now we call a php-file I prepared. It is exactly this:
                 * <?php
                 *              echo "POSTed data: '".$_POST['data']."'";
                 * ?>*/
                rQueue.queueRequest("http://www.anddev.org/postresponse.php", "POST",
                                headers, myEvH, baos, POSTbytes.length,false);
 
                /* Wait until the request is complete.*/
                rQueue.waitUntilComplete();
        }
        
        // ===========================================================
        // Worker Class
        // ===========================================================
        
        private class MyEventHandler implements EventHandler {
                private static final int RANDOM_ID = 0x1337;
 
                /** Will hold the data returned by the URLCall. */
                ByteArrayBuffer baf = new ByteArrayBuffer(20);
                
                /** Needed, as we want to show the results as Notifications. */
                private Activity myActivity;
 
                MyEventHandler(Activity activity) {
                        this.myActivity = activity;  }
 
                public void data(byte[] bytes, int len) {
                        baf.append(bytes, 0, len);  }
 
                public void endData() {
                        String text = new String(baf.toByteArray());
                        myShowNotificationAndLog("Data loaded: n" + text);  }
 
                public void status(int arg0, int arg1, int arg2, String s) {
                        myShowNotificationAndLog("status [" + s + "]");  }
 
                public void error(int i, String s) {
                        this.myShowNotificationAndLog("error [" + s + "]");  }
 
                public void handleSslErrorRequest(int arg0, String arg1, SslCertificate arg2) { }
                public void headers(Iterator arg0) { }
                public void headers(Headers arg0) { }
 
                private void myShowNotificationAndLog(String msg) {
                        /* Print msg to LogCat and show Notification. */
                        Log.d(DEBUG_TAG, msg);
                        NotificationManager nm = (NotificationManager) this.myActivity
                                        .getSystemService(Activity.NOTIFICATION_SERVICE);
                        nm.notifyWithText(RANDOM_ID, msg, NotificationManager.LENGTH_LONG, null);
                }
        }
}
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Regards,
plusminus

cabernet1976 · by **cabernet1976** » Fri Jan 11, 2008 3:13 pm

Hi plusminus,
I haven't use android.net.http.RequestQueue (I cannot find it in android official document) to do POST, I have two questions about your implement:
1. Is RequestQueue better then HttpURLConnection?
2. or could you make explaina about RequestQueue? For example, when there are large count of packages need to be POSTed, whether the RequestQueue will have better perfermance?

Please tell me if I haven't clarified them. The following is my code to do POST:

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    private InputStream doPost(String urlString, String content) throws IOException {
 
        URL url = new URL(urlString);
 
        HttpURLConnection con = (HttpURLConnection) url.openConnection();
 
        InputStream in = null;
 
        OutputStream out;
 
        byte[] buff;
 
        con.setRequestMethod("POST");
 
        con.setDoOutput(true);
 
        con.setDoInput(true);
 
        con.connect();
 
        out = con.getOutputStream();
 
        buff = content.getBytes("UTF8");
 
        out.write(buff);
 
        out.flush();
 
        out.close();
 
        in = con.getInputStream();
 
        return in;
 
    }
 
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cabernet1976 · by **cabernet1976** » Fri Jan 11, 2008 3:33 pm

Hi plusminus,

Continue to talk about RequestQueue, how do you think about this thread? :arrow:

http://www.anddev.org/upload_files_to_w ... -t443.html :?:

RequestQueue should be able to do upload file to web server, right?

If the program need to upload so many files one by one in a period, sure you are clear this scenario, a queue should be fine, but I have no idea to use RequestQueue to implement it.

BTW. happy week end :!:

cabernet1976 · by **cabernet1976** » Fri Jan 11, 2008 4:57 pm

Hi plusminus,

Well, after minutes, I get the different of those two sloutioins, yours is a event-drive asynchronous mode implement, and another one is a synchronous implement.

* event-drive mode make it able to implement the program with only one thread even the HTTP connect cast long time.

* synchronous mode is easy to write the code, but the main thread will timeout if HTTP connection cast too long time, unless add a new thread to do HTTP.

Please correct me.
Thanks.

plusminus · by **plusminus** » Fri Jan 11, 2008 5:24 pm

Hello cabernet,

exactly, your code will be blocking probably when reading from the InputStream. Mine got a few lines more, but is probably more handy to implement, for example because you get notified of Errors and no need to create a thread on your own (internally there will be created one for you).

Regards,
plusminus

cabernet1976 · by **cabernet1976** » Sat Jan 12, 2008 1:57 am

Thanks for your reply, plusminus.
I got it.

tangoman · by **tangoman** » Sun Jan 13, 2008 8:08 pm

Hi PlusMinus!
Congrats about your tutorial, it's really clear!
How ever I got a problem trying it.

I just changed it your URL, for:

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rQueue.queueRequest("http://localhost:8080/postresponse.htm" "POST",
 
                            headers, myEvH, baos, POSTbytes.length,false);
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and I exposed a controller in Java that attends that URL, and prints the data that came in mydata (I tried it from a browser and works right)

The error I'm a having is a " Error, Connection Refused"
Any Idea?

one more question!, lets say I got to pass another variable. Is as easy as concat the that new var to the firstone? (without &)

Thanks! in advance!

Tangoman.

plusminus · by **plusminus** » Sun Jan 13, 2008 8:51 pm

Hello tangoman,

Remember that the emulator you are running is a fully separated system :!:

So "localhost"/"127.0.0.1" is the Emulator itself :!:

You access the WebServer which is probably running on your Desktop-PC via an IP like "192.168.X.X" or "10.10.X.X". Determine your actual IP with "ipconfig" / "ifconfig" on CmdLine / Shell.

Regards,
plusminus

tangoman · by **tangoman** » Sun Jan 13, 2008 9:17 pm

Thanks a lot!, PlusMinus!.

Excelent tut!!!

later!

Tangoman

Nanodeath · by **Nanodeath** » Tue Jan 15, 2008 7:07 am

Hi all. Very nice work plusminus -- I thought I'd pack the code into a tidy class and add a bit of functionality. It now supports GET as well as POST.

Class:

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import java.io.ByteArrayInputStream;
 
import java.io.UnsupportedEncodingException;
 
import java.net.URLEncoder;
 
import java.util.HashMap;
 
import java.util.Iterator;
 
import java.util.Map;
 
import java.util.Set;
 
import org.apache.http.util.ByteArrayBuffer;
 
import android.content.Context;
 
import android.net.http.EventHandler;
 
import android.net.http.Headers;
 
import android.net.http.RequestQueue;
 
import android.net.http.SslCertificate;
 
import android.util.Log;
 
public class HTTP_Request {
 
        // ===========================================================
 
        // Fields
 
        // ===========================================================
 
        private Context context;
 
        private String url;
 
        private String variables;
 
        private Method method;
 
        public enum Method {
 
                POST,
 
                GET
 
        }
 
        // ===========================================================
 
        // 'Constructors'
 
        // ===========================================================
 
        // Constructor for requests without variables
 
        public HTTP_Request(Context c, String url, Method method){
 
                this(c, url, method, null);
 
        }
 
        // Constructor for requests with variables
 
        public HTTP_Request(Context c, String url, Method method, Map<String,String> variables) {
 
                this.context = c;
 
                this.url = url;
 
                this.variables = "";
 
                this.method = method;
 
                /* Prepare the variables we are going to send. */
 
                if(variables != null){
 
                        try {
 
                                StringBuilder b = new StringBuilder();
 
                                Set keys = variables.keySet();
 
                                for(Iterator i = keys.iterator(); i.hasNext();){
 
                                        String key = (String)i.next();
 
                                        b.append(key);
 
                                        b.append("=");
 
                                        b.append(URLEncoder.encode(variables.get(key), "UTF-8"));
 
                                        if(i.hasNext()){
 
                                                b.append("&");
 
                                        }
 
                                }
 
                                this.variables = b.toString();
 
                        } catch (UnsupportedEncodingException e) {
 
                                Log.e("HTTP_Request", "Unsupported Encoding Exception");
 
                                return;
 
                        }
 
                }
 
        }
 
        private PostHandler handler;
 
        public void setHandler(PostHandler h){
 
                handler = h;
 
        }
 
        public void go(){
 
                /* Create a new EventHandler defined above, to handle what gets returned. */
 
                MyEventHandler myEvH = new MyEventHandler(handler);
 
                /* Create a new HTTP-RequestQueue. */
 
                android.net.http.RequestQueue rQueue = new RequestQueue(context);         
 
                /* Create a header-hashmap */
 
                Map<String, String> headers = new HashMap<String, String>();
 
                /* and put the Default-Encoding for html-forms to it. */
 
                headers.put("Content-Type", "application/x-www-form-urlencoded");
 
                if(method == Method.GET){
 
                        // Perform the request with GET
 
                        if(!variables.equals("")){
 
                                url = url + "?" + variables;
 
                        }
 
                        rQueue.queueRequest(url, "GET", headers, myEvH, null, 0, false);
 
                } else if(method == Method.POST){
 
                        /* And put the encoded bytes into an BAIS,
 
                         * where a function later can read bytes from. */
 
                        byte[] POSTbytes = variables.getBytes();
 
                        ByteArrayInputStream baos = new ByteArrayInputStream(POSTbytes);
 
                        rQueue.queueRequest(url, "POST", headers, myEvH, baos, POSTbytes.length, false);                        
 
                }
 
                /* Wait until the request is complete.*/
 
                rQueue.waitUntilComplete();
 
        }
 
        // ===========================================================
 
        // Worker Class
 
        // ===========================================================
 
        private class MyEventHandler implements EventHandler {
 
                private PostHandler handler;
 
                /** Will hold the data returned by the URLCall. */
 
                ByteArrayBuffer baf = new ByteArrayBuffer(20);
 
                MyEventHandler(PostHandler callback) {
 
                        this.handler = callback;
 
                }
 
                public void data(byte[] bytes, int len) {
 
                        baf.append(bytes, 0, len);
 
                }
 
                public void endData() {
 
                        handler.run(new String(baf.toByteArray()));
 
                }
 
                public void status(int arg0, int arg1, int arg2, String s) {
 
                        // Status can be OK, Not Found, others...
 
                        handler.status(s);
 
                }
 
                public void error(int i, String s) {
 
                        handler.error(s);
 
                }
 
                public void handleSslErrorRequest(int arg0, String arg1, SslCertificate arg2) { }
 
                public void headers(Iterator arg0) { }
 
                public void headers(Headers arg0) { }
 
        }
 
        public static abstract class PostHandler {
 
                abstract void run(String response);
 
                void status(String status) {}
 
                void error(String error) {}
 
        }
 
}
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Also, here is some sample usage:

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Map<String,String> vars = new HashMap<String,String>();
 
                        vars.put("test", "value");
 
                        vars.put("othertest", "valuedos");
 
                        HTTP_Request request = new HTTP_Request(NutriScan.this, "http://www.samplewebsite.com/test.php", HTTP_Request.Method.GET, vars);
 
                        request.setHandler(new PostHandler(){
 
                                void run(String response) {
 
                                        Log.d(TAG, "RESPONSE: " + response);
 
                                }
 
                                @Override
 
                                void error(String error) {
 
                                        Log.e(TAG, "ERROR: " + error);
 
                                }
 
                                @Override
 
                                void status(String status) {
 
                                        Log.i(TAG, "STATUS:" + status);
 
                                }
 
                        });
 
                        request.go();
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tangoman · by **tangoman** » Tue Jan 15, 2008 2:01 pm

Hi Nano, nice Job!

I got a few questions that probably any could answer.
In the line:

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HTTP_Request request = new HTTP_Request(NutriScan.this, "http://www.samplewebsite.com/test.php", HTTP_Request.Method.GET, vars);
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What NutriScan.this does mean? a Context? And that's when my second question comes:
How would you do to get a Context, if your not in a Activity class when you inherite from Context and just pass this. What alternatives does we have to get a context?
I think that is a really common doubt dealing with context, so if any could help to clear it would really nice!.

Thanks a lot!!

Tangoman.

Nanodeath · by **Nanodeath** » Tue Jan 15, 2008 6:02 pm

NutriScan is the name of the project I happened to be testing this application from. That line gets the context -- I can't simply say this because it happens to be in a OnClick listener and so simply saying this would actually refer to the click handler (I think). So somehow, if you're calling the function from an activity, you have to say either this or thatActivity.this, depending on the circumstances/whatever works. I don't fully understand it myself, but hopefully that's enough.

I'm pretty sure that you can't do this without the context. If Activity A calls Class B, and you're trying to use this function in Class B, then you're going to have to force Activity A to pass its context to Class B for use with functions like this. Or possibly you could still say A.this? I'm not really sure.

Hope some of this helps you a bit -- this is my learning project as well.

plusminus · by **plusminus** » Wed Jan 16, 2008 12:28 am

Hello Nanodeath,

big thx for your submission. This will be really useful for others!

Nanodeath wrote:NutriScan is the name of the project I happened to be testing this application from. That line gets the context -- I can't simply say this because it happens to be in a OnClick listener and so simply saying this would actually refer to the click handler (I think). So somehow, if you're calling the function from an activity, you have to say either this or thatActivity.this, depending on the circumstances/whatever works. I don't fully understand it myself, but hopefully that's enough.

Yes, the example code you provided was probably contained in a private/anonymous class (like an anonymous OnClickListener). So using this within such an OnClickListener if you want to refer to the OnClickListener we are typing the code in. So we explicitly have to say that we want to refer to the 'surrounding' Activity (Note: Activity extends Context!).

Nanodeath wrote:I'm pretty sure that you can't do this without the context.

Yes, because the constructor of RequestQueue wants to be fed with the context.

Nanodeath wrote:If Activity A calls Class B, and you're trying to use this function in Class B, then you're going to have to force Activity A to pass its context to Class B for use with functions like this. Or possibly you could still say A.this? I'm not really sure.

Hope some of this helps you a bit -- this is my learning project as well.

No the context is needed nowhere in this example except in the constructor of RequestQueue.

@tangoman

What alternatives does we have to get a context?

Actually none

Regards,
plusminus

Nanodeath · by **Nanodeath** » Wed Jan 16, 2008 1:05 am

Thanks for confirming some of that. Also, with respect to the Context stuff, I was referring to a case not demonstrated by my sample code, if that makes any difference.

tangoman · by **tangoman** » Wed Jan 16, 2008 12:11 pm

Thanks!!!! Both!, Nanodeath and PlusMinus for the answers!

Tangoman

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