Table of Contents
1. Overview
This quick tutorial will show how to configure the Apache HttpClient 4 to automatically follow redirects for POST requests.
If you want to dig deeper and learn other cool things you can do with the HttpClient – head on over to the main HttpClient tutorial.
By default, only GET requests resulting in a redirect are automatically followed. If a POST requests is answered with either HTTP 301 Moved Permanently or with 302 Found – the redirect is not automatically followed.
This is specified by the HTTP RFC 2616:
If the 301 status code is received in response to a request other than GET or HEAD, the user agent MUST NOT automatically redirect the request unless it can be confirmed by the user, since this might change the conditions under which the request was issued.
There are of course usecases where we need to change that behavior and relax the strict HTTP specification.
First, let’s check the default behavior:
@Test
public void givenPostRequest_whenConsumingUrlWhichRedirects_thenNotRedirected()
throws ClientProtocolException, IOException {
HttpClient instance = HttpClientBuilder.create().build();
HttpResponse response = instance.execute(new HttpPost("http://t.co/I5YYd9tddw"));
assertThat(response.getStatusLine().getStatusCode(), equalTo(301));
}
As you can see, the redirect is not followed by default, and we get back the 301 Status Code.
2. Redirecting on HTTP POST
2.1. For HttpClient 4.3 and After
In HttpClient 4.3, a higher level API has been introduced for both creation and configuration of the client:
@Test
public void givenRedirectingPOST_whenConsumingUrlWhichRedirectsWithPOST_thenRedirected()
throws ClientProtocolException, IOException {
HttpClient instance =
HttpClientBuilder.create().setRedirectStrategy(new LaxRedirectStrategy()).build();
HttpResponse response = instance.execute(new HttpPost("http://t.co/I5YYd9tddw"));
assertThat(response.getStatusLine().getStatusCode(), equalTo(200));
}
Notice the HttpClientBuilder is now the starting point of a fluent API which allows full configuration of the client in a more readable way than before.
2.2. For HttpClient 4.2
In the previous version of HttpClient (4.2) we can configure the redirect strategy directly on the client:
@SuppressWarnings("deprecation")
@Test
public void givenRedirectingPOST_whenConsumingUrlWhichRedirectsWithPOST_thenRedirected()
throws ClientProtocolException, IOException {
DefaultHttpClient client = new DefaultHttpClient();
client.setRedirectStrategy(new LaxRedirectStrategy());
HttpResponse response = client.execute(new HttpPost("http://t.co/I5YYd9tddw"));
assertThat(response.getStatusLine().getStatusCode(), equalTo(200));
}
Notice that now, with the new LaxRedirectStrategy, the HTTP Restrictions are relaxed and the redirect is followed over POST as well – leading to a 200 OK status code.
2.3. Pre HttpClient 4.2
Before HttpClient 4.2, the LaxRedirectStrategy class didn’t exist, so we need to roll our own:
@Test
public void givenRedirectingPOST_whenConsumingUrlWhichRedirectsWithPOST_thenRedirected()
throws ClientProtocolException, IOException {
DefaultHttpClient client = new DefaultHttpClient();
client.setRedirectStrategy(new DefaultRedirectStrategy() {
/** Redirectable methods. */
private String[] REDIRECT_METHODS = new String[] {
HttpGet.METHOD_NAME, HttpPost.METHOD_NAME, HttpHead.METHOD_NAME
};
@Override
protected boolean isRedirectable(String method) {
for (String m : REDIRECT_METHODS) {
if (m.equalsIgnoreCase(method)) {
return true;
}
}
return false;
}
});
HttpResponse response = client.execute(new HttpPost("http://t.co/I5YYd9tddw"));
assertThat(response.getStatusLine().getStatusCode(), equalTo(200));
}
3. Conclusion
This quick guide illustrated how to configure any version of the Apache HttpClient 4 to follow redirects for HTTP POST requests as well – relaxing the strict HTTP standard.
The implementation of all these examples and code snippets can be found in my github project – this is an Eclipse based project, so it should be easy to import and run as it is.
