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class="theme-default-content content__default"><h1 id="httpurlconnection"><a href="#httpurlconnection" class="header-anchor">#</a> HttpURLConnection</h1> <h2 id="get-response-body-from-a-url-as-a-string"><a href="#get-response-body-from-a-url-as-a-string" class="header-anchor">#</a> Get response body from a URL as a String</h2> <div class="language-java extra-class"><pre class="language-java"><code><span class="token class-name">String</span> <span class="token function">getText</span><span class="token punctuation">(</span><span class="token class-name">String</span> url<span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">IOException</span> <span class="token punctuation">{</span>
<span class="token class-name">HttpURLConnection</span> connection <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token class-name">HttpURLConnection</span><span class="token punctuation">)</span> <span class="token keyword">new</span> <span class="token function">URL</span><span class="token punctuation">(</span>url<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">openConnection</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">//add headers to the connection, or check the status if desired..</span>
<span class="token comment">// handle error response code it occurs</span>
<span class="token keyword">int</span> responseCode <span class="token operator">=</span> conn<span class="token punctuation">.</span><span class="token function">getResponseCode</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">InputStream</span> inputStream<span class="token punctuation">;</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token number">200</span> <span class="token operator"><=</span> responseCode <span class="token operator">&&</span> responseCode <span class="token operator"><=</span> <span class="token number">299</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
inputStream <span class="token operator">=</span> connection<span class="token punctuation">.</span><span class="token function">getInputStream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
inputStream <span class="token operator">=</span> connection<span class="token punctuation">.</span><span class="token function">getErrorStream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token class-name">BufferedReader</span> in <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">BufferedReader</span><span class="token punctuation">(</span>
<span class="token keyword">new</span> <span class="token class-name">InputStreamReader</span><span class="token punctuation">(</span>
inputStream<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">StringBuilder</span> response <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">StringBuilder</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">String</span> currentLine<span class="token punctuation">;</span>
<span class="token keyword">while</span> <span class="token punctuation">(</span><span class="token punctuation">(</span>currentLine <span class="token operator">=</span> in<span class="token punctuation">.</span><span class="token function">readLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span>
response<span class="token punctuation">.</span><span class="token function">append</span><span class="token punctuation">(</span>currentLine<span class="token punctuation">)</span><span class="token punctuation">;</span>
in<span class="token punctuation">.</span><span class="token function">close</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">return</span> response<span class="token punctuation">.</span><span class="token function">toString</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre></div><p>This will download text data from the specified URL, and return it as a String.</p> <p><strong>How this works:</strong></p> <li>
First, we create a `HttpUrlConnection` from our URL, with `new URL(url).openConnection()`. We cast the `UrlConnection` this returns to a `HttpUrlConnection`, so we have access to things like adding headers (such as User Agent), or checking the response code. (This example does not do that, but it's easy to add.)
</li> <li>
Then, create `InputStream` basing on the response code (for error handling)
</li> <li>
Then, create a `BufferedReader` which allows us to read text from `InputStream` we get from the connection.
</li> <li>
Now, we append the text to a `StringBuilder`, line by line.
</li> <li>
Close the `InputStream`, and return the String we now have.
</li> <p><strong>Notes:</strong></p> <li>
This method will throw an `IoException` in case of failure (such as a network error, or no internet connection), and it will also throw an **unchecked** `MalformedUrlException` if the given URL is not valid.
</li> <li>
It can be used for reading from any URL which returns text, such as webpages (HTML), REST APIs which return JSON or XML, etc.
</li> <li>
See also: [Read URL to String in few lines of Java code](http://stackoverflow.com/questions/4328711/read-url-to-string-in-few-lines-of-java-code).
