To send HTTP requests and process responses using the Apache HttpClient library in Java, follow these steps:

1. Add the HttpClient Dependency

If you're using Maven, include the following dependency in your pom.xml:

<dependency>
  <groupId>org.apache.httpcomponents</groupId>
  <artifactId>httpclient</artifactId>
  <version>4.5.13</version>
</dependency>

2. Instantiate the HTTP Client

Use HttpClientBuilder to create a reusable client instance:

import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClientBuilder;

CloseableHttpClient client = HttpClientBuilder.create().build();

3. Construct the HTTP Request

Create an appropriate request object based on the desired method:

import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;

HttpGet getReq = new HttpGet("https://api.example.com/data");
HttpPost postReq = new HttpPost("https://api.example.com/submit");

4. Configure Request Details

Set headers or body content as needed:

import org.apache.http.entity.StringEntity;

postReq.setHeader("Content-Type", "application/json");
String jsonPayload = "{\"name\": \"test\"}";
postReq.setEntity(new StringEntity(jsonPayload, "UTF-8"));

5. Execute the Request and Capture the Response

Use the client to execute the request and handle the response:

import org.apache.http.client.ResponseHandler;
import org.apache.http.impl.client.BasicResponseHandler;

ResponseHandler<String> handler = new BasicResponseHandler();
String responseBody = client.execute(postReq, handler);

6. Processs the Response

The response body is now available as a string for further processing.

Complete Example

import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.BasicResponseHandler;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClientBuilder;

import java.io.IOException;

public class HttpClientExample {
    public static void main(String[] args) throws IOException {
        try (CloseableHttpClient httpClient = HttpClientBuilder.create().build()) {
            HttpPost postRequest = new HttpPost("http://localhost:8082/unit/queryunitbybase");
            postRequest.setHeader("Content-Type", "application/json");
            String payload = "{\"chineseName\":\"横须贺港\"}";
            postRequest.setEntity(new StringEntity(payload, "UTF-8"));

            BasicResponseHandler responseHandler = new BasicResponseHandler();
            String response = httpClient.execute(postRequest, responseHandler);
            System.out.println("Response: " + response);
        }
    }
}