How to set the default header for all requests in apache http client?

For example the default user agent could be set like: client.getParams().setParameter(CoreProtocolPNames.USER_AGENT, someName);
But how to set the "Accept" header?

How do I change HTTP headers?

After installing the extension, Go to app.requestly.io/rules.Then create rule and select "Modify Headers". After that give the rule name, and from here you can add, override and remove headers by providing a Header name and value for that header.

HttpClient 4.3 now allows configuring a collection of default headers on the client itself:

Header header = new BasicHeader(HttpHeaders.CONTENT_TYPE, "application/json");
List<Header> headers = Lists.newArrayList(header);
HttpClient client = HttpClients.custom().setDefaultHeaders(headers).build();
HttpUriRequest request = RequestBuilder.get().setUri(SAMPLE_URL).build();
client.execute(request);

Now, all requests executed by that client will be send with the default headers. Hope that helps.