</li> <p>Usage:</p> <p>Is very simple:</p> <div class="language-java extra-class"><pre class="language-java"><code><span class="token class-name">String</span> text <span class="token operator">=</span> <span class="token function">getText</span><span class="token punctuation">(</span>”http<span class="token operator">:</span><span class="token operator">/</span><span class="token operator">/</span>example<span class="token punctuation">.</span>com"<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">//Do something with the text from example.com, in this case the HTML.</span>
</code></pre></div><h2 id="post-data"><a href="#post-data" class="header-anchor">#</a> POST data</h2> <div class="language-java extra-class"><pre class="language-java"><code><span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">post</span><span class="token punctuation">(</span><span class="token class-name">String</span> url<span class="token punctuation">,</span> <span class="token keyword">byte</span> <span class="token punctuation">[</span><span class="token punctuation">]</span> data<span class="token punctuation">,</span> <span class="token class-name">String</span> contentType<span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">IOException</span> <span class="token punctuation">{</span>
<span class="token class-name">HttpURLConnection</span> connection <span class="token operator">=</span> <span class="token keyword">null</span><span class="token punctuation">;</span>
<span class="token class-name">OutputStream</span> out <span class="token operator">=</span> <span class="token keyword">null</span><span class="token punctuation">;</span>
<span class="token class-name">InputStream</span> in <span class="token operator">=</span> <span class="token keyword">null</span><span class="token punctuation">;</span>
<span class="token keyword">try</span> <span class="token punctuation">{</span>
connection <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token class-name">HttpURLConnection</span><span class="token punctuation">)</span> <span class="token keyword">new</span> <span class="token function">URL</span><span class="token punctuation">(</span>url<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">openConnection</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
connection<span class="token punctuation">.</span><span class="token function">setRequestProperty</span><span class="token punctuation">(</span><span class="token string">"Content-Type"</span><span class="token punctuation">,</span> contentType<span class="token punctuation">)</span><span class="token punctuation">;</span>
connection<span class="token punctuation">.</span><span class="token function">setDoOutput</span><span class="token punctuation">(</span><span class="token boolean">true</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
out <span class="token operator">=</span> connection<span class="token punctuation">.</span><span class="token function">getOutputStream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
out<span class="token punctuation">.</span><span class="token function">write</span><span class="token punctuation">(</span>data<span class="token punctuation">)</span><span class="token punctuation">;</span>
out<span class="token punctuation">.</span><span class="token function">close</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
in <span class="token operator">=</span> connection<span class="token punctuation">.</span><span class="token function">getInputStream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">BufferedReader</span> reader <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">BufferedReader</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">InputStreamReader</span><span class="token punctuation">(</span>in<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">String</span> line <span class="token operator">=</span> <span class="token keyword">null</span><span class="token punctuation">;</span>
<span class="token keyword">while</span> <span class="token punctuation">(</span><span class="token punctuation">(</span>line <span class="token operator">=</span> reader<span class="token punctuation">.</span><span class="token function">readLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>line<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
in<span class="token punctuation">.</span><span class="token function">close</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span> <span class="token keyword">finally</span> <span class="token punctuation">{</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>connection <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span> connection<span class="token punctuation">.</span><span class="token function">disconnect</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>out <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span> out<span class="token punctuation">.</span><span class="token function">close</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>in <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span> in<span class="token punctuation">.</span><span class="token function">close</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre></div><p>This will POST data to the specified URL, then read the response line-by-line.</p> <h3 id="how-it-works"><a href="#how-it-works" class="header-anchor">#</a> How it works</h3> <ul><li>As usual we obtain the <code>HttpURLConnection</code> from a <code>URL</code>.</li> <li>Set the content type using <code>setRequestProperty</code>, by default it's <code>application/x-www-form-urlencoded</code></li> <li><code>setDoOutput(true)</code> tells the connection that we will send data.</li> <li>Then we obtain the <code>OutputStream</code> by calling <code>getOutputStream()</code> and write data to it. Don't forget to close it after you are done.</li> <li>At last we read the server response.</li></ul> <h2 id="delete-resource"><a href="#delete-resource" class="header-anchor">#</a> Delete resource</h2> <div class="language- extra-class"><pre class="language-text"><code>
