Using HttpClientUtil for HTTP Requests and JSON Parsing in Java

In many projects you need to call third‑party interfaces such as a weather forecast API. The article shows the complete workflow for doing this in a Java backend.

Usage Process

1. Preparation : Import the HttpClientUtil class (or use Spring's RestTemplate) which provides methods for GET and POST requests with and without parameters.

package com.njsc.credit.util;

import java.io.IOException;
import java.net.URI;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import org.apache.http.NameValuePair;
import org.apache.http.client.entity.UrlEncodedFormEntity;
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.client.utils.URIBuilder;
import org.apache.http.entity.ContentType;
import org.apache.http.entity.StringEntity;
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;

public class HttpClientUtil {
    /**
     * GET request with parameters
     */
    public static String doGet(String url, Map<String, String> param) {
        CloseableHttpClient httpclient = HttpClients.createDefault();
        String resultString = "";
        CloseableHttpResponse response = null;
        try {
            URIBuilder builder = new URIBuilder(url);
            if (param != null) {
                for (String key : param.keySet()) {
                    builder.addParameter(key, param.get(key));
                }
            }
            URI uri = builder.build();
            HttpGet httpGet = new HttpGet(uri);
            response = httpclient.execute(httpGet);
            if (response.getStatusLine().getStatusCode() == 200) {
                resultString = EntityUtils.toString(response.getEntity(), "UTF-8");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                if (response != null) {
                    response.close();
                }
                httpclient.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return resultString;
    }
    // ... other doGet/doPost overloads omitted for brevity ...
}

2. Create URL and access key : Build the request URL by appending the API key and required parameters (e.g., ID card and real name for an identity‑verification service).

/**
 * Identity verification via Juhe API
 */
public boolean identityCheck(String idCard, String realName) {
    String key = "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX";
    String url = "http://op.juhe.cn/idcard/query?key=" + key + "&idcard=" + idCard + "&realname=" + realName;
    String result = HttpClientUtil.doGet(url);
    // parse result with JsonUtils ...
    // return true if verification succeeds
    return match;
}

3. Request the third‑party API : Use HttpClientUtil.doGet (or doPost) to send the request and obtain a JSON string response.

4. Parse the returned JSON : The article provides a JsonUtils utility class that wraps FastJSON (or Gson) to convert JSON strings to Java objects, extract specific fields, format JSON, and handle malformed JSON.

public final class JsonUtils {
    public static final int TYPE_FASTJSON = 0;
    public static final int TYPE_GSON = 1;

    public static String toJson(final Object obj) {
        return JSON.toJSONString(obj);
    }

    public static <T> T parse(final String json, final Class<T> clazz) {
        return JSON.parseObject(json, clazz);
    }

    public static <E> E parse(final String json, final String path) {
        String[] keys = path.split(",");
        JSONObject obj = JSON.parseObject(json);
        for (int i = 0; i < keys.length - 1; i++) {
            obj = obj.getJSONObject(keys[i]);
        }
        return (E) obj.get(keys[keys.length - 1]);
    }
    // ... other helper methods omitted for brevity ...
}

5. Handle JSON format issues : The correctJson method cleans common malformed patterns (e.g., escaped quotes) before parsing.

Overall, the guide walks through preparing the utility classes, constructing request URLs, sending HTTP GET/POST calls, and converting the JSON responses into usable Java objects, providing ready‑to‑copy code snippets for developers.