How do I write to an OutputStream using DefaultHttpClient?

Question

How do I get an OutputStream using org.apache.http.impl.client.DefaultHttpClient?

I'm looking to write a long string to an output stream.

Using HttpURLConnection you would implement it like so:

HttpURLConnection connection = (HttpURLConnection)url.openConnection();
OutputStream out = connection.getOutputStream();
Writer wout = new OutputStreamWriter(out);
writeXml(wout);

Is there a method using DefaultHttpClient similar to what I have above? How would I write to an OutputStream using DefaultHttpClient instead of HttpURLConnection?

e.g

DefaultHttpClient client = new DefaultHttpClient();

OutputStream outstream = (get OutputStream somehow)
Writer wout = new OutputStreamWriter(out);

Answer 1

You can't get an OutputStream from BasicHttpClient directly. You have to create an HttpUriRequest object and give it an HttpEntity that encapsulates the content you want to sent. For instance, if your output is small enough to fit in memory, you might do the following:

// Produce the output
ByteArrayOutputStream out = new ByteArrayOutputStream();
Writer writer = new OutputStreamWriter(out, "UTF-8");
writeXml(writer);

// Create the request
HttpPost request = new HttpPost(uri);
request.setEntity(new ByteArrayEntity(out.toByteArray()));

// Send the request
DefaultHttpClient client = new DefaultHttpClient();
HttpResponse response = client.execute(request);

If the data is large enough that you need to stream it, it becomes more difficult because there's no HttpEntity implementation that accepts an OutputStream. You'd need to write to a temp file and use FileEntity or possibly set up a pipe and use InputStreamEntity

EDIT See oleg's answer for sample code that demonstrates how to stream the content - you don't need a temp file or pipe after all.

Answer 2

I know that another answer has already been accepted, just for the record this is how one can write content out with HttpClient without intermediate buffering in memory.

    AbstractHttpEntity entity = new AbstractHttpEntity() {

        public boolean isRepeatable() {
            return false;
        }

        public long getContentLength() {
            return -1;
        }

        public boolean isStreaming() {
            return false;
        }

        public InputStream getContent() throws IOException {
            // Should be implemented as well but is irrelevant for this case
            throw new UnsupportedOperationException();
        }

        public void writeTo(final OutputStream outstream) throws IOException {
            Writer writer = new OutputStreamWriter(outstream, "UTF-8");
            writeXml(writer);
            writer.flush();
        }

    };
    HttpPost request = new HttpPost(uri);
    request.setEntity(entity);

Answer 3

This worked well on android. It should also work for large files, as no buffering is needed.

PipedOutputStream out = new PipedOutputStream();
PipedInputStream in = new PipedInputStream();
out.connect(in);
new Thread() {
    @Override
    public void run() {
        //create your http request
        InputStreamEntity entity = new InputStreamEntity(in, -1);
        request.setEntity(entity);
        client.execute(request,...);
        //When this line is reached your data is actually written
    }
}.start();
//do whatever you like with your outputstream.
out.write("Hallo".getBytes());
out.flush();
//close your streams

Answer 4

I wrote an inversion of Apache's HTTP Client API [PipedApacheClientOutputStream] which provides an OutputStream interface for HTTP POST using Apache Commons HTTP Client 4.3.4.

Calling-code looks like this:

// Calling-code manages thread-pool
ExecutorService es = Executors.newCachedThreadPool(
  new ThreadFactoryBuilder()
  .setNameFormat("apache-client-executor-thread-%d")
  .build());


// Build configuration
PipedApacheClientOutputStreamConfig config = new      
  PipedApacheClientOutputStreamConfig();
config.setUrl("http://localhost:3000");
config.setPipeBufferSizeBytes(1024);
config.setThreadPool(es);
config.setHttpClient(HttpClientBuilder.create().build());

// Instantiate OutputStream
PipedApacheClientOutputStream os = new     
PipedApacheClientOutputStream(config);

// Write to OutputStream
os.write(...);

try {
  os.close();
} catch (IOException e) {
  logger.error(e.getLocalizedMessage(), e);
}

// Do stuff with HTTP response
...

// Close the HTTP response
os.getResponse().close();

// Finally, shut down thread pool
// This must occur after retrieving response (after is) if interested   
// in POST result
es.shutdown();

Note - In practice the same client, executor service, and config will likely be reused throughout the life of the application, so the outer prep and close code in the above example will likely live in bootstrap/init and finalization code rather than directly inline with the OutputStream instantiation.