public static void delete (String urlString, String contentType) throws IOException {
HttpURLConnection connection = null;
try {
URL url = new URL(urlString);
connection = (HttpURLConnection) url.openConnection();
connection.setDoInput(true);
connection.setRequestMethod("DELETE");
connection.setRequestProperty("Content-Type", contentType);
Map<String, List<String>> map = connection.getHeaderFields();
StringBuilder sb = new StringBuilder();
Iterator<Map.Entry<String, String>> iterator = responseHeader.entrySet().iterator();
while(iterator.hasNext())
{
Map.Entry<String, String> entry = iterator.next();
sb.append(entry.getKey());
sb.append('=').append('"');
sb.append(entry.getValue());
sb.append('"');
if(iterator.hasNext())
{
sb.append(',').append(' ');
}
}
System.out.println(sb.toString());
} catch (Exception e) {
e.printStackTrace();
} finally {
if (connection != null) connection.disconnect();
}
}
</code></pre></div><p>This will DELETE the resource in the specified URL, then print the response header.</p> <h3 id="how-it-works-2"><a href="#how-it-works-2" class="header-anchor">#</a> How it works</h3> <ul><li>we obtain the <code>HttpURLConnection</code> from a <code>URL</code>.</li> <li>Set the content type using <code>setRequestProperty</code>, by default it's <code>application/x-www-form-urlencoded</code></li> <li><code>setDoInput(true)</code> tells the connection that we intend to use the URL connection for input.</li> <li><code>setRequestMethod("DELETE")</code> to perform HTTP DELETE</li></ul> <p>At last we print the server response header.</p> <h2 id="check-if-resource-exists"><a href="#check-if-resource-exists" class="header-anchor">#</a> Check if resource exists</h2> <div class="language-java extra-class"><pre class="language-java"><code><span class="token comment">/**
* Checks if a resource exists by sending a HEAD-Request.
* @param url The url of a resource which has to be checked.
* @return true if the response code is 200 OK.
*/</span>
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token keyword">boolean</span> <span class="token function">checkIfResourceExists</span><span class="token punctuation">(</span><span class="token class-name">URL</span> url<span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">IOException</span> <span class="token punctuation">{</span>
<span class="token class-name">HttpURLConnection</span> conn <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token class-name">HttpURLConnection</span><span class="token punctuation">)</span> url<span class="token punctuation">.</span><span class="token function">openConnection</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
conn<span class="token punctuation">.</span><span class="token function">setRequestMethod</span><span class="token punctuation">(</span><span class="token string">"HEAD"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">int</span> code <span class="token operator">=</span> conn<span class="token punctuation">.</span><span class="token function">getResponseCode</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
conn<span class="token punctuation">.</span><span class="token function">disconnect</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">return</span> code <span class="token operator">==</span> <span class="token number">200</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre></div><h3 id="explanation"><a href="#explanation" class="header-anchor">#</a> Explanation:</h3> <p>If you are just checking if a resource exists, it better to use a HEAD request than a GET. This avoids the overhead of transferring the resource.</p> <p>Note that the method only returns <code>true</code> if the response code is <code>200</code>. If you anticipate redirect (i.e. 3XX) responses, then the method may need to be enhanced to honor them.</p> <h3 id="example"><a href="#example" class="header-anchor">#</a> Example:</h3> <div class="language-java extra-class"><pre class="language-java"><code><span class="token function">checkIfResourceExists</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token function">URL</span><span class="token punctuation">(</span><span class="token string">"http://images.google.com/"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// true</span>
<span class="token function">checkIfResourceExists</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token function">URL</span><span class="token punctuation">(</span><span class="token string">"http://pictures.google.com/"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// false</span>
</code></pre></div><h4 id="remarks"><a href="#remarks" class="header-anchor">#</a> Remarks</h4> <li>
Using HttpUrlConnection on Android requires that you add the Internet permission to your app (in the `AndroidManifest.xml`).
</li> <li>
There are also other Java HTTP clients and libraries, such as Square's [OkHttp](http://github.com/square/okhttp/), which are easier to use, and may offer better performance or more features.
</li></div> <footer class="page-edit"><div class="edit-link"><a href="https://github.com/devtut/generate/edit/master/docs/java/httpurlconnection.md" target="_blank" rel="noopener noreferrer">Edit this page on GitHub</a> <span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></div> <!----></footer> <div class="page-nav"><p class="inner"><span class="prev">
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