There are three ways to send http requests in java. In addition to the native connection method HttpURLConnection, there are two other ways: HTTPClient and CloseableHttpClient
The following briefly introduces the methods of using HTTPClient and CloseableHTTPClient to make Get and Post requests.
Use link for details

HttpClient

Using commons-httpclient.jar, maven depends on the following:

<!-- https://mvnrepository.com/artifact/commons-httpclient/commons-httpclient -->
    <dependency>
        <groupId>commons-httpclient</groupId>
        <artifactId>commons-httpclient</artifactId>
        <version>3.1</version>
    </dependency>

The simple code is as follows:

private static String doGet(String url) {
    String res = null;
    HttpClient client = new HttpClient();
    GetMethod getMethod = new GetMethod(url);
    int code = 0;
    try {
        code = client.executeMethod(getMethod);
        if (code == 200) {
            res = getMethod.getResponseBodyAsString();
        }
    } catch (IOException e) {
        e.printStackTrace();
    }
    return res;
}

private static String doPost(String url, Map<String, Object> paramMap) {
    String res = null;
    HttpClient client = new HttpClient();
    PostMethod postMethod = new PostMethod(url);
    postMethod.getParams().setContentCharset("UTF-8");
    Iterator<Map.Entry<String, Object>> iterator = paramMap.entrySet().iterator();
    while (iterator.hasNext()) {
        Map.Entry<String, Object> next = iterator.next();
        postMethod.addParameter(next.getKey(), next.getValue().toString());
    }
    try {
        int code = client.executeMethod(postMethod);
        if (code == 200) {
            res = postMethod.getResponseBodyAsString();
        }
    } catch (IOException e) {
        e.printStackTrace();
    }
    return res;
}

public static void main(String[] args) {
    //get
    System.out.println(doGet("http://localhost:8080/hello"));

    //post
    //Set the format of the incoming parameters: request parameters are in the form of map
    Map<String, Object> paramMap = new HashMap<>(2);
    paramMap.put("name", "Zhao Yun");
    paramMap.put("age", 21);
    System.out.println(doPost("http://localhost:8080/hello1", paramMap));
}

Called method:

Test result:

CloseableHttpClient

Using httpclient.jar, maven depends on the following:

<!-- https://mvnrepository.com/artifact/org.apache.httpcomponents/httpclient -->
<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.12</version>
</dependency>

The simple code is as follows:

/**
   * Send HttpGet request
 * @param url
 * @return
 */
public static String doGet(String url) {
    //1. Obtain an httpclient object
    CloseableHttpClient httpclient = HttpClients.createDefault();
    //2. Generate a get request
    HttpGet httpget = new HttpGet(url);
    CloseableHttpResponse response = null;
    try {
        //3. Execute the get request and return the result
        response = httpclient.execute(httpget);
    } catch (IOException e1) {
        e1.printStackTrace();
    }
    String result = null;
    try {
        //4. Processing the result, here the result is returned as a string
        HttpEntity entity = response.getEntity();
        if (entity != null) {
            result = EntityUtils.toString(entity);
        }
    } catch (ParseException | IOException e) {
        e.printStackTrace();
    } finally {
        try {
            response.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    return result;
}

/**
   * Send HttpPost request, the parameter is map
 * @param url
 * @param map
 * @return
 */
public static String doPost(String url, Map<String, Object> map) {
    CloseableHttpClient httpclient = HttpClients.createDefault();
    List<NameValuePair> formparams = new ArrayList<NameValuePair>();
    for (Map.Entry<String, Object> entry : map.entrySet()) {
        //Assign a value to the parameter
        formparams.add(new BasicNameValuePair(entry.getKey(), String.valueOf(entry.getValue())));
    }
    UrlEncodedFormEntity entity = new UrlEncodedFormEntity(formparams, Consts.UTF_8);
    HttpPost httppost = new HttpPost(url);
    httppost.setEntity(entity);
    CloseableHttpResponse response = null;
    try {
        response = httpclient.execute(httppost);
    } catch (IOException e) {
        e.printStackTrace();
    }
    HttpEntity entity1 = response.getEntity();
    String result = null;
    try {
        result = EntityUtils.toString(entity1);
    } catch (ParseException | IOException e) {
        e.printStackTrace();
    }
    return result;
}

public static void main(String[] args) {
    //get
    System.out.println(doGet("http://localhost:8080/hello"));

    //post
    //Set the format of the incoming parameters: request parameters are in the form of map
    Map<String, Object> paramMap = new HashMap<>(2);
    paramMap.put("name", "Zhang Fei");
    paramMap.put("age", 55);
    System.out.println(doPost("http://localhost:8080/hello1", paramMap));
}

Called method:

Test result: