HTTP Requests
A web service wouldn't be a “web” service if we didn't use HTTP to access it. Making an HTTP request on Android is straightforward using the Apache-provided HttpClient classes that are included with Android in the org.apache.http package.
First we need to create an HttpClient object, which will actually be a DefaultHttpClient object.
HttpClient httpclient = new DefaultHttpClient();
Following that, we can construct the request. In this case, we'll be making an HTTP GET request, which puts any parameters on the URL in the form of a query string. This is as opposed to an HTTP POST request, which sends additional data as the body of the request message, which is not part of the URL.
To create an HTTP GET request, we'll instantiate an HttpGet object, passing in a URL to the page that we would like to retrieve. In this case, we are passing in a URL to the page about this book on Apress's site.
HttpGet httpget = new HttpGet("http://www.apress.com/book/view/9781430232674");
We'll then execute the request by passing the HttpGet object to the HttpClient object via the execute method. This will return an HttpResponse object.
HttpResponse response = httpclient.execute(httpget);
The HttpResponse will contain an HttpEntity, which is basically an HTTP message. Both requests and responses contain entities.
HttpEntity entity = response.getEntity();
The getContent method on the HttpEntity returns an InputStream that we can use to read the actual content that was sent in response.
InputStream inputstream = entity.getContent();
Let's go through a short example to illustrate.
package com.apress.proandroidmedia.ch12.simplehttprequest;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
public class SimpleHTTPRequest extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
First we'll instantiate our HttpClient and HttpGet objects.
HttpClient httpclient = new DefaultHttpClient();
HttpGet httpget = new HttpGet("http://www.apress.com/book/view/9781430232674");
The execute method on our HttpClient may throw an exception, so we need to wrap it in a try catch block.
try {
HttpResponse response = httpclient.execute(httpget);
HttpEntity entity = response.getEntity();
if (entity != null) {
If the HttpEntity exists, we can get access to the InputStream, which can be used to read the response.
InputStream inputstream = entity.getContent();
We'll wrap the InputStream in a BufferedReader and utilize a StringBuilder object to turn it into a normal String that we can work with in the end.
BufferedReader bufferedreader =
new BufferedReader(new InputStreamReader(inputstream));
StringBuilder stringbuilder = new StringBuilder();
String currentline = null;
try {
while ((currentline = bufferedreader.readLine()) != null) {
stringbuilder.append(currentline + "
");
}
} catch (IOException e) {
e.printStackTrace();
}
After fully reading the content, we use the toString method on our StringBuilder object to get the resulting String, which will then print out via the Log.
String result = stringbuilder.toString();
Log.v("HTTP REQUEST",result);
inputstream.close();
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
Of course, we'll need to have permission to access the Internet, so we'll need to specify that in our AndroidManifest.xml.
<uses-permission android:name="android.permission.INTERNET"></uses-permission>
Now that we know how to make an HTTP request for a generic web resource, let's look at how we can deal with the type of data that may be returned after a request to a web service. We'll start with JSON-formatted data.