package com.memorynotfound.httpclient;

import org.apache.http.Consts;
import org.apache.http.HttpEntity;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.ResponseHandler;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.util.EntityUtils;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

/**
 * This example demonstrates the use of {@link HttpPost} request method.
 * And sending HTML Form request parameters
 */
public class HttpClientHttpFormExample {

    public static void main(String... args) throws IOException {

        try (CloseableHttpClient httpclient = HttpClients.createDefault()) {

            List<NameValuePair> form = new ArrayList<>();
            form.add(new BasicNameValuePair("foo", "bar"));
            form.add(new BasicNameValuePair("employee", "John Doe"));
            UrlEncodedFormEntity entity = new UrlEncodedFormEntity(form, Consts.UTF_8);

            HttpPost httpPost = new HttpPost("http://httpbin.org/post");
            httpPost.setEntity(entity);
            System.out.println("Executing request " + httpPost.getRequestLine());

            // Create a custom response handler
            ResponseHandler<String> responseHandler = response -> {
                int status = response.getStatusLine().getStatusCode();
                if (status >= 200 && status < 300) {
                    HttpEntity responseEntity = response.getEntity();
                    return responseEntity != null ? EntityUtils.toString(responseEntity) : null;
                } else {
                    throw new ClientProtocolException("Unexpected response status: " + status);
                }
            };
            String responseBody = httpclient.execute(httpPost, responseHandler);
            System.out.println("----------------------------------------");
            System.out.println(responseBody);
        }
    }
}

请求头:

Executing request POST http://httpbin.org/post HTTP/1.1
----------------------------------------
{
  "args": {}, 
  "data": "", 
  "files": {}, 
  "form": {
    "foo": "bar", 
    "employee": "John Doe"
  }, 
  "headers": {
    "Accept-Encoding": "gzip,deflate", 
    "Connection": "close", 
    "Content-Length": "27", 
    "Content-Type": "application/x-www-form-urlencoded; charset=UTF-8", 
    "Host": "httpbin.org", 
    "User-Agent": "Apache-HttpClient/4.5.3 (Java/1.8.0_20)"
  }, 
  "json": null, 
  "origin": "123.123.123.123", 
  "url": "http://httpbin.org/post"